COMPOUNDS COMPRISING POLYENE CHAIN STRUCTURE AND PROCESSES FOR PREPARING THE SAME

Technical Field The present invention relates to compounds having polyene chain structure, and processes for preparing the same. More specifically, it relates to intermediate compounds, which can be effectively used in the synthesis of β -carotene, processes for preparing the same, processes for preparing β -carotene by using the intermediate compounds, and "retinyl sulfide" named by the present inventors, and a process for preparing the same.

Background Art

Carotenoid compounds have polyene chain structure, and specific examples of such include β -carotene, lycopene, astaxanthin, or the like. Among them, β -carotene is known as pro- vitamin A which decomposes to vitamin A according to the necessity of living body.

Carotenoid compounds are generally used as natural pigments for foodstuffs, and are apt to selectively react with carcinogens such as singlet oxygen, radical and the like, so that they are expected as a prophylactic agent for cancers. To meet the expectation, the necessity of developing a process, which can effectively synthesize the polyene chain structure, is getting increased.

Meanwhile, β -carotene has been manufactured by Hoffmann-La Roche since 1954, and by BASF since 1972 (Paust, J. Pure Appl. Chem. 1991, 63, 45-58).

According to the process of Roche, two C₁₉ molecular units are connected by using bis(magnesium halide) acetylide, and the resulting product is subjected to partial hydrogenation of the triple bond and dehydration in the presence of acid catalyst, to provide β -carotene, as shown in Scheme 1 below: Scheme 1

However, in the Roche process, the synthesis of C₁₉ compound from C_H compound is not a convergent process, which requires two consecutive enol ether condensations, thereby having low effectiveness.

On the other hand, BASF synthesizes β -carotene via Wittig reaction of C_]5 phosphonium salt and Cio dialdehyde, as is shown in Scheme 2 below.

According to this process, double bond can be effectively formed by Wittig reaction, however, the process has a problem in that phosphine oxide (Ph₃P=0) produced as a by-product, cannot be easily separated or removed. Scheme 2

X

+

β-Carotene

Disclosure of the Invention

The technical object of the present invention is to provide intermediate compounds used for the efficient synthesis of the polyene chain structure with fully taking advantage of its symmetry and with solving the problem of by-products such as phosphine oxide by the employment of the Julia type sulfone olefination strategy, processes for preparing the same, and processes for preparing β -carotene by using the same.

Another technical object of the present invention is to provide a process for preparing 2, 7-dimethyl-2,4,6-octatriene-l , 8-dial used in the process for preparing β -carotene according to BASF through the synthetic steps with reducing two stages from the conventional process. Still another technical object of the present invention is to provide a novel compound having polyene chain structure which is synthesized via said intermediate compound, and a process for preparing the same.

The first object of the present invention is achieved by diallylic sulfide represented by the following Chemical Formula 1 : Chemical Formula 1

wherein, Rj and R₂ are independently selected from the group consisting of -CHO, -CH₂C1, -CH₂Br, -CH₂I, -CH₂OH, -CH₂OS0₂CF₃, -CH₂OS0₂Ph, -CH₂OSθ₂C₆H₄CH₃ and -CH₂OS0₂CH₃.

Preferably, Rj and R₂ both are -CHO or -CH₂C1. The second object of the present invention is achieved by a process for preparing diallylic sulfide represented by Chemical Formula 1, which comprises the steps of (a-1) oxidizing isoprene to give isoprene monoxide;

(b-1) reacting the isoprene monoxide with cupric halide (CuX₂)/ lithium halide (LiX) to provide an allylic halide (A); and

(c-1) reacting the allylic halide (A) with sodium sulfide (Na₂S).

R'_l S R₂

<Chemical Formula 1>

In the Formula, R] and R₂ are independently selected from the group consisting of -CHO, -CH₂C1, -CH₂Br, -CH₂I, -CH₂OH, -CH₂OSO₂CF₃, -CH₂OS0₂Ph, -CH₂OS0₂C₆H₄CH₃ and -CH₂OS0₂CH₃, and X represents CI, Br or I.

The allylic sulfides represented by Chemical Formula 1, wherein Rj and R₂ are -CH C1, -CH₂Br or -CH₂I, are synthesized by further performing steps of reducing and halogenating the resultant product from step (c-1 ), after step (c-1 ).

Step (c-1) is preferably performed via the sequence of adding a catalytic amount of acid to the allylic halide (A) in alcoholic solvent to form an acetal in situ, and of reacting said acetal with sodium sulfide for a predetermined period, and then of evaporating the solvent and hydrolyzing the residue.

The third technical object of the present invention can be achieved by a process for preparing 2,7-dimethyl-2,4,6-octatriene-l, 8-dial represented by Chemical Formula 2, which comprises the steps of

(a-2) protecting the aldehyde group of allylic halide (A) to provide the corresponding acetal compound (G);

(b-2) reacting the acetal compound (G) with Na₂S to provide di(3-formyl-3-methyl-2-propenyl)sulfide, dialkyl diacetal (H);

(c-2) selectively oxidizing the di(3-formyl-3-methyl-2-propenyl)sulfide, dialkyl diacetal (H) to provide the corresponding allylic sulfone compound (I);

(d-2) applying Ramberg-Backlund reaction to the allylic sulfone compound (I) to provide the corresponding triene compound (J); and (e-2) hydrolyzing the triene compound (J).

<Chemical Formula 2>

In the Formulas, X represents a halogen atom, and R₃ and R₄ independently represent hydrogen or methyl group.

The selective oxidation reaction of step (c-2) is preferably performed by adding a mixture of urea-hydrogen peroxide (here-in-after, referred to as "UHP") and phthalic anhydride dropwise to a solution containing di(3-formyl-3-methyl-2-propenyl)sulfide, dialkyl diacetal at low temperature.

The fourth object of the present invention is achieved by a process for preparing β -carotene represented by Chemical Formula 3, which comprises the steps of (a-3) deprotonating the sulfone compound (B), and reacting not more than 1/2 equivalent (based on the sulfone compound) of allylic sulfide represented by Chemical Formula 1 (C) (Ri, R₂=CH₂X, X=halogen atom) thereto, to provide sulfide compound (D);

(b-3) selectively oxidizing the sulfide compound (D) to prepare the sulfone compound (E);

(c-3) subjecting the sulfone compound (E) to Ramberg-Backlund reaction to prepare

1 l,20-di(benzenesulfonyl)-l 1,12,19,20-tetrahydro-β -carotene (F); and

(d-3) reacting l l,20-di(benzenesulfonyl)-l l,12,19,20-tetrahydro-β -carotene (F) with a base.

<Chemical Formula 3>

In case that X is CI, step (a-3) is preferably performed by adding a stoichiometric amount of sodium iodide (Nal) in terms of reactivity . The selective oxidation of step (b-3) is preferably carried out by adding a mixture of UHP and phthalic anhydride dropwise to a solution containing the sulfide compound (D) at low temperature. The base used in step (d-3) is not specifically restricted. As specific examples of the base, NaNH₂/NH_3j or metal alkoxides such as CH₃OK/CH₃OH, CH₃CH₂OK/CH₃CH₂OH and CH₃CH₂θNa/CH₃CH₂θH, t-BuOK/f-BuOH may be mentioned. Among them, metal alkoxides are more preferable.

The fifth technical object of the present invention can be achieved by retinyl sulfide represented by the following Chemical Formula 4: Chemical Formula 4

In order to achieve the sixth technical object, the present invention provides a process for preparing retinyl sulfide represented by the Chemical Formula 4, which comprises Wittig reaction of diallylic sulfide (C-1) and the Wittig salt (K).

In the formula, X is a halogen atom.

The diallylic sulfide represented by Chemical Formula 1 , which is used as a basic material in the synthesis of a compound having polyene chain structure, is synthesized according to the following procedure (Scheme 3).

First, isoprene is oxidized to obtain isoprene monoxide. The oxidation may be carried out under the condition of using an oxidant such as m-chloroperoxybenzoic acid (MCPBA), or the condition of forming a corresponding halohydrin, which is then reacted with a base {J. Am. Chem. Soc. 1950, 72, 4608), or the like. Among these, the latter process is more preferable, when considering the regio-selectivity on two double bonds of isoprene.

Then, said isoprene monoxide is subjected to ring opening reaction by reacting with cupric halide (CuX₂-2H₂0)/ lithium halide (LiX), to obtain allylic halide (A). For the ring opening reaction, the reaction condition disclosed in literature (J. Org. Chem. 1976, 41, 1648) is referred, and the reaction condition of cupric chloride (CuCl₂-2H₂0)/ lithium chloride (LiCl) is preferably employed. Then, from the allylic halide (A), allylic sulfide represented by

Chemical Formula 1 is obtained (Scheme 3). Scheme 3

<C emical Formula 1>

In case that Rj and R₂ of the allylic sulfide of Chemical Formula 1 are aldehyde groups, allylic halide (A) is allylated to obtain diallylic sulfide (C-1) which has aldehyde functional groups at both ends. The allylation is preferably carried out by adding a catalytic amount of acid such as ?-toluenesulfonic acid (p-TsOH) in alcoholic solvent to form an acetal, which is then reacted with sodium sulfide and hydrolyzed. In such a reaction condition, allylation can be proceeded without side reactions. The acid such as / TsOH serves as a catalyst that promotes the formation of acetal. In case that Rj and R₂ of the allylic sulfide of Chemical Formula 1 are -CH₂X (wherein, X is a halogen atom), the allylic sulfide (C-1) is firstly reduced to give the corresponding diol compound, which is then halogenated to obtain diallylic sulfide (C) in which halogen atoms have been introduced at both ends (Scheme 4). The halogenation of diol compounds may be carried out under various reaction conditions. For example, halogenation is performed by using a reaction condition of CH₃S0₂Cl/LiCl, HC1, HBr, PPh₃/CCl₄, or the like. Scheme 4

Meanwhile, 2,7-dimethyl-2,4,6-octatriene-l, 8-dial represented by Chemical Formula 2 is an important compound which is used for the synthesis of β -carotene of Chemical Formula 3 by reacting with Wittig salt (K) according to the process suggested by BASF as described above. Here-in-after, the process for preparing

2,7-dimethyl-2,4,6-octatriene-l, 8-dial of Chemical Formula 2 is described by referring to the Scheme 5 below.

In order to obtain 2,7-dimethyl-2,4,6-octatriene-l , 8-dial of Chemical Formula 2, the aldehyde group of the allylic halide (A) must be protected, first of all. The protection of aldehyde group is performed by converting the compound to the corresponding cyclic acetal compound (G) by using glycol compounds such as neopentyl glycol, propylene glycol, ethylene glycol, or the like.

Then, the cyclic acetal compound (G) is reacted with Na₂S to obtain the corresponding allylic sulfide, dialkyl diacetal (H). The compound (H) is used as a basic material for the synthesis of compounds having polyene chain structure. The sulfur of the compound (H) is then selectively oxidized to obtain the corresponding allylic sulfone compound (I). The selective oxidation is performed under a condition of slowly adding an oxidant to the allylic sulfide compound (H) at low temperature. As the oxidant, peroxyphthalic acid, which is the resulting product of reaction of UHP and phthalic anhydride, is preferably used.

Through the Ramberg-Backlund reaction, the corresponding triene compound (J) is obtained from the allylic sulfone compound (I). Deprotection by hydrolysis of acetal groups of the triene compound (J) gives 2,7-dimethyl-2,4,6-octatriene-l, 8-dial represented by Chemical Formula 2. Scheme 5

The process for preparing 2,7-dimethyl-2,4,6-octatriene-l, 8-dial as described above, having two stages shorter than the conventional process, made this process simpler in terms of manufacturing.

Now, the process for preparing β -carotene of Chemical Formula 3, according to the present invention, is described (Scheme 6).

The process for preparing β -carotene according to the present invention is characterized in that Ramberg-Backlund reaction is performed on diallylic sulfone which was obtained by the oxidation of diallylic sulfide.

In order to prepare β -carotene, allylic sulfide (C) and 2 equivalent or more of sulfone compound (B) based on the amount of the allylic sulfide are firstly coupled according to the Julia process {Bull. Soc. Chim. Fr. 1973). As a result of the coupling, obtained is the allylic sulfide (D) which contains all the carbons required for the synthesis of β -carotene. The coupling reaction of allylic sulfide (C) with sulfone compound (B) may be carried out under various reaction conditions. If X is CI, it is preferable to quantitatively add sodium iodide (Nal). Under such a reaction condition, the halogen atoms at both end of allylic sulfide (C) are substituted by iodine, and then allylation of the sulfone compound actively occurs.

Then, only the sulfur atom of allylic sulfide (D) is selectively oxidized to obtain the corresponding sulfone compound (E). The selective oxidation is preferably carried out under the reaction condition of adding an oxidant to the allylic sulfide compound at low temperature. Under such a reaction condition, the double bond of allylic sulfide (D) is not oxidized, but only the sulfur is selectively oxidized. Subsequently, S0₂ of the central part of the structure of sulfone compound (E) is removed by forming a double bond, to give compound (F). The reaction is preferably carried out by applying

Ramberg-Backlund reaction to sulfone compound (E).

Finally, compound (F) is heated in the presence of alcoholic solvent and alkoxide base such as sodium alkoxide to remove two benzenesulfonyl groups, thereby obtaining β -carotene of Chemical Formula 3. Scheme 6

<Chemical Formula 3>

In the meanwhile, the process for preparing retinyl sulfide of Chemical Formula 4 is described with reference to Scheme 7 below.

Retinyl sulfide can be obtained by Wittig reaction of allylic sulfide (C-1) having aldehyde groups at both ends, with Wittig salt (K). Scheme 7

Retinyl sulfide of Chemical Formula 4 has a structure wherein the units of vitamin A are linked by a sulfur atom, and the compound is expected to have an activity of vitamin A.

Brief description of the drawings

Fig. la is the *H NMR spectrum of trans-β -carotene as the authentic sample;

Fig. lb is the ^!H NMR spectrum of trans-β -carotene prepared according to Synthetic Example 6 of the present invention; and

Fig. 2 is the ^]H NMR spectrum of retinyl sulfide (Chemical Formula 4) prepared according to Synthetic Example 9 of the present invention.

Now, the present invention is described in detail with reference to Examples. However, it should be noted that these examples are not intended to limit or restrict the scope of this invention in any way.

Synthetic Example 1: Di(3-formyl-3-methyl-2-propenyl) Sulfide

To a solution of 4-chloro-2-methyl-2-buten-l-al (10.48 g, 88.2 mmol) in MeOH (80 mL) was added -TsOH (48 mg, 0.25 mmol). The mixture was stirred for 1 h, and then Na₂S^»9H₂0 (10.59 g, 44.1 mmol) was added. The resulting mixture was stirred at room temperature for 10 h.

When the reaction was completed, most of solvent was removed by evaporating the reaction mixture under reduced pressure. After adding 1 M HCl (50 mL) thereto, the resultant mixture was stirred for 1 h, and extracted with methylene chloride (50 mL x 3). The combined methylene chloride layer was dried over anhydrous Na₂S0₄, filtered, and concentrated under reduced pressure. The crude product was purified by flash chromatography over silica gel to give di-(3-formyl-3-methyl-2-ρropenyl) sulfide (7.43 g, 37.5 mmol) in 85% yield.

*H NMR δ 1.78 (6H, s), 3.44 (4H, ά, J= 7.7 Hz), 6.53 (2H, t, J = 7.7 Hz), 9.49 (2H, s)

¹³C NMR 9.3, 29.1, 140.9, 147.5, 194.4

Synthetic Example 2: Di(4-chloro-3-methyl-2-butenyl) Sulfide

To a stirred solution of di(3-formyl-3-methyl-2-propenyl) sulfide (10.5 g, 53.0 mmol) in THF (80 mL) was added LiAlFU (1.33 g, 35.0 mmol). The mixture was stirred for 1 h, and then quenched with 1 M HCl (30 mL). The mixture was extracted with EtOAc (50 mL x 3). The combined organic layer was dried over anhydrous Na₂S0₄, filtered, and concentrated under reduced pressure. The above residue was dissolved in CH₃CN (50 mL), and then PPh₃

(30.43 g, 0.116 mol) and CC1₄ (20 mL) were added thereto. The resulting mixture was stirred for about 5 h, diluted with ether (100 ml), and subsequently washed with 1 M HCl (20 mL x 2) and H₂0 (30 mL).

The organic phase was dried over anhydrous Na₂S0₄, filtered and concentrated under reduced pressure. The crude product was purified by flash chromatography over silica gel to produce di(4-chloro-3-methyl-2-butenyl) sulfide (9.26 g, 38.7 mmol) in 73% yield.

*H NMR δ 1.78 (6H, s), 3.14 (4H, ά, J = 7.7 Hz), 4.03 (4H, s),

5.62 (2H, t, = 7.7 Hz) MS (El, 70eV): 240 [(M+2)⁺], 239 [(M+l)⁺], 238 (M⁺), 203, 135,

102, 67

Synthetic Example 3: Di(ll-benzenesulfonyl-ll,12-dihydroretinyl) Sulfide

To a stirred solution of sulfone compound (B) (14.4 g, 41.8 mmol) in THF (80 mL), was added NaH (1.20 g, 50.1 mmol). The mixture was stirred for 15 min, and then di(4-chloro-3-methyl-2-butenyl) sulfide (5.0 g, 20.9 mmol) and Nal (7.5 g, 50.1 mmol) were added consecutively. The resulting mixture was stirred at room temperature for 15 h and diluted with ether. The dilute mixture was subsequently washed with 1 M HCl (20 mL x 2) and distilled water (30 mL), dried over anhydrous Na₂S0₄, filtered, and concentrated under reduced pressure. The crude product was purified by flash chromatography over silica gel to give di(l l-benzenesulfonyl-l l,12-dihydroretinyl) sulfide (D) (15.7 g, 17.8 mmol) in 85% yield.

*H NMR δ 0.93 (6H, s), 0.96 (6H, s), 1.21 (6H, s), 1.45-1.65 (8H, m), 1.63 (12H, s), 2.00 (4H, t, J = 6.0 Hz), 2.39 (2H, dά, J = 13.2, 11.5 Hz), 2.90 (4H, ά, J= 6.8 Hz), 2.90-3.10 (2H, m), 4.02 (2H, dt, J_d = 3.1, J_t

= 11.0 Hz), 5.07 (2H, d, J = 10.3 Hz), 5.21 (2H, X, J = 7.0 Hz), 5.93 (4H, s), 7.45-7.53 (4H, m), 7.58-7.65 (2H, m), 7.78-7.84 (4H, m)

¹³C NMR 12.3, 16.0, 16.0, 19.2, 21.6, 28.9, 28.9, 33.0, 34.2, 37.4, 39.5, 64.1, 122.3, 125.8, 129.2, 129.6, 130.2, 130.4, 134.0, 134.4, 136.8, 138.1, 138.5, 143.2

Synthetic Example 4: Di(ll-benzenesulfonyl-ll,12-dihydroretinyl) Sulfone

The mixture of UHP (6.88 g, 73.1 mmol) and phthalic anhydride (5.41 g, 36.5 mmol) in CH₃CN (70 mL) was stirred vigorously at room temperature for 2 h to give a clear solution. This solution was charged in a dropping funnel, and slowly added over three hour period to a solution of di(l l-benzenesulfonyl-l l,12-dihydroretinyl) sulfide (D) (10.8 g, 12.2 mmol) in CH₃CN (30 mL). The temperature of the reaction mixture was adjusted to be maintained at 0 ^°C .

When the dropping was completed, the reaction mixture was stirred at 0 °C for 1 h. After adding 1 M aqueous HCl (30 mL) thereto, the reaction mixture was extracted with ether (50 mL x 2). The combined ether layer was dried over anhydrous Na₂S0 , filtered, and concentrated under reduced pressure to give a white solid. The crude solid was dissolved in CHCI₃, and insoluble solid was filtered off. The filtrate was concentrated, and the residue was purified by flash chromatography over silica gel to give di(l l-benzenesulfonyl-l l,12-dihydroretinyl) sulfone (8.06 g, 8.77 mmol) in 72% yield. Two stereo isomers of the obtained allylic sulfone compound were found, and one of which was isolated in pure state through silica gel column chromatography.

^!H NMR δ 0.91 (6H, s), 0.96 (6H, s), 1.22 (6H, s), 1.37-1.49 (4H, m), 1.55-1.67 (4H, m), 1.62 (6H, s), 1.65 (6H, s), 1.99 (4H, t, J= 5.9 Hz), 2.47 (2H, dd, J= 13.0, 11.3 Hz), 3.05 (2H, d, J= 13.0 Hz), 3.47 (4H, d, J = 4.5 Hz), 4.06 (2H, dt, J_d = 3.1, J_t = 10.8 Hz), 5.07 (2H, d, J= 10.5 Hz), 5.24 (2H, t, J= 7.4 Hz), 5.92 (2H, A of ABq, J= 16.4 Hz), 5.97 (2H, B of ABq, J = 16.4 Hz), 7.40-7.55 (4H, m), 7.55-7.70 (2H, m), 7.75-7.90 (4H, m)

¹³C NMR 12.3, 17.0, 19.1, 21.5, 28.7, 28.8, 32.8, 34.0, 37.3, 39.3, 51.0, 63.4, 114.1, 121.0, 128.8, 129.0, 129.3, 129.7, 133.7, 135.5, 137.1, 137.2, 140.8, 142.8

Synthetic Example 5: ll,20-Dibenzenesulfonyl-ll,12,19,20- tetrahydro-β -carotene

To a stirred solution of di(l l-benzenesulfonyl-l l,12-dihydroretinyl) sulfone (E) (1.51 g, 1.64 mmol) in /-BuOH (20 mL) and CC1₄ (20 mL), was added KOH (1.85 g, 32.9 mmol) under argon atmosphere. The mixture was stirred vigorously for 5 h.

When the reaction was completed, most of solvent was removed from the reaction mixture under reduced pressure. The crude product was dissolved in CH₂C1₂ (60 mL) and washed with 1 M HCl (20 mL). The combined methylene chloride layer was dried over anhydrous Na₂S0₄, filtered, and concentrated. The crude product was purified by flash chromatography over silica gel to give l l,20-dibenzenesulfonyl-l l,12,19,20-tetrahydro-β -carotene (F) (932 mg, 1.13 mmol) in 69% yield. ^JH NMR δ 0.93 (6H, s), 0.96 (6H, s), 1.20 (6H, s), 1.37-1.50 (4H, m), 1.53-1.65 (4H, m), 1.63 (6H, s), 1.68 (6H, s), 1.98 (4H, br s), 2.45 (2H, dd, J= 13.0, 11.6 Hz), 3.04 (2H, ά, J= 14.2 Hz), 4.05 (2H, άt, J_d = 3.0, J_t = 10.9 Hz), 5.82-5.98 (2H, m), 5.92 (4H, s), 6.15-6.28 (2H, m), 7.40-7.54 (4H, m), 7.56-7.67 (2H, m), 7.76-7.90 (4H, m)

¹³C NMR 12.3, 12.3, 16.7, 16.8, 19.1, 21.5, 28.8, 32.8, 34.1, 39.4, 64.2, 121.4, 127.8, 128.1, 128.7, 129.0, 129.3, 129.5, 132.9, 133.5, 136.0, 137.2, 137.6, 142.1

Synthetic Example 6: β -Carotene

Sodium (674 mg, 29.3 mmol) was added to a stirred solution of 11 ,20-di(benzenesulfonyl)- 11,12,19,20-tetrahydro-β -carotene (F) (602 mg, 0.73 mmol) in EtOH (20 mL) under argon atmosphere.

The reaction mixture was heated under reflux for 10 h with vigorous stirring.

When the reaction was completed, the reaction mixture was concentrated under reduced pressure to remove most of the solvent. Toluene (50 mL) was added thereto to dissolve the residue, and the resultant mixture was washed with 1 M HCl, dried over anhydrous Na₂S0₄, filtered, and concentrated under reduced pressure. The crude product was purified by flash chromatography over silica gel to give exclusively trans-β -carotene of Chemical Formula 3 (295 mg, 0.55 mmol) in 75% yield.

NMR spectrum (JEOL, 300 MHz) data of trans- β-carotene is shown in Fig. lb. The NMR data of the synthetic sample was identical to that of the authentic sample, shown in Fig. la.

Synthetic Example 7: Di(3-formyl-3-methyl-2-propenyl) Sulfide, Dineopentyl Diacetal To a solution of 4-chloro-2-methyl-2-buten-l-al (15.8 g, 0.134 mol) in toluene (100 mL) were added neopentyl glycol (16.7 g, 0.161 mol) and -TsOH (190.2 mg, 6.7 mol). The mixture was heated under reflux for 3 h and cooled to room temperature. The mixture was diluted with ether (100 mL) and washed with distilled water (20 mL x 3). The organic phase was dried over anhydrous Na₂S0₄, filtered and concentrated under reduced pressure. The crude product was purified by flash chromatography over silica gel to give acetal (G) (R₃, R₄ = CH₃) (20.6 g, 0.100 mol) in 75% yield.

*H NMR δ 0.73 (3H, s), 1.20 (3H, s), 1.79 (3H, s), 3.47 (2H, A of ABq, J= 11.0 Hz), 3.62 (2H, B of ABq, J= 11.0 Hz), 4.09 (2H, d, J= 7.9 Hz), 4.72 (1H, s), 5.85 (1H, t, J= 7.2 Hz)

¹³C NMR 11.3, 21.7, 22.8, 30.1, 39.4, 77.1, 103.4, 124.2, 138.1 MS (El, 70eV): 205 [(M+2)⁺], 203 (M⁺), 169, 119, 83, 69, 55.

The above acetal (G) (20.6 g, 0.100 mmol) was dissolved in MeOH (100 mL) and Na₂S^«9H₂0 (12.0 g, 50 mmol) was added thereto. The resulting mixture was stirred at room temperature for 10 h.

When the reaction was completed, most of solvent was removed by evaporating under reduced pressure. The crude oil was dissolved in ether (100 mL) and washed with distilled water (30 mL x 2), dried over anhydrous Na₂S0₄, filtered and concentrated under reduced pressure. The crude product was purified by flash chromatography over silica gel to give di(3-formyl-3-methyl-2-propenyl) sulfide, dineopentyl diacetal (17.6 g, 47.5 mmol) in 95% yield.

^JH NMR δ 0.68 (6H, s), 1.15 (6H, s), 1.68 (6H, s), 3.09 (4H, d, J = 7.5 Hz), 3.43 (4H, A of ABq, J = 11.1 Hz), 3.58 (4H, B of ABq, J = 11.1 Hz), 4.66 (2H, s), 5.63 (2H, t, J= 7.5 Hz)

^,3C NMR 11.2, 21.8, 22.9, 28.0, 30.1, 77.1, 104.4, 125.4, 135.8

Synthetic Example 8: 2,7-Dimethyl-2,4,6-octatriene-l, 8-dial of Chemical Formula 2

The mixture of UHP (5.17 g, 54.9 mmol) and phthalic anhydride (4.07 g, 27.5 mmol) in CH₃CN (30 mL) was stirred vigorously at room temperature for 2 h to give a clear solution. This solution was charged in a dropping funnel, and slowly added over three hour period to a solution of di(3-formyl-3-methyl-2-propenyl)sulfide dineopentyl diacetal (3.39 g, 9.15 mmol) in CH₃CN (20 mL). The temperature of the reaction mixture was adjusted to be maintained at 0 ^°C .

When the dropping was completed, the reaction mixture was stirred at 0 ^°C for 1 h. After adding 30 mL of distilled water thereto, the reaction mixture was extracted with ether (100 mL). The combined ether layer was dried over anhydrous Na₂S0₄, filtered, and concentrated under reduced pressure to give a white solid. The crude solid was dissolved in CHC1₃, and insoluble solid was filtered off. The filtrate was concentrated under reduced pressure, and the residue was purified by flash chromatography over silica gel to give allylic sulfone compound (I) (R , R₄ = CH₃) (2.94 g, 7.3 mmol) in 80% yield.

^!H NMR δ 0.75 (6H, s), 1.20 (6H, s), 1.79 (6H, s), 3.50 (4H, A of ABq, J=10.9 Hz), 3.66 (4H, B of ABq, J=\0.9 Hz), 3.72 (4H, ά, J =1.1 Hz), 4.76 (s, 2H), 5.79 (2H, t, J=7.7Hz).

The allylic sulfone compound (I) (R₃, R₄ = CH₃) (3.00 g, 7.45 mmol) was dissolved in a mixed solvent of r-butanol (30 mL) and carbon tetrachloride (30 mL), and KOH (4.18 g, 74.5 mmol) was added thereto under argon atmosphere. The reaction mixture was stirred vigorously for

6 h.

When the reaction was completed, most of solvent was removed from the reaction mixture under reduced pressure. The crude product was dissolved in ether (70 mL), and washed with distilled water (20 mL x 2). The organic layer was filtered and concentrated. The crude product was purified by flash chromatography over silica gel to give triene compound (J) (R₃, Rι= CH₃) (2.04 g, 6.07 mmol) in 82% yield. *H NMR δ 0.73 (6H, s), 1.22 (6H, s), 1.85 (6H, s), 3.51 (4H, A of

ABq, J= 9.8 Hz), 3.66 (4H, B of ABq, J= 9.8 Hz), 4.75 (2H, s), 6.30 (2H, d, =8.1 Hz), 6.50 (2H, dd, =7.7, 2.8 Hz)

¹³C NMR δ 11.7, 21.4, 22.6, 29.8, 76.8, 103.9, 127.6, 129.1, 134.2

The triene compound (J) (R , R₄ = CH₃) (66 mg, 1.97 mmol) was dissolved in THF (30 mL), and 1 M HCl (30 mL) was added thereto.

The reaction mixture was stirred at room temperature for 3 h. Then the reaction mixture was extracted with ether (50 mL x 2). The organic layer was filtered and concentrated. The crude product was purified by flash chromatography over silica gel to give

2,7-dimethyl-2,4,6-octatriene-l, 8-dial (226 mg, 1.38 mmol) in 70% yield.

'H NMR δ 1.96 (6H, s), 7.00-7.15 (4H, m), 9.56 (2H, s)

¹³C NMR δ 9.7, 134.3, 140.8, 146.1, 194.4

Synthetic Example 9: Retinyl Sulfide of Chemical Formula 4

Wittig salt compound (K) (7.75 g, 14.2 mmol) and di(3-formyl-3-methyl-2-propenyl)sulfide (1.41 g, 7.1 mmol) of Chemical Formula 1 were dissolved in DMF (50 mL). The reaction mixture was sufficiently stirred at -20 ^°C .

To the reaction mixture, sodium methoxide (8.1 g, 0.15 mmol) was added, and the resultant mixture was stirred for 30 minutes. After raising the temperature to room temperature, the reaction mixture was further stirred for 3 h. The reaction mixture was diluted with toluene (100 ml), and washed with 1 M HCl (30 mL x 2). The organic layer was dried over anhydrous Na₂S0₄, filtered, and concentrated. The crude product was purified by flash chromatography over silica gel to give retinyl sulfide (2.75 g, 4.82 mmol) comprising three stereo isomers in 68% yield. *H NMR for the major isomer δ 0.97 (6H, s), 1.38-1.47 (2H, m),

1.54 (3H, s), 1.55-1.65 (2H, m), 1.59 (3H, s), 1.77 (3H, s), 1.92 (2H, t, J= 6.3 Hz), 2.88 (2H, ά, J= 6.4 Hz), 4.96 (1H, m), 5.24 (3H, m), 5.54 (1H, t, J = 6.8 Hz), 6.05 (1H, ά, J = 15.6 Hz). Characteristic peaks for the minor isomers: δ 1.55 (3H, s), 1.58 (3H, s), 2.69 (2H, ά, J = 7.1 Hz), 2.69 (2H, d, = 6.8 Hz), 5.49 (1H, t, J= 6.4 Hz), 6.01 (1H, d, = 7.5 Hz).

As described above, in case that β -carotene is prepared according to Synthetic Examples 1 to 6, the process becomes simpler as compared to the conventional processes, and the problem involved with the by-products such as phosphine oxide can be avoided. According to Synthetic Example 8, 2, 7-dimethyl-2,4,6-octatriene-l, 8-dial of Chemical Formula 2 can be prepared through synthetic steps having two stages reduced as compared with the conventional process.

In addition, the yield of retinyl sulfide of Chemical Formula 4 prepared according to Synthetic Example 9 was 68%. Retinyl sulfide is expected to have an activity of vitamin A.

Industrial Applicability

The allylic sulfide compounds of Chemical Formula 1 according to the present invention may be effectively used as an intermediate for the synthesis of compounds having polyene chain structure such as β -carotene. The compound represented by Chemical Formula 2, 2,7-dimethyl-2,4,6-octatriene-l, 8-dial, is also an important intermediate used for the synthesis of β -carotene. According to the present invention, the process for 2,7-dimethyl-2,4,6-octatriene-l, 8-dial can be shortened by two stages as compared to the process according to BASF, so that the time required for the production and production cost may be reduced.

According to the present invention, allylic sulfide compound (D) is oxidized to provide the corresponding diallylic sulfone compound, to which Ramberg-Backlund reaction is applied to provide the carotene compound of Chemical Formula 3, having the polyene chain structure. In case that β -carotene is prepared according to the present invention, the process can be easily performed as compared to the conventional process according to BASF or Roche, and problems involved with by-products can be avoided. In the meanwhile, retinyl sulfide of Chemical Formula 4 is expected to have the activity of vitamin A.