Triphenylphosphonium bromide → [1-(2,2-Dimethyl-1,3-benzodithiol-5-yl)ethyl]triphenylphosphonium bromide

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반응 단계

28.9 g of aluminum chloride were added portionwise at 0° C. to 16.8 ml of acetyl chloride in 360 ml of methylene chloride. After an additional 30 minutes at 0° C., a solution of 35.9 g of 2,2-dimethyl-1,3-benzodithiol in 180 ml of methylene chloride was slowly added dropwise and the mixture was stirred at 0° C. for an additional 12 hours and thereafter at 20° C. for 5 hours. Thereafter, the mixture was poured on to ice, extracted with methylene chloride and the extracts were washed neutral with dilute sodium hydroxide solution and water, dried over sodium sulfate and evaporated. After recrystallization from methanol/water, there were obtained 41.8 g of 2,2-dimethyl-1,3-benzodithiol-5-yl methyl ketone, melting point 75°-76° C. Then, 41.8 g of this ketone were dissolved in 1 l of ethanol, cooled to 0° C. and 7 g of sodium borohydride were added portionwise. Thereafter, the mixture was stirred at 20° C. for 3 hours, evaporated in a vacuum to a large extent, 200 ml of water were added, the mixture was adjusted slowly to pH 4 with 1N sulfuric acid while cooling and extracted three times with ether. The extracts were washed with water, dried and evaporated, and 42.6 g of α,2,2-trimethyl-1,3-benzodithiol-5-methanol were obtained. Thereafter, 39.5 g of this alcohol were reacted with 65.9 g of triphenylphosphine hydrobromide in 500 ml of acetonitrile and worked-up as described in Example 8 and 96.3 g of [1-(2,2-dimethyl-1,3-benzodithiol-5-yl)ethyl]triphenylphosphonium bromide were obtained. Then, 17.0 g of this phosphonium salt were reacted with methyl 4-formyl-benzoate in analogy to Example 8. After working-up and recrystallization from ethyl acetate/hexane, there were obtained 4.9 g of methyl p-[(E)-2-(2,2-dimethyl-1,3-benzo-dithiol-5-yl)propenyl]benzoate in the form of colorless crystals, melting point 86°-87° C.

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