Diisopropylamine → (3S,4S)-3-[(1R)-1-(tert-butyldimethylsilyloxy)ethyl]-4-[(1R)-1-[(methylthio)thiocarbonyl}ethyl]-2-oxoazetidine

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반응 단계

To a solution of diisopropylamine (152 mg) in anhydrous tetrahydrofuran (2 ml) cooled to 0° C. was added a 1.56M solution of n-butyllithium in n-hexane (0.95 ml). After stirring for 30 minutes at 0° C., the solution was cooled to -78° C. and methyl dithiopropionate (120 mg) and a 1M solution of chlorotitanium triisopropoxide in hexane (4.0 ml) were added successively thereto. The mixture was warmed to -40° C. and (3R,4R)-4-acetoxy-3-[(1R)-1-(tert-butyldimethylsilyloxy)ethyl]-2-oxoazetidine (287 mg) was added thereto. The solution was allowed to warm to 0° C., quenched by 1N hydrochrolic acid, and extracted with diethyl ether. The organic layer was washed with brine, dried, and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel (10% diethyl ether-hexane) to afford a mixture (202 mg) of (3S,4S)-3-[(1R)-1-(tert-butyldimethylsilyloxy)ethyl]-4 -[(1R)-1-[(methylthio)thiocarbonyl}ethyl]-2-oxoazetidine and (3S,4S)-3-[(1R)-1-(tert-butyldimethylsilyloxy)ethyl]-4-[(1S)-1-{(methylthio)thiocarbonyl}ethyl]-2-oxoazetidine. Recrystallization of the product obtained above from n-hexane gave (3S,4S)-3-[(1R)-1-(tert-butyldimethylsilyloxy)ethyl]-4-[(1R)-1-{(methylthio)thiocarbonyl}ethyl]-2-oxoazetidine as a yellow needle.

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