LICLO4-CATALYZED NUCLEOPHILIC-ADDITION TO ALPHA-CHIRAL ALDEHYDES, ALDIMINES, AND OXIRANES

The diastereoselectivity of lithium perchlorate-induced addition of tr imethylsilyl cyanide and O-silylated ketene acetals to alpha-chiral al dehydes is studied. Whereas aldehyde 1 reacts with the ketene acetal 2 exclusively to form the syn-ester 3, a divergent selectivity is obser ved in the case of trimethylsilyl cyanide addition to 5 and 11a-c. Als o the reaction of O-silylated ketene acetals with aldimines 16 in the presence of lithium perchlorate proceeds smoothly to afford the corres ponding beta-amino esters 17 in high yields. While the silyl ketene ac etal of methyl acetate leads preferentially to the corresponding anti- diastereomer, in the case of the silyl ketene acetal of methyl isobuty rate a syn-/anti-selectivity in the range of 79:21 to 44:56 is observe d. In the presence of lithium perchlorate solution in ether the oxiran es 27a-d undergo facile nucleophilic ring opening reactions with 2, 29 , and 30.