Efficient asymmetric synthesis of alpha-alkylated 1,4-cyclohexanedione derivatives, important chiral building blocks in the synthesis of natural products

Alkylation of 1,4-cyclohexanedione monoethylene acetal SAMP-hydrazone with various electrophiles (10 examples given) and subsequent cleavage of the hy drazones with saturated oxalic acid furnished highly enantiomerically enric hed alpha-alkylated mono-protected 1,4-cyclohexanedione derivatives in high yields and enantiomeric excesses of ee = 28, 80-greater than or equal to 9 9%. Reduction of the ketones gave the corresponding alcohols in good yields with high enantiomeric excesses (ee = 80-greater than or equal to 98%) and cis/trans-ratios of usually 85:15. (C) 2000 Wiley-Liss, Inc.