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

Abstract

Alkylation of 1,4-cyclohexanedione monoethylene acetal SAMP-hydrazone with various electrophiles (10 examples given) and subsequent cleavage of the hydrazones with saturated oxalic acid furnished highly enantiomerically enriched alpha-alkylated mono-protected 1,4-cyclohexanedione derivatives in high yields and enantiomeric excesses of ee = 28, 80->/=99%. Reduction of the ketones gave the corresponding alcohols in good yields with high enantiomeric excesses (ee = 80->/=98%) and cis/trans-ratios of usually 85:15.