Regioselective Aldol Addition Reaction of Nitroalkane Dianions.

Previously we reported regioselective formation of dianions derived from liner nitroalkanes in the presence of n-BuLi and HMPA. The formation of nitroalkane dianions either α,α- or α,β-dianions depended on the order of addition of reagents. However, the usage of a carcinogen suspected compound like HMPA is undesirable. Therefore we re-investigated the new combination of bases and aprotic dipolar solvents other than HMPA. After exploration of a variety of their combination, it was found that the combination of LDA and DMPU resulted in the formation of α,β-dianion with the best regioselectivity; the ratio of α- to β-adduct was 1 to 14 in the reaction of nitroethane with benzaldehyde.