Regioselective Aldol Addition Reaction of Nitroalkane Dianions
Seiji TANAKA*, Kazunori KAWASAKI, Mariko HIRAO, Keiki KISHIKAWA, Shigeo KOHMOTO and Makoto YAMAMOTO
Department of Materials Technology, Faculty of Engineering, Chiba University; 1-33 Yayoi-cho, Inage-ku, Chiba-shi 263-8522 Japan
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.
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