Synthesis and conjugate addition reactions of N-(β-nitroalkyl)amides

Abstract

Nitration of several di- and trisubstituted alkenes with lithium nitrate/TFAA in nitrile solvents afforded N-(β-nitroalkyl)amides in 28-72% yields. Nitration of 1,1-diphenylethene gave 1,1-diphenyl-2-nitroethene in 52% yield instead of the N-(β-nitroalkyl)amide. Reaction of 1-methylcyclohexene using excess lithium nitrate/TFAA in acetonitrile gave a single diastereomer of N-(2,6-dinitro-1-cyclohexyl)acetamide in 55% yield. N-(β-Nitroalkyl)amides underwent diastereoselective Michael addition to a variety of Michael acceptors. Diastereoselectivity is rationalized on the basis of internal hydrogen-bonding within the intermediate nitronate resulting in a strongly-biased Michael donor conformation.