Michael monoadditions of nitromethane or nitroethane with electrophilic gem-disubstituted alkenes over alumina under microwave irradiation

Nitromethane 1a or nitroethane 1b react with electrophilic alkenes 2a-i RCHC(CN)(Y) with Y=CO₂R′, CN, CONH₂ adsorbed on alumina to give selectively at room temperature or under focused microwave irradiation new Michael monoadducts 5 (two diastereoisomers) or 6 (four diastereoisomers) after a few minutes. It is possible to obtain only two diastereoisomers of 6 by reaction of the corresponding nitroalkene and methylcyanoacetate in the presence of catalytic amounts of piperidine. Mechanisms are proposed. Some examples of addition of nitroalkanes with electron-deficient alkynes in dry media coupled with microwave irradiation conditions are also described.