Cycloaddition reactions of chiral 2-amino-1,3-butadienes with nitroalkenes: Synthesis of enantiomerically pure 4-nitrocyclohexanones

2-Amino-1,3-butadienes bearing commercially available S-(+)-2-(methoxymethyl)pyrrolidine as chiral auxiliary undergo a [4 + 2] cycloaddition reaction with nitroalkenes to furnish 4-nitrocyclohexanones upon hydrolysis of the resulting enamine. The cycloadducts are obtained with good yields and very high enantiomeric excesses. The reaction has been performed with aromatic and aliphatic conjugated nitroalkenes. Moreover, a 2-amino diene which features a (Z) double bond undergoes a Michael addition reaction with nitroalkenes, which gives rise to open chain compounds with high enantioselectivity. After acidic hydrolysis, the open chain compounds cyclize to form chiral substituted furans.