Tandem Cycloaddition Chemistry of Nitroalkenes: Preparative and Theoretical Studies on the Stereochemical Course of [3 + 2] Cycloaddition of Cyclic Nitronates.

Intermolecular [3 + 2] cycloadditions between two cyclic nitronates and a series of dipolarophiles are examined. High facial selectivity is observed in all cases and is analyzed with the aid of ab initio transition structure calculations. Monosubstituted dipolarophiles reacted with exclusive regiocontrol. Disubstituted dipolarophiles reacted with varying degrees of regiocontrol, which was dependent on the substituent. A theoretical approach for predicting regioselectivity is discussed. Exo selectivity was generally favored due to steric effects, and was especially high with cis-disubstituted dipolarophiles.