Stereochemical Study on 1,3-Dipolar Cycloaddition Reactions of Heteroaromatic N-Ylides with Unsymmetrically Substituted Olefinic Dipolarophiles

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Abstract
Regioselectivity and stereoselectivity of the cycloadditions of heteroaromatic N-ylides with unsymmetrically-substituted olefins such as methyl-substituted cis olefins, an acrylate, the related olefins, trans nitro olefins, and other trans olefins have been investigated. These cycloadditions are highly regioselective, while the stereoselectivity depends upon both the electronic and steric nature of substituents of the ylide and olefin. The 1-endo-2-exo cycloadducts of the anti form of ylides which have been formed as kinetically controlled products undergo the isomerization into either the 1-endo-2-exo cycloadducts of the syn ylides through a retro cycloaddition process or the 1-exo-2-endo cycloadducts of the syn ylides via betaine intermediates.