STEREOCHEMICAL FEATURES OF CYCLOADDITION OF HETEROAROMATIC N-YLIDES. SELECTIVE PARTICIPATION OF THE ANTI AND SYN YLIDES
In the cycloaddition of heteroaromatic N-ylides to symmetrically substituted trans olefins, the anti ylide exclusively participates if the ylide is carbonyl-stabilized, while the syn ylide does if it has a substituent of non-carbonyl type. The cycloadducts isomerize into thermodynamically more stable isomers through a retro reaction.