Thermal and photochemical transformation of conformational chirality into configurational chirality in the crystalline state

Because they crystallize in chiral conformations in which abstraction of only one of two diastereotopic γ-hydrogen atoms is possible, salts formed between achiral keto-acids possessing the tricyclo[4.4.1.0]undecane ring system and optically pure amines undergo Norrish type II cleavage in the solid state in enantiomeric excesses as high as 95% at 98% conversion, following removal of the ionic chiral auxiliaries. Thermal enolene rearrangement of the same salts results in optical yields approximately half those observed for the photochemical reaction. Copyright © 2003 American Chemical Society.