Regio and Stereo Selectivity on the α-Aryl-δ-epoxynitrile Anionic Cyclization Reactions: Modulation towards a 5-Endo or 4-Exo Process

Abstract

Here we present a study focused on the regio and stereoselectivity of the anionic intramolecular cyclization reactions of several 4-(3,3-dimethyloxiran-2-yl)-2-arylbutanonitriles. The first part comprises the exploration of the reaction varying the temperature/solvent as well as the base counter-ion; switching between Li, Na and K that companies hexamethyldisilylamide anion. This is a well-known base used widely. In the second part, we provide a pair of methodologies that lead almost exclusively to pentacarbocycles through a 5-endo pathway, although is known to be a non-favored process in many cases. We found that both the metal counter-ion and the temperature have an important effect on the regioselectivity of the reaction and, independently of the pathway presented, the preferred diastereoselectivity is trans.