Carbonium vs. carbenium ion-like transition state geometries for carbocation cyclization – how strain associated with bridging affects 5-exo vs. 6-endo selectivity

摘要

Quantum chemical calculations are used to explore the origins of regioselectivity for proton-, Pt(II)- and Pd(II)-promoted cyclizations of 1,5-hexadienes, 5-aminoalkenes, and allylic acetimidates. The strain associated with achieving carbonium ion-like transition state geometries is shown to be a key factor in controlling 5-exo vs. 6-endo selectivity.