"Concerted" transition state, stepwise mechanism. Dynamics effects in C2-C6 enyne allene cyclizations.

ABSTRACT: The C2-C6 (Schmittel)/ene cyclization of enyne-allenes is studied by a combination of kinetic isotope effects, theoretical calculations, and dynamics trajectories. For the cyclization of allenol acetate 9, the isotope effect (k(CH3)/k(CD3) is approximately 1.43. The isotope effect is interpreted in terms of a highly asynchronous transition state near the concerted/stepwise boundary. This is supported by density functional theory calculations that locate a highly asynchronous transition structure for the concerted ene reaction. However, calculations of both the experimental system and a model reaction were unable to locate a transition structure for formation of the diradical intermediate of a stepwise mechanism. The stepwise mechanism and the asynchronous concerted mechanism start out geom

SUBMITTER: Bekele T 

PROVIDER: S-EPMC2501108 | biostudies-literature | 2005 Jun

REPOSITORIES: biostudies-literature