Organoiron- and Fluoride-Catalyzed Phosphinidene Transfer to Styrenic Olefins in a Stereoselective Synthesis of Unprotected Phosphiranes

Catalytic phosphiranation has been achieved, allowing preparation of trans-1-R-2-phenylphosphiranes (R = t-Bu: 1-t-Bu; i-Pr: 1-i-Pr) from the corresponding dibenzo-7-(R)-7-phospha-norbornadiene (RPA, A = C14H10, anthracene) and styrene in 73% and 57% isolated yields, respectively. The cocatalyst system requires tetramethylammonium fluoride (TMAF) and [Fp­(THF)]­[BF4] (Fp = Fe­(η5-C5H5)­(CO)2). In the case of the t-Bu derivative, the reaction mechanism was probed using stoichiometric reaction studies, a Hammett analysis, and a deuterium labeling experiment. Together, these suggest the intermediacy of iron-phosphido FpP­(F)­(t-Bu) (2), generated independently from the stoichiometric reaction of [Fp­(t-BuPA)]­[BF4] with TMAF. Two other plausible reaction intermediates, [Fp­(t-BuPA)]­[BF4] and [Fp­(1-t-Bu)]­[BF4], were prepared independently and structurally characterized.