Allylmetal-directed addition of O-1(2): Scope, mechanism and synthetic utility

Allylic silyl and stannyl groups strongly influence the regio- and stereoch emistry of alkene oxygenations by O-1(2), even within functionalized system s. Allylstannanes undergo anti-S(E)2' oxygenation to form both Z-stannylalk enyl hydroperoxides and 4-stannyl-1,2-dioxolanes; the ene-like reaction is generally preferred unless limited by allylic strain. The alkenylstannane p roducts, as well as the derived iodides, are effective substrates for palla dium-mediated cross-couplings, additions, carbonylations, and acylations to form peroxydienes, peroxyenones, and peroxyenoates. Allylsilanes are less effective directing groups, possessing reactivity surprisingly similar to s imple alkenes, and undergoing oxidation to form regioisomeric mixtures of h ydroperoxides. The different reactivities and product distributions observe d for allylstannanes and allylsilanes reflect different nucleophilicities o f the ground state alkenes as well as variable polarization of the developi ng perepoxides by the neighboring C-Sn or C-Si bond. The observed selectivi ty for production of Z-alkenylmetals appears to result from the preferentia l formation of a single perepoxide pyramidal isomer and the tendency for th is perepoxide to abstract the inside hydrogen on the metal-bearing carbon a t a rate which is faster than either perepoxide inversion or single bond ro tation to deliver the outside hydrogen for abstraction.