Perrhenate Esters as Intermediates in Molecular Complexity-Increasing Reactions

Abstract

Allylic alcohols form perrhenate esters upon reaction with Re2O7 or HOReO3. These species undergo non-stereospecific and non-regiospecific alcohol transposition reactions through cationic intermediates. Sequencing these non-selective processes with reversible trapping by electrophiles results in cyclization reactions where regio- and stereocontrol are dictated by thermodynamics. The cationic intermediates can also be utilized as electrophiles in intra- or intermolecular dehydrative reactions with nucleophiles. These processes serve as the basis for applications to the catalytic syntheses of a wide range of heterocyclic and carbocyclic structures that often show high increases of molecular complexity. This Account describes the sequence of events that started from a need to solve a problem for the completion of a natural product synthesis and evolved into a central element in the design of numerous new transformations that proceed under mild conditions from readily accessible substrates.

Solvent Effects and Mechanistic Studies for Re2O7-Catalyzed Allylative Annulation Reactions

“…Whitlock defined molecular complexity in terms of size (more bonds equate to greater complexity) and structural features such as rings, stereocenters, unsaturations, and heteroatoms . We have been engaged in a program in which reactions based on the interaction of allylic and benzylic alcohols with Re 2 O 7 and related species are employed to increase molecular complexity. , We reported a process (Scheme ) in which allylic alcohol transposition is followed by addition into a carbonyl group to form a cyclic hemiacetal or hemiketal, ionization to form an oxocarbenium ion, and bimolecular nucleophilic addition. , The process couples two fragments while creating a ring and at least one stereocenter, and the reversibility of the initial steps of the process allows for relative stereocontrol.…”