Mechanistic Investigation of the Pd-Catalyzed Intermolecular Carboetherification and Carboamination of 2,3-Dihydrofuran: Similarities, Differences, and Evidence for Unusual Reaction Intermediates

Abstract

The mechanism of the Pd-catalyzed intermolecular syn carboetherification and syn carboamination of 2,3-dihydrofuran was investigated experimentally. Crystallographic, spectroscopic, and spectrometric methods have shed light on the nature of a number of catalytically competent palladium complexes. Several oxidative addition complexes as well as their cationic derivatives have been characterized by X-ray diffraction analyses. In the latter, the complexes derived from 2-bromophenol displayed an unorthodox η6 binding mode of the privileged Buchwald-type dialkylbiarylphosphine ligands. The hemilabile character of this interaction was found to facilitate coordination of the polarized olefinic substrate, as evidenced by NMR spectroscopy. In contrast, coordination of the pendant sulfonyl group in the cationic complexes derived from 2-bromo-N-sulfonylated anilines prevented direct binding of 2,3-dihydrofuran. Deprotonation of these species induced aggregation of monomeric units through various weak noncovalent int...