In Tandem Enantioselective Intramolecular Heck-Matsuda Reactions directly from anilines

Abstract

A new enantioselective intramolecular strategy for the synthesis of enantioenriched bridged benzoxacines, unsaturated spirobenzofurans, methyl-2,3-dihydrobenzofuran acetates, and methyl-2,3-indoline acetate scaffolds in a tandem-like diazotization/Heck Matsuda process directly from anilines has been developed. The process combines the in situ diazotization of the aniline, followed by the intramolecular Heck-Matsuda reaction, thus skipping the isolation and purification of unstable or hard-to-synthesize aryldiazonium salts. The practicality and robustness of the sequence were demonstrated by the synthesis of 26 examples of complex structural motifs with yields up to 91% and enantiomeric ratio (er) up to 97:3, including quaternary stereocenters. The in-tandem processes from anilines were compared to conventional Heck Matsuda reactions using pre-synthesized aryldiazonium salts. With few exceptions, the reactions starting directly from the anilines afforded better overall yields and er, demonstrating the efficiency of this method.