LIGAND EXCHANGE AND LIGAND COUPLING VIA THE σ-SULFURANE INTERMEDIATE IN THE REACTION OF ALKYL 2-PYRIDYL SULFOXIDE WITH GRIGNARD REAGENTS: CONVENIENT PREPARATION OF 2,2′-BIPYRIDINES

Abstract

The reaction between methyl 2-pyridyl sulfoxide (1) with Grignard reagents afforded 2,2′-bipyridine (2) in moderate yield. The reaction is considered to involve initial ligand exchange to generate 2-pyridylmagnesium halide which in the subsequent step attacks the original sulfoxide to form the σ-sulfurane that undergoes ligand coupling to afford 2. The reaction of t-butyl 2-pyridyl sulfoxide (3) with C₆H₅MgBr, however, gave only 2-phenylpyridine (4). This may be due to steric hindrance to the initial ligand exchange. Formation of 2 is a convenient process for preparation of 2,2′-bipyridines bearing various substituents.