Ligand coupling within σ-sulphurane intermediates formed in the reaction of benzyl 2-pyridyl and related sulphoxides with Grignard reagents

The reaction of benzyl or 1-phenylethyl 2-pyridyl sulphoxide (1) or (18) with a Grignard reagent was found to give the ligand-coupling product, i.e., 2-benzylpyridine or 2-(1-phenylethyl)pyridine (2) or (22) in excellent yield. This coupling reaction was found to proceed within the σ-sulphurane formed as an intermediate upon treatment of benzyl 2-pyridyl and related sulphoxides with a Grignard reagent. The stereochemical course of this coupling reaction involves complete retention at the benzylic carbon.