A Facile Synthesis of 4-Aryl-1H-2-benzothiopyran-3-carboxylic Acid Derivatives from o-Bromobenzyl Mercaptans

The synthesis of 4-aryl-1H-2-benzothiopyran-3-carboxylic acid derivatives by a sodium hydride-mediated thiopyran ring formation of 2-[(2-aroylphenyl)methylsulfanyl]acetic acid derivatives is reported. The precursors were prepared by successive treatment of lithium o-lithiobenzyl mercaptides, which were generated by the reaction of o-bromobenzyl mercaptans with two equivalents of butyllithium, with aromatic aldehydes and 2-bromoacetonitrile or tert-butyl 2-bromoacetate, followed by oxidation of the resulting sulfanyl alcohols with pyridinium chlorochromate (PCC).