Thioester Acyl Anion Equivalent Effective as a Soft Nucleophile

Tris(phenylthio)methane (1) is one of the orthoformate derivatives and is used as a thioester acyl anion equivalent. The anion species prepared from butyllithium and 1 shows soft nucleophilicity and the 1,4-addition reaction with enones proceeds to form the related enolate anion species. This enolate anion subsequently reacts with an electrophile and the three-component adduct 2 is produced. The given product 2 is treated with silver trifluoromethanesulfonate (AgOTf) to proceed with the elimination of a phenylthio group affording the desired cyclic compound 3. In this transformation, when using excess amounts (3 equivalents) of AgOTf, further elimination of another phenylthio group proceeds and the aromatized product 4 is given. In this way, 1 is a useful soft thioester acyl anion equivalent for introducing a one-carbon unit as a component.