Benzylic Metallation of Thiobenzamides and Thionaphthamides

Various secondary thiobenzamides and thionaphthamides have been prepared, and features of their conformations [orthogonality of the arene and thioamide planes, (Z) geometries in solution etc.] have been determined. Deprotonation with sec-butyllithium selectively provided either the monoanion or the dianion, according to the stoichiometry of the base. The monoanion reacted with soft electrophiles (alkyl halides) through the sulfur atom and with hard electrophiles (acyl halides) through the nitrogen centre. Formation of the dianion, more reactive than the thioamide anionic moiety, allowed reaction at the benzylic centre. Addition of electrophiles allowed selective formation of C−C or C−X bonds. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)