Directed Ortho Metalation of N,N-Diethylbenzamides. Silicon Protection of Ortho Sites and the o-Methyl Group

Article abstract of DOI:10.1021/jo00279a028

New general methodology of value in aromatic chemistry based on silicon protection of preferred ortho metalation sites in benzamides and o-methyl groups in o-toluamides (1, 2, Scheme I) is described.According to these methodologies, routes (Scheme II and V) to 1,2,5-, 1,2,4,5-, and 1,2,3-substituted aromatics with a variety of functionalities and oxidation states have been developed (Tables I and II).These tactics are used for the synthesis of difficult to access halo (10a-b, Scheme III) and methyl (21,25, Scheme VI) heterocycles.Ipso bromodesilylation reactions with bromine lead regiospecifically to o-bromobenzamides (12a,c, 14, Scheme IV).Walk-around-the-ring metalation processes provide highly substituted aromatics 27, 28, 29, and 30 (Scheme VII); the X-ray structure of the hexasubstituted derivative 30 shows a significant puckering of the aromatic ring.Cesium fluoride induced carbodesilylation of o-silylbenzamides with benzaldehyde affords, after TsOH cyclization, phthalides (31a-c, Scheme VIII) and constitutes a neutral alternative to the directed ortho metalation approach. α- and α,α-silylated o-toluamides are used in fluoride-mediated carbodesilylation (34a,d, Scheme IX) and desilylative Peterson olefination (35, Scheme X) procedures, respectively.The utility of α-silylated o-toluamide for the synthesis of a tetralin (38, Scheme XI) via an o-quinodimethane species is given.