Serendipitous discovery of Pd-catalyzed intramolecular cyclization of ortho-bromo(hetero)aryl-substituted (hetero)aryl-1,2-diketones: Applications in the synthesis of carba- and heterocyclic benzoin derivatives

and heterocyclic benzoin derivatives were prepared by Sonogashira coupling of alkynes with 1,2-dihaloalkenes and subsequent oxidation of the alkyne to a 1,2-diketone. The Pd-catalyzed reaction of the product with (2-bromophenyl)boronic acid in the presence of phenylacetylene resulted in formation of cyclic benzoin derivatives by Suzuki-Miyaura reaction and subsequent Pd catalyzed nucleophilic addition to the carbonyl group. Hitherto unprecedented 5-hydroxy-5-phenylbenzo[b]naphtho[1,2-d]thiophene-6(5H)-ones and their regioisomers were prepared from 2,3-dibromobenzothiophene. Phenanthrene benzoin derivatives were prepared from 2-bromo-1-iodobenzene. [Display omitted]