Tungsten-catalyzed heterocycloisomerization approach to 4,5-dihydro-benzo[b]furans and -indoles

A W(CO)(5)·THF-catalyzed cycloisomerization of bicyclo4.1.0] substrates to afford mono C4-substituted 4,5-dihydro-benzob]furans and -indoles is reported. The title compounds are versatile intermediates that lead to a range of fused bicycles including the cores of various furan-, benzofuran-, and indole-containing natural products. In many cases, the functionalization of the dihydro-benzob]furans and -indoles is orthogonal to that of the corresponding benzofurans and indoles and, thus, offers complementary approaches for synthesis.