Dirhodium(II)-catalyzed intramolecular carbon-hydrogen insertion reaction of alpha-diazoketones: Synthesis of 7-silyloxyoctahydrobenzo[b]furan-2-ones

A dirhodium(II)-catalyzed intramolecular C-H insertion reaction of 2-oxygen-substituted cyclohexyl diazo-acetoacetates 1a-f was investigated. In contrast to the trans-2-methoxy-1a and trans-2-(p-methoxybenzyloxy)-cyclohexyl derivatives 1b, which, upon treatment with 1 mol% dirhodium(II) tetraacetate in boiling benzene, gave a complex mixture, the trans-2-(tert-butyldimethylsilyloxy)cyclohexyl derivative 1c gave, in addition to the p-lactone 3c (16%), cis- and trans-fused octahydrobenzo[b]furan-2-ones 2c in 22 and 18% yields, respectively. Similar treatment of the cis-isomer 1d gave the beta-lactone 3d as the major product (34%) and cis- and trans-fused gamma-lactones 2d (7 and 18% yields, respectively) as minor products. The (1R*,2R*,3R*)-3-benzyloxy-2-(tert-butyldimethyl-silyloxy)cyclohexyl derivative le gave the gamma-lactones 2e in 75% combined yield as a 5:2 mixture of cis- and transfused isomers, while the (1R*,2S*,3R*)-isomer 1f afforded the trans-fused gamma-lactone 2f in 62% yield as a single product.