Spirolactones from Dirhodium(II)-Catalyzed Diazo Decomposition with Regioselective Carbon-Hydrogen Insertion

Article abstract of DOI:10.1021/jo00115a018

Dirhodium(II) caprolactamate, Rh2(cap)4, catalyzes diazo decomposition of cycloalkylmethyl diazoacetates which form spirolactones in moderate to high yield by insertion into a tertiary carbon-hydrogen bond.Similar results are obtained with diazoacetates derived from tetrahydropyran-2-methanol and tetrahydrofurfuryl alcohol but not from cyclopropylmethanol.With tetrahydrofuran-3-ylmethyl diazoacetate, Rh2(cap)4 catalysis promotes δ-lactone formation via insertion into the oxygen-activated secondary C-H bond instead of γ-lactone formation by carbene insertion into the unactivated tertiary C-H bond.However, when both 1,5- and 1,6-positions are activated for insertion by adjacent oxygen atoms, as in (2,2-dimethyl-1,3-dioxolan-4-yl)methyl diazoacetate, five-membered ring formation occurs exclusively in Rh2(cap)4-catalyzed reactions, whereas use of dirhodium(II) acetate leads to both insertion products.