Ligand effects in the organolithium-mediated enantioselective α-deprotonation of achiral epoxides

Construction of bicyclic ring systems via a transannular SmI2-mediated ketone-olefin cyclization strategy

The development of novel methods and strategies for the formation of polycyclic ring structures is of utmost importance in organic synthesis. The present study describes the investigation of a transannular cyclization strategy for constructing bicyclic ring systems. To test the viability of the approach, the SmI2-mediated ketone-olefin coupling reaction, a method previously developed in this laboratory, was examined. Investigation of the transannular cyclization of cyclooctene, cyclodecene, and cycloundecene derivatives revealed that the process proceeds with high yield and diastereoselectivity, and in the case of larger ring-sized compounds, with excellent regioselectivity. The regioselectivity of the annulation process could be rationalized based on examining the low energy conformations of the keto alkene starting materials. These results demonstrate the efficiency and the potential of the transannular cyclization tactic for the creation of bicyclic ring systems.

Functionalized bicyclo[3.3.0]octanes by enantioselective transannular desymmetrization

[figure: see text] Enantioselective alpha-deprotonation-rearrangement of achiral substituted cyclooctene oxides 7, 17, and 18 using organolithiums in the presence of (-)-sparteine (3) or (-)-alpha-isosparteine (4) gives the functionalized bicyclo[3.3.0]octan-2-ols 8, 19, and 20 in 56-72% yields and 83-89% ee's.