Stereoselectivity in the TiCl4-Catalyzed [4+2] Cycloaddition of Cyclopentadiene to (2R)-Bornane-10,2-sultam Derivatives of Fumaric Acid Monoesters

The 4+2] cycloaddition of cyclopentadiene to the (2R)-bornane-10,2-sultam derivative (−)- 1b of fumaric monomethyl ester proceeds with high endo and π-facial diastereoselectivity in the presence of 0.5 mol-equiv. of TiCl₄. The major diastereoisomer endo-(2R,3R)- 2b , isolated in 87% yield by crystallization, was subjected to X-ray crystal-structure analysis. Steric influence of ethyl- and benzyl-ester analogues (−)- 1c and (−)- 1d , respectively, is also reported.