Ruthenium(II)-catalyzed [2+2] cycloadditions of anti 7-substituted norbornenes

The ruthenium (II)-catalyzed [2+2] cycloadditions of anti 7-substituted norbornenes with an alkyne were investigated. The cycloadditions were found to proceed with a high degree of stereoselectivity, giving only the exo stereoisomers in moderate to good yields using an improved protocol. Comparative rate studies between a variety of anti 7-substituted norbornenes and an alkyne revealed that the reactivity of the alkene component decreases dramatically as the alkene becomes more electron deficient. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).