Ring-opening metathesis-cross-metathesis reactions (ROM-CM) of substituted norbornadienes and norbornenes

Ring-opening metathesis-cross-metathesis reactions (ROM-CM) of substituted norbornadienes and norbornenes were investigated. The reactions with symmetrical 2,3-disubstituted norbornadienes were found to be highly chemoselective, with the ROM reactions occurring only on the less substituted or less sterically hindered double bonds regardless of the electronic nature of the substituents, giving highly substituted cyclopentenes in moderate to good yields. This study provides an efficient method for the stereoselective synthesis of highly substituted cyclopentenoids. Long-range electronic effect of a remote substituent on unsymmetrical norbornenes in the ROM-CM reactions was also investigated. Low levels of regioselectivities were observed (50:50 to 69:31) with various remote substituents on the norbomenes. (C) 2002 Elsevier Science Ltd. All rights reserved.