Application of a metathesis reaction in the synthesis of sterically congested medium-sized rings. A direct ring closing versus a double bond migration–ring closing process

An efficient double bond migration–ring closing metathesis reaction leading to cycloheptene derivatives is observed when specific sterically congested 1,9-dienes are treated with the Grubbs' imidazolidene ruthenium catalyst. The simultaneous use of the Grubbs' catalyst and RuClH(CO)(PPh₃)₃ facilitates the tandem bond migration–metathesis process. RuClH(CO)(PPh₃)₃ alone is capable of triggering an unactivated double bond migration that may have preparative applications.