Abstract
Square planar cationic rhodium(I) dicarbonyl complexes [{Rh((mim) 2CH 2)(CO) 2} +BPh 4 −] ( 1) and [{Rh((mBnzim) 2CH 2)(CO) 2} +BPh 4 −] ( 2) [mim= N-methylimidazol-2-yl, mBnzim= N-methylbenzimidazol-2-yl] are catalysts for the cyclisation of alkynoic acids to lactones. The unsaturated acids, 4-pentynoic acid, 4-hexynoic acid and 5-hexynoic acid were cyclised to γ-methylene-γ-butyrolactone, E-5-ethylidenetetrahydro-2-furanone and 6-methylidenetetrahydo-2-pyrone, respectively. Cyclisation of 4-hexynoic acid proceeds stereoselectively with exclusive formation of the E-isomer of 5-ethylidenetetrahydro-2-furanone. Complexes 1 and 2 also catalyse cyclisation of acetylenic alcohols to oxygen-containing heterocycles.
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