| Abstract
| - Cobalt carbonyl complex Co2(CO)8 implemented an intramolecular carbonylation of cis-epoxyalkynesto generate Co2(CO)6-stabilized γ-lactonyl allene species. For 1,1,2-trisubstituted epoxyalkynes, this Co2(CO)6-allene species reacted with a tethered olefin to give [2 + 2]-cycloadducts, and with CO and atethered olefin to produce [2 + 2 + 1]-cycloadducts. These resulting cycloadducts have a 5,6-diydropyran-2-one core fused with a cyclobutane and a cyclopentanone ring, respectively. For 1,2-disubstituted cis-epoxyalkyne and 1,1,2-trisubstituted cis-epoxyalkynes bearing a heteroatom constituent, cyclization ofthe corresponding epoxyalkyne with a tethered alkene is invariably accompanied by incorporation of COto produce a [2 + 2 + 1]-cycloadduct, even in the absence of CO. We have prepared various 1,1,2-trisubstituted and 1,2-disubstituted cis-epoxyalkynes to generalize such cycloaddition pathways. Attemptto use an organic promoter to perform these tandem cycloadditions was unsuccessful because of acompeting Pauson−Khand reaction. Cyclization of a 1,2-disubstituted epoxyalkyne with a tethered dienewas achieved successfully in one case, but the yield was low (25%).
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