A New Co2(CO)8-Mediated Tandem [5 + 1]/[2 + 2 + 1]-Cycloaddition Reaction: A One-Pot Synthesis of Tricyclic δ-Lactones from cis-Epoxy Ene-ynes
摘要:
In the presence of Co2(CO)8 and CO, cis-epoxyalkynes bearing a tether olefin undergo a tandem [5 + 1]/[2 + 2 + 1]-cycloaddition to give tricyclic delta-lactones efficiently in a one-pot operation. The reaction mechanism is proposed to involve a cobalt-coordinated cyclic allene species.
A New Co2(CO)8-Mediated Tandem [5 + 1]/[2 + 2 + 1]-Cycloaddition Reaction: A One-Pot Synthesis of Tricyclic δ-Lactones from cis-Epoxy Ene-ynes
摘要:
In the presence of Co2(CO)8 and CO, cis-epoxyalkynes bearing a tether olefin undergo a tandem [5 + 1]/[2 + 2 + 1]-cycloaddition to give tricyclic delta-lactones efficiently in a one-pot operation. The reaction mechanism is proposed to involve a cobalt-coordinated cyclic allene species.
Dicobaltoctacarbonyl-Mediated Synthesis of Tricyclic 5,6-Diydropyran-2-one Derivatives via Tandem Cycloaddition Reaction between <i>cis</i>-Epoxyalkynes, a Tethered Olefin, and Carbon Monoxide
作者:Arjan Odedra、Shie-Fu Lush、Rai-Shung Liu
DOI:10.1021/jo0620617
日期:2007.1.1
[GRAPHIC]Cobalt carbonyl complex Co-2(CO)(8) implemented an intramolecular carbonylation of cis-epoxyalkynes to generate Co-2(CO)(6)-stabilized gamma-lactonyl allene species. For 1,1,2-trisubstituted epoxyalkynes, this Co-2(CO)(6)-allene species reacted with a tethered olefin to give [2 + 2]-cycloadducts, and with CO and a tethered 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 of the corresponding epoxyalkyne with a tethered alkene is invariably accompanied by incorporation of CO to 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. Attempt to use an organic promoter to perform these tandem cycloadditions was unsuccessful because of a competing Pauson-Khand reaction. Cyclization of a 1,2-disubstituted epoxyalkyne with a tethered diene was achieved successfully in one case, but the yield was low (25%).