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Tandem catalysis for asymmetric coupling of ethylene and enynes to functionalized cyclobutanes

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Science  06 Jul 2018:
Vol. 361, Issue 6397, pp. 68-72
DOI: 10.1126/science.aat6205

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Cyclobutanes sourced right from ethylene

Ethylene is one of the highest-volume commodity chemicals manufactured from fossil fuels. It is mainly used to make plastic, although its ready availability incentivizes its expanded use in pharmaceutical synthesis. Pagar and RajanBabu now report that a cobalt catalyst can couple ethylene with enynes (another comparatively inexpensive feedstock bearing carbon-carbon double and triple bonds) to make complex chiral molecules. Initially, the ethylene reacts with the enyne's triple bond to form an isolable cyclobutene compound. At longer reaction times, the same catalyst can add a second equivalent of ethylene enantioselectively to form cyclobutanes with a quaternary chiral carbon center.

Science, this issue p. 68

Abstract

Transformation of simple precursors into structurally complex cyclobutanes, present in many biologically important natural products and pharmaceuticals, is of considerable interest in medicinal chemistry. Starting from 1,3-enynes and ethylene, both exceptionally inexpensive starting materials, we report a cobalt-catalyzed route to vinylcyclobutenes, as well as the further enantioselective addition of ethylene to these products to form complex cyclobutanes with all-carbon quaternary centers. These reactions can proceed in discrete stages or in a tandem fashion to achieve three highly selective carbon-carbon bond formations in one pot using a single chiral cobalt catalyst.

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