ORGN 17 |
Air-initiated reactions: Vinyl cyclopropane openings with aryl sulfur radicals
| Mitchell A. deLong1, Julie A. Mathews1, Fred C. Wireko2, Amanda L. Ritter2, and Anna D. Gudmundsdottir1. (1) Department of Chemistry, University of Cincinnati, P.O. Box 210172, Cincinnati, OH 45221, (2) Central Research, Procter & Gamble, 11810 East Miami River Road, Cincinnati, OH 45252 |
Vinylcyclopropanes, particularly strained vinylcyclopropanes such as those derived from an arene-olefin meta-photocyclization reaction, are sensitive to 1,5 ring-opening addition of nucleophilic radicals. Described are conditions for opening silyl-stabilized arene-olefin products, as are the scope and limitations of this reaction. Sulfur radicals are easily generated in refluxing acetonitrile with catalytic benzoyl peroxide; but at room temperature, either under solvent-free or with minimal ethanol, nascent thiophenol radicals, presumably formed by air-oxidation, could be trapped before disulfide formation by the vinylcyclopropanes, generating single isomers of complex materials in only two steps from simple, readily-available starting materials using environmentally-benign agents (light and air). In contrast to the arene-olefin derived vinylcyclopropanes, not all of the other substrates explored give radical-initiated addition products. (-) Thujopsene (3), a sesquiterpene natural product that contains a naturally occurring vinylcyclopropane moiety, gives, when reacted with methyl meta mercaptobenzoate under these ‘Green’ conditions, not the expected (4), but rather (5). |
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