Formal [2+2+2] Cycloaddition Strategy Based on an Intramolecular Propargylic Ene Reaction/Diels-Alder Cycloaddition Cascade
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Danheiser Revised JACS 2010 132 11039.pdf
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Author(s)
Robinson, Julia M.
Sakai, Takeo
Okano, Katsuhiko
Kitawaki, Takafumi
Danheiser, Rick Lane
Date Issued
July 2010
Journal
Journal of the American Chemical Society
Publisher
American Chemical Society
Citation
Robinson, Julia M. et al. “Formal [2 + 2 + 2] Cycloaddition Strategy Based on an Intramolecular Propargylic Ene Reaction/Diels−Alder Cycloaddition Cascade.” Journal of the American Chemical Society 132 (2010): 11039-11041. Web. 16 Dec. 2011. © 2011 American Chemical Society
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Author's final manuscript
Abstract
A formal, metal-free, [2 + 2 + 2] cycloaddition strategy is described based on a cascade of two pericyclic processes. The first step involves an intramolecular propargylic ene reaction of a 1,6-diyne to generate a vinylallene, which then reacts in an inter- or intramolecular Diels−Alder reaction with an alkenyl or alkynyl dienophile. Reactions involving unsymmetrical alkenyl and alkynyl dienophiles proceed with good to excellent regioselectivity, and the diastereoselectivity in the Diels−Alder step is also high, with endo cycloadducts produced as the exclusive products of the reaction. In the case of alkynyl dienophiles, [4 + 2] cycloaddition initially generates an isotoluene-type intermediate that isomerizes to the isolated aromatic product upon exposure to a catalytic amount of DBU at room temperature. The mechanism of several earlier fully intramolecular related transformations have been shown to involve an analogous process rather than the diradical-mediated pathways proposed previously.
Description
Experimental procedures, characterization data, and [superscript 1]H and [superscript 13]C NMR spectra for all new compounds. This material is available free of charge via the Internet at http://pubs.acs.org.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
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DOI of Published Version
https://doi.org/10.1021/ja1053829
