K. J. Berg, A. Leusen
Sep 2, 2010
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Journal
Recueil des Travaux Chimiques des Pays-Bas
Abstract
2,3-Dimethylene-2,3-dihydrothiophene (1), the thiophene analog of o-xylylene (o-quinodimethane), was generated in situ from the (trialkylammoniomethyl)-(trimethylsilylmethyl)thiophene iodides 4 or 5 by fluoride-induced 1,4 elimination, and was trapped by [4 + 2] cycloadditions with a series of dienophiles. The reaction of 1 with dimethyl fumarate was considerably faster than with dimethyl maleate. Unsymmetrical dienophiles gave mixtures of regio-isomers. In the absence of dienophiles. 1 formed [4 + 2] spiro dimers, of which 15a is the major component, as determined by H-1-NMR comparison with a tetradeutero analog of 15a. The syntheses of the new precursors of 1 and dideutero-1: compounds 4, 5a,b, as well as the 3,4-isomer of 4, are described.