Preparation of the first gem-dialkylthio-analogues of Meisenheimer complexes from troponoids

Abstract

Both the labile gem-dialkylthio-adduct (2) of equilibrium with the prevailing non-cyclized form, have attack of methanethiolate a t C(2) of 2-methylthio-5-been obtained ; the absence of the 5-nitro-group leads nitrotropone and its spiro analogue (l), which is in either to non-gem-adducts or to no adduct at all.

Revival of troponoid chemistry

“…The obvious spiroannelation route27 failed, due to unexpectedly high repulsions in the dithiane ring (Scheme XI, A),28 but species 15 was finally obtained. 28 Clearly, in the case of 15 attack at C-2 benefits from charge acceptance by the nitro group, whereas attack at C-7 could not do so.…”

“…One such study of particular note was recently reported by Krabbenhoft286 who reported an investigation of the cycloaddition of dichloroketene with a series of substituted benzaldehydes, including many of the same derivatives we used in the analogous chlorocyanoketene study. Here it was observed that the reaction is most facile with the more electropositive benzaldehyde de- (28) (a) W. T. Brady and L. Smith, J. Org. Chem., 36,1637 (1971); (b) D. Borrman and R. Wegler, Chem. Ber., 99, 1245 (1966); (c) D. Borrman and R. Wegler, ibid., 102, 64 (1969); (d) D. Borrman and R. Wegler, ibid., 100, 1575 (1967); (e) .…”

“…For example, dichloro-, methyl-, chloro-, isopropoxy-, and phenoxyketene do cycloadd to aldehydes, but unlike chlorocyanoketene, they react rapidly with electron-deficient aldehydes and slowly or not at all with electron-rich analogues. 28 As mentioned, the opposite is true for chlorocyanoketene. One such study of particular note was recently reported by Krabbenhoft286 who reported an investigation of the cycloaddition of dichloroketene with a series of substituted benzaldehydes, including many of the same derivatives we used in the analogous chlorocyanoketene study.…”