Reactions of Benzocyclic β-Keto Esters with Sulfonyl Azides. 2. Further Insight into the Influence of Azide Structure and Solvent on the Reaction Course.

The reactions of 2-ethoxycarbonyl-1-benzosuberone with 4-methoxybenzenesulfonyl, 2,4,6-triisopropylbenzenesulfonyl, methanesulfonyl, and trifluoromethanesulfonyl azide, in the presence of triethylamine, have been investigated in ,-dimethylformamide, acetonitrile, or tetrahydrofuran with the intent of clarifying the influence of both the azide electrophile and solvent on the reaction course. The present findings, in addition to those previously obtained with tosyl and 4-nitrobenzenesulfonyl azide, indicate that both the electronic features of the sulfonyl azide and the solvent polarity greatly affect the possible occurrence of azidation and/or Favorskii-type ring contraction at the expense of deacylating diazo transfer. Azidation is promoted by the less electrophilic azides, while it is virtually avoided by the more electrophilic ones. Ring contraction occurs to a limited extent with the less electrophilic azides, but it becomes the main process with those more electrophilic. Moreover, azidation is virtually unaffected by the solvent polarity, while ring contraction can markedly be enhanced by a highly polar solvent. Firm evidence has additionally been obtained that, in contrast to a previous claim, trifluoromethanesulfonyl azide can normally perform diazotization of acyclic β-keto esters in preference to azidation.