Reactions of Benzocyclic β-Keto Esters with Tosyl and 4-Nitrophenyl Azide. Structural Influence of Dicarbonyl Substrate and Azide Reagent on Distribution of Diazo, Azide and Ring-Contraction Products

Article abstract of DOI:10.1021/jo980223w

The reactions of β-keto esters derived from 1- and 2-indanone, 1- and 2-tetralone, and benzosuberone with toluene-4-sulfonyl- (tosyl) and 4-nitrobenzenesulfonyl azide (PNBSA) in the presence of Et₃N have been investigated in order to evaluate the influence of both dicarbonyl substrate and azide reagent on the product distribution. With tosyl azide the keto esters derived from both 2-benzocycloalkanones exhibit deacylating diazo transfer, but those derived from the 1-benzocycloalkanones undergo additional azido transfer to a significant or even exclusive extent. The finding is mainly explained in terms of the lesser reactivity of the conjugate aryl ketone than alkyl ketone moiety. This would discourage cyclization of the initial sulfonyltriazenyl anion-the presumable azide precursor-to the triazoline adduct, in turn envisaged as the diazo progenitor. With PNBSA both indanones smoothly undergo diazo transfer, whereas their higher homologues lead to ring-contraction products ascribable to corresponding triazolines that curiously prefer to suffer Favorskiitype ring fragmentation. Evidence has been obtained that tosyl azide acts as a azide-transfer reagent superior to PNBSA. A possible explanation of this fact is discussed. An X-ray crystal structure analysis of the phthalazine compound 18 (Ar = 4-Me-C₆H₄) has been performed.