Intra- and Intermolecular Cyclization of Olefinic Tosylhydrazones under Acidic Conditions. A Facile Synthesis of Bicyclic Azoalkanes

Article abstract of DOI:10.1021/ja00525a029

Tosylhydrazones of olefinic ketones and aldehydes have been observed to undergo a variety of unusual cyclizations under acidic conditions.The intramolecular version of this novel cyclization reaction has been applied in the synthesis of previously unaccessible bicyclo<3.2.1>- and bicyclo<2.2.1>azoalkanes.Of these two bicyclic systems, the less strained <3.2.1> system is formed with the greater ease, and in either system the intramolecular cyclization is favored by more nucleophilic olefins (isopropenyl better than vinyl).Those systems that do not undergo efficient azoalkane formation, either due to excessive ring strain or lack of olefin nucleophilicity, undergo novel intermolecular cyclizations instead.The assignments of structure to these products has been based upon 300-MHz NMR data and an X-ray crystal study of the most unusual of these condensation products, 9.From this structural information an internally consistent mechanistic framework for the formation of these products has been developed.Thus, while these intermolecular condensation reactions produce a structurally diverse set of products, all of these products seem to originate from an initial cyclization between a molecule of tosylhydrazone and its highly nucleophilic enamine tautomer.