Intramolecular Cycloaddition Reactions of Olefinic Tosylhydrazones

Article abstract of DOI:10.1021/jo01307a008

A series of olefinic tosylhydrazones were prepared, and their base- and acid-induced behavior was investigated.Thermolysis of the sodium salt of the tosylhydrazones generates diazoalkenes which undergo intramolecular 1,3-dipolar cycloaddition reactions.The exclusive formation of the tetrahydroindeno<1,2-c>pyrazole ring from thermolysis of o-allylbenzaldehyde tosylhydrazones is unusual and cannot be easily accounted for on the basis of frontier molecular orbital theory.Our results indicate that geometrical factors can force the reaction to occur in a manner opposite to that normally encountered.Further heating of several methyl-substituted indeno<1,2-c>pyrazolines indicates that benzobicyclo<3.1.0>hexene formation proceeds with predominant inversion of configuration.The results are consistent with a mechanism involving C-N bond cleavage followed by rotation about the ? bond and back-side displacement of nitrogen.Treatment of the olefinic tosylhydrazones with boron trifluoride etherate resulted in a novel cyclization reaction.The regioselectivity associated with the acid-induced cyclization is the consequence of a carbocation pathway.