Journal of Organic Chemistry p. 3756 - 3766 (1980)
Update date:2022-07-30
Topics:
Padwa, Albert
Ku, Hao
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.
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Doi:10.1039/c9ob01563a
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