Synthetic Applications of Dipolar Cycloadditions

3-DCA reactions are an important means of synthesis of a wide variety of heterocyclic molecules, some of which are useful intermediates in multistage syntheses. Pyrazolines, which are formed from alkenes and diazo compounds, for example, can be pyrolyzed or photolyzed to give cyclopropanes. 

150j M. Martin-Villa, N. Hanafi, J. M. Jiminez, A. Alvarez-Larena, J. F. Piniella, V. Branchadell, A. Oliva, and R. M. Ortuno, J. Org. Chem., 63, 3581 (1998). 

Concerted Cycloadditions, Unimolecular Rearrangements, and Thermal Eliminations 

These reactions are highly stereoselective, provided a substituent is present at C(3). The stereochemistry is consistent with a chairlike TS having the 3-subsituent in an equatorial position. 

Torssell, Nitrile Oxides, Nitrones and Nitronates in Organic Synthesis, VCH Publishers, New York, 1988. 

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