1,3-Dipolar cyeloadditions

Synthetie Applieations of 1,3-dipolar Cyeloaddition Chemistry Toward Heteroeyeles and Natural Produets", (A. Padwa and W. El. Pearson, eds.), p. 681, Wiley, New York (2002). 

Due to the electrophilic character of carbenes, they are not expected to easily react with electron-poor alkenes, and the only reported examples concern reactions with diazo compounds (i.e., diazomethane,156-" 7 diazofluorene. 38 ethyl diazoacetate,159 and phenyldiazomethane160). However, depending on the reaction conditions, carbenes are not always the reactive species. Cyclopropanes are often obtained by decomposition of pyrazolines which arise from 1,3-dipolar cyeloaddition reactions (see Section 2.1.1.6.2.3.1.). Even when reactions are performed under irradiation, pyrazolines can be obtained as the result of a diradical addition. 56... 

Some examples of the preparation of oxiranes, thiiranes and aziridines by the reaction of diazo compounds with trifiuoromethyl-substituted carbonyl161 164 and thiocarbonyl compounds,165 imines,166,167 and oximes 68 are known. However, as noted in Section 2.1.1.6.2.5.1., carbenes are not always the reactive species. Thus, the reaction can consist of a 1,3-dipolar cyeloaddition, followed by decomposition of the resulting pyrazoline. 

A highly diastereoselective 1,3-dipolar cycloaddition of a nitrone employing the sultam auxiliary has been used in the synthesis of 215, a major metabolite of nicotine <04T9997>. i-gulose-derived nitrone 212, upon treatment with a, P-unsaturated sultam (25)-213, undergoes 1,3-dipolar cyeloaddition to afford the isoxazolidine 214 with high endo stereoselectivity, which is further elaborated to hydroxycotinine (-i-)-215. 

---