Diazoalkanes, preparation with carbonyl compounds

While alkyldiazonium salts are unstable, their conjugate bases, diazoalkanes, are stable enough to be prepared and are nucleophilic towards carbonyl compounds. Diazoalkanes are neutral com-poundij having one fewer proton than diazonium salts and are delocalized structures with a central sp nitrogen atom. 

Diazocyclopropane can be prepared from N-cyclopropyl-iV-nitrosourea or from the corresponding carbamates. Just as ordinary diazoalkanes, the cyclopropyldiazo compounds react with ketones with epoxide formation and homologation of the carbonyl compounds (equation 128) Readily accessible cyclopropylidenephosphoranes provide a convenient synthetic route for methylenecyclopropanes . ... 

The twofold extrusion of nitrogen and sulfur and selenium and sulfur from 1-thia- and l-selena-3,4-diazolines(77), readily available from the reaction of diazoalkanes with thio- and selenaketones, respectively, as well as from the reductive coupling of carbonyl compounds such as 78, is the preferred method for preparation of olefins of type I and II (98,99). Examples of the extrusion method, developed by Barton (100), and the McMurry reaction (101) are given in Scheme 1. 

Dipolar cycloaddition reactions constitute a powerful and convergent tool for the preparation of various heterocyclic compounds, which have been widely applied in the synthesis of numerous natural products, pharmaceuticals, and functional materials. The chemistry of 1,3-dipolar cycloaddtion reactions has been well documented in a number of reviews [3]. In this section the focus is on transition-metal-mediated 1,3-dipolar cycloaddition reactions with some important 1,3-dipoles, including azides, diazoalkanes, carbonyl ylides, and azomethine ylides, rather than a full review of the reactions of all types of 1,3-dipoles. 

---