Ketones, tetrasubstituted dibromo

Although limited to tri- and tetrasubstituted cyclopropanones, the most general in situ synthesis of these strained cyclic ketones consists of the reaction of a,a -dibromo ketones with the (nitrosyl)carbonylmetalate [PPN][Cr(CO)4NO] as organometallic reducing agent. ... 

Alternatively, a,a -dibromo ketones are reductively debrominated with concomitant cyclization by [Cr(C0)4N0][PPN] at -78 or — 95°C in dichloromethane. This method is particularly suited for NMR tube scale experiments, but is limited to tri- and tetrasubstituted cyclopropanones. Bicyclo[1.1.0]butanones are also accessible by this synthetic procedure which utilizes 1,3-elimination of two bromine atoms from 2,4-dibromocyclobutanones. ... 

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