Cyclopropanones metal catalyzed

The transition metal-catalyzed cyclopropanation of alkenes is one of the most efficient methods for the preparation of cyclopropanes. In 1959 Dull and Abend reported [617] their finding that treatment of ketene diethylacetal with diazomethane in the presence of catalytic amounts of copper(I) bromide leads to the formation of cyclopropanone diethylacetal. The same year Wittig described the cyclopropanation of cyclohexene with diazomethane and zinc(II) iodide [494]. Since then many variations and improvements of this reaction have been reported. Today a large number of transition metal complexes are known which react with diazoalkanes or other carbene precursors to yield intermediates capable of cyclopropanating olefins (Figure 3.32). However, from the commonly used catalysts of this type (rhodium(II) or palladium(II) carboxylates, copper salts) no carbene complexes have yet been identified spectroscopically. 

TRANSITION METAL CATALYZED REACTIONS OF CYCLOPROPANONES AND RELATED 1200 COMPOUNDS... 

Phenylethynylcopper and phenacyl bromide afford intractable tars upon long reflux in DMF. However, at higher temperatures ( 240°C) a-haloketones can be converted in one step to furan derivatives [Eqs. (68a), (68b)] uncyclized acetylenic ketones are not isolated. The cycliza-tion is catalyzed by copper(I) through the copper-coordinated enol 128). Reaction of a,a -dibromoketones with an excess of a diorganocuprate is a new method for the a-alkylation of a ketone 231a). Only the monoalkyl derivative is isolated. The evidence points to the formation of a cyclopropanone intermediate which reacts with more of the cuprate to give an a-alkylated metal enolate. 

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