Carbonyl ylides metallocarbenoids

Over the past decade, a reliable, high-yielding method has been developed for the preparation of carbonyl ylide intermediates, namely, the addition of stabilized metallocarbenoid species to carbonyl compounds. 

Carbonyl ylides can be viewed as an adduct between a carbonyl group and a carbene and, in fact, some ylides have been prepared this way (see above). The application of carbonyl ylides to the synthesis of complex natural products has been greatly advanced by the finding that stabilized carbenoids can be generated by the decomposition of ot-diazocarbonyl compounds with copper and rhodium complexes. The metallocarbenoids formed by this method are highly electrophilic on carbon and readily add nucleophiles such as the oxygen of many carbonyl derivatives to form carbonyl ylides. This type of reaction is in fact quite old with the first report being the addition of diazomalonate and benzaldehyde (33,34). 

Decomposition of diazoketone 110 with rhodium acetate produced the highly electrophilic rhodium stabilized metallocarbenoid that suffers attack by the Lewis basic oxygen of the pendant ketone, producing cyclic carbonyl ylide 111. This ylide was trapped by the addition of an activated acetylene such as DMAD to furnish... 

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