Carbalkoxy carbenes

We have already reported above the interest of Pd(0) and Ni(0) as catalysts for the synthesis of macrolides [39] and of various heterocycles through intramolecular reactions [40, 43]. Moreover, carbene chemistry also affords some interesting pathways to heterocyclic systems for example, the insertion reaction of carbalkoxy carbenes into an enol (acetylace-tone) yields furan derivatives [98] whereas the insertion reaction into diols affords lactones [99],... 

Carbonyl carbenes insert into various X—H bonds (X = O, N, C) in the presence of rhodium carboxylates. An application of the insertion of carbalkoxy carbene into the OH group of alcohols is illustrated by a synthesis of chorismic acid [104]. 

Further fluorinated synthons 20 (equation 17)92 and 21 lead to Reformatsky intermediates which are synthetic equivalents of a formal 4,4-difluoroacetoacetate dianion and of a carbalkoxy trifluoromethyl carbene, respectively. The latter has been exploited in a synthesis of E-22 and Z-22, both inhibitors of GABA aminotransferase (equation 18)93. 

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