Acylpalladium derivatives alkynes

In addition to alcohols, some other nucleophiles such as amines and carbon nucleophiles can be used to trap the acylpalladium intermediates. The o-viny-lidene-/j-lactam 30 is prepared by the carbonylation of the 4-benzylamino-2-alkynyl methyl carbonate derivative 29[16]. The reaction proceeds using TMPP, a cyclic phosphite, as a ligand. When the amino group is protected as the p-toluenesulfonamide, the reaction proceeds in the presence of potassium carbonate, and the f>-alkynyl-/J-lactam 31 is obtained by the isomerization of the allenyl (vinylidene) group to the less strained alkyne. 

When 2-propargyl-l,3-dicarbonyl compounds are treated with aryl iodides under a balloon of carbon monoxide 2,3,5-trisubstituted-furans containing a 5-acylmethyl group (Scheme 7a) or its enol ester (Scheme 7b) can be obtained. Formation of the acyhnethyl derivative or its enol ester depends on the aryl iodide to alkyne ratio. Excess alkyne affords the acyhnethyl derivative as the main product whereas employment of an excess of the aryl iodide favors the formation of the enol ester. The enol ester product is very likely formed from the acyhnethyl product via trapping of the corresponding enolate with an acylpalladium complex. 

All of the acylpalladation processes discussed above involve interaction of acylpalladium bonds with C=C bonds. The corresponding acylpalladation of C C bonds proved to be rather elusive. Thus, for example, attempts to observe cyclic acylpalladation of alkyne-containing iodobenzenes totally failed, even though the corresponding alkene derivatives undergo cyclic acylpalladationt (Scheme 23). The contrasting behavior of alkene and alkyne substrates is also schematically summarized in Scheme 23. 

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