Enolates acylpalladium derivative trapping

All of the examples of trapping of acylpalladium species with enolates discussed above as part of the Type III Ac-Pd process involve trapping with O-enolates. As discussed earlier, however, acylpalladium derivatives can also be trapped with C-enolates (Eqs. 4 and 5 in Scheme 11), and this trapping with C-enolates has since been exploited for terminating acyclic carbopalla-dation process [135] (Scheme 48). However, this process does not appear to have been used for terminating cyclic acylpalladation processes. 

In principle, a variety of other tandem and cascade processes terminated by trapping of acylpalladium derivatives by enolates are conceivable. In reality, examples of such processes are still very rare. One such process shown in Scheme 25 involves a cyclic carbopaUadation-cyclic ketone formation via a 5-C-exo trapping tandem process. Many additional examples of such tandem and cascade processes will be devised in efforts to develop efficient routes to bicyclic and polycyclic natural products and related compounds. 

For trapping of acylpalladium derivatives with enolates, see J. M. Tour and E. Negishi, Tetrahedron Lett, 1986, 27, 4869. 

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. 

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