These products correspond to the formal loss of MeCO2H from the intermediate acyl(oxy) carbenes M(SnPh3)(CO){=C(OCOMe)CH2R}(h-C5H5). The presence of protons on the carbon a to the carbene is essential, as is the presence of the labile acyl(oxy) substituent.
One of these has been characterised by X-ray crystallography:
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