ACYLPALLADATION OF INTERNAL ALKYNES AND PALLADIUM-CATALYZED CARBONYLATION OF (Z)-BETA-IODOENONES AND RELATED DERIVATIVES PRODUCING GAMMA-LACTONES AND GAMMA-LACTAMS

The reaction of either an internal alkyne-organic halide mixture or (Z )-beta-iodoenones with CO in the presence of a Pd-phosphine catalyst, e.g., Cl2Pd(PPh(3))2, can give one of the three discrete types of comp ounds as the major products depending on the substrate structure and t he reaction conditions. Those substrates which are convertible to (Z)- gamma-oxo-alpha,beta-unsaturated acylpalladium derivatives lacking del ta-H atoms are converted to the corresponding 2-butenolides (13) in th e presence of water, which serves as a H donor. Carbon monoxide most l ikely is the source of two electrons. Either in the absence of water ( or any other suitable H source) or in the presence of some factors dis favoring the butenolide formation, the same reaction gives the corresp onding dimeric product (16). Even in cases where there is an alpha-H a tom in the alpha-substitutent, 1,4-elimination products (11), reported to be the major products in a related Pd-catalyzed reaction of termin al alkyne-aryl iodide mixtures with CO, were not detected. In sharp co ntrast, those substrates which can give rise to (Z)-gamma-oxo-alpha, b eta-unsaturated acylpalladium derivatives containing delta-H atoms giv e, under comparable reaction conditions, enol lactones (12), i.e., (Z) -3-alkylidene-2-butenolides, contaminated with only very minor amounts of 22 even in cases where an excess (4 equiv) of water was present. T he required (Z)-beta-iodoenones can be readily prepared in one pot via ZrCp(2)-promoted cyclization of alkynes with nitriles. The ready avai lability of the starting compounds and the high Z stereoselectivity ma ke the overall sequence an attractive synthetic route to 12. The cours es of the Pd-catalyzed carbonylation reactions of (Z)-beta-iodo-alpha, beta-unsaturated imines 23 closely parallel the reactions of enones an d produce the corresponding lactams, i.e., 24 and 25.