Synthesis of heterocycles via palladium-catalyzed carbonylative annulation of internal and terminal alkynes

The subject of this dissertation is the study of palladium-catalyzed reactions of internal and terminal alkynes with ortho-substituted aryl iodides such as, o-iodophenols and N-substituted o-iodoanilines, in the presence of carbon monoxide (carbonylative annulation). The exploration of these reactions have led to the development of efficient syntheses of the important heterocycles coumarins and 2-quinolones.; 3,4-Disubstituted coumarins are efficiently synthesized by the palladium-catalyzed annulation of internal alkynes by o-iodophenols in the presence of just one atmosphere of carbon monoxide. The use of a sterically unhindered pyridine base is essential to achieve high yields. The reaction accommodates a number of organic functional groups both on the alkyne and the o-iodophenol, thus affording a wide variety of coumarins in moderate to good yields. The main disadvantage of the process is formation of mixtures of regioisomers in reactions employing unsymmetrical alkynes.; The use of N-substituted o-iodoanilines as annulating agents provides an efficient synthesis of 3,4-disubstituted 2-quinolones. In this process, the selection of the nitrogen protecting group is crucial for the success of the reaction. The best results are obtained utilizing alkyl carbamates, tosylamides and trifluoroacetamides. The major features of this process are similar to those of the coumarin synthesis.; These annulation processes are the first examples of the insertion of an alkyne into the arylpalladium bond occurring in preference to the insertion of CO. We have shown that the unusual order of insertion arises from the low reactivity of the initially formed acylpalladium complex towards internal alkynes.; Utilizing the reaction conditions developed for the carbonylative annulation of internal alkynes we have been able to affect the carbonylative annulation of terminal alkynes by o-iodophenols or o-iodoaniline derivatives to afford coumarins or 2-quinolones, respectively, in modest yields. The formation of coumarins and 2-quinolones in this process is in stark contrast with all previously described palladium-catalyzed carbonylative annulations of terminal alkynes, which have afforded chromones and 4-quinolones. Moreover, under our reaction conditions terminal alkynes insert into the carbon-palladium bond instead of undergoing a Sonogashira-type coupling. This reaction pathway is confirmed by an isotope labeling experiment.