| Palladium-catalyzed coupling is a very convenient and useful method for the synthesis of heterocycles in organic synthesis. We have successfully developed the palladium-catalyzed coupling of vinylic halides and functionally-substituted alkenes for the synthesis of oxygen and nitrogen heterocycles. The palladium-catalyzed coupling of vinylic halides and o-vinylic benzoic acids affords good yields of 3,4-dihydroisocoumarins under very mild reaction conditions. The palladium-catalyzed coupling of vinylic halides with o-vinylic and allylic phenols provides mixtures of 2,3-dihydrobenzofurans and 3,4-dihydrobenzopyrans in most cases with high isomeric ratios.; This process has been applied successfully to the synthesis of nitrogen heterocycles. The palladium-catalyzed coupling of vinylic halides and olefinic sulfonamides provides pyrrolidines and piperidines in good yields. Like the analogous reactions of phenols, the palladium-catalyzed coupling of vinylic halides with o-vinylic and allylic anilines produces a mixture of 2,3-dihydroindoles and 1,2,3,4-tetrahydroquinolines with high isomeric ratios in most cases. Interestingly, the reactions of N-tosyl-o-isopropenylaniline provides 2,3-dihydrobenzazepines exclusively in moderate to good yields.; The synthesis of carbocycles via palladium-catalyzed coupling hasn't been accomplished successfully and further investigation is needed. |
