The vast majority of medicinally important drugs contain a heterocyclic or carbocyclic ring. The electrophilic cyclization of functionally-substituted alkynes has been little studied, although it would appear to be a very promising route to an extraordinary range of medicinally interesting, functionally-substituted heterocycles and carbocycles. The Larock group has carried out preliminary work suggesting that the electrophilic cyclization of functionally-substituted alkynes readily affords very high yields of a wide variety of halogen-, sulfur- and selenium-substituted benzothiophenes, isoquinolines, benzofurans, and isocoumarins under exceptionally mild reaction conditions. This work will be continued and extended to a wide variety of additional cyclizations including coumestans, furocoumarins, furoflavones, indoles, benzoselenophenes, benzolactams, dihydropyrimidines, 2-furanones, 2-pyrrolinones, benzopyrans, chromones and heteroatom analogues, furans, thiophenes, pyrroles, oxazoles, isoxazoles, pyrazoles, pyridines, quinolines, coumarins, indenes, indenones, naphthols, and phenols. Sequential iodocyclization, Sonogashira coupling and further electrophilic cyclization appears promising as an efficient route to fused polycyclic heterocycles. Analogous cyclizations of functionally-substituted allenes also appear quite promising. The range of electrophiles, which might be employed in these cyclizations, including organopalladium compounds, will also be explored. Subsequent elaboration of the resulting halogen-containing hetero- and carbocycles via palladium-catalyzed processes provides highly, efficient methodology for the construction of pharmaceutically interesting compounds, whose synthesis will be pursued.
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