About two decades after Kobayashi's discovery in 1983 of a very mild way of generating highly reactive aryne intermediates, the synthetic community embraced o-(trimethylsilyl)aryl triflates as convenient and versatile aryne precursors for the synthesis of carbocycles and heterocycles, as well as natural products and pharmaceutically promising drug candidates. This review provides a comprehensive overview of the construction of heterocycles using Kobayashi's silylaryl triflate aryne precursors. It is organized according to the type of heterocycle generated.
Pyrido[1,2-a]indoles are known as medicinally and pharmaceutically important compounds, but there is a lack of efficient methods for their synthesis. We report a convenient and efficient route to these privileged structures starting from easily accessible 2-substituted pyridines and aryne precursors. A small library of compounds has been synthesized utilizing the developed method, affording variously substituted pyrido[1,2-a]indoles in moderate to good yields.
A microwave-assisted, one-pot, three-component coupling reaction for the synthesis of indoles has been developed. The reaction is carried out in two steps under standard Sonogashira coupling conditions from an N-substituted/N,N-disubstituted 2-iodoaniline and a terminal alkyne, followed by the addition of acetonitrile and an aryl iodide. A variety of polysubstituted indoles have been prepared in moderate to excellent yields using the present method.
An efficient one-pot method for the synthesis of 2,3-disubstituted benzo[b]furans from commercially available 2-iodophenols, terminal acetylenes and aryl iodides has been developed utilizing Sonogashira reaction conditions. After an initial Sonogashira coupling of the 2-iodophenol with the terminal alkyne, cyclization involving the aryl iodide provides the 2,3-disubstituted benzo[b]furan in good to excellent yields. The use of microwave irradiation shortens the reaction times and minimizes the side products. This methodology is especially useful for the construction of libraries of highly substituted benzo[b]furans and their analogues.
Synthesis of a 105 membered library of 1,2-dihydroisoquinolines is described. The 1,2-dihydroisoquinoline compounds have been prepared in good yields using a Lewis acid and organocatalyst-cocatalyzed multicomponent reaction of 2-(1-alkynyl)benzaldehydes, amines and ketones. Various indoles have also been employed as pronucleophiles, furnishing 1-(3-indolyl)-1,2-dihydroisoquinolines. The halogen functionality present in some of the synthesized compounds allows for further diversification by palladium-catalyzed Suzuki-Miyaura and Sonogashira cross-couplings to give more diversified 1,2-dihydroisoquinoline derivatives.
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