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A novel solvent-free, TfOH-promoted decyanative cyclization approach for the synthesis of 2,1-benzisoxazoles has been developed. The reactions are complete instantly at room temperature and result in the formation of the desired 2,1-benzisoxazoles in a 34-97% isolated yield.

Treatment of propargylamides or propargylamidines with cesium carbonate in DMSO results in the formation of the corresponding oxazoles or imidazoles in good yields. A large variety of substrates with various functional groups are tolerated. DFT study on a model substrate reveals that the reactions proceed via a sequence involving allene formation, intramolecular cyclization, and double‐bond isomerization. A cesium carbonate promoted, transition metal and halogen‐free 5‐exo‐dig type cyclization reaction for the synthesis of oxazoles and imidazoles has been developed. [ABSTRACT FROM AUTHOR]

The base‐mediated 5‐exo‐dig type cyclization reaction of homopropargyl pyridines for the construction of indolizines has been reported for the first time. A variety of indolizine derivatives could be obtained in moderate to excellent isolated yields by treatment of homopropargyl pryidines with cesium carbonate in DMSO at 100 °C. This strategy could also be adapted to the synthesis of pyrrolo[1,2‐a]quinolines and pyrrolo[1,2‐a]pyrimidines from the corresponding homopropargylquinolines and homopropargylpyrimidines, respectively. The mechanism involves α C−H deprotonation, 5‐exo‐dig cyclization, and isomerization of the exocyclic double bond to provide the heteroaromatic system. The transformation reported herein does not require the aid of transition metal catalysts or halogens, and is thus environmentally friendly. Treatment of homopropargyl pyridines with cesium carbonate in DMSO at 100 °C resulted in the formation of indolizines in moderate to excellent isolated yields. The approach could also be readily adapted to the syntheses of pyrrolo[1,2‐a]quinolines and pyrrolo[1,2‐a]pyrimidines. [ABSTRACT FROM AUTHOR]

A facile transition-metal-free method for the synthesis of benzofuran was developed via potassium t -butoxide promoted intramolecular cyclization of o -bromobenzylketones. This method showed a wide range of substrate tolerability affording substituted benzofurans in moderate to good isolated yields. In addition, thio-ketones and imines could also be converted to corresponding benzothiophenes and indoles applying this approach. The practicability of this method is further proved by a four-step total synthesis of natural product coumestrol. [Display omitted] [ABSTRACT FROM AUTHOR]