[4 + 2] Benzannulation of 3‑Alkenylpyrroles/Thiophenes with Propargylic Alcohols: Access to Substituted Indoles, Benzothiophenes, and Aza[5]helicenes

An efficient and practical one-pot [4 + 2] benzannulation method to produce highly substituted indoles and 1-benzothiophenes via sequential acid-catalyzed propargylation/base-mediated cycloisomerization reactions has been developed. This method allows access to differently substituted (mainly on phenyl ring) indoles and 1-benzothiophenes from the reaction of 3-alkenylpyrroles/-thiophenes as C4 synthons with 1-aryl/1-heteroaryl propargylic alcohols as C2 synthons. Interestingly, dialkynyl substrates can undergo tandem benzannulations to give substituted aza[5]­helicenes in 82–83% yield

Metal-free propargylation/aza-annulation approach to substituted beta-carbolines and evaluation of their photophysical properties

International audienceAn efficient acid-catalyzed propargylation/aza-annulation sequence was developed under metal-free reaction conditions, thus leading to a one-pot synthesis of a variety of substituted beta-carbolines starting from propargylic alcohols and indole 2-carbonyls. This versatile strategy was further extended to the synthesis of 5-azaindoles and 5-azabenzothiazoles. Optical properties suggested that manipulation of electron donor and acceptor moieties on beta-carbolines has an impact on their ground and excited state electronic behavior. This leads to blue or green emission and should facilitate the development of organic light emitting diodes (OLEDs). Electrochemical and stability studies revealed that 4a-6 shows ease of redox activity and photostability during illumination