process that involves the Meyer–Schusterrearrangement of alkynols followed by the Diels–Alder cycloaddition of the resulting enones. These reactions were performed under mild conditions in the presence of 5 mol-% of the catalyst to afford the cycloadducts in good yields with almost 100 % endo stereoselectivity. In-depth computational studies of the cycloaddition mechanism provided the preferred geometry
Re catalysis in one‐pot reactions: An atom‐economical, one‐pot strategy that involves alkyne deprotonation and a subsequent rhenium(V)‐catalysed Meyer–Schuster rearrangement of the alkynol to provide α,ß‐unsaturated enones in high yield has been developed (see scheme). Subsequent in situ hydride reduction or Diels–Alder reaction of the enones provided products in good‐to‐high overall yields.
Al(OTf)3-Catalyzed Preparation of 4-Hydroxy-3-propargylic Coumarins and Subsequent Regioselective Cyclization towards Furo- or Pyrano[3,2-c]coumarins
作者:Barend Bezuidenhoudt、Sudipta Ponra、Mukut Gohain、Johannes van Tonder
DOI:10.1055/s-0034-1379971
日期:——
An efficient and economical approach to functionalized furo[3,2-c]coumarin and pyrano[3,2-c]coumarin derivatives has been developed from 4-hydroxy-3-(prop-2-ynyl)coumarin derivatives through organocatalysis or metallo-organocatalysis. Selective 5-exo-dig' or 6-endo-dig' cyclization of the 4-hydroxy-3-(prop-2-ynyl)coumarin substrates could be achieved under organocatalytic 1,8-diazabicyclo[5.4.0]undec-7-ene} or metallo-organocatalytic (N-methylmorpholine/CuBr) conditions, respectively, to yield potentially bioactive heterocycles in excellent yields.
InCl3-assisted one-pot synthesis of 1-aminocarbazoles
A novel InCI3-mediated one-pot reaction leading to 1-aminocarbazoles is reported. Starting from easily available 2-acetyl-1H-indole, the reaction involves the allcylation of C-3 with a prop-2-yn-1-ol followed by a domino aminobenzannulation reaction in the presence of a secondary amine. The indium salt is most likely involved as catalyst in all three steps of the one-pot reaction. Starting from 2-acetyl-1H-indole and a series of prop-2-yn-1-ols and secondary amines a small library of products has been obtained. (C) 2011 Elsevier Ltd. All rights reserved.