PAPER	Synthesis 2007: 400-406   DOI: 10.1055/s-2006-958960
© Georg Thieme Verlag Stuttgart · New York
Cy2NH·HX-Promoted Cyclizations of o-(Alk-1-ynyl)benzoates and (Z)-Alk-2-en-4-ynoate with Copper Halides to Synthesize Isocoumarins and α-Pyrone
Yun Liang, Ye-Xiang Xie, Jin-Heng Li*
Key Laboratory of Chemical Biology & Traditional Chinese Medicine Research (Ministry of Education), College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha 410081, P. R. of China Fax: +86(731)8872531; e-Mail: jhli@hunnu.edu.cn;
Received 1 September 2006

Abstract

Cy₂NH·HX was found to improve the cyclization reactions of o-(alk-1-ynyl)benzoates and (Z)-alk-2-en-4-ynoate with CuX₂ (X = Cl, Br) to synthesize the corresponding 4-haloisocoumarins and 5-bromo-2-pyrone, respectively. In the presence of two equivalents of CuCl₂, cyclization of methyl 2-(2-phenylethynyl)benzoate was conducted smoothly to afford the corresponding desired product in 83% yield after 24 hours, whereas the yield was enhanced to 91% in eight hours when 0.1 equivalent of Cy₂NH·HCl was added. Under the standard reaction conditions, a variety of o-(alk-1-ynyl)benzoates and (Z)-alk-2-en-4-ynoate underwent the cyclization reaction with CuX₂ to provide the corresponding 4-haloisocoumarins and 5-bromo-2-pyrone, respectively, in moderate to excellent yields.

Key words

cyclization - o-(alk-1-ynyl)benzoate - (Z)-alk-2-en-4-ynoate - 4-haloisocoumarin - 5-bromo-2-pyrone - Cy₂NH·HX - copper(II) halide