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Communication | Special issue | Vol 101, No. 2, 2020, pp.417-422
Published online, 25th September, 2019
DOI: 10.3987/COM-19-S(F)34
An Approach to a 2-Hydroxy-3-phenyldibenzofuran Skeleton Based on Rh(PPh3)3Cl-Catalyzed [2+2+2] Cycloaddition between a 1-Ethynyl-2-(ethynyloxy)benzene and an (Alkoxyethynyl)benzene

Daisuke Sato, Kenshu Fujiwara,* Yoshihiko Kondo, Uichi Akiba, and Tetsuo Tokiwano

*Graduate School of Engineering Science, Department of Life Science, Akita University, 1-1 Tegatagakuen-machi, Akita 010-8502, Japan

Abstract

A Rh(PPh3)3Cl-catalyzed [2+2+2] cycloaddition of a 2-(trimethylsilylethynyl)-1-(ethynyloxy)benzene derivative (a 1,6-diyne unit) with an (alkoxyethynyl)benzene (an alkoxyacetylene unit) was studied for the construction of the 2-hydroxy-3-phenyldibenzofuran skeleton of kehokorin E. Although the dimerization of the 1,6-diyne unit was a serious problem in the initial trial, installation of a bulky substituent at the terminal of the ethynyloxy group of the 1,6-diyne unit was found to inhibit the dimerization to produce cycloadducts in good yield. It was also found that the use of a 2-hydroxypropan-2-yl group as the bulky group increased the ratio of the desired 2-alkoxy-3-phenyldibenzofuran isomer to a 3-alkoxy-2-phenyldibenzofuran isomer.