Synthesis of multisubstituted phenols by formal [4 + 2] cycloaddition of nucleophilic alkynes with
Takeo Kuzuguchi1, Yuto Yabuuchi, Tomoyuki Yoshimura
1Division of Pharmaceutical Sciences, Graduate School of Medical Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan. jimatsuo@p.kanazawa-u.ac.jp.
Abstract:
Nucleophilic alkynes bearing sulfonamide, trimethylsilyl, or p-methoxyphenyl groups at the sp carbon reacted with 3-ethoxycyclobutanones to give formal [4 + 2] cycloadducts by activation with TiCl4. Reactions with 2-monoalkyl and 2-nonsubstituted 3-ethoxycyclobutanones gave phenol derivatives directly by benzannulation, while the use of 2,2-dimethyl-3-ethoxycyclobutanone gave the corresponding dienones, which were converted to pentasubstituted phenols by dienone-phenol rearrangement. Regioselectivity that depended on the activation conditions of dienone-phenol rearrangement is also described.
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