Abstract Mexican Bentonitic earth (Tonsil) catalyzed the Claisen rearrangement of aryl 1, 1- dimethylpropargyl ethers under mild conditions to provide 2, 2-dimethyl-2H-1-benzopyrans. The synthesis of encecalin 2f and desmethoxyencecalin 2i, two biologically active products among other natural products (2b, 2e) was performed by this procedure.
[Kawase, Yoshiyuki; Yamaguchi, Seiji; Horita, Hisanori; Takeno, Junko; Kameyama, Hideaki Bulletin of the Chemical Society of Japan, 1982 , vol. 55, # 4 p. 1153 - 1155]
