Synthesis of 2,3-dihydrobenzofuran-2-ones and 2,3-dihydrobenzothiophen-2-and 3-ones by rearrangements of 3-hydroxy analogs

Reactions of 2-hydroxybenzophenones 7a-c and 2-sulfanylbenzophenones 13a-c with 1-(1-chloroalkyl) benzotriazoles 8a-c gave 2-(1-benzotriazolylalkoxy)- and 2-(1-benzotriazolylalkylsulfanyl)-benzophenones 9a-h and 14a-h, respectively. Treatment of 9a-h and 14a-h with lithium diisopropylamide (LDA) formed 2-(benzotriazol-1-yl)-3-substituted-2,3-dihydrobenzofuran-3-ols 10a-h and -2,3-dihydrobenzothiophen-3-ols 15a-h. Rearrangement of derivatives 10a-h by ZnBr2 afforded 3-alkyl-3-aryl-2,3-dihydrobenzofuran-2-ones 11a-h. Rearrangement of derivatives 15a-h gave 2-alkyl-2-aryl-2,3-dihydrobenzothiophen-3-ones 16a-g, 3-alkyl-3-aryl-2,3-dihydrobenzothiophen-2-ones 17b,c,g, and benzothiophenes 18g,h depending on reaction conditions and substituents.