Novel Syntheses of 2,3-Disubstituted Benzofurans

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

“…Intermediates 9a-h were prepared by the reaction of 2-hydroxybenzophenones 7a-c with compounds 8a-c (available from aldehydes, benzotriazole and thionyl chloride in 87-96% yields 6 ) similar to published procedure, 3,7 but in the presence of anhydrous potassium carbonate as a base instead of sodium hydroxide in DMF solution at 20-25 °C. Intermediates 9a-h were treated with an equimolar amount of LDA in THF at temperatures ranging from -78 °C to 0 °C to give the corresponding lithium salts of 2-(benzotriazolyl)-2,3-dihydrobenzofuran-3-ols 10a-h 3 (mixtures of diastereoisomers according to TLC analysis; for 9a, a single isomer was observed), which were treated without isolation with 2-3 equivalents of zinc bromide in 1,1,2,2-tetrachloroethane under reflux for 24 h to give new products.…”

“…Intermediates 9a-h were treated with an equimolar amount of LDA in THF at temperatures ranging from -78 °C to 0 °C to give the corresponding lithium salts of 2-(benzotriazolyl)-2,3-dihydrobenzofuran-3-ols 10a-h 3 (mixtures of diastereoisomers according to TLC analysis; for 9a, a single isomer was observed), which were treated without isolation with 2-3 equivalents of zinc bromide in 1,1,2,2-tetrachloroethane under reflux for 24 h to give new products. The 1 H NMR spectra of these products show no signals corresponding to those assigned to the Nsubstituted benzotriazole groups of intermediates 9a-h (7.2-8.1 ppm).…”

“…3 The mechanism of transformation 10a → 12 is unclear and may involve the reduction of 10a by bromide anion. We isolated intermediate 10a (82%, single isomer) to support the proposed reaction pathway (Scheme 2).…”

Benzotriazole-Mediated Synthesis of Oxygen-Containing Heterocycles

“…Intermediates 102 were then lithiated with an equivalent amount of LDA in THF at low temperatures to give the corresponding 2-(benzotriazol-1-yl)-3-substituted-2,3-dihydro-1-benzofuran-3-ols of type 103. Compounds 103 were reacted with an equivalent amount of a low valent titanium reagent to provide benzofurans 104 in moderate to good yields [39].…”

Ortho-hydroxy assisted and copper-catalyzed oxidation of benzylic alcohol

“…Ortho-hydroxyarylketones are important intermediates for the synthesis of natural products, pharmaceuticals, agrochemicals and organic materials [1,2]. They have also been extensively used as light stabilizers and UV absorbers in cosmetics and coatings for preventing the damage of human skin from UV.…”