Syntheses of [1,2,3]selenadiazolo[4,5‐e]benzofuran or benzothiophene, [1,2,3]thiadiazolo[4,5‐e]benzofuran or benzothiophene, and 2‐benzofuranyl‐1,3,4‐oxodiazole derivatives

Abstract

Dehydrogenation of ethyl 3-methyl-4-oxo-4,5,6,7-tetrahydrobenzofuran-2-carboxylate 1 with 2,2′-azobisisobutyronitrile and N-bromosuccinimide gave ethyl 4-hydroxy-3-methylbenzofuran-2-carboxylate 3. Reaction of compounds 3-4 with hydrazine hydrate afforded the corresponding hydrazides 5a-b. The reaction of 5a-b with aldehydes yielded substituted hydrazones 6a-l. Compounds 7a-d were prepared from compounds 6a-d and bromine in acetic acid. Lead tetraacetate oxidation of compounds 6e-l afforded substituted oxadiazoles 8e-l. Selenium dioxide oxidation of 4-oxo-4,5,6,7-tetrahydrobenzofuran semicarbazones 9, 14a and 4-oxo-4,5,6,7-tetrahydrobenzothiophene 14b gave the tricyclic 1,2,3-selenadiazoles 10, 15a and 15b respectively. Reaction of semicarbazones 9, 14a and 14b with thionyl chloride afforded the corresponding 1,2,3-thiadiazoles 12, 16a and 16b respectively.

Synthesis of Substituted Furans through Domino Aldol/Homo‐Michael Reactions of Formylcyclopropane 1,1‐Diesters with 1,3‐Dicarbonyls

“…4‐Oxybenzofuran is a common substructure existing in natural and synthetic compounds (Figure 1) and synthetic biologically active compounds. Oxidation of 3a easily afforded compound 14 in excellent yield (Scheme ) 14. This supplied an efficient method to prepare suitably substituted benzofuran products and their analogues.…”

Understanding the Scope of Feist–Bénary Furan Synthesis: Chemoselectivity and Diastereoselectivity of the Reaction Between α‐Halo Ketones and β‐Dicarbonyl Compounds

“…Ethyl 3‐Methyl‐4‐oxo‐4,5,6,7‐tetrahydrobenzofuran‐2‐carboxylate (IVh): The title compound was obtained as a colorless oil (166 mg, 75 % yield). 1 H NMR (400 MHz, CDCl 3 ): δ = 4.37 (q, J = 7.1 Hz, 2 H), 2.91 (t, J = 6.3 Hz, 2 H), 2.55 (s, 3 H), 2.53–2.46 (m, 2 H), 2.23–2.09 (m, 2 H), 1.38 (t, J = 7.1 Hz, 3 H) ppm.…”