Grob-type fragmentation of 5-oxabicyclo[2.1.1]hexane system: A strategy for synthesis of annulated and 2,2,5-trisubstituted tetrahydrofurans

Mahadevegowda, S H and Khan, Faiz Ahmed (2013) Grob-type fragmentation of 5-oxabicyclo[2.1.1]hexane system: A strategy for synthesis of annulated and 2,2,5-trisubstituted tetrahydrofurans. Tetrahedron, 69 (39). pp. 8494-8504. ISSN 0040-4020

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Abstract

Acid mediated, efficient Grob-type fragmentation reaction facilitated by vicinal ketal and ester moieties in variety of 5-oxabicyclo[2.1.1]hexanes leading to the corresponding annulated and 2,2,5-trisubstituted tetrahydrofurans is reported. Among the Brønsted and Lewis acids tested, BF 3·OEt2 appears to give the best results, furnishing near quantitative yield (>99%) of tetrahydrofuran tricarboxylate derivatives under mild reaction condition. In case of unsymmetrical monosubstituted 5-oxabicyclo[2.1.1]hexanes two regioisomeric products are obtained. A strategy to transform one of the ester groups of the title compounds to protected hydroxymethyl moiety was evolved, which allows access to differentially protected 2-hydroxymethyl THF derivatives upon fragmentation. Employing TiCl4/R or S-BINOL as chiral Lewis acid, an enantioselective fragmentation (up to 66% ee) was described for the meso bis-furan derivative

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