Grob-type fragmentation of 5-oxabicyclo[2.1.1]hexane system: a strategy for synthesis of annulated and 2,2,5-trisubstituted tetrahydrofurans |
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Authors: | Surendra H. Mahadevegowda Faiz Ahmed Khan |
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Affiliation: | 1. Department of Chemistry, Indian Institute of Technology Hyderabad, Ordnance Factory Estate, Yeddumailaram 502205, India;2. Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India |
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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, BF3·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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Keywords: | Grob-type fragmentation 5-Oxabicyclo[2.1.1]hexane Tetrahydrofurans Lewis acid |
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