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Synthesis of Functionalized 2,5-Dihydrooxepines by [3,3]-Sigmatropic Rearrangement of Cyclopropane Derivatives
19 March 2002 (online)
Swern oxidation of 2-alkenyl substituted 2-siloxycyclopropyl alcohols provided 2,5-dihydrooxepine derivatives in high yield, while alcohols bearing a 2-styryl substituent gave dihydrofurans. Formation of these heterocycles can be rationalized by ring enlargement of intermediate cyclopropyl aldehydes giving 2,5-dihydrooxepines by [3,3]-sigmatropic rearrange-ment, or dihydrofurans via a stabilized 1,3-zwitterion.