Protected propargylic acetals. Nicholas–Prins cyclization leading to functionalized 2-alkynyl-tetrahydropyrans. Intramolecular trapping by allenes

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• 作者：Clarisse Olier ; Sté ; phane Gastaldi ; Gé ; rard Gil ; Michè ; le P. Bertr
• 关键词：Alkyne complexes ; Nicholas reaction ; Prins cyclization ; Carbocations ; Tetrahydropyrans
• 刊名：Tetrahedron Letters
• 出版年：2007
• 期刊代码：109_00404039
• 类别：ch
• 出版时间：29 October 2007
• 卷：48
• 期：44
• 页码：7801-7804
• 文件大小：139 K

摘要

Dicobalt hexacarbonyl complexes derived from propargylic acetals undergo Lewis acid-mediated Nicholas–Prins cyclization in the presence of homoallylic alcohols. The trapping of the resulting cyclic carbocation enables the synthesis of a series of functionalized tetrahydropyrans. The complexation of the triple bond contributes to the suppression of the side reactions and very significantly increases both the yield and the diastereoselectivity of the reaction. Homoallenic alcohols lead to dienic compounds through proton elimination.