Intramolecular low-temperature 1,3-dipolar cycloadditions of nitrones: synthesis of chromano-heterocycles
- 作者：Gurpinder Singh ; M.P.S. Ishar ; Vivek Gupta ; Gurmit Singh ; Mohit Kalyan ; Surinderjit Singh Bhella
- 关键词：Chromone ; Nitrone ; Isoxazolidine ; 1 ; 3-Dipolarcycloadditions ; Stereoselectivity ; π ; -Facial selectivity
- 刊名：Tetrahedron
- 出版年：2007
- 期刊代码：107_00404020
- 类别：ch
- 出版时间：28 May 2007
- 卷：63
- 期：22
- 页码：4773-4778
- 文件大小：321 K
摘要
In contrast to the reported facile intramolecular 1,3-dipolar cycloadditions of in-situ generated nitrone on heterocyclic systems, reactions of 2-(N-allyl/crotyl/cinnamyl-anilino)-3-formylchromones with N-phenyl-/methylhydroxylamine under comparable conditions, afford fused isoxazolidines only in low to moderate yields; the corresponding amides derived from rearrangement of in situ generated nitrones are formed as major products. However, when reactions were carried by stirring the reactants at an ice-cold temperature in dichloromethane, highly stereoselective intramolecular 1,3-dipolar cycloadditions lead to novel fused isoxazolidines in high yields (80–90%).