OXAZOLE ACTIVATION FOR AZOMETHINE YLIDE TRAPPING - SINGLY AND DOUBLY TETHERED SUBSTRATES

被引:28
作者
VEDEJS, E
PIOTROWSKI, DW
机构
[1] Chemistry Department, University of Wisconsin, Madison
关键词
D O I
10.1021/jo00058a010
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
Bicyclic oxazolium salts 18, 24, 37, and 44 can be generated from tethered haloalkyloxazoles by internal alkylation. Reductive alkylation of the oxazolium salts using CsF/PhSiH3 converts the salts initially into the corresponding 4-oxazoline derivatives. Subsequent electrocyclic ring opening generates stabilized azomethine ylides that can be trapped by suitable dipolarophiles. Intermolecular dipole trapping followed by DDQ oxidation affords the ring-fused pyrroles 22 and 26. When tethered alkynoates are used for internal dipole trapping, the adducts 38 and 45 can be obtained by a similar reductive activation sequence, followed by DDQ workup. Effective procedures for the internal oxazole N-alkylation step are described using an acetonitrile-trifluoroethanol solvent system. Also, an improved method for the generation of the dichlorocerium derivative of ethyl propiolate and intermolecular trapping by an aldehyde is reported.
引用
收藏
页码:1341 / 1348
页数:8
相关论文
共 41 条