Radical cyclisation onto pyrazoles: synthesis of withasomnine

被引：56
作者：
Allin, SM [1 ]
Barton, WRS
Bowman, WR
McInally, T
机构：
[1] Univ Loughborough, Dept Chem, Loughborough LE11 3TU, Leics, England
[2] AstraZeneca R&D Charnwood, Loughborough LE11 5RH, Leics, England
来源：
TETRAHEDRON LETTERS | 2002年 / 43卷 / 23期
基金：
英国工程与自然科学研究理事会;
关键词：
radical cyclisation; pyrazoles; withasomnine; tributyltin hydride; 1,2-b]-fused bicyclic pyrazoles;
D O I：
10.1016/S0040-4039(02)00763-3
中图分类号：
O62 [有机化学];
学科分类号：
070303 ; 081704 ;
摘要：
A novel synthetic protocol for the synthesis of [1,2-b]-fused bicyclic pyrazoles has been developed using radical cyclisation. The protocol uses cyclisation of pyrazole-1-(omega-alkyl) radicals generated from 1-[omega-(phenylselenyl)alkyl]-pyrazole precursors. The pyrazole natural product, withasomnine (3-phenyl-5,6-dihydro-4H-pyrrolo[1,2-b]pyrazole), and larger ring analogues have been synthesised in good yield using the protocol. A Bu3SnH-mediated oxidative cyclisation mechanism is facilitated by azo or Et3B radical initiators acting as oxidants of the intermediate pi-radicals. (C) 2002 Elsevier Science Ltd. All rights reserved.
引用
收藏
页码：4191 / 4193
页数：3
相关论文
共 25 条
[21]   WITHASOMNINE . A PYRAZOLE ALKALOID FROM WITHANIA SOMNIFERA DUN [J].
SCHROTER, HB ;
NEUMANN, D ;
KATRITZKY, AR ;
SWINBOUR.FJ .
TETRAHEDRON, 1966, 22 (08) :2895-+
[22]   PYRAZOLO[1,5-A]-INDOLE DERIVATIVES .5. INTRAMOLECULAR REACTION OF THE HYDRAZONYL GROUP WITH FORMYL AND OXO GROUPS - PREPARATION OF PYRAZOLO[1,5-A]INDOLES AND RELATED PYRAZOLO COMPOUNDS [J].
SHEN, JK ;
KATAYAMA, H ;
TAKATSU, N ;
SHIRO, I .
JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 1, 1993, (17) :2087-2097
[23]   A novel synthesis of spirocyclic pyrrolidin-2-ones [J].
Storey, JMD .
TETRAHEDRON LETTERS, 2000, 41 (42) :8173-8176
[24]  
Studer A, 2001, RADICALS ORGANIC SYN, V2, P62
[25]   A SYNTHESIS OF WITHASOMNINE FROM 4-PHENYLPYRAZOLE [J].
TAKANO, S ;
IMAMURA, Y ;
OGASAWARA, K .
HETEROCYCLES, 1982, 19 (07) :1223-1225
123