Approaches to the quaternary stereocentre and to the heterocyclic core in diazonamide A using the Heck reaction and related coupling reactions
作者:James E. M. Booker、Alicia Boto、Gwydion H. Churchill、Clive P. Green、Matthew Ling、Graham Meek、Jaya Prabhakaran、David Sinclair、Alexander J. Blake、Gerald Pattenden
DOI:10.1039/b609604b
日期:——
In model studies towards the quaternary centre at the heart of diazonamide A (early structure 2; revised structure 1), cyclisations of the alkene-substituted iodoaryls 4, 13, 18 and 23, under Heck reaction conditions, were shown to lead to the corresponding benzodihydrofuran 5, benzofuranone 14 and the oxindoles 19 and 24 respectively, in 50–80% yield. Further manipulation of the benzodihydrofuran 5 then led to the intermediates 30, 33 and 39, which make up parts of the oxazole–indole heterocyclic core in diazonamide A. Attempts to perform a corresponding 13-exo-trig Heck cyclisation from the precursor 46a, prepared from 44 and 45, leading to 47 were not successful. A similar outcome was obtained during attempts to effect Heck cyclisations from the ester 57 and the related ether 59. Treatment of the chromene-substituted iodoaryl 62 with Pd(OAc)2, PPh3 and Ag2CO3 led to the spirocycle 64 as a crystalline solid. X-Ray crystal structure analysis established that the quaternary centre in 64 had the same configuration as that present in diazonamide A (1).
在对二氮酰胺A(早期结构2;修订后的结构1)中四次碳中心进行的模型研究中,显示在Heck反应条件下,碱基取代的碘芳烃4、13、18和23的环化反应分别生成了相应的苯并二氢呋喃5、苯并噁唑酮14以及氧吲哚19和24,得率为50-80%。进一步操作苯并二氢呋喃5后,得到了中间体30、33和39,它们构成了二氮酰胺A中噁唑–吲哚杂环核心的一部分。从前体46a(由44和45制备而成)进行相应的13-exo-trig Heck环化反应以生成47的尝试未能成功。在试图从酯57和相关醚59进行Heck环化时也得到了类似的结果。用Pd(OAc)2、PPh3和Ag2CO3处理含克罗门的碘芳烃62,生成了结晶固体螺环64。X射线晶体结构分析确定64中的四次碳中心的构型与二氮酰胺A(1)中的构型相同。