Palladium- and cobalt-mediated cyclisations of halo-polyenes: a comparative study
作者:Amjad Ali、G. Bryon Gill、Gerald Pattenden、Graeme A. Roan、Toh-Seok Kam
DOI:10.1039/p19960001081
日期:——
Cobalt(I)-mediated mono- and bi-cyclisations of halo-polyenes are compared and contrasted with corresponding reactions using the Heck reaction. The procedures are found to complement one another, with each having advantages and disadvantages, in the cases studied. Thus, treatment of the vinyl iodide 1 under Heck conditions led to the novel 1,3-diene 3 in 93% yield, whereas reaction between 1 and cobalt(I) salophen resulted in the formation of the organocobalt complex 4 (∼50%) as black crystals. Subsequent irradiation of 4 then led to the 6,5-ring fused bicycle 5 in 85% yield. In similar fashion, a Heck reaction with the analogous vinyl iodide 8 produced the product 9 of 6-ring cyclisation followed by β-hydride elimination, whereas the corresponding cobalt-mediated reaction with 8 led to the new organocobalt 10 albeit in only low yield (∼20%). In reactions akin to those studied by Overman et al., Heck reaction with the dienyl aryl iodide 14 was shown to lead to a mixture of the bicycle 16 and the tricycle 17 in a 1:1 ratio. By contrast treatment of 14 with cobalt(I) salophen produced largely the tetralin 18. The iodo-diene 33 gave rise to the spirocycle 35 under Heck reaction conditions, and the related spirocycle 42 was produced from the bromo-acetal 40 via 41, using cobalt(I) mediated reactions.
钴(I)介导的卤代多烯的单环化和双环化与相应的Heck反应进行了比较和对比。研究发现这些方法互为补充,各有优缺点,在所研究的案例中均适用。因此,在Heck条件下将乙烯基碘1处理后,得到了新型1,3-二烯3,产率为93%;而将1与钴(I)水杨酮反应则生成了有机钴配合物4(约50%),呈黑色晶体。随后对4进行辐照处理,得到了6,5-双环5,产率为85%。类似地,与类似的乙烯基碘8进行Heck反应,得到6-环化产物9,随后发生β-氢消除反应;而与8进行相应的钴介导反应,则得到了新的有机钴10,尽管产率较低(约20%)。在与Overman等人研究的反应类似的情况下,向二烯基芳基碘14进行Heck反应,得到了16和17的双环和三环混合物,比例为1:1。相比之下,将14与钴(I)水杨酮反应,则主要得到了四氢萘18。碘代二烯33在Heck反应条件下生成了螺环35,而通过钴(I)介导反应从溴代缩醛40经过41生成了相关螺环42。