Discovery of a Phosphine-Mediated Cycloisomerization of Alkynyl Hemiketals: Access to Spiroketals and Dihydropyrazoles via Tandem Reactions
作者:Jaideep Saha、Chris Lorenc、Bikash Surana、Mark W. Peczuh
DOI:10.1021/jo3001854
日期:2012.4.20
functionality (R2) on the cyclic keto enol ether, a rapid and facile dimerization occurs, giving spiroketal products. When the enone is substituted (i.e., R2 = Ph), the cyclic keto enol ether is sufficiently stable so that it can be isolated; it can then be further reacted in the same pot to provide the corresponding dihydropyrazoles. Both the spiroketal and dihydropyrazole products arise by a tandem reaction
这里报道的是关于膦催化的半缩酮的异构化以及环状酮-烯醇醚产物的后续反应的详细信息。新的环异构化是对先前报道的胺催化过程的补充,该过程从相同的半缩醛起始原料制得了环氧庚烷酮。在环状酮烯醇醚上不存在官能团(R 2)的情况下,发生快速且容易的二聚,得到螺缩酮产物。当烯酮被取代时(即R 2=),则环状酮烯醇醚足够稳定,因此可以将其分离出来;然后可以将其在同一罐中进一步反应以提供相应的二氢吡唑。螺环酮和二氢吡唑产物均通过串联反应产生,该串联反应始于新的环异构化。该方法允许从相对简单的起始材料快速引入产品的复杂性。它应在天然产物样分子的合成中找到应用。