Regio- and Stereoselective Ring Opening of Enantiomerically Enriched 2-Aryl Oxetanes and 2-Aryl Azetidines with Aryl Borates
作者:Ferruccio Bertolini、Stefano Crotti、Valeria Di Bussolo、Franco Macchia、Mauro Pineschi
DOI:10.1021/jo801568a
日期:2008.11.21
The regioselective ring opening of 2-aryl-substituted four-membered heterocyclic rings with phenols, including catechol, was achieved by the use of aryl borates in mild and neutral reaction conditions without the aid of any transition metal catalysts. While N-alkyl azetidines were found not to be reactive, optically active N-tosyl azetidines gave the corresponding beta-aryloxy amines in a racemic form
通过在温和和中性的反应条件下使用硼酸芳基酯而不借助任何过渡金属催化剂,可以实现2-芳基取代的四元杂环与苯酚(包括邻苯二酚)的区域选择性开环。虽然发现N-烷基氮杂环丁烷不具有反应性,但旋光性的N-甲苯磺酰基氮杂环丁烷以消旋形式给出了相应的β-芳氧基胺,因此表明过渡态具有相当大的碳阳离子特性。已显示能够锚定芳基硼酸酯并指导随后的亲核传递的氮杂环丁烷环(即氮杂环丁醇)中羟基的引入确定了主要反转构型的开环过程。当使用对映异构体富集的2-芳基氧杂环丁烷时,观察到的消旋程度有所降低(最高93:通过经由六元过渡态的分子内递送使7 er)合理化,得到具有主要保留构型(即,顺式-立体选择性开环)的β-芳氧基醇。具有适当官能度的所得芳氧基醇可以被环化以得到对映异构体富集的2-芳基-1,5-苯并二氧杂环丁烷。