Catalytic Intramolecular Formal [3 + 2] Cycloaddition for the Synthesis of Benzobicyclo[4.3.0] Compounds
作者:Xun Han、Long-Wu Ye、Xiu-Li Sun、Yong Tang
DOI:10.1021/jo9001917
日期:2009.5.1
In the presence of 20 mol % of tributylphosphine, tert-butyl carbonate substrate 3a undergoes smoothly an intramolecular formal [3 + 2] cycloaddition reaction at room temperature to give benzobicyclo[4.3.0] compounds in 99% yield with a 19/81 ratio of 2a and 2a′. The mechanism of the isomerization of the product 2a into 2a′ has been investigated in detail. On the basis of this mechanism, two strategies
在20mol%的三丁基膦的存在下,碳酸叔丁酯底物3a在室温下顺利地进行分子内的甲醛[3 + 2]环加成反应,以99%的收率以19/81的比率得到苯并双环[4.3.0]化合物。的图2a和图2a '。已经详细研究了产物2a异构化为2a '的机理。基于该机理,有两种策略,在20 mol%的Ti(O i Pr)4存在下使用20 mol%的三苯基膦或10 mol%的三丁基膦。已经建立了用于选择性构建苯并双环[4.3.0]化合物的化合物。在中性条件下,化合物3a - g的反应可提供高选择性的苯并双环[4.3.0]化合物2a - g,收率高至优异。另外,α-甲基α,β-不饱和酯3h在中性和室温条件下也能很好地产生具有一个季碳中心的相应产物2h,产率为99%。