Development of a Formal [4 + 1] Cycloaddition: Pd(OAc)<sub>2</sub>-Catalyzed Intramolecular Cyclopropanation of 1,3-Dienyl β-Keto Esters and MgI<sub>2</sub>-Promoted Vinylcyclopropane−Cyclopentene Rearrangement
作者:Rockford W. Coscia、Tristan H. Lambert
DOI:10.1021/ja809226x
日期:2009.2.25
A formal [4 + 1] cycloaddition of 1,3-dienyl beta-keto esters has been developed. This two step process involves Pd(II)-catalyzed intramolecular cyclopropanation to produce vinylcyclopropanes and a subsequent mild vinylcyclopropane-cyclopentene rearrangement promoted by MgI(2). The cyclopropanation method notably requires the use of Mg(ClO(4))(2), presumably to facilitate keto-enol tautomerization
1,3-Dienyl β-keto esters are cyclised into bicyclolactones using the Bi(OTf)3/TfOH catalytic system. This reaction represents a rare case of simultaneous C–C and C–O bond formation at positions 1 and 3 of a 1,3-diene. Application to the synthesis of ramulosin is presented.