Synthesis of the C20–C32 Tetrahydropyran Core of the Phorboxazoles and the C22 Epimer via a Stereodivergent Michael Reaction
作者:Paul A. Clarke、Kristaps Ermanis
DOI:10.1021/ol3026523
日期:2012.11.2
A stereoselective synthesis of the C20-C32 tetrahydropyran core of the phorboxazoles has been achieved in only seven steps and in a 31% overall yield. The C22 epimer was also synthesized. The key step was a silyl ether deprotection/oxy-Michael cyclization. When this step was conducted under Bronsted acid conditions, the C20-C32 core was formed with the desired 2,6-cis-stereochemistry. However, when the silyl ether deprotection/oxy-Michael cyclization was conducted under fluoride conditions buffered with acetic acid, the C22 epimer of the core was the sole product.