Total Synthesis of Solandelactones A, B, E, and F Exploiting a Tandem Petasis−Claisen Lactonization Strategy
作者:James D. White、Christopher M. Lincoln、Jongtae Yang、William H. C. Martin、David B. Chan
DOI:10.1021/jo800335g
日期:2008.6.1
Solandelactones A, B, E, and F were synthesized using Nozaki-Hiyania-Kishi coupling of iododiene 13 with aldehydes 14 and 99 obtained by oxidation of alcohols 92 and 94. Key steps in the synthesis of 92 and 94 were (i) a Nagao asymmetric acetate aldol reaction of aldehyde 77 with thionothiazolidine 78 to set in place an alcohol that becomes the (7S) lactone center of solandelactones, (ii) a Simmons-Smith cyclopropanation of 80 directed by this alcohol, and (iii) Petasis methylenation of cyclic carbonate 90 in tandem with a Claisen rearrangement that generates the octenalactone portion of solandelactones. Synthesis of solandelactones A, B, E, and F confirmed their gross structure and absolute configuration at C7, 8, 10, and 14 but showed that alcohol configuration at C11 must be reversed in pairs, A/B and E/F, from the previous assignment made to these hydroid metabolites. Thus, solandelactones A and B are correctly represented by 2 and 1, respectively, whereas solandelactones E and F are 6 and 5. A biogenesis of solandelactones is proposed for these C(22) oxylipins that parallels a hypothesis put forward previously to explain the origin of C(20) cyclopropane-containing algal products.