Enantioselective syntheses of (+)- and ()-nephrosteranic acid employing the Nicholas-Schreiber reaction
作者:Peter A. Jacobi、Prudencio Herradura
DOI:10.1139/cjc-79-11-1727
日期:——
(+)- and (-)-Nephrosteranic acid (16) have been prepared in an enantioselective fashion from alkyne acid 19 (or ent-19) by a three step sequence involving debenzylation-lactonization, oxidative cleavage, and selective epimerization at C-4. Acids 19 and ent-19 were obtained as single enantiomers employing a Nicholas-Schreiber reaction.
Formation of γ-Lactones through CAN-Mediated Oxidative Cleavage of Hemiketals
作者:Alexander M. Jacobine、Weimin Lin、Bethany Walls、Charles K. Zercher
DOI:10.1021/jo801258h
日期:2008.9.19
The generation of substituted gamma-lactones can be accomplished through application of a tandem chain extension-aldol reaction, followed by CAN-mediated oxidative cleavage of the aldol product. The oxidative cleavage requires the intermediacy of a hemiketal and the presence of an alpha-heteroatom. Formation of the gamma-lactone through the oxidative cleavage is used to assign stereochemistry of the
The vicinal dianion 2 derived from triethyl ethanetricarboxylate reacted regioselectively with aldehydes and ketones at C(p) to provide paraconic acid derivatives 5a-f in moderate to high yields as mixtures of diastereoisomers. The paraconic acid derivatives 5e and 5f were utilized as the starting materials for the syntheses of (+/-)-lichesterinic acid (12), (+/-)-phaseolinic acid (13), (+/-)-nephromopsinic acid (14), (+/-)-rocellaric acid (15), and (+/-)-dihydroprotolichesterinic acid (16).