Chromium(0)-Promoted Multicomponent Cycloaddition of Tethered Diynes with Cyclic Trienes:  Application to the Total Synthesis of 9-epi-Pentalenic Acid

Abstract

An efficient protecting group controlled regioselective chromium(0)-mediated three-component higher order cycloaddition of tethered diynes with cyclic trienes that generates five rings and six stereogenic centers in one step is described. Following a sequence of reactions featuring a chemoselective Baeyer-Villiger rearrangement and a regioselective cyclopropane hydrogenolysis, the total synthesis of 9-epi-pentalenic acid was achieved.

Asymmetric Total Synthesis of Rumphellclovane E

“…Subsequently, we sought to develop tactics of hydrogenolysis of cyclopropane in 7a and 7b to generate quaternary C 4 with gem -dimethyl. Accordingly, 7a was separated from 7b and subjected to Pd­(OH) 2 /H 2 in EtOH to provide the intermediate 13 (Scheme ). However, the following base-mediated hydrolysis of ester and decarboxylation unfortunately gave rise to compound 14 with considerable epimerization at C 9 , plausibly through a retro-aldol-aldol process.…”

Application of Pauson–Khand reaction in the total synthesis of terpenes

“…Following the original isolation in 1957 by Koe and co-workers, McBride and co-workers, 324,325 the structure and absolute conguration were eventually assigned in 1970 by combination of spectroscopic and X-ray crystallographic methods. 326,327 The structure of pentalenolactone A 497 was determined by NMR analysis of its methyl ester derivative. The analysis showed that the structure consists of a highly compact carbon framework with a rare, angularly fused tricyclic pentanoid lactone having various oxidation states in each of the rings.…”

Bioactive C-Glycosides from Bacterial Secondary Metabolism

“…This suggested that oxidative cleavage occurs prior to C-glycosidation via Baeyer-Villiger-type oxidation of the orthoquinones 120 or 121, mediated by the oxygenase GilOI. This oxidation, probably producing a cyclic anhydride 123, is apparently without precedent in the biosynthetic literature [199], although similar processes have been utilized in organic synthesis [200].…”