Enantioselective Synthesis of 5,7-Bicyclic Ring Systems from Axially Chiral Allenes Using a Rh(I)-Catalyzed Cyclocarbonylation Reaction

A transfer of chirality in an intramolecular Rh­(I)-catalyzed allenic Pauson–Khand reaction (APKR) to access tetrahydroazulenones, tetrahydrocyclopenta­[<i>c</i>]­azepinones and dihydrocyclopenta­[<i>c</i>]­oxepinones enantioselectively (22–99% ee) is described. The substitution pattern of the allene affected the transfer of chiral information. Complete transfer of chirality was obtained for all trisubstituted allenes, but loss of chiral information was observed for disubstituted allenes. This work constitutes the first demonstration of a transfer of chiral information from an allene to the 5-position of a cyclopentenone using a cyclocarbonylation reaction. The absolute configuration of the corresponding cyclocarbonylation product was also established, something that is rarely done

An Allenic Pauson–Khand Approach to 6,12-Guaianolides

Cyclocarbonylation of α-methylene butyrolactone-containing allene-ynes affords 6,12-guaianolide ring systems. Incorporation of the α-methylene butyrolactone early in a synthetic sequence is rare for reactivity reasons; however, this moiety proves to be beneficial to the allenic Pauson–Khand reaction. The three double bonds and the ketone in the resulting 5–7–5 ring system bear significant differences in their reactivity and are ideally positioned for synthetic application to 6,12-guaianolides and analogs