Bicyclic- and Tricyclic-β-lactones via Organonucleophile-Promoted Bis-Cyclizations of Keto Acids: Enantioselective Synthesis of (+)-Dihydroplakevulin
摘要:
A highly diastereoselective, nucleophile-promoted bis-cyclization process, employing readily available and tractable keto acid substrates, is described. This methodology provides concise access to bicyclic- and tricyclic-beta-lactones bearing tertiary carbinol centers and quaternary carbons, greatly extending the scope of previous routes to bicyclic-beta-lactones from aldehyde acid substrates. The utility of the method was demonstrated by application to an enantioselective synthesis of (+)-dihydroplakevulin A. This and related processes may be revealing a subtle interplay between [2+2] cycloaddition and nucleophile-catalyzed aldol lactonization (NCAL) reaction manifolds.
Conjugate reduction and reductive aldol cyclization of α,β-unsaturated thioesters catalyzed by (BDP)CuH
作者:Ninglin Li、Jun Ou、Michel Miesch、Pauline Chiu
DOI:10.1039/c1ob05352c
日期:——
A conjugate reduction of α,β-unsaturated thioesters catalyzed by copper hydride using PMHS as stoichiometric reductant has been developed. 1,2-Bis(diphenylphosphino)benzene (BDP) was the most effective ligand for this reduction. Saturated thioesters could be produced in excellent yields when the substituent on the thiol is not sterically-demanding. This protocol was applied to induce the reductive aldol cyclization of keto-enethioates, which could offer β-hydroxythioesters in moderate to good yields.