Abstract
Enantioselective synthesis of some natural products possessing a chiral quaternary center has been developed starting from the chiral γ-hydroxymethyl-γ-lactone derivatives. Stereoselective alkylation of the lactone substrates due to α,γ-nonbonding interaction allowed a formation of (R)- or (S)- quarternary center at the α-position of the lactones arbitrarily. Subsequent transformation of the lactones thus, formed furnished the following compounds containing a quaternary carbon in high optical purity: (1) both (+)- and (-)-enantiomers of the Aspidosperma type indole alkaloid, quebrachamine(13), from the single chiral lactone (15); (2)(-)-mesembrine(36), the parent compound of the Sceletium alkaloids, from the lactone(29); (3) the gibbane derivatives, (53) and (55), from the lactone(14).
