Synthesis of (+)-Xylogiblactones B and C through a Kinetic Resolution of the Allenoate γ-Addition: Stereochemical Establishment.

Concise syntheses of naturally occurring γ-butenolides (+)-xylogiblactones B and C have been achieved for the first time starting from commercial methyl crotonate in 5-8 steps. The synthetic course involves allenoate γ-addition to racemic aldehydes through a kinetic resolution to establish the required stereochemical framework as center and axial chirality and subsequent oxacyclization via gold catalysis to complete the (+)-xylogiblactone skeleton. Both key transformations proceed in a regio- and stereospecific manner. This outcome relies on finding an efficient synthetic method for racemic aldehydes as precursors for the kinetic resolution. Completion of the synthesis provides stereochemical clarification for (+)-xylogiblactones B and C.