4,5-Didehydro-7-silyloxymethyl-2-oxepanone and formal total syntheses of Hagen's gland lactones and trans-kumausynes

Base-catalyzed single-step rearrangement of 7-substituted-4,5-epoxy-2-oxepanone into the 2,6-dioxabicyclo[3.3.0]octan-3-one skeleton leads to formal total syntheses of (7R)-cis-Hagen's gland lactones and (+)- and (−)-trans-kumausynes.