Ketyl radical cyclization of β-disubstituted acrylates: formal syntheses of (+)-secosyrin 1 and longianone and the total synthesis of (+)-4-epi-secosyrin 1.

A novel approach to the synthesis of a series of 1,7-dioxaspirononanes that applies a ketyl radical cyclization strategy is described. Radical cyclization of the β-disubstituted acrylate 23, prepared in five steps from (R)-1,2-isopropylideneglycerol, gives both 2,3-syn- and 2,3-anti-furan products. The densely functionalized furan heterocycles are used to complete a concise formal synthesis of secosyrin 1, a metabolite of Pseudomonas syringae, and the total synthesis of 4-epi-secosyrin 1.