No abstract

A general synthetic route to the set of polyhydroxylated agarofurans that comprise the core structures of esters present in plants of the Celastraceae family has been devised. The pathway is exemplified with total syntheses of (±)-3,4-dideoxymaytol (3), the nucleus of ever-1 (6), and (±)-euonyminol (4), the sesquiterpenoid core of several cathedulins including K-19 (5). A focal intermediate 19, prepared by Diels−Alder addition of 11 to 12, was identified that permitted stereoselective introduction of an isopropenyl substituent via chelation-controlled, conjugate Grignard addition to give 34. Triflic acid-catalyzed cyclization of 39 afforded the agarofuran skeleton of 3, and subsequent epimerization of the hydroxyl substituent at C1 via a reversible aldol sequence gave 41. Sequential reductions using hydride and catalytic hydrogenation yielded 3 and 4-epi-3,4-dideoxymaytol (51). The route from 19 was extended toward 4 via 56, prepared by directed epoxidation of 34. A trifuoroacetic acid-catalyzed “epoxide-cascade” cyclization of 56 furnished 61, which was advanced to γ-lactone 63 prior to epimerization at C1. Introduction of the 8β hydroxyl function of 69 was followed by an α-ketol transposition to give 71 which was reduced and protected as polysilyl ether 80. Osmylation and replacement of protecting groups produced euonyminol octaacetate 78 which underwent methanolysis to (±)-4.

No abstract

No abstract

No abstract