12 Total Synthesis of Furanoeremophilanes and Eudesmanolides by a Route Involving Alkylation of 2,4-Dimethyl-3-furoic Acid or 2-Methyl-3-furoic Acid
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Some sesquiterpene lactones and furans with a perhydronaphtho-furan ring system, furanoeremophilanes and eudesmanolides, have been synthesized by a route involving alkylation of 2,4-dimethyl-3-furoic acid and 2-methyl-3-furoic acid. 1) Reaction of a dianion (D) generated from 2,4-dimethyl-3-furoic acid with 2-methyl-3-methoxy-2-cyclohexenone gave an acid (11). Acid-catatyzed cyclization of dihydro acid (12), obtained by hydrogenation of 11, yielded a diketone (13) stereoselectively. Furanoeremophilane-3,6-dione (3) and furanoeremophilan-14,6α-olide (4) were synthesized in 5 steps from the diketone (13), respectively. 2) Similar alkylation reaction of 2-methyl-3-furoic acid with 3-methoxy-2-cyclohexenone gave an acid (23). A diketone (25) was obtained by reaction of methyl ester (24) of 23 with LiMe_2Cu. Oxidation of furans with peracid to create γ-lactones was investigated. 13-Nordihydrocallitrisin (5a) was synthesized from 27.
