The C(1)-C(10) Bond Cleavage and B Ring Aromatization of Some 6-Hydrpoxy-5βH-abieta-6,8,11,13-tetraen-18-oic Acid 18,6-Lactones

Article abstract of DOI:10.1246/bcsj.55.891

Fusion of 6-hydroxy-5βH-abieta-6,8,11,13-tetraen-18-oic acid 18,6-lactone (2) with potassium hydrogensulfate at 220 deg C afforded bis<3-(2,3-dihydro-7-isopropyl-3,4-dimethyl-2-oxonaphtho<2,3-b>furan-3-yl)propyl> ether (12) in 37percent yield, together with two minor products in 12percent yield: 2,3-dihydro-7-isopropyl-3,4-dimethyl-3-propylnaphtho<2,3-b>furan-2-one and 3-allyl-2,3-dihydro-7-isopropyl-3,4-dimethylnaphtho<2,3-b>furan-2-one.Treatment of 12 with p-toluenesulfonic acid at 160 deg C gave 2,3-dihydro-7-isopropyl-3,4-dimethyl-3-(3-tosyloxypropyl)naphtho<2,3-b>furan-2-one, which was converted into 2,3-dihydro-3-(3-hydroxypropyl)-7-isopropyl-3,4-dimethylnaphtho<2,3-b>furan-2-one (16).The alcohol 16 was further characterized as its acetate (17).After several attempts, the above C(1)-C(10) bond cleavage and B ring aromatization reaction were improved by use of concentrated sulfuric acid in refluxing acetic acid.Under this conditions, 2 gave 17 in 47percent yield.Hydrolysis of 17 with hydrochloric acid afforded 16.Subsequently, 12-hydroxy-, 12-methoxy-, 12-acetoxy-, and 12-nitro-6-hydroxy-5βH-abieta-6,8,11,13-tetraen-18-oic acid 18,6-lactones were each refluxed with concentrated sulfuric acid in acetic acid to give 6-hydroxy-, 6-methoxy-, 6-acetoxy-, and 6-nitro-3-(3-acetoxypropyl)-2,3-dihydro-7-isopropyl-3,4-dimethylnaphtho<2,3-b>furan-2-ones, respectively.From the present study, the 12-acetoxy derivative seems to be a suitable intermediate for the synthesis of coleon A.