3-Hydroxy-dihydrosantoninとTsOHの反応.Dihydrocotunolideの形式的合成

概要

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In connection with our another project a relatively large quantity of 5 was required. We, therefore, investigated the reaction of 3 with TsOH ; this gave a diene mixture 7a, 7b, 6 and 5 in a ratio of 8 : 2 : 4 : 1. Almost the same 8 : 2 : 1"equilibrium mixture"of the dienes 7a, 7b and 5 was also obtained when the purified samples of 5 and 7a were independently treated with TsOH under the same conditons. The above results suggest that the dienes might be produced in the following way ; β-elimination of H_2O from 3 gives a homoannular diene 5. The protonation to the more electron-rich tetrasubstituted C_4-C_5 double bond of 5 from the less hindered α-side followed by the isomerization of the double bond gives 7a. 7b is formed via 7a and/or 5 by the double bond isomerizations. On the other hand, 6 is formed by concerted elimination of H_2O between C_3-OH and C_6-H. As a result of these studies, the synthetic precursor of dihydrocostunolide 7b which was already prepared by Corey in 6 steps (ca. 7%) from santonin was synthesized in 3 steps (ca. 6%) from the latter.
公益社団法人日本薬学会の論文
1996-09-25