Triptolide synthesis yield

Hydroxymethylation of ketone (155) was followed by protection of the aliphatic hydroxy group (2-methoxypropyl ether) and addition of an a-benzyloxymethylene group at C-4. Acidic workup at the last stage of the reaction sequence produced (156). Its transformation to aldehyde (157) was carried out by successive treatment with methoxypropyl ether, acetic anhydride and pyridine, hydrochloric acid and methanol, and finally chromic acid, pyridine and hydrochloric acid. Dehydration of (157) led to the formation of (158) in 20% yield. Reagents other than the mentioned produced appreciable quantities of the cis A/B isomer. The butenolide (159) was finally synthesized by oxidation and hydrogenolysis. In order to complete the synthesis of triptolide it was necessary to introduce the... 

The second synthesis of triptolide (149) by van Tamelen [52] requires fewer steps and proceeds in an overall yield 40-50 times than that realized earlier [50], and this is described in Fig. (19). 

The method described for the synthesis of triptolide is concise and affords good yield in most of the steps. We believe that the experimental procedures are complicated and requires skilled experimentalists. Yang et al [72] have also accomplished an enantioselective total synthesis of (-)-triptolide. 

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