Question

18-23 The taxane skeleton has been a popular target for synthesis due to the highly useful anticancer properties of Taxol", especially against solid tumor, and the limited sup- plies of the natural material. Each of the following oxidations has been carried out on the taxane ring system. Suggest the reagent for each transformation. Where more than one option is available, suggest which would be best and tell why. [J. Org. Chem. 2000, 65, 7865] H Aco O OTES Aco_?, OTES (b) TESOM V E Y "Br [Chem. Eur. J. 1999, 5, 121] I TESO

Answer 1

SeO2 + сHз он VIH Haco CH3 *OH H OH CH3COOH HOHI Stereoselective allylic hydroxylation is carried out with Selenium dioxide with tert-butyl hydroperoxide. This reaction proceeds via an ene reaction at electrophilic selenium atom. Aco Aco OTES Ji ? OTES CuBr + TESO Y CH3 TESO Photo сн, CH3C Hс OTES Stereoselective allylic bromination is achived by reaction of the starting material with CuBr and tert-butyl benzenecarboperoxoate. This actually gives intermediate as a major compound but that can be TESC converted by heating the reaction mixture with CuBr to 50°C. intermediate 5 ,0 Br