1. A concise synthesis approach to optically active taxol C-ring fragment
2. (Z)-4-t-butyldimethylsilyloxy-3-methyl-2-butenoate 2 was prepared as follows.2:1H NMR δ 7.64–7.66 (m, 4H), 7.37–7.39 (m, 6H), 5.64 (s, 3H), 4.86 (s, 2H), 3.56 (s, 3H), 2.07 (s, 3H), 1.07 (s, 9H); IR (neat, cm−1) 3072, 2956, 2860, 1720, 1430, 1230, 1152, 1112, 1060, 822, 742, 702; HRMS m/z (M+-H) calcd 367.1729, obsd 3671723.
3. Stereospecific synthesis of trisubstituted and tetrasubstituted olefins. Conjugate addition of dialkylcopper-lithium reagents to .alpha.,.beta.-acetylenic esters
4. The dibromide was immediately used for the next step after workup without purification.
5. The stereochemistry of the tetrasubstituted alkenes was determined by 1H-NMR techniques (noe measurement) and comparison with authentic samples prepared by another procedure.