Studies Towards the Total Synthesis of Rapamycin

Abstract

Abstract Discussion Points How would it be possible to recycle the undesired synisomer obtained in step a? What is the mechanism of step c? Explain the diastereoselectivity observed in the (EJ-crotylborane addition to aldehyde 4. Rationalise the diastereoselectivity observed in the epoxidation of homoallylic alcohol 5. How could the stereoselectivity of this reaction be reversed? Further Reading For an analysis of the mechanism in the oxazaborolidine catalysed reduction of ketones, see: B. Ganem, Chemtracts: Org. Chem.,1988, 1,40. For a review on enantioselective reduction of ketones, see: V. K. Singh, Synthesis,1992, 7, 607. For a review on the diastereoselectivity in nucleophilic additions to unsymmetrically substituted carbonyls, see: B. W. Gung, Tetrahedron,1996, 52,5263. For reviews on the synthesis of chiral epoxides, see: P. Besse and H. Veschambre, Tetrahedron,1994, 50,8885; W. Adam and M. J. Richter, Acc. Chem. Res.,1994, 27, 57; K. A. J rgensen, Chem. Rev.,1989, 89,431. For a review on substrate-directable reactions, see: A.H. Hoveyda, D. A. Evans and G. C. Fu, Chem. Rev.,1993, 93,1307. For a review on epoxide chemistry, see: J. Gorzynski Smith, Synthesis, 1984, 629. For a review on intramolecular reactions of allylic and propargylic silanes, see: D. Schinzer, Synthesis,1988, 4,263. For a review on the use of chiral boranes in synthesis, see: D.S. Matteson, Chem. Rev.,1986, 973.