Regio- and Stereocontrolled 6-Endo-Trig Radical Cyclization of Vinyl Radicals: A Novel Entry to Carbasugars from Carbohydrates

A Reverse Approach to the Total Synthesis of Halichondrin B

A new strategy is described for the total synthesis of halichondrin B featuring reversal of the sequential construction of a number of its cyclic ethers from the classical approach by instead forming C-O bonds first followed by C-C bond formation. Employing the Nicholas reaction to generate linear ethers as precursors for the total synthesis of halichondrin B and other members of the halichondrin and eribulin families of compounds, this novel approach provides new opportunities for the development of improved syntheses of these complex and valuable compounds. In this Article, we report the syntheses of defined fragments I, MN, EFG, and A. Fragments I and MN were then coupled and elaborated to advanced intermediate IJKLMN, which was joined with fragment EFG to afford, after appropriate elaboration and macrolactonization, the more advanced polycyclic intermediate EFGHIJKLMN. Elaboration of the latter and coupling with fragment A followed by further functionalization completed the total synthesis of halichondrin B through a short and convergent pathway.

Preparation and structural study of the enantiomers of alpha,alpha'-bis(trifluoromethyl)-9,10-anthracenedimethanol and its perdeuterated isotopomer, highly effective chiral solvating agents

Enantiopure forms of alpha,alpha'-bis(trifluoromethyl)-9,10-anthracenedimethanol and the corresponding perdeuterated isotopomers were prepared. The conformational study was carried out by (1)H NMR, and the absolute configuration was determined by the X-ray study of the crystallized diastereoisomeric carbamate derivative. This compound was tested as a chiral solvating agent (CSA). The results showed very good discrimination for several racemic mixtures that improved other classical methods. The study of diastereomeric complexes was carried out by determination of the stoichiometry of the complex and the binding constant of the equilibrium.