Chiral Mo-binol complexes: Activity, synthesis, and structure. Efficient enantioselective six-membered ring synthesis through catalytic metathesis

A new class of chiral Mo-based complexes 2a and 2b, bearing functionalized chiral binol ligands, is disclosed. Mo complex 2a promotes the asymmetric r ing-closing metathesis (ARCM) of various dienes and trienes to afford six-m embered carbo- and heterocycles efficiently and in high optical purity. The binol-based chiral Mo catalysts complement the previously reported biphen- based complexes, which are particularly effective in the enantioselective s ynthesis of five-membered rings by ARCM. Studies regarding catalytic kineti c resolutions and asymmetric desymmetrizations are described. It is possibl e to obtain optically pure products in high yield from catalytic reactions without the use of solvent (cf. eq 1). The structural attributes of these c omplexes are detailed on the basis of the data available from an X-ray stru cture and variable-temperature H-1 NMR studies. The results of this investi gation indicate the following: (i) The anti-Mo.THF complex exists as a mixt ure of diastereomers, whereas the syn isomer is formed stereoselectively. ( ii) The anti-Mo isomers are likely more Lewis acidic.