Synthesis,Characterization And Catalytic Studies Of Chiral Hydrobenzoin Derivatives

Asymmetric catalystic reaction has recently been the subject of intense research in chiral syntheses where novel chiral catalysts are the core of the construction. Using (R,R)-hydrobenzoin as chiron, a series of chiral derivatives of nitrogen-containing heterocycles were synthesized.The crystal structures of relative compounds and catalytic effects of some chiral derivatives on the enantioselective addition of diethylzinc to benzaldehyde have been studied.1. The (R,R)-hydrobenzoin with high enantio-purity was prepared by Sharpless Asymmetric Dihydroxylation. The chiral derivatives containing hydroxyl group were synthesized from the reaction of 2-(Bromomethyl)pyridine hydrobromide, methoxy or N-morpholino derivatives of cyanuric chloride and the mono silicon etherification product of (R,R)-hydrobenzoin, followed by deprotection in the presence of (n-Bu)4NF.2. Using (R,R)-hydrobenzoin as chiron, esters and ethers containing pyridine were synthesized by the reaction with pyridine acid or 2-(Bromomethyl)pyridine hydrobromide.3. Using (R,R)-hydrobenzoin as raw material, two methods were studied to synthesize (1R,2R)-2-methoxy-1,2-bibenphenylethanol. The C2-symmetric chiral derivatives with one s-triazine ring were synthesized from (1R,2R)-2-methoxy-1,2-bibenphenylethanol and the derivatives of cyanuric chloride which were mono-substituted by alkoxy or amino group. The C2-symmetric chiral derivatives with double s-triazine rings were synthesized from (R,R)-hydrobenzoin and the derivatives of cyanuric chloride which were bi-substituted by methoxy or N-morpholino.4. The crystal structures of (1R,2R)-1,2-diphenyl-1,2-diethyl isonicotinate (1R,2R)-2-hydroxy-1,2-diphenylethyl nicotinate and di(2-((1R,2R)-1,2-diphenylethyl-2-hydroxyethoxy)methy)) pyridine have been studied. The crystal of (1R,2R)-1,2-diphenyl-1,2-diethyl isonicotinate is monoclinic with space group P21,α= 11.925(10) A,b= 5.826(5) A, c= 17.787(15) A,α=γ= 90°,β= 105.629(10)°.It can be seen that two molecules exist in one unit cell. The crystal of (1R,2R)-2-hydroxy-1,2-diphenylethyl nicotinate is monoclinic with space group P21, a= 8.939(2) A, b= 5.8128(14) A, c 16.191(4) A,α=γ= 90°,β= 100.303(3)°. It can be seen that two molecules exist in one unit cell. The crystal of di(2-((1R,2R)-1,2-diphenylethyl-2- hydroxyethoxy)methy)) pyridine is Orthorhombic with space group P212121, a= 5.4370(11)A, b= 19.911(4)A, c= 26.962(6) A,α=γ=β= 90°. It can be seen that four molecules exist in one unit cell. The three crystal structures are stabilized by O-H...N or C-H...O hydrogen bond.5. Six derivatives containing pyridine or triazine were studied as catalysts for the enantioselective addition of diethylzinc to benzaldehyde. The preliminary studies indicated that the enantioselectivity of pyridine-containing derivatives of (R,R)-hydrobenzoin is higher than that of triazine-containing derivatives. The results showed that stereoselectivity of catalysts is related to hydroxyl group attached to chiral carbon.Ether derivatives were proved to be the better catalysts than the ester ones with regard to enantioselectivity. (1R,2R)-2-(2-pyridinemethoxy)-1,2-diphenylethanol yields in 78% and the enantioselectivity is 56%ee.