Four new chiral aminodiols 1-4, which were prepared from methyl L proline in 2 steps, were applied in the enantioselective addition of diethylzinc to benzaldehyde. The results indicated that the enantioselectivities e...Four new chiral aminodiols 1-4, which were prepared from methyl L proline in 2 steps, were applied in the enantioselective addition of diethylzinc to benzaldehyde. The results indicated that the enantioselectivities enhance with increasing the bulkiness of substituents on chiral ligands and with chiral ligand 4 giving the best result. When ligand 4 was used to catalyze the enantioselective addition of diethylzinc to aromatic aldehydes, the substituents affect the enantioselectivities slightly and 1 naphthaldehyde gives the best enantiomeric excess(up to 75.3% ). On the other hand, 4 (dimethylamino)benzaldehyde gives a low enantiomeric excess, which may most likely arise from a non steroselective ethyl transfer to aldehyde promoted by zinc coordination of amino group. For aliphatic aldehydes, poor enantiomeric excesses are generally given.展开更多
A new polymer supported BINOL ligand(4) was prepared by means of anchoring binaphthyl molecule(3) to aminoethylated polystyrene through a procedure of solid phase peptide synthesis. The key compound ( R ) 2,2 dihydr...A new polymer supported BINOL ligand(4) was prepared by means of anchoring binaphthyl molecule(3) to aminoethylated polystyrene through a procedure of solid phase peptide synthesis. The key compound ( R ) 2,2 dihydroxy 1,1 binaphthyl 3 carboxylic acid(3) was prepared from R BINOL by protection of hydroxyl groups and then reaction with n butyllithium followed by carboxylation. By controlling the amount of BuLi, (3) was obtained in 55% overall yield. Ligand (4) was prepared through condensation of (3) with aminoethylated polystyrene in the presence of DCC and HOBt and found to have a loading of 0.40 mmol/g (by mass increase). The linkage between binaphthyl and aminoethylated polystyrene was indicated by a new absorption in IR spectrum of (4) at 1 644 cm -1 in comparing with what of the polystyrene. By mixing (4) with Ti(OiPr) 4 in dry CH 2Cl 2, a complex was easily prepared and this complex was found to be an efficient heterogeneous catalyst in asymmetric addition of diethylzinc to aldehydes. Optical active alcohols with up to 82% ee were obtained from the asymmtric addition with high chemical yields when 20% of (4) was used. And when benzaldehyde was used as substrate, we found that enantioselectivity increased obviously when the amount of (4) used in reaction increased from 5% to 20%;decreased the load of BINOL in ligand (4) reduced the ee of addition product; and R form of products was resulted. [WT5HZ]展开更多
文摘Four new chiral aminodiols 1-4, which were prepared from methyl L proline in 2 steps, were applied in the enantioselective addition of diethylzinc to benzaldehyde. The results indicated that the enantioselectivities enhance with increasing the bulkiness of substituents on chiral ligands and with chiral ligand 4 giving the best result. When ligand 4 was used to catalyze the enantioselective addition of diethylzinc to aromatic aldehydes, the substituents affect the enantioselectivities slightly and 1 naphthaldehyde gives the best enantiomeric excess(up to 75.3% ). On the other hand, 4 (dimethylamino)benzaldehyde gives a low enantiomeric excess, which may most likely arise from a non steroselective ethyl transfer to aldehyde promoted by zinc coordination of amino group. For aliphatic aldehydes, poor enantiomeric excesses are generally given.
文摘A new polymer supported BINOL ligand(4) was prepared by means of anchoring binaphthyl molecule(3) to aminoethylated polystyrene through a procedure of solid phase peptide synthesis. The key compound ( R ) 2,2 dihydroxy 1,1 binaphthyl 3 carboxylic acid(3) was prepared from R BINOL by protection of hydroxyl groups and then reaction with n butyllithium followed by carboxylation. By controlling the amount of BuLi, (3) was obtained in 55% overall yield. Ligand (4) was prepared through condensation of (3) with aminoethylated polystyrene in the presence of DCC and HOBt and found to have a loading of 0.40 mmol/g (by mass increase). The linkage between binaphthyl and aminoethylated polystyrene was indicated by a new absorption in IR spectrum of (4) at 1 644 cm -1 in comparing with what of the polystyrene. By mixing (4) with Ti(OiPr) 4 in dry CH 2Cl 2, a complex was easily prepared and this complex was found to be an efficient heterogeneous catalyst in asymmetric addition of diethylzinc to aldehydes. Optical active alcohols with up to 82% ee were obtained from the asymmtric addition with high chemical yields when 20% of (4) was used. And when benzaldehyde was used as substrate, we found that enantioselectivity increased obviously when the amount of (4) used in reaction increased from 5% to 20%;decreased the load of BINOL in ligand (4) reduced the ee of addition product; and R form of products was resulted. [WT5HZ]
