| 68 % ee |
With 2,2-dimethylpropanoic anhydride; N-ethyl-N,N-diisopropylamine In diethyl ether at 20℃; for 12 h; |
Test Example 5Production of Optically Active 2-Hydroxy Ester Using Various Types of Racemic 2-Hydroxy Ester (3) As shown in the above reaction scheme, to diethyl ether (0.2 M) containing 0.6 equivalents of pivalic acid anhydride and 0.5 equivalents of diphenylacetic acid were added 1.2 equivalents of diisopropyl ethylamine, 5percent by mole of (+)-benzotetramisole (BTM), and a solution containing 1 equivalent of a racemic 2-hydroxy ester in diethyl ether at room temperature in this order, and this reaction mixture was stirred at room temperature for 12 hrs. Thereafter, the reaction was stopped with a saturated aqueous sodium bicarbonate solution. After the organic layer was fractionated, the aqueous layer was extracted with diethyl ether three to five times. After the organic layers were admixed, the mixture was dried over anhydrous sodium sulfate. The solution was filtered and thereafter vacuum concentrated. Thus obtained mixture was fractionated on silica gel thin layer chromatography (developing solvent: hexane/ethyl acetate=3/1) to afford a corresponding diester and unreacted optically active 2-hydroxy ester. The results are shown in Table 5. TABLE 5 Yield [percent] [a] cc [percent] No.R5 R6 5a; 5b 5a; 5b s 29 Et n-Pr 47; 47 97; 89 217 30 Me Me 47; 23 97; 68 119 [a] Isolation yieldAs is seen from Table 5, prominently high enantiomeric excess ee and reaction velocity ratio s were exhibited also when a material other than the benzyl ester was used (Entries 29 and 30).The physical properties of the optically active hydroxy esters and the diesters in Table 5 are shown below.(Entry 29)Ethyl (S)-2-hydroxypentanoate1H NMR (CDCl3): δ4.19 (dq, J=14.0, 7.0 Hz, 1H, Eta), 4.18 (dq, J=14.0, 7.5 Hz, 1H, Eta), 2.96 (br d, J=3.5 Hz, 1H, OH), 1.75-1.65 (m, 1H, 3-H), 1.62-1.52 (m, 1H, 3-H), 1.48-1.30 (m, 2H, 4-H), 1.24 (dd, J=7.5, 7.0 Hz, 3H, Eta), 0.89 (t, J=7.3 Hz, 3H, 5-H);13C NMR (CDCl3): δ175.3, 70.2, 61.4, 36.4, 17.9, 14.1, 13.6.Ethyl (R)-2-(diphenylacetyloxy)pentanoateHPLC (CHIRALCEL AD-H, i-PrOH/hexane=1/50, flow rate=1.0 mL/min): tR=15.0 min (1.4percent), tR=17.5 min (98.6percent);IR (neat): 1745, 1496, 1454, 745, 701 cm-1;1H NMR (CDCl3): δ7.33-7.17 (m, 10H, Ph), 5.08 (s, 1H, 2'-H), 4.98 (dd, J=7.0, 6.0 Hz, 1H, 2-H), 4.12 (dq, J=14.0, 7.5 Hz, 3H, Eta), 4.11 (dq, J=14.0, 7.0 Hz, 3H, Eta), 1.78-1.71 (m, 2H, 3-H), 1.32-1.28 (m, 2H, 4-H), 1.16 (dd, J=7.5, 7.0 Hz, 3H, Eta), 0.81 (t, J=7.5 Hz, 3H, 5-H);13C NMR (CDCl3): δ172.1, 170.1, 138.4, 138.3, 128.7, 128.6, 128.4, 127.3, 127.2, 120.4, 72.9, 61.2, 56.8, 33.0, 18.3, 14.0, 13.5;HR MS: calcd for C21H24O4Na (M+Na+) 363.1567. found 363.1569.(Entry 30)Methyl (S)-lactate1H NMR (CDCl3): δ4.24 (q, J=7.0 Hz, 1H, 2-H), 3.72 (s, 3H, MeO), 3.16 (br s, 1H, OH), 1.36 (d, J=7.0 Hz, 3H, 3-H);13C NMR (CDCl3): δ176.0, 66.6, 52.3, 20.2.Methyl (R)-2-(diphenylacetyloxy)propanoateHPLC (CHIRALCEL AD-H, i-PrOH/hexane=1/50, flow rate=0.75 mL/min): tR=16.4 min (98.3percent), tR=19.7 min (1.7percent);IR (neat): 1744, 1496, 1454, 748, 699 cm-1;1H NMR (CDCl3): δ7.28-7.20 (m, 8H, Ph), 7.19-7.13 (m, 2H, Ph), 5.07 (q, J=7.0 Hz, 1H, 2-H), 5.03 (s, 1H, 2'-H), 3.60 (s, 3H, MeO), 1.37 (d, J=7.0 Hz, 3H, 3-H);13C NMR (CDCl3): δ171.9, 170.9, 138.3, 138.2, 128.7, 128.63, 128.55, 128.4, 127.3, 127.2, 69.2, 56.6, 52.2, 16.8;HR MS: calcd for C18H18O4Na (M+Na+) 321.1097. found 321.1091. |
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