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Easily recyclable chiral polymeric Mn(III) salen complexes for oxidative kinetic resolution of racemic secondary alcohols

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Chiral polymeric Mn(III) salen complexes were used efficiently for oxidative kinetic resolution of racemic secondary alcohols at room temperature. High chiral purity (ee; >99%) was achieved for the oxidative kinetic resolution of racemic secondary
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  Easily Recyclable Chiral Polymeric Mn(III) Salen Complexes for Oxidative Kinetic Resolution of Racemic Secondary Alcohols RUKHSANA I. KURESHY,* IRSHAD AHMAD, KAVITA PATHAK, NOOR-UL H. KHAN, SAYED H. R. ABDI, JAYA K. PRATHAP,  AND  RAKSH V. JASRA  Silicates and Catalysis Discipline, Central Salt and Marine Chemicals Research Institute (CSMCRI), Bhavnagar 364 002, Gujarat, India  ABSTRACT   Chiral polymeric Mn(III) salen complexes were used efficiently for oxida-tive kinetic resolution of racemic secondary alcohols at room temperature. High chiral pu-rity (ee; > 99%) was achieved for the oxidative kinetic resolution of racemic secondary alco-hols with 0.6 mol % catalyst loading in 60 min. The catalyst was easily recycled for five suc-cessive catalytic experiments.  Chirality 19:352–357, 2007.  V V C  2007 Wiley-Liss, Inc.  KEY WORDS:  polymeric Mn(III) salen; oxidative kinetic resolution; racemic secondary alcohols; recyclable INTRODUCTION  The oxidation of alcohols is one of the most widely stud-ied reactions in chemistry. 1,2 Excellent catalytic enantiose-lective methods are reported for a variety of oxidation proc-esses, such as epoxidation, 3–5 dihydroxylation, 6,7 and aziri-dination. 8–10 However, there are few enantioselectivecatalysts reported for alcohol oxidation. 11–16 One of the im-portant strategies for achieving optically pure enantiomersof alcohols is the resolution of economically produced race-mic alcohols. In this direction, enzyme-catalyzed kinetic re-solution through selective reaction toward one of the enan-tiomers has been extensively studied. 17–21 In recent years,attempts have been made for the development of chiralcatalysts for nonenzymatic kinetic resolution. For example,BINOL-derived Ru(salen) 22 and Mn(salen) 23 complexes were used for the enantioselective oxidation of racemic sec-ondary alcohols, however, with moderate success. Recently,highly oxidative kinetic resolution of secondary alcoholshas been reported using chiral Mn (salen) complexes ascatalysts to produce chiral alcohols in high chiral purity under homogeneous conditions. 24,25 However, the catalyst stability, separation of the catalyst from the reaction mixtureand product remains strenuous with homogeneous catalyst. As chiral catalysts are expensive, their reusability is an im-portant aspect. In an effort to develop recyclable chiral cata-lysts, the use of polymeric and dimeric chiral salen com-plexes as catalysts for various organic transformations hasbeen reported 26–37 in the literature. In the present study, we report the application of recyclable chiral polymericMn(III) salen complexes as active catalysts for oxidative ki-netic resolution of racemic secondary alcohols usingPhI(OAc) 2  as an oxidative source in the presence of variousadditives in water/organic solvent mixture at room tempera-ture. Secondary alcohols with high chiral purity (ee;  > 99%) was achieved for the oxidative kinetic resolution of racemicsecondary alcohols with 0.6 mol % catalyst loading in 60min. The catalyst was easily recycled for five successive cat-alytic experiments. EXPERIMENTAL  Materials and Methods  Commercial grade reagents and solvents were used without further purification. PhI(OAc) 2 , tetraethylammo-nium bromide, tetrabutylammonium bromide, KBr, LiBr,and NaBr were purchased from Across Organics, Bel-gium. Hexylpyridinium bromide was prepared accordingto the known procedures. 38 1-Phenyl-2-propanol and men-thol were purchased from Aldrich, other racemic alcohols, viz., 4-fluorophenylethanol, 4-chlorophenylethanol, 4-meth- ylphenylethanol, 2-methylphenylethanol, 1-phenyl-1-propa-nol, 1-(4-methylphenyl)-1-propanol, and 1-(2-naphthyl)etha-nol were prepared by reduction of the correspondingketones with NaBH 4 . (   R,R   ) polymeric Mn(III) salen com-plexes  P1  and  P3  were synthesized according to the liter-ature procedure. 26 Synthesis of Poly[(   R,R   )-  N,N -bis-{3-(1,1-dimethylethyl)- 5-methylene salicylidine}cyclohexane-1,2-diaminato (2-) manganese(III) bromide] (P2)  Chiral poly[(   R  ,  R   )-  N,N  -bis{3-(1,1-dimethylethyl)-5-methylenesalicylidine}1,2-diaminocyclohexane 26 (0.001 mmol) was dis-solved in CH 2 Cl 2  (10 ml), while Mn(OAc) 2  (0.002 mmol) wastaken in CH 3 OH (5 ml) and the two solutions were mixedand refluxed under an inert atmosphere for 10–12 h. A slow stream of air was allowed to pass through the reaction mix-ture for an additional 1 h. Under vigorous stirring, 2 ml of a saturated aqueous solution of NaBr (0.002 mmol) was addedand the suspension was allowed to cool to room temperatureand stirred for 4 h. After addition of 10 ml of CH 2 Cl 2  to the Contract grant sponsor: CSIR (SRF).*Correspondence to: Rukhsana I. Kureshy, Silicates and Catalysis Disci-pline, Central Salt and Marine Chemicals Research Institute (CSMCRI),Bhavnagar 364 002, Gujarat, India. E-mail: rukhsana93@yahoo.co.inReceived for publication 10 November 2006; Accepted 13 January 2007DOI: 10.1002/chir.20387Published online 12 March 2007 in Wiley InterScience(www.interscience.wiley.com). CHIRALITY 19:352–357 (2007) V V C 2007 Wiley-Liss, Inc.  reaction mixture, the mixture was washed three times with10 ml of water and once with 10 ml NaBr (aq). The organiclayer was dried over anhydrous Na  2 SO 4  and the recrystalliza-tion of the crude product was done with petroleum ether/CH 2 Cl 2  to yield the desired complex as brown powder in 94% yield. IR (KBr): 3428 (br), 2943 (s), 2868 (s), 1614 (s), 1536(s), 1422 (sh), 1389 (m), 1344 (s), 1310 (s), 1283 (sh), 1238(sh), 1200 (m), 1174 (m), 1106 (w), 1033 (m), 942 (w), 838(m) cm  1 ; Anal. Calcd. for C 29 H 39  BrN 2 O 3 Mn: C, 58.19; H,6.52; N, 4.68%. Found: C, 58.12; H, 6.48; N, 4.65%; [ a ] 25D  ¼ 228 (  c ¼ 0.05, CH 2 Cl 2  ). Instrumentation  FTIR spectra were recorded on a Perkin Elmer Spec-trum GX spectrophotometer in a KBr/nujol mull. Micro-analysis of the complex was done on CHNS analyzer,Perkin Elmer model 2400. Optical rotations were meas-ured with a Digipol 781 Automatic Polarimeter Rudolphinstrument. ee values of chiral secondary alcohols weredetermined by HPLC (Shimadzu SCL-10AVP) usingChiralcel OD/OB columns. The analysis of the products was determined by gas chromatography (GC) using a Shimadzu GC 14B using dodecane as an internal standard. General Procedure for the Oxidative Kinetic Resolution of Racemic Secondary Alcohols Catalyzed by Chiral Polymeric Mn(III) Salen Complexes   A mixture of the substrate (1 mmol), chiral polymericMn(III) salen complexes  P1–P3  (0.006 mmol, 0.6 mol %),additive (0.012, 1.2 mol %), CH 2 Cl 2  (0.3 ml), and water (0.6ml) was stirred in a 5-ml tube for 10 min at room tempera-ture. The oxidant PhI(OAc) 2  (0.7 mmol) was then addedand the system was stirred for (60–120 min) at room tem-perature. After the desired conversion was achieved,  n -hexane was added to the reaction mixture. The catalyst thus precipitated was filtered off, the mixture of product and chirally enriched alcohol was extracted by diethylether. The organic layer was dried over anhydrousNa  2 SO 4  and concentrated under reduced pressure. Con- version and ee values were determined by performing GCand HPLC analysis. 1-Phenylethanol. 39 Chiralcel OD column eluted withhexane: 2-propanol (97:3); 1 ml/min; UV detector: 220 nm;retention times: 13.4 min for (   R   ) and 16.5 min for (  S   ). 1-(4-Fluorophenyl)ethanol.  Chiralcel OD columneluted with hexane: 2-propanol (97.5:2.5); 1 ml/min; UV detector: 220 nm; retention times: 45.3 min for (   R   ) and46.7 min for (  S   ). 1-(4-Chlorophenyl)ethanol.  Chiralcel OD columneluted with hexane: 2-propanol (98:2); 1 ml/min; UV detec-tor: 220 nm; retention times: 34.5 min for (   R   ) and 35.8 minfor (  S   ). 1-(4-Methylphenyl)ethanol. 15 Chiralcel OB columneluted with hexane: 2-propanol (98:2); 0.5 ml/min; UV de-tector: 220 nm; retention times: 25.9 min for (  S   ) and 31.4min for (   R   ). 1-(2-Methylphenyl)ethanol.  Chiralcel OD columneluted with hexane: 2-propanol (98:2); 1 ml/min; UV detector:220 nm; retention times: 16.1 min for(   R   ) and 16.8 min for (  S   ). 1-Phenyl-1-propanol.  Chiralcel OD column eluted withhexane: 2-propanol (97.5:2.5); 1 ml/min; UV detector: 220nm; retention times: 14.9 min for (   R   ) and 16.8 min for (  S   ). 1-Phenyl-2-propanol.  Chiralcel OD column eluted withhexane: 2-propanol (90:10); 0.5 ml/min; UV detector: 220nm; retention times: 13.3 min for (   R   ) and 15.1 min for (  S   ). 1-(2-Naphthyl)ethanol. 15 Chiralcel OD column eluted with hexane: 2-propanol (98:2); 0.5 ml/min; UV detec-tor: 220 nm; retention times: 63.0 min for (  S   ) and 66.6 minfor (   R   ). Menthol.  Chiralcel OD column eluted with hexane: 2-propanol (97.5:2.5); 1 ml/min; UV detector: 220 nm; reten-tion times: 11.5 min for (   R   ) and 13.6 min for (  S   ). Recycling Experiment   The polymeric Mn(III) salen complex   P1  (0.6 mol %),KBr (1.2 mol %), and 1-phenylethanol (5 mmol) in CH 2 Cl 2 (1 ml) and water (2 ml) was stirred in a 5-ml tubefor 10 min at room temperature. The oxidant PhI(OAc) 2 (3.5 mmol) was then added and the system was stirred for  Scheme 1.  Chiral polymeric Mn(III) salen complexes. 353 OXIDATIVE KINETIC RESOLUTION OF RACEMIC SECONDARY ALCOHOLS Chirality   DOI 10.1002/chir   (60 min) at room temperature. After the desired conver-sion was achieved, the catalyst was precipitated out fromthe reaction mixture by the addition of   n -hexane and wasremoved by filtration. The recovered catalyst was washed with diethyl ether (3  3  5 ml), dried under vacuum. Therecovered catalyst was then reused for the subsequent runs by adding fresh substrate and reactants. RESULTS AND DISCUSSION  The chiral polymeric Mn(III) salen complexes  P1 ,  P2 ,and  P3  (2 mol %, based on monomeric salen unit)(Scheme 1) were used for the oxidative kinetic resolutionof racemic 1-phenylethanol with PhI(OAc) 2  as an oxidant using KBr as an additive at room temperature and theresults are summarized in Table 1. The complex   P1  wasfound to be the better catalyst in terms of excellent enan-tiomeric excess (98%) with a   k rel  value of 17 (Table 1, entry 1). Changing the counter ion from Cl  to Br   (complex  P2  ) did not improve the ee of the product (Table 1, entry 2). On the other hand, complex   P3  was less effective cata-lyst as evidenced by low ee of the alcohol (entry 3). There-fore, the chiral polymeric Mn(III) salen complex   P1  wasstudied in detail for optimization of reaction parametersand its applicability to catalyze oxidative kinetic resolutionof different racemic secondary alcohols. We first examinedthe influence of catalyst loading using 1-phenylethanol asa representative substrate. Increasing the catalyst loadingfrom 2 to 5 mol %, there was no improvement in enantiose-lection of the reaction (ee, 94%) (entry 4). A catalyst load-ing of 0.6 mol % gave results (ee, 96%) similar to thoseachieved with 2 mol % catalyst loading but the reactiontime was increased from 15 to 60 min (entry 5). Further reduction in catalyst loading to a level of 0.2 mol % causedreduction in the enantioselection of oxidative kinetic reso-lution (ee, 91%) (entry 6). To check the efficiency of complex   P1  with optimizedcatalyst loading (0.6 mol %), the oxidative kinetic resolu-tion of other racemic secondary alcohols, viz., 4-fluorophe-nylethanol, 4-chlorophenylethanol, 4-methylphenylethanol,2-methylphenylethanol, 1-phenyl-1-propanol, 1-(4-methyl-phenyl)-1-propanol, 1-phenyl-2-propanol, 1-(2-naphthyl)ethanol, and menthol, was performed with KBr as an addi-tive using PhI(OAc) 2  as an oxidant in CH 2 Cl 2 :H 2 O solvent system (Table 1). It can be observed from Table 1 that 1-phenylethanol with substituents at the  p -position favor high enantioselectivity (ee,  > 99%) with (51–63%) conver-sion (Table 1, entries 7–9) in 60 min. However, the reac-tion was sluggish (only 11% conversion in 120 min) for   o -substituted 1-phenylethanol with poor enantioselection(ee, 5%) (Table 1, entry 10). Further, when the  R  0 group of the substrate was changed from methyl to ethyl, the enan-tioselectivity of the reaction was severely affected (ees,10–23%) (Table 1, entries 11, 12). On the other hand, 1-phenyl-2-propanol gave good results in terms of enantiose-lectivity (83%) (Table 2, entry 13). Bulkier secondary alco-hols like 2-naphthylethanol took long time (80 min) toaffect ee up to 76% (Table 1, entry 14). Noticeably, mentholexhibited high enantioselectivity (ee; 94%) with high  k rel  value (entry 15). The choice of solvent and additives has a significant effect on the activity and the enantioselectivity of the chiral  TABLE 1. Oxidative kinetic resolution of racemic secondary alcohols using chiral polymeric Mn(III) salen complexes a  Entry Catalyst Catalyst loading (mol %) Substrate Time (min) Conversion (%) b ee (%) c k reld 1 P1 2 1-Phenylethanol 15 62 98 172 P2 2 1-Phenylethanol 15 56 95 253 P3 2 1-Phenylethanol 15 52 88 294 P1 5 1-Phenylethanol 15 60 94 155 P1 0.6 1-Phenylethanol 60 53 96 486 P1 0.2 1-Phenylethanol 90 49 91 1187 P1 0.6 4-Fluorophenylethanol 60 63  > 99 198 P1 0.6 4-Chlorophenylethanol 60 51 92 539 P1 0.6 4-Methylphenylethanol 60 60 93 1510 P1 0.6 2-Methylphenylethanol 120 11 5 211 P1 0.6 1-Phenyl-1-propanol 60 50 23 312 P1 0.6 1-(4-Methylphenyl)-1-propanol 60 42 10 213 P1 0.6 1-Phenyl-2-propanol 60 55 83 1314 P1 0.6 1-(2-Naphthyl)ethanol 80 52 76 1115 P1 0.6 Menthol 60 48 94 398 a   All reactions were carried out at room temperature in mentioned time. b Determined by GC analysis using an internal standard. c Determined by HPLC using chiralcel OD/OB column. d Selectivity factor   k rel  was determined using equation,  k rel  ¼  ln[1    c (1    ee)]/ln[1    c (1  þ  ee)] (where the  c  is the conversion of secondary alcoholand ee is the enantiomeric excess of secondary alcohol). The data represents an average of at least three experiments. 354  KURESHY ET AL. Chirality   DOI 10.1002/chir   Mn(III) salen complexes. 25  We have further studied theeffect of the solvent and additives on the activity of oxida-tive kinetic resolution taking 1-phenylethanol as a repre-sentative substrate using complex   P1  as catalyst (Table 2).In the case of H 2 O alone as a solvent (Table 2, entry 16) with KBr as an additive, a conversion of 57% with 35% eefor 1-phenylethanol was obtained in 60 min, possibly dueto some solubility of catalyst   P1  in the alcoholic substrate.Solvents like toluene, 1,2-dichloroethane, and chloroform when mixed with H 2 O gave good to excellent enantiose-lectivity (83–94%) in the case of 1-phenylethanol (Table 2,entries 17–19), while ethyl acetate gave poor results (entry 20). On conducting the reaction in the solvent system of CH 2 Cl 2 :H 2 O using different bromide salts viz., NaBr, LiBr,and hexylpyridinium bromide as an additive, the systemexhibited high enantioselectivity (87–91%) (Table 2,entries 21–23). Considering the biphasic nature of theabove reaction system, it was pertinent to study the effect of a phase transfer catalyst like tetraethyl ammonium bro-mide or tetrabutyl ammonium bromide in oxidative kineticresolution of 1-phenylethanol in CH 2 Cl 2 :H 2 O solvent sys-tem. The presence of phase transfer catalyst gave moder-ate to high enantioselectivity (58–93%) (Table 2, entries24, 25). However, when the reaction was conducted usingKCl as an additive or in the absence of an additive, oxida-tive kinetic resolution reaction did not proceed at all(entries 26, 27). These observations suggested that thepresence of bromide ion is desirable for oxidative kineticresolution to take place. 25  To compare the reactivity of polymeric Mn(III) salencomplex   P1  with its monomeric counterpart, we have con-ducted oxidative kinetic resolution of 1-phenylethanol as a representative substrate with Jacobsen’s monomericMn(III) salen complex as catalyst using KBr as an addi-tive. Kinetic profile for both the complexes showed linear increase in the product formation up to 10 min after whichno significant increase was observed (see Figure 1). Therefore, the initial rate constants  K  obs  were determinedfrom the data in this time range for the polymeric Mn(III)salen complex   P1  and monomeric complex that gives  K  obs  values 36  3  10  2 M/h and 24  3  10  2 M/h, respectively. This enhanced  K  obs  value can be attributed to the morenumber of catalytically active sites present in the poly-meric complex   P1 , which may not be working in isolation. The interesting feature of this polymeric Mn(III) salencomplex lies in its inherent tendency to get precipitated ina nonpolar solvent like  n -hexane due to its higher molecu-lar weight and lower solubility in the reaction medium. Af-ter one catalytic run, the catalyst was recovered and  TABLE 2. Effect of solvent systems and additives in oxidative kinetic resolution of 1-phenylethanol using chiral polymericMn(III) salen catalyst P1 a  Entry Solvent system Additives Time (min) Conversion (%) b ee (%) c 16 H 2 O KBr 60 57 3517 H 2 O þ  Toluene KBr 60 55 9218 H 2 O þ DCE KBr 60 61 9419 H 2 O þ CHCl 3  KBr 60 47 8320 H 2 O þ Ethyl acetate KBr 60 39 1421 H 2 O þ CH 2 Cl 2  NaBr 60 49 9122 H 2 O þ CH 2 Cl 2  LiBr 60 58 8723 H 2 O þ CH 2 Cl 2  60 60 9024 H 2 O þ CH 2 Cl 2  N(C 2 H 5  ) 4 Br 60 56 9325 H 2 O þ CH 2 Cl 2  N(C 4 H 9  ) 4 Br 60 48 5826 H 2 O þ CH 2 Cl 2  KCl 120 5 127 d H 2 O – 120 7  < 1 a  Reactions were carried out using 0.6 mol % polymeric Mn(III) salen complex- P1 , KBr (1.2 mol %), racemic secondary alcohols (1 mmol), PhI(OAc) 2 (0.7 mmol) in 0.3 ml CH 2 Cl 2 þ 0.6 ml H 2 O at rt in mentioned time. b Determined by GC analysis using an internal standard. c Determined by HPLC using chiralcel OD column. d Reaction was carried out in absence of additive. Fig. 1.  Time-dependent plot of oxidative kinetic resolution of 1-phenyl-ethanol at room temperature. [Catalyst   P1 ]  ¼  0.80  3  10  2 M, [1-phenyl-ethanol]  ¼  111.0  3  10  2 M, [KBr]  ¼  1.3  3  10  2 M, [Oxidant]  ¼  77.6  3 10  2 M. 355 OXIDATIVE KINETIC RESOLUTION OF RACEMIC SECONDARY ALCOHOLS Chirality   DOI 10.1002/chir   reused for the subsequent runs for the oxidative kinetic re-solution of 1-phenylethanol as a representative substrateby adding fresh reactants. The results are shown in Table3. It is evident that the catalyst   P1  worked well up to fiverepeat experiments with small decrease in reactivity dueto some physical loss during post work up process but  with retention of enantioselectivity in reuse experiments. To the best of our knowledge, polymeric Mn(III) salencomplex is the most efficient recyclable catalyst for theoxidative kinetic resolution of racemic secondary alcohols. CONCLUSIONS In summary, we have used chiral polymeric Mn(III)salen complexes as an effective recyclable catalysts in oxi-dative kinetic resolution of various racemic secondary alcohols. High chiral purity (ee;  >  99%) was achieved for the oxidative kinetic resolution of racemic secondary alco-hols with 0.6 mol % catalyst loading in 60 min. The catalyst  P1  was recycled up to five times with retention of enantio-selectivity.  ACKNOWLEDGMENTS I. Ahmad and K. Pathak are thankful to CSIR (SRF) for financial support; R.I.K. to DST, CSIR Net Work Project on Catalysis and also to Dr. P. K. Ghosh, the Director of the Institute for providing the instrumentation facility. LITERATURE CITED 1. Sheldon RA, Kochi JK. Metal-catalyzed oxidations of organic com-pounds. New York: Academic Press; 1984.2. Hudlicky M. Oxidations in organic chemistry. ACS Monograph Series186; American Chemical Society: Washington DC; 1990.3. Katsuki T, Sharpless KB. The first practical method for asymmetricepoxidation. J Am Chem Soc 1980;102:5974–5976.4. Johnson RA, Sharpless KB. Asymmetric oxidations and related reac-tions. In: Ojima I, editor. Catalytic asymmetric synthesis. New York: Wiley; 2000. p 231–280.5. Katsuki T. Asymmetric oxidation. In: Ojima I, editor. Catalytic asym-metric synthesis. New York: Wiley; 2000. p 287–325.6. Jacobsen EN, Marko´ IE, Mungall WS, Schro¨der GW, Sharpless KB. Asymmetric dihydroxylation via ligand-accelerated catalysis. J AmChem Soc 1988;110:1968–1970.7. Bolm C, Hildebrand JP, Muniz K. Recent advances in asymmetricdihydroxylation and aminohydroxylation. In: Ojima I, editor. Catalyticasymmetric synthesis. New York: Wiley; 2000. p 399–428.8. Mu¨ller P. Oxidative amination of alkenes features catalytic transfer of an electrophilic nitrene. In: Doyle MP, editor. Advances in catalyticprocesses, Vol. 2. Greenwich, CT: JAI Press; 1997; p 113–151.9. Evans DA, Woerpel KA, Hinman MM, Faul MM. Bis(oxazolines) aschiral ligands in metal-catalyzed asymmetric reactions. Catalytic,asymmetric cyclopropanation of olefins. J Am Chem Soc1991;113:726–728.10. Li Z, Conser KR, Jacobsen EN. Asymmetric alkene aziridination withreadily available chiral diimine-based catalysts. J Am Chem Soc1993;115:5326–5327.11. Nishibayashi I, Takei I, Uemura S, Hidai M. Extremely high enantio-selective redox reaction of ketones and alcohols catalyzed by RuCl 2 (PPh 3  )(oxazolinylferrocenylphosphine). Organometallics 1999;18:2291–2293.12. Hashiguchi S, Fujii A, Haack KJ, Matsumura K, Ikariya T, Noyori R.Kinetic resolution of racemic secondary alcohols by ruthenium(II)-cat-alyzed transfer hydrogenation. Angew Chem Int Ed 1997;36:288–290.13. Ferreira EM, Stoltz BM. The Palladium-catalyzed oxidative kinetic re-solution of secondary alcohols with molecular oxygen. J Am ChemSoc 2001;123:7725–7726.14. Bagdanoff JT, Ferreira EM, Stoltz BM. Palladium-catalyzed enantiose-lective oxidation of alcohols: A dramatic rate acceleration by Cs 2 CO 3 / t  -BuOH. Org Lett 2003;6:835–837.15. Nishibayashi Y, Yamauchi A, Onodera G, Uemura S. Oxidative kineticresolution of racemic alcohols catalyzed by chiral ferrocenyloxazoli-nylphosphine-ruthenium complexes. J Org Chem 2003;68:5875–5880.16. Sigman MS, Jensen DR. Ligand-modulated palladium-catalyzed aero-bic alcohol oxidations. Acc Chem Res 2006;39:221–229.17. Faber K. Biotransformations in organic chemistry. Heidelberg:Springer; 1992.18. Persson BA, Larsson ALE, Ray ML, Backvall J-E. Ruthenium- andenzyme-catalyzed dynamic kinetic resolution of secondary alcohols. J Am Chem Soc 1999;121:1645–1650.19. Jesus PC, Rezende MC, Nascimento MG. Enzymatic resolution of alcohols via lipases immobilized in micro emulsion based-gels. Tetra-hedron: Asymmetry 1995;6:63–66.20. Stampfer W, Kosjek B, Faber K, Kroutil W. Biocatalytic oxidative ki-netic resolution of   sec -alcohols: Stereo control through substrate-modi-fication. Tetrahedron: Asymmetry 2003;14:275–280.21. Jacobsen EE, Andersen LS, Anthonsen T. Immobilization does not influence the enantioselectivity of CAL-B-catalyzed kinetic resolutionof secondary alcohols Tetrahedron: Asymmetry 2005;16:847–850.22. Masutani K, Uchida T, Irie R, Katsuki T. Catalytic asymmetric andchemoselective aerobic oxidation: Kinetic resolution of   sec -alcohols. Tetrahedron Lett 2000;41:5119–5123.23. Hamada T, Irie R, Mihara J, Hamachi K, Katsuki T. Highly enantiose-lective benzylic hydroxylation with concave type of (salen)manganese(III) complex. Tetrahedron 1998;54:10017–10028.24. Sun W, Wang H, Xia C, Li J, Zhao P. Chiral-Mn(salen)-complex-cata-lyzed kinetic resolution of secondary alcohols in water. Angew ChemInt Ed 2003;42:1042–1044.25. Li Z, Tang ZH, Hu XX, Xia CG. Insight into the mechanism of oxida-tive kinetic resolution of racemic secondary alcohols by using manga-nese(III)(salen) complexes as catalysts. Chem Eur J 2005;11:1210–1216.26. Kureshy RI, Khan NH, Abdi SHR, Singh S, Ahmad I, Jasra RV. Cata-lytic asymmetric epoxidation of non-functionalised alkenes using poly-meric Mn(III) salen as catalyst and NaOCl as oxidant. J Mol Catal A:Chem 2004;218:141–146.27. Kureshy RI, Khan NH, Abdi SHR, Singh S, Agrawal S, Jasra RV. Enan-tioselective aminolytic kinetic resolution (AKR) of epoxides catalyzedby recyclable polymeric Cr(III) salen complexes Tetrahedron: Asym-metry 2006;17:1638–1643.28. Khan NH, Agrawal S, Kureshy RI, Abdi SHR, Mayani VJ, Jasra RV.Easily recyclable polymeric V(V) salen complex for the enantioselec-tive  O -acetyl cyanation of aldehydes. J Mol Catal A: Chem 2006;264:140–145.29. Pathak K, Bhatt AP, Abdi SHR, Kureshy RI, Khan NH, Ahmad I, Jasra RV. Enantioselective phenylacetylene addition to aldehydes andketones catalyzed by recyclable polymeric Zn(salen) complex. Chiral-ity 2007;19:82–88.  TABLE 3. Recycling data of chiral polymeric Mn(III) salencatalyst P1 for oxidative kinetic resolution of 1-phenylethanol as a representative substrate a  Catalytic cycle 1 2 3 4 5 Time (min) 60 60 60 60 60Conversion (%) b 52 51 48 45 43ee (%) c 96 96 95 95 95 a  0.6 mol % polymeric Mn(III) salen complex-  P1 , KBr (1.2 mol %), 1-phenyl-ethanol (5 mmol), PhI(OAc) 2  (3.5 mmol) in 1 ml CH 2 Cl 2 þ 2 ml H 2 O at rt. b Determined by GC analysis using an internal standard. c Determined by HPLC using chiralcel OD column. 356  KURESHY ET AL. Chirality   DOI 10.1002/chir 
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