1-Phenyl-ethanol acylation

Figure 15 Gas chromatographic chiral separation of (left) racemic l-(4-methoxy-phenyl)ethanol 22 and its corresponding acetate 22a (reference) and (right) lipase-catalyzed transesterification of l-(4-methoxy-phenyl)ethanol 22 (4 hrs) using isopropenyl acetate as acyl donor in toluene as organic solvent ees= 99.9 eep= 87 conv. =53.4, E=141.

Figure 57 Some of the biocatalytic steps using lipase developed at BASF Lipase-catalyzed kinetic resolution of a) phenyl ethanol 18 using succinic anhydride, b) Secondary amine 120 using ethyl methoxyacetate as acyl...

Scheme 10.5 Enantioselective acylation reaction of 1-phenyl ethanol (Reproduced from Ref. [86], with kind permission of Springer Verlag-Berlin)...

Consequently, in a stereoselective reaction, one stereoisomer is formed preferentially over other possible stereoisomers, as illustrated in Fig. 2.24, or enantiomers can be separated as shown in Fig. 2.25 for acylation of 1-phenyl-ethanol with vinyl acetate using lipase as enzyme in the so-called kinetic resolution approach. 

The reaction of 3,4-diacyl-l,2,5-oxadiazole 2-oxides (furoxans) with activated nitriles in ionic liquids and in ethanol unexpectedly resulted in 3-acyl-4-acylamino-l,2,5-°xadiazoles (furazans) <2003MC230>. 3-Formyl-4-phenyl-l,2,5-oxadiazole Ar-oxide 105 is a good precursor for the synthesis of functional substituted furoxans (Scheme 28) <1999JME1941, 2000MOL520, 2000JFA2995>. 

Having proved the synthetic utility of their system, the authors subsequently evaluated a second supported base, 4-dimethylaminopyridine (AO-DMAP) 118, toward the acylation of 2° alcohols (Scheme 30). Employing a premixed solution of phenyl-l-ethanol 119, Et3N 14 and acetic anhydride 37 (0.33, 0.50, and 0.50 M) in hexane, reactions were conducted at room temperature and the effect of residence time evaluated (10-50 s). Using a 60 cm packed bed, the authors were able to obtain near quantitative conversions to 120 employing residence times <20 s, with flow reactions providing superior results to those obtained in analogous batch reactions. 

Csajagi et al. (2008) recently demonstrated the enantioselective acylation of racemic alcohols in a continuous flow bioreactor, using Candida antarctica lipase B (CaLB) 167. Employing a packed-bed reactor, containing 0.40 g of enzyme 167, and pumping a solution of rac-phenyl-1-ethanol 119 (10 mg ml-1) in hexane THF vinyl acetate 168 (2 1 1) at a flow rate of 100 gl min-1 (at 25 °C), the authors found the reactor reached steady state after 30 min of operation. Under the aforementioned conditions, the... 

Scheme 46 Schematic illustrating the biochemical acylation of roc-phenyl-l-ethanol 119.

Pentryl. See 2-(2 , 4, 6-TrInitro-N-nitranilino Ethanol Nitrate under Aniline ethanol and Derivatives A425-L to A42 )-R Pentryl Homologs A429-R Peracetic Acid, Benzylester. See Acetyl-benzyl peroxide A55-L P hen acyl Azide. See a>-Azido acetophenone under Acetophenone A47-R Phenazone. See Antipyrine A471-R Phenetidine. See Aminophenetole A240-R Phenyl Abietate. See under Abietic Acid A4rL... 

A related triazole synthesis utilizes phosphorous ylids, such as 264. The initially formed triazenes cyclize with elimination of triphenylphosphine oxide. The reaction proceeded sluggishly with phenyl azide, but good results have been obtained with acyl or sulphonyl azides. Tosyl azide and 264 yielded 98% of the 1-tosyl-triazole 265. The tosyl group could be removed by solvolysis in boiling ethanol... 

Nitro-4H-1 -benzopyrone reagieren mit Hydrazin-Hydrat (Ethanol 10 min, 20°) zu z, B..3(5)-(2-Hydroxy-phenyl)-5(3)-methyl-4-nitro-lH-pyrazol (88% Schmp. 201-2020)1187-, 188 ,37 analog verhalten sich Methyl- und Phenyl-hydrazin1187, mit Carbonsaure-hydraziden werden in hoher Ausbeute die 1-Acyl-Derivate erhalten. Der Acyl-Rest laBt sich durch Basen leicht abspalten1188. 

Dioxo-3-ethyl-l, 5,6,7-tetrahydro- 677 Pyrazolo[3,4-d]-l, 3-oxazin l,3-Dimethyl-4-oxo-6-(2-oxo-propyl)-dihydro- 557 1- Acyl-3-methylthio-6-oxo-l,6-dihydro- 676 2- Benzyl-6-(4-nitro-phenyl)-4-oxo-2,4-dihydro-676 4-Amino-7-chlor-phenyl- 976 2-(4-Aminosulfonyl-phenyl)-4,7-dichIor- 977 2-(4-Aminosulfonyl-phcnyl)-4,7-dihydroxy- 922 4-Anilino-7-chlor-2-(3-thienyl)- aus 4,7-DichIor-2-(3-thicnyI)- pyriclazino-[4,5-d]-l,3-thia7.ol)/Ethanol 976 7-Chlor-4-ethoxy-2-methyl- 972 7-Chlor-4-methoxy-2-phenyl- 972 7-ChIor-4-(3-pyrroIidino-propyloxy)-2-(2-thienyI)- 972... 

Scheme 6.37 Schematic illustrating the enantioselective acylation of rac-phenyl-l-ethanol (101).

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