Hydroxycarboxylic acids (ether carboxylic acids) and esters P 0280
Synthesis of Alkyl (R)-Lactates and Alkyl (S,S)-O-Lactyllactates by Alcoholysis of rac-LactideUsing Novozym 435. -Alcoholysis of the racemic lactide (I) in the presence of Novozym 435 provides a new synthetic route for the highly enantioselective formation of (R)-lactates (III) and (S,S)-O-lactyllactates (IV). -(JEON, N. Y.; KO, S.-J.; WON, K.; KANG, H.-Y.; KIM, B. T.; LEE, Y. S.; LEE*, H.; Tetrahedron Lett.
Significance: A recyclable polystyrene-supported ruthenium catalyst promoting racemization of secalcohols was developed and combined with a lipase to convert racemic sec-alcohols into the corresponding optically pure acetates via dynamic kinetic resolution (DKR). Thus, the DKR of racemic 1-phenylethanol with isopropenyl acetate (1.5 mol equiv) was performed at 25°C with catalyst 1, K 3 PO 4 (1.0 mol equiv) and Novozym 435 in toluene under aerobic conditions to give (R)-1-phenylethylacetate in 99% yield with 99% ee (for more results see scheme). Eight examples of the DKR of various secondary alcohols were demonstrated to afford the corresponding acetates in 86-99% yield with 92-99% enantiomeric purity.Comment: The combination of the enzymatic kinetic resolution with a metal-catalyzed racemization via hydrogen transfer was introduced for preparing enantiomerically pure alcohols by Williams in 1996 and Bäckvall in 1997. The authors previously reported on the racemization catalyst [2,3,4,5-Ph 4 ( 5 -C 4 CNH-i-Pr)]Ru(CO) 2 Cl for the dynamic kinetic resolution of a wide scope of secondary alcohols with lipases under argon (81-99% ee; ). In the current paper, they have developed an air-stable and recyclable racemization catalyst that was applicable to alcohol DKR at room temperature.
RuPh Ph Ph Ph OC CO Cl Ph OH Ph OH 1 K 3 PO 4 O O O 1 OAc Novozym 435 25 °C, 20 h toluene, air Ph OAc 1st: 99% (99% ee) 2nd: 99% (99% ee) 3rd: 95% (99% ee) 4th: 36% (99% ee) SYNFACTS Contributors:
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