Highly regioselective propanoylation of dihydroxybenzenes mediated by Candida antarctica lipase B in organic solvents

Candida antarctica lipase B (CAL-B) was found to be a highly active biocatalyst for the direct acylation of the phenolic hydroxyls of substituted hydroquinones and resorcinols with vinyl propanoate as an acyl donor. The acylation reactions took place generally in a very regioselective manner. Especially in the case of 4-substituted resorcinols, the hydroxyl remote from the substituent was regiospecifically acylated to afford only the 1-O-propanoylated resorcinols.     

On the use of succinic anhydride as acylating agent for practical resolution of aryl-alkyl alcohols through lipase-catalyzed acylation

A comparison is carried out of the E-values recorded in the lipase-catalyzed resolution of a series of secondary aryl-alkyl alcohols with enol esters versus succinic anhydride. Whereas all the substrates could be resolved by a proper choice of the lipase/enol ester couple with moderate (E=50) to good (E>100) enantioselectivities, only some of them showed satisfactory enantioselectivity (E>50) with the use of succinic acid as acylating agent. Notably, indanol and 1-quinolin-3-yl-ethanol were resolved in a practical way, with E>100 and E>80, respectively.     

Candida antarctica lipase B-catalyzed synthesis of acetamides using [BMIm(PF6)] as a reaction medium

An efficient protocol has been developed for synthesis of acetamides using Candida antarctica lipase B (CaL B) in [BMIm(PF₆)] as a greener reaction medium. The reaction is applicable to a wide variety of aliphatic esters/acetic acid and amines providing excellent yields of corresponding acetamide. The catalyst exhibits remarkable activity and is reusable for up to four consecutive cycles.     

Friedel-Crafts catalysts as assistants in the tritylation of less reactive hydroxyls

Less reactive hydroxyls, such as those present in secondary alcohols and in some primary alcohols, phenols and carboxylic acids, were easily tritylated with the homogeneous assistance of equimolar quantities of chlorides of di- and trivalent metals in aprotic solvents. The metal ions allowed both high concentration of the effective reagent triphenylmethylcarbenium ion and mobilisation of the hydroxyl proton, thus giving rise to rapid, room temperature substitution reactions. The experimental conditions were so mild that other protected groups, such as alkyl- or trityl-protected carboxyls and (9-fluorenylmethoxycarbonyl)- or trityl-protected amino groups, remained unaffected.     

Aldehyde-based racemization in the dynamic kinetic resolution of N-heterocyclic α-amino esters using Candida antarctica lipase A

The present research introduces approaches for the dynamic kinetic resolution of the methyl esters of proline and pipecolic acid. As the result, a method was developed which is based on the acylation of the secondary amino group of the amino esters with vinyl butanoate by Candida antarctica lipase A. In the optimized method, acetaldehyde as a racemizing agent is released in situ from vinyl butanoate in the presence of triethylamine, allowing ca. 90% of the racemic proline and 70% of the pipecolic acid methyl esters to be acylated in the forms of highly enantiopure (ee=97%) butanamides with the S-absolute configurations.