Halogenation Hantzsch ester

Halogenation, maleic acid derivatives, 60 Hammett equation, 138, 139 Hammett sigma values, 372 Hantzsch ester hyrogen donor, 43 MA reduction, 43 Heat of copolymerization MA-allyl chloride pair, 405 MA-yV-butyl vinyl ether pair, 405 MA-isopropenyl acetate pair, 333 MA-a-methylstyrene pair, 404, 405 MA-styrene pair, 404, 405 MA-vinyl acetate pair, 333, 405 polyester-styrene mixtures, 487 vinyl acetate with maleates and fumarates, 333 Heat of polymerization MA-epoxide reactions, 482 MA monomer, 244... 

The first case in which organocatalysis by halogen bonding was postulated, a report by Bolm et al. in 2008 [124], in fact involves C-X-based halogen-bond donors. As a test reaction, the reduction of quinoline derivatives by a Hantzsch Ester was chosen. Previously, this type of reaction had been reported to proceed enantioselectively with Ir[COD]Cl2/(5)-SegPhos or chiral Brpnsted acids (Scheme 13) [125]. 

The most widely used method for the preparation of carboxylic acids is ester hydrolysis. The esters are generally prepared by heterocyclization (cf. Chapter II), the most useful and versatile of which is the Hantzsch s synthesis, that is the condensation of an halogenated a- or /3 keto ester with a thioamide (1-20). For example ethyl 4-thiazole carboxylate (3) was prepared by Jones et al. from ethyl a-bromoacetoacetate (1) and thioformamide (2) (1). Hydrolysis of the ester with potassium hydroxide gave the corresponding acid (4) after acidification (Scheme 1). 

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