Yamaguchi reagent

Esterification using 2,4,6-trichlorobenzoyl chloride (the Yamaguchi reagent). 

The Yamaguchi Esterification allows the mild synthesis of highly functionalized esters. After formation of a mixed anhydride between the Yamaguchi Reagent (2,4,6-trichlorobenzoyl chloride) and the carboxylic acid, the volatiles are removed and the reaction of the anhydride with an alcohol in presence of a stoichiometric amount of DMAP generates the desired ester. 

The Yamaguchi esterification utilises 2,4,6-trichlorobenzoyl chloride, also known as the Yamaguchi reagent, to form esters from carboxylic acids and alcohols. 

The regioselectivity of the addition of terminal alkynes to epoxides is improved, when the reagents prepared from the lithiated alkynes and either trifluoroborane or chlorodiethyl-aluminum arc employed (M. Yamaguchi, 1983 S. Danishefsky, 1976). (Ethoxyethynyl)lithium-trifluoroborane (1 1) is a convenient reagent for converting epoxides to y-lactones (M. Naka-tsuka, 1990 see p. 327f. cf. S. Danishefsky, 1976). 

In an earlier and similar study Angeloni and co-workers (59) reduced several 0-aminoketones with (- )-menthol-LAH reagents and obtained higher optical yields in the reduction of 32 and of 30 n = 2, Y = NMe2) than were obtained by Yamaguchi and Kabuto (58). These results are summarized in Table 1. The yields of alcohols were essentially quantitative, and the highest optical yields were obtained with the 3 1 (- )-menthol-LAH reagent at the lower temperature. 

Yamaguchi, Mosher, and Pohland (97,98) studied the properties of a chiral reducing reagent prepared by the reaction of 2 to 3 equivalents of (+ )-(2S,3J )-... 

With the aid of BOP [benzotriazol-l-yl-oxytris(dimethylamino) phosphonium hexafluorophosphate, Castro s reagent]20 in the presence of DMAP it is possible to transform the free carboxylic acid 33 into activated intermediate 34 in preparation for subsequent esterification with 14 Other methods for esterification include application of DCC and the procedures introduced by Yamaguchi and Mukaijama (see Chapters 5, 6, and 9). 

Hirashita, T. Kamei, T. Horie, T. Yamamura, H. Kawai, M. Araki, S. Preparation of y-het-erosubstituted allylindium and diindium reagents and their reactions with carbonyl compounds./. Org. Chem. 1999, 64,172-177. Yamaguchi, M. Mukaiyama, T. The stereoselective synthesis of d- and L-ribose. Chem. Lett. 1981, 1005-1008. 

N. Nishi, N. Fujimora, Y. Yamaguchi, W. Jyomori, and T. Fukuyama, Reversed-phase HPLC separation of enantiomers of dena-pamine after derivatization with GITC chiral reagent, Chromato-grahic, 50 186 (1990). 

The Yamaguchi-Mosher reagent and BINAL-H (1) have been most used over the last few years. Although these reagents have proved to be quite efficient, their manipulation is not easy and requires very low temperatures, sometimes below -78°C, to secure good stereoselectivity. 

Yamaguchi M, Yoshida H, Nohta H. 2002. Luminol-type chemiluminescence derivatiza-tion reagents for liquid chromatography and capillary electrophoresis. J. Chromatogr. A 950 1-19. 

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