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20.6.1.4.5 Variation 5: The Yamaguchi Method

DOI: 10.1055/sos-SD-020-01369

Maier, M. E.Science of Synthesis, (2007201462.

This method exploits the high catalytic activity of 4-(dimethylamino)pyridine in acyl transfer reactions. Carboxy activation is achieved via formation of the mixed anhydride between the ω-hydroxy acid and 2,4,6-trichlorobenzoyl chloride (136) (Scheme 59).[‌173‌] Among the two carbonyl groups, the one from the benzoic acid part is sterically hindered. In addition, the good leaving group ability of the corresponding benzoate facilitates lactone formation. Typically, formation of the mixed anhydride 137 is performed in tetrahydrofuran in the presence of triethylamine. After filtration of the triethylamine hydrochloride, the filtrate is concentrated and the crude mixed anhydride brought to high dilution with toluene. This solution is then slowly added to a refluxing toluene solution of 4-(dimethylamino)pyridine. It is believed that the lactonization takes place via the pyridinium salt 138. The Yamaguchi lactonization is the most frequently used method for the formation of various macrolactones;[‌174‌,‌175‌] Table 11 lists some examples.

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