Mukaiyama method, macrolactonization

Ley et al. [22] recently applied this method to the total synthesis of the antibiotic ( + )-milbemycin jSi(ii). Thus, hydroxy acid 31 was cyclized to macrolactone 32 in good yield (more than 49%) by slow addition (over 9 h) of a solution of 31 and triethylamine in acetonitrile to a refluxing solution of 28 in acetonitrile (Scheme 11). Another recent application of the Mukaiyama method is due to White and Bolton [23],... 

Mukaiyama developed l-alkyl-2-halopyridinium salts, which are useful reagents for the preparation of carboxylic esters and lactones in the presence of tertiary amines [22]. After generation of activated onium salts from the corresponding co-hydroxycarboxylic acids, spontaneous lactonization smoothly proceeds to produce various macrolactones. Bartlett first used this lactonization method for the... 

---