ZnCl₂‐Mediated Synthesis of Carboxylic Anhydrides using 2‐Acyl‐4,5‐dichloropyridazin‐3(2H)‐ones

Recent Progress in the Chemistry of Pyridazinones for Functional Group Transformations

“…For developing the synthetic methodology of amidation, these methods have advantages such as easy workup, use of water solvent, high yield, and/or the quantitative recovery of Amberlite resin and the acyl group carrier, pyridazinone. Park et al demonstrated the ZnCl 2 -mediated synthesis of carboxylic anhydrides using 2-acyl-4,5-dichloropyridazin-3­(2 H )-ones. The treatment of 3 with ZnCl 2 (0.5 equiv) in air in refluxing THF or acetonitrile affords the corresponding symmetric anhydrides in good to excellent yields (Scheme c).…”

<b>Efficient and convenient synthesis of symmetrical carboxylic anhydrides from carboxylic acids with sulfated zirconia by phase transfer catalysis</b>

“…Generally speaking, they are prepared by dehydration of carboxylic acids with powerful acylating or dehydrating agents such as acid chlorides [4], acid anhydrides [5], thionyl chlorides [6,7], sulfonyl chlorides [8], phophoranes [9], phosgene [10], pyridazin-3(2H)-ones [11,12], ketene [13], imidazolinium chlorides [14], 1,3,5-triazines [15], DCC [16], dinitrogen tetroxide [17], chlorosulfonyl isocyanate [18], carbodiimides [19], trichloroacetonitrile/triphenylphosphine [20], and P 2 O 5 [21]. Carboxylic anhydrides can also be prepared by the reaction of acid chlorides with carboxylates [22,23] or carboxylic acids [24][25][26][27], as well as by reaction of acid chlorides under ultrasound basic media [28].…”