Acylation by carboxylic anhydrides

C-C linkage by replacement of O-acyl by carbon 1. Acylation by carboxylic anhydrides 

As mentioned above, / -diketones can be obtained by condensation of esters with ketones, but they can also be prepared in another way, namely, by reaction of methyl ketones with acid anhydrides in the presence of boron 

RCOCH3 + (CH3C0)20 BF3 RCOCH2COCH3 + ch3cooh For example, Meerwein and Vossen773 describe the preparation of benzoyl-acetone (1-phenyl- 1,3-butanedione) as follows  

Acetophenone (20 g) and acetic anhydride (34 g, 2 moles) are mixed and boron trifluoride is led in, with ice-cooling, to saturation. 4The mixture becomes almost filled with yellowish crystals and is poured into a solution of crystalline sodium acetate (45 g) in water (100 ml) and distilled in steam. A small amount of oil first distils and is followed by the benzoyl-acetone which tends to solidify in the condenser. This product is taken up in ether, washed with sodium hydrogen carbonate solution, dried over sodium sulfate, and distilled in a vacuum. The yield is 83.3% (22.5 g). 

Other examples are recorded by Hauser and Adams.774 Other acylations by acetic anhydride recorded on previous pages are those of aromatic compounds on page 939, of acetylides on page 931, of alkylcadmiums on page 911, and of diazo compounds on page 948. 

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Acylation by carboxylic anhydrides or acids. Carboxylic anhydrides can be used in place of acyl chlorides, the reaction being ... 

Acylation by carboxylic anhydrides is usually performed in the presence of a basic catalyst such as pyridine or triethylamine. 

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