Heptanoic acid, anhydride from

The dihydro-cyclopentano-phenanthrene (120) has been synthesized (Scheme 9) from 2-acetyl-3-methylnaphthalene (115), which was converted into the fur-furylidene derivative (116). Treatment with acid afforded the expected dioxo-heptanoic acid (117), which on treatment with base provided the cyclopentenone (118). This keto-acid (118) readily underwent cyclization when boiled with acetic anhydride, furnishing ll-acetoxy-15,16-dihydro-7-methylcyclopenta[a]-phenanthren-17-one (119a). Deoxygenation at C(ll) was performed through... 

A soln. of 1-heptanoylimidazole prepared from heptanoic acid and N,N -thiongl-diimidazole in tetrahydrofuran allowed to react with the Mg-enolate of monoethyl malonate (s. Synth. Meth. 14, 888) ethyl heptanoylacetate. Y 74%.— The use of mild acylating agents, such as 1-acylimidazoles or carboxylic alkoxy-formic anhydrides, prevents diacylation, which occurs with acid chlorides. F. e. and modifications s. G. Bram and M. Vilkas, Bl. 1964, 945. 

Acid chlorides are useful precursors to anhydrides, including both symmetrical and mixed (unsymmetrical) anhydrides. In one experiment, heptanoyl chloride (50) reacted with heptanoic acid (51), with benzene as a solvent and in the presence of pyridine (53), to give the symmetrical heptanoic anhydride (53) in 83% isolated yield. Unsymmetrical anhydrides are prepared by choosing which half of the anhydride comes from the acid chloride and which comes from the carboxylic acid. This choice allows one to control formation of the mixed anhydride. If heptanoyl chloride (50) and butanoic acid (7) react in the presence of triethylamine as the base, anhydride 54 is formed. Anhydride 54 can also be prepared by the reaction of butanoyl chloride with hexanoic acid, but the easiest to obtain and cheapest combination is usually used. 

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