Methyl coumalate

The procedure for preparing methyl coumalate is based on a method described by von Pechmann. Methyl coumalate has also been prepared by direct esterification of the reaction mixture from malic acid and fuming sulfuric acid and from comnalyl chloride and methanol. ... 

The regioselective formation of a cw-hexalone containing a homonuclear diene which is useful for elaboration into ocddentalol [178] by the condensation of 4-methyl-3-cyclohexenone with methyl coumalate is rather surprising. It seems that C-3 of the cyclohexenone, under the influence of the ketone group (perhaps via the enol), prefers an acceptor role. 

The nucleophilic carbon of diazomethane attacks the ring of pyran-2-ones, especially when electron-withdrawing substituents are present for example, methyl 2-oxo-pyran-5-carboxylate (methyl coumalate, 269) is methylated successively at C-6 and C-4... 

The second variant is the reaction of a pyran-2-one (methyl coumalate, 313) as dienophile with a cyclopentadiene (314). The balance between the dienic and dienophilic capabilities of pyran-2-one is tipped in favour of the latter by the electron-withdrawing properties of the carboxylic ester group and this fine balance enhances the potential of these compounds as synthons (72CC388). 

The highly functionalised pyran 1 can be prepared in a one-pot operation and in yields up to 30% by reaction of the readily available sulfone 2 with methyl coumalate 3, using methylene chloride as solvent and DBU as base. 

Conversion of the derived methyl coumalate into methyl 6-hydroxy-nicotinate (Expt 8.35) is effected by the action of concentrated aqueous ammonia subsequent hydrolysis with aqueous alkali yields 6-hydroxynicotinic acid. 

Reaction of methyl coumalate 327a (Scheme 65) with an electron-poor dienophile such as fumaronitrile at high temperature (120°C, no solvent) gives the [4 -I- 2]-adduct 332 in 28% yield (89NKK1765). However, the reaction of 327a with acrylonitrile takes place only under irradiation in the presence of a sensitizer (benzophenone) to give two types of [4 + 2]-cycloadducts 333 endo 17% exo 12%) along with [2 -1- 2]-cycloadduct 334 (9%). 

Fig. 28. Formation of the lactone (112) from methyl coumalate 116 and the steric energy (SE) of cycloadduct (111) and the lactone (112)...

Pearson and Ong86 have extended their route to trichothecane sesquiterpenoids via organoiron complexes by the synthesis of (144) (Scheme 14). The Diels-Alder approach to the construction of the cw-fused AB ring junction of the tricho-thecanes has been much in evidence. The use of methyl coumalate (145) as a... 

Write out a mechanism for the conversion of 4-pyrone into l-phenyl-4-pyridone by reaction with aniline. Write structures for the products you would expect from reaction of methyl coumalate (5-methoxycar-bonyl-2-pyrone) with benzylamine. 

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