Methoxy carbonyl maleic anhydride

Whereas maleic anhydride can react with furan (139a) at ambient pressure, citraconic anhydride (140) reacts only at high pressures due to the strong deactivating effect of the methyl group (Schemes 5.21 and 5.22). The two-step synthesis [53] of the palasonin (141), in an overall yield of 96 %, is a good example of the acceleration of the Diels-Alder by high pressure (Scheme 5.21). Previous synthesis [54] based on the thermal Diels-Alder reaction of furan with methoxy carbonyl maleic anhydride required 12 steps. 

Extensive studies on the synthesis of 4-ylidenetetronic acids conducted by Pattenden and his colleagues have been based mainly upon furan-2,5-diones (maleic anhydrides) in which a carbonyl reacts selectively. Unexpectedly, metal hydride attacks both carbonyl groups about equally in the methyl derivative, but in the methoxyfuran-2,5-diones, where electron release from the methoxy group greatly reduces the activity of the distal carbonyl group,... 

The selectivities demonstrated by unsymmetrical maleic and phthalic anhydrides for attack of a nucleophile on one carbonyl group rather than on the other are large enough to demand explanation. In principle, maleic anhydride 126 can undergo attack by a nucleophile at either of the two carbonyl carbons Ca and Cp. However, there is exclusive attack at C by lithium aluminum hydride when R is a methoxy group. The ratio of attack at C versus Cp reduces only slightly to 88 12 when R is a... 

An efficient synthesis of 11 was developed based on the double methoxy-carbonylation of the inexpensive Diels-Alder adduct of fiuan to maleic anhydride [169]. Under a CO pressure of 1-3 atm and the presence of CUCI2 (oxidant) and a catalytical amount of Pd on charcoal in MeOH, adduct 21 furnishes the all-exo tetraester 22, the esterification of the anhydride being complete due to HCl formation. Reduction with IiAlH4 gives the corresponding tetrol 23, which is chlorinated with SOCl2/pyridine into 24. Treatment with f-BuOH/THF (0-20 C) gives 11 (64% overall yield based on 21). The method has also been successful in the syntheses of 2,3,5,6-... 

In studies of the reactions between 2-methoxysubstituted maleic anhydrides viz 172) and the stabilized phosphoranes (161) and (164), it has been shown that the condensations are regioselective leading to those products viz 173) resulting from nucleophilic addition to the carbonyl functions nearest to the methoxy-substituent 136). 

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