Furan 2.5- diacetic acid

A further route to the cycloocta[l,2-c 5,6-c ]difuran system makes use of a Perkin-type reaction. Condensation of furan-3,4-dicarboxaldehyde with furan-3,4-diacetic acid in acetic anhydride and triethylamine at room temperature, followed by esterification with methanol and sulfuric acid, gave... 

Alkylfurans, halofurans, alkoxyfurans, furfuryl ester and ethers, and furfural diacetate [613-75-2] behave similarly. Furans containing electron withdrawing constituents, for example, furfural, 2-furoic acid, and nitrofurans, fail as dienes even with very strong dienophiles. 

A novel synthesis of the sesquiterpene ( )-cinnamodial (148) utilizes the furan ring as a latent 1,4-dialdehyde synthon (81JA3226). The triol (141) was thus oxidized to the ketofuran (142). Oxidation of the furan moiety with lead tetraacetate afforded a 90% yield of epimeric diacetates (143) which when exposed briefly to DBU gave dienone (144). Epoxidation of (144) and exposure of the epoxide (145) to p-toluenesulfonic acid gave the bis-acetal (146). Reduction of this intermediate to a diol and hydrolysis of the bis-acetal furnished dialdehyde (147). Acetylation of the secondary hydroxyl group completed the synthesis of cinnamodial (Scheme 32). 

Furans can be nitrated with a mixture of fuming nitric acid and acetic anhydride at low temperature. The initial products from the nitration of furan-2-carbaldehyde and its diacetate are (525), (526), (527) and (528), indicating that both 1,4- and 1,2-addition to the diene system may occur (76KGS601) (see Section 3.11.2.2.3). Analogous products are obtained from the nitration of furan-2-carboxylate (75KGS883). Carboxylic acid groups are often replaced thus 5-bromofuran-2-carboxylic acid on nitration yields 5-bromo-2-nitrofuran, which may be readily converted to 5-iodo-2-nitrofuran and 2,5-dinitrofuran (61ZOB263). 

To convert labdanolic acid (8.27) to the naphthofuran (8.10), it is necessary to shorten the side chain and then cyclise the residue onto the alcohol to form the furan ring. In this synthesis, Bolster and de Groot carried out the chain shortening in two steps.816 Firstly, after protection of the ring hydroxyl group by conversion to the acetate, the terminal acidic carbon atom was removed by photo-decarboxylation in the presence of iodine and iodobenzene diacetate. This gave the iodinated material (8.29). Treatment of (8.29) with potassium tert-butoxide... 

The oxidation of a ( )-flavanone with Tl(ni) nitrate, Pb tetracetate, phenyliodonium diacetate (PIDA), or [hydroxyl(tosyloxy)iodo]benzene in trimethyl orthofonnate affords the corresponding ( )-2,3-dihydrobenzo[h]furan derivative as a major product. The structures, including the relative stereochemistry, and a plausible mechanism of formation are reported. The preferred formation of a flavone from the ( )-flavanone by PIDA is explained by quantum-chemical calculations on the intermediate formed by the addition of this reagent to the enol ether derivative of the ( )-flavanone." Formation of mixed anhydrides by rapid oxidation of aldehydes, activated by pivalic acid, Bu OCl in presence of pyridine and MeCN is catalysed by TEMPO (2,2,6,6-tetramethylpiperidin-l-oxyl). The anhydrides can be converted in situ to esters, secondary, tertiary or Weinreb amides in high yield. Oxidation of the aldehyde to 2-propyl esters is also possible using only catalytic amounts of pivalic acid." ... 

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