5- Bromofuran-2-carboxylic acid

The analogous reactions of 5-nitro- [227] and 5-bromofuran-2-carboxylic acids [228] lead to addition of two fluorine atoms and replacement of the nitro group... 

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). 

Efficient synthesis of 2-chlorofuran is best achieved by decarboxylation of 2-chlorofuran-5-carboxylic acid (63JGU1397) or via the lithium derivative of furan. When furan or 3-bromofuran were treated in turn with ethyl-lithium and hexachloroethane, 2-chlorofuran (48%) or 3-chlorofuran (54%) was formed, uncontaminated by any polychlorinated products (73SC213). Chlorodesilylation of ethyl 5-trimethylsilyl-2-furoate with sul-furyl chloride in acetonitrile gave the 5-chloro ester in —85% yield (91MI4). 

The intrinsically high reactivity of the furan nucleus is further exempUlied by the reaction of furfural with excess halogen to produce mucohalic acids incidentally, mucobromic acid reacts with formamide to provide a useful synthesis of 5-bromopyrimidine. On the other hand, with control, methyl furoate can be cleanly converted into its 5-monobromo or 4,5-dibromo derivatives hydrolysis and decarboxylation of the latter then affording 2,3-dibromofuran bromination of 3-furoic acid produces 5-bromofuran-3-carboxylic acid. ... 

Carboxylic acid anhydrides or halides normally require the presence of a Lewis acid (often boron trifluoride) for Friedel-Crafts acylation of furans, though trifluoroacetic anhydride will react alone. Aluminium-chloride-catalysed acetylation of furan proceeds 7 x lO times faster at the a-position than at the P-position. 3-Alkyl-furans substitute mainly at C-2 2,5-dialkyl-furans can be acylated at a P-position, but generally with more difficulty. 3-Bromofuran is efficiently acetylated at C-2 using aluminium chloride catalysis. ... 

Decarboxylation of halofurancarboxylic acids is usually carried out with copper and quinoline at 150-230 °C and the product often distills from the reaction mixture (71BSF242). Heating chloromercuriofurans with iodine and potassium iodide in water yields iodofurans. Thus 3,4-bis(chloromercurio)-2,5-dimethylfuran yields the diiodo compound (41%), and tetrakis(chloromercurio)furan yields tetraiodofuran (67%). Boiling sodium furan-2,5-dicar-boxylate with potassium iodide and iodine in water yields the diiodofuran, and 2,5-dibromofuran (78%) is similarly available from sodium 5-bromofuran-2-carboxylate, potassium bromide and bromine (74ZOR1341). 

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