1,1-Dicarboxylic acids, decarboxylation halogenation

The reaction of isatins 9 with halogen-substituted acids or their esters 61 takes place even at room temperature. The obtained dicarboxylic acids 62 are decarboxylated in situ, and the final products are derivatives of 3-hydroxy-4-quinolinecarboxylic acid 63 [48, 49],... 

The aromatization of bicyclo[4.1.0]hept-3-enes gives access to a wide variety of cycloproparenes the substrates are readily available via Diels — Alder reaction of butadienes w ith cyclopropcnes. 1,2-Dihalo- and tetrahalocyclopropenes have been used for this purpose. In the aromatization step, it is important that the halo substituents arc located at Cl and C6 of the bicyclo[4.1. OJhept-3-ene. Halogens at C2 and C5 result in ring enlargement rather than aromatization on reaction with base. Oxidative bis-decarboxylation of bicyclo[4.1.0]hept-3-ene-l, 6-dicarboxylic acid was investigated as an alternative route to cycloproparenes however, the products were derived from carbenium ion capture after monodecarboxylation. 

Halogenation of furan carboxylic acids may proceed with decarboxylation to yield the halofuran treatment of sodium furan-2,5-dicarboxylate with iodine and potassium iodide gives 2,5-diiodofuran (see Section 3.11.2.2.5). 

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