Dicarboxylic halogenation

For the ordinary Diels-Alder reaction the dienophile preferentially is of the electron-poor type electron-withdrawing substituents have a rate enhancing effect. Ethylene and simple alkenes are less reactive. Substituent Z in 2 can be e.g. CHO, COR, COOH, COOR, CN, Ar, NO2, halogen, C=C. Good dienophiles are for example maleic anhydride, acrolein, acrylonitrile, dehydrobenzene, tetracya-noethylene (TCNE), acetylene dicarboxylic esters. The diene preferentially is of the electron-rich type thus it should not bear an electron-withdrawing substituent. 

The list of suitable substituents includes acylamino groups, but especially halogen atoms such as chlorine or bromine. Halogenated derivatives are obtained from tetrahalogen phthalic anhydride or naphthalene-2,3-dicarboxylic anhydride, by... 

Chloroquinolines are reactive groupings due to electron-deficient carbon to which the halogen is attached. This carbon is electron-deficient due to the combined electron-withdrawing effects of the chlorine substituent and the quinoline nitrogen. The electrophilic carbon is thus able to react readily with nucleophiles present in the body. The impact of this grouping on a molecule is illustrated by 6-chloro-4-oxo-10-propyl-4H-pyrano[3,2-g]quinoline-2,8-dicarboxylate (Figure 8.28). In contrast to many related compounds (chromone-carboxylates) lacking the chloroquinoline, 6-chloro-4-oxo-10-propyl-4H-pyrano[3,2-g]quinoline-2,8-dicarboxylate is excreted as a... 

Fig. 3.23 Oxidation of halogenated quinolines to halogenopyridine-2,3-dicarboxylic acids [260]...

Mercury(II) oxide together with a halogen is an early development of the classic Hunsdiecker reaction (bromodecarboxylation of a carboxylic acid silver salt, see below) which is still in use.20 22 A double Hunsdiecker reaction of cyclobutane-1,1-dicarboxylic acid with red mer-cury(ll) oxide in the presence of bromine gave 1,1-dibromocyclobutane (2) in 46% yield.21 However, a similar reaction performed on spiro[3.3]heptane-2-carboxylic acid afforded 2-bro-mospiro[3.3]heptane (3) in only 16% yield.22... 

Dicarboxylic acid halogen amides, their salts and use in crosslinking of cellulose fibers thru urethane formation 5 D1202... 

Condensation monomers having the benzimidazolin-2-one ring system have found utility as modifiers in polyester synthesis. In particular, halogenated diols (73) and dicarboxylic acids (74) may be incorporated (78MI11100) into polyethylene terephthalate) or poly(butyl-ene terephthalate) at fairly low levels to impart flame retardancy. This can be accomplished without adverse effects upon other polymer properties. 

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). 

Complexes containing unidentate coordination have depended for their characterization upon physicochemical methods rather than structural determinations. The monomeric octahedral co-balt(III) complex [Co(en)2X(ox)], where X = halogen or OH, provides one of the few examples of unidentate oxalate coordination the conformation was determined from IR data.65 By contrast, there are numerous examples of structurally characterized chelating dicarboxylate systems. There are several structural determinations of different forms of oxalic acid and its ions but the most useful for comparative purposes are those of a-oxalic acid and anhydrous sodium oxalate. Using the planar ( >2 ) oxalate ion and acid as benchmarks it can be seen (Table 4) that the rj4 oxalate ligand (bite = 265 pm)66 has two long and two short C—O bonds. The coordinated C—O(M) bond resembles the C—O bond of the acid while the free C=0 bonds are similar to those in the oxalate... 

Pyridine-2,3-dicarboxylic acids containing a halogen in the 5- or 6-position were prepared by oxidation of the corresponding quinolines using either ozone/H202 or catalytic R.UO4. Diacids substituted in the 6-position by Cl or Br, or in the 5-position by F, Cl, or Br, respectively, were isolated in 46-71% yields. The yields of 6-fluoro and 6- or 5-iodo diacids were low (<30%) (Equation 40) <2001S2495>. 

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],... 

Anodic and cathodic elimination is simply the reverse of cathodic [eqn (16)] and anodic [eqn (15)] addition, respectively. Important cases are anodic bisdecarboxylation, either in the 1,2- (Corey and Casanova, 1963 Radlick et al., 1968 Westberg and Dauben, 1968) or 1,3-fashion (Vellturo and Griffin, 1966), with the preparation of Dewar benzene and dimethyl bicyclobutane-2,4-dicarboxylate as the more prominent cases [eqns (25) and (26)], and cathodic dehalo-genation of dihalides with the halogens in the 1,2- (Zavada et al., 1963), 1,3- (Casanova, 1974 Gerdil, 1970 Rifi, 1967, 1969), 1,4-(Casanova and Rogers, 1974 Wiberg et al., 1974) and 1,6- (Covitz, 1967) positions. The synthesis of bicyclobutanes (27) and [2,2,2]propellane (28) bear witness to the usefulness of this reaction type. 

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