Picoline halogenation

Haque I, Wood JL (1967) The infra-red spectra of y-picoline-halogen complexes. Spectrochim Acta A 23 2523-2533... 

Other auxin-like herbicides (2,48) include the chlorobenzoic acids, eg, dicamba and chloramben, and miscellaneous compounds such as picloram, a substituted picolinic acid, and naptalam (see Table 1). Naptalam is not halogenated and is reported to function as an antiauxin, competitively blocking lAA action (199). TIBA is an antiauxin used in receptor site and other plant growth studies at the molecular level (201). Diclofop-methyl and diclofop are also potent, rapid inhibitors of auxin-stimulated response in monocots (93,94). Diclofop is reported to act as a proton ionophore, dissipating cell membrane potential and perturbing membrane functions. 

Chloromethylbenzo-l,2,4-thiadiazine 1,1-dioxide forms quaternary salts, e.g. 8 (n = 1), with pyridine, 2- and 3-picolines, and iso-quinoljne, but the 3-(2 -chloroethyl) compound gives a lower yield of the salt, e.g. 8 (% = 2), because some of the halogen derivative is converted into the 3-vinyl compound. ... 

Pyridine pesticides are usually synthesized by starting with pyridine or a picoline nucleus, which is then further treated by halogenation, ammoniation, oxidation, etc. Quite often however it is impossible to introduce the desired substituents into the adequate ring position, in which case the corresponding aliphatic compound is prepared and then cyclised. 

N-Halogenation and other oxidative reactions of pyridines and related heterocycles have been re-viewed. ° Thus, pyridines and some diazines can be aminated by mesitylenesulfonylhydroxylamine (32) and similar reagents. / -Nitration of 2-picoline by nitronium tetrafluoroborate gives the salt (46) which is itself a nitrating agent. 

In a few instances, not only methyl ketones but other alkyl ketones are degraded to shorter carboxylic acids resulting from halogenation of the methylene group adjacent to the carbonyl and subsequent hydrolysis [103, 160,1172]. The reaction between propiophenone and sodium hypobromite at 22-25 °C gives a 96% yield of benzoic acid [303]. Under similar conditions, 5-butyl-2-butyrylpyridine is converted into 5-butyl-a-picolinic acid in 79% yield [160]. Methyl 3-(a-pyridyl)propyl ketone yields not only the... 

Cyanopyrazines were previously prepared by treatment of bromopyrazines with copper(I) cyanide in refluxing 4-picoline <56JA2i4i>. These compounds can also be synthesized by palladium-catalyzed cyanation of the less reactive chloropyrazines with potassimn cyanide (Section 6.03.5.4.2). Sodium dicyanocuprate is similarly effective for the cyanation of 2-amino-3-bromopyrazine, the halogen of which is almost inert to copper(I) cyanide. Dehydration of pyrazinecarboxamides with phosphoryl chloride, acetic anhydride or phosphorus pentoxide gives the carbonitriles. 

Our synthesis began with the diisopropyl amide of picolinic acid (39, Scheme 11). Introduction of an iodine at the 3-position was accomplished in 80% yield by lithiation with LDA and trapping with iodine. A second metalation with LDA and trapping with iodine provided the 3,4-diiodo species 41, probably via the 3-lithio-4-iodo compound (40) that is produced by a 1,2-halogen-dance. Unfortunately, attempted preparation of 36 by treatment of 41 with LDA and quenching with water... 

Alkylpyridines undergo reactions analogous to benzene such as side-chain halogenation and oxidative functionalization (cf. p 291). In addition, C-H bonds directly attached to the heterocycle display a kinetic acidity which is greater by a factor of > 10 compared to the corresponding benzene derivatives. This is more pronounced in the 2- and 4-positions than in the 3-position. H/D-Exchange experiments of 2-, 3- and 4-picoline with a relative exchange rate of 130 1 1810 (MeOD/MeONa at 20°C, cf toluene 10" ) demonstrate this point. 

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