Halo aromatics

In a case analogous to the combination of the two plasmid encoded ortho- and mta-fission pathways in B13 for specific halo-aromatic utilization, another bacterium was modified with a hybrid pathway for this purpose. B. cepacia G4 degrades toluene, phenol, benzene, and ortho-cresol via a unique toluene ottfw-monooxygenase (Tom) pathway (Shields et al., 1989) encoded by the toluene catabolic plasmid TOM (Shields et al., 1995). 

Correspondingly, many toxic organic compounds (particularly halo-aromatics) have been shown to be oxidizable to innocuous compounds at Ti02 photoanodes with a counter-electrode of platinum (Bard, 1980 Fox, 1986). In 1980 Guruswamy suggested a design for a colloidal solar reactor for wastes that worked on photoelectro-chemical principles. 

Substituted-2,3-dihydrobenzo[h]furans were obtained in very good yields by SRN1 photo-stimulated reactions in liquid ammonia from appropriate halo-aromatic compounds ortho-substituted with a suitable double bond and Me3Sn, Ph2P, I3" and CH2N02 anions. 

Halogen bound to an aromatic ring is rendered considerably more reactive by nitro groups in the para- or, especially, the ortho-position to it carboxyl, sulfonyl, and cyano groups have considerably less effect. Among such activated halo aromatic compounds the relative reactivities of the halogens are reversed, and fluorine is much the most reactive. This is used for, e.g.9 determination of A-terminal amino acids in peptides by means of l-fluoro-2,4-dinitrobenzene.547 The ease of reaction is illustrated in the following example ... 

Much later, an alternate synthesis of naphthyridinones and quinoli-nones was discovered. Palladium-catalyzed amidation of halo aromatic rings with an ortho carbonyl group with primary or secondary amides to from substituted naphthyridinones and quinolinones (Scheme 97) (04OL2433). 

AllAmmonolysis of halo-aromatics. Transition metal-ion-exchanged X type zeolites are able to catalyze the substitution of the halide by the NH2 group in the presence of NH3. This ipso subsitution is conducted at temperatures within the 320 - 570°C range. The observed side reaction is transchlorination. CuX proved to be the best catalyst. Table 2 shows the product distribution observed with ZnX and CuX in a continuous flow procedure with NH3/C5H5CI ratio of 8 and liquideHSV of 1.3. 

M-unsubsituted thiohydantoin 29 was prepared from the ketone with anhydrous ammonia and trimethylsilyl cyanide (Scheme 2). The 1-amino carbonitrile 27 was treated with isothiocyanate to form thiohydantoin-4-imine 28, followed by hydrolysis to produce M-unsubsituted thiohydantoins 29. These intermediates were subjected to an SnAt reactions with several 4-halo-aromatic derivatives, such as 4-fluorocyanobenzene, to afford a series of M-aromatic group-substituted thiohydantoins 30. 

Table 5.1. Dehalognenation polymerization of halo aromatic compounds with magnesium in the presence of transition metal catalysts ... 

Figure 13.18 (a) SI group interacting with Tyr-228 [89], (b) Displacement of structural water by halo-aromatic SI group binder [90],... 

Aromatic aldehydes or ketones can be coupled to give stilbenes by the low-valent titanium method without affecting carboxylate, tosylate, or halo-aromatic substituents in the substrates/ ... 

Attempts to circumvent these problems by using mixed halo-aromatic systems and varying CO pressures was not successful (equation 4). 

Beecroft, R. A., Davidson, R. S., and Goodwin, D. C., The amine assisted photo-dehalogenation of halo-aromatic compounds. Tetrahedron Lett., 24, 5673, 1983. 

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