Bromo analogues

The organic iodine compounds have lower heats of formation and greater reactivities than their chloro and bromo analogues. As ia the case of the inorganic iodides, their iadexes of refraction and specific gravities are higher than the corresponding chloro and bromo derivatives (121). 

In view of the high price and other difficulties associated with the use of phosphoryl bromide, the transhalogenation of 2-chloro- and 2-chloro-4,6-dimethyl-pyrimidine (919) by treatment with inexpensive phosphorus tribromide to give their bromo analogues in >50% yield, assumes potential importance as a general method (67JCS(C)1204). 

In a series of reactions with potassium amide in liquid ammonia, 6-chloropyrido[2,3-f)]pyrazine gave reduction and ring contraction (Section 2.15.13.3), the 6-bromo analogue underwent only reduction, whilst the 6-fluoro derivative gave only the 6-amino substitution product (79JHC305). 

In practice the bromo analogue has been more widely used. This arises from a combination of two reasons. In the first instance the tetrabromo resin contains 48% halogen whilst the tetrachloro resin contains 30% halogen. 

The syntheses of perhalogenated dithiethanes and their oxidation products (214-219) have been recently reported247. The method is based on the photochemical dimerization of thiophosgen or its fluoro- and bromo-analogues followed by partial oxidation with trifluoroperacetic acid to the desired sulfoxides (or sulfones)248 as shown in equation 84. 

HPLC of the dinitrobenzoylated derivatives of mixed chlor-bromo analogues of TRINOL... 

Guanidines attached to a group of appropriate lipophilicity have proven to be useful antihypertensive agents, active by virtue of their peripheral sympathetic blocking activity. Debrisoguine (72) is m fact used clinically for that indication. The 7-bromo analogue (76) also shows antihypertensive... 

This explodes both on melting and impact. The bromo-analogue is more sensitive, the chloro-compound is not known. 

Examination of the Merrell Dow series of haloallylamines as inactivators of bovine plasma amine oxidase recently has been reported. The (E)- and (Z)-3-fluoroallylamines were more potent than the 3-bromo analogues. In addition, the Z-isomers were more potent than the E-isomers, in contrast to the result reported for inactivation of MAO [81]. 

Nucleophilic displacement of an a- or y-halogen atom by the classical SAE mechanism of nucleophilic displacement via a Meisenheimer intermediate (e.g. 900) is facilitated by mesomeric stabilization of the transition state. However, the mechanistic balance is fine whereas 4-bromopyridine 1-oxide reacts with potassium amide by the A-E mechanism, the 2-bromo analogue prefers the E-A route. Again, nucleophilic displacement in chloropyrazines can involve the ANRORC mechanism. 

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