Halo Groups Transformations

The halogen atom of 2-chloro- and 2-bromo-l,2,4-triazolo[l,5-c]pyrim-idines (164,169) was displaced by alkoxy (65JCS3357), amino (65JCS3357  

Reaction of 5-chloro-l,2,4-triazolo[l,5-c]pyrimidines (165) with sodium hydroxide, thiourea, or hydrazine hydrate (79AJC1585) or with sodium azide (85EUP152841) also caused the displacement of the chlorine atom to 

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The halometacyclophanes formed by this route were easily converted to other derivatives by functional group transformations starting at the aromatic halo substituent. 

When a general group (such as halo) is used, its priority is that of the lowest member of its group (see footnote 913). Thus the general name for this transformation is halo-alkylsulfonyl-addition because halo has the same priority as fluoro, its lowest member. 

Rearrangements of nitrones due to migration of the A-oxide oxygen can be induced both, photochemically and by various reagents, but in specific conditions it can proceed spontaneously. On one hand, such transformations are caused by the O-nucleophilic character of nitrones able to react easily with acid anhydrides, their halo anhydrides, sulfonyl chloride and other agents on the other hand, by a significant CH-acidity of a-alkyl groups. 

Cyano, halo, amino, and nitro groups in the 2- or 4-position of pyridinium ions are susceptible to nucleophilic substitution. Treatment of these compounds with aqueous alkali gives the corresponding pyridones. Since this transformation is not the result of oxidation, it will not be further considered here. 

Hydroxyl groups in partially substituted compounds may be transformed into halo, amino, oxo, deoxy, and other functional groups. Free 1,6-anhydrohexopyranoses199,200 and their aminodeoxy201,202 derivatives tend to form cationic and anionic complexes, in particular with l,6-anhydro-/J-D-allopyranose, which has a vicinal triol system in axial-equatorial-axial arrangement.200... 

In contrast to the above intramolecular reactions, Yamamoto and coworkers have demonstrated that aromatic halo-ketones having an alkyl substituent at their a-position are transformed to cyclized products at the carbonyl carbon (Eq. 21) [60]. This suggests that a new mechanism, nucleophilic addition of the arylpalladium moiety in the key intermediate to the carbonyl group (Scheme 2), can occur. Addition of an alcohol such as 1-hexanol is essential for the reaction. A possible role of it might be to facilitate the reduction of Pd(II) to Pd(0). 

The exchange of halogen for the amino group is important in the formation of other polyfunctional compounds, particularly the amino acids. In several of these transformations with aqueous or liquid ammonia, it has been shown that the presence of ammonium salts minimizes the formation of secondary and tertiary aminesExcellent directions for the synthesis of a-amino acids (C,-C ) from a-halo acids and ammonia are given. The methods have been reviewed. Long-chain amino acids are prepared by this and other procedures. ... 

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