Halides continued

Representative Functional Group Transformations by Nucleophilic Substitution Reactions of Alkyl Halides (Continued)... 

B. From Cyano-compounds and Phosphorus(v) Halides.—Continued reports of the reactions of alkyl cyanides with phosphorus pentachloride appear. With dicyanides the formation of phosphazenes occurs via a series of intermediates whose stability varies with the nature of X ... 

Table 9. organosilane reduction of acyl Halides (continued)... 

Phosphonitrilic halides (continued) primary amines and, 1 360-362 secondary amines and, 1 350-362 tertiaiy amines and, 1 362-363 structural theory further aspects of, 1 375 structure, 1 365-366 high polymer and, 1 372 medium polymers and, 1 368-372 spectroscopic data and, 1 369-372 structural theory and, 1 372-375 tetrameric compounds and, 1 367-368 trimeric compounds and, 1 366-367 Phosphonium cations, 9 243-250 halogenated, 9 243-249 salts... 

Evaporation of the solution yields FeCl2 4 H20, but, as in the case of many other aqueous halides, continued heating of the solid leads to decomposition rather than dehydration. However, the anhydrous dichloride can be prepared by the reaction of iron with gaseous HC1 ... 

Synthetic Methods.— Direct routes to phosphonic acid derivatives from olefins and phosphorus halides continue to be explored. In the presence of oxygen, phosphorus tribromide reacts with olefins by a radical mechanism in a manner analogous to the corresponding chloride, giving 2-bromoalkyl-l-phosphonyl dibromides. The reaction of phosphorus trichloride and per-chloryl fluoride with hex-1-ene gives moderate yields of (55), the direction of... 

Despite the efficient utilization of benzophenone imine and metal amides as ammonia surrogates, the quest for the direct coupling of ammonia with aryl halides continued. The biggest challenge was to suppress the polyarylation of ammonia, which arises from the reaction of the corresponding anihne. Hartwig et al. [72] were the first to master this task and to report the Pd-catalyzed monoarylation of ammonia (Scheme 13.19). 

The more stable a cation is, the less reactive it is and, conversely, the less stable a cation is, the more reactive it is. This means that, although a methyl cation is very reactive if it forms, this higher energy carbocation has a higher activation barrier to formation, relative to a more stable ion such as a tertiary carbocation. As noted, this information leads to the conclusion that it is easier to form a tertiary cation by ionization of a tertiary halide than it is to form a secondary carbocation by ionization of a secondary halide. Continuing the trend, it should be very difficult to form a primary cation from a primary halide such as 1-bromopentane (72) and very difficult indeed to form a methyl carbocation from iodomethane or bromomethane. 

Azide displacements on sugar sulphonates and halides continue to be used extensively in the synthesis of amino-sugars. Such displacements have been used in the synthesis of derivatives of the methyl 3-amino-2,3-dideoxy-a-L-hexopyranosides... 

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