Trityl azide

A fourth preparation for a stable iminosilane as the THF adduct is the reaction of a silylene with trityl azide.23... 

Sodium azide can react with 1,3-benzodithiolylium tetrafluoroborate (32) in acetonitrile to form the azide (38) which on treatment with trityl tetrafluoroborate yields trityl azide and (32) (80JOC2024). The last step of this reaction does not lead to the expected 2-azido-l,3-benzodithiolylium salt. 

When the azido group is linked to a tertiary carbon atom, an alkyl or aryl shift occurs, and the resulting A -substituted azomethines can often be isolated. Trityl azide (53) yielded, by action of heat or light , benzophenone anil (54). 

As the migrating aptitudes of the aryl groups are only slightly influenced by substituents in the thermal reaction and not at all in the photochemical one, trityl azides containing differently substituted aryl groups always yield mixtures of anils. 

In contrast, thermal decomposition of these trityl azides in inert solvents at 170-190° is sensitive to para substitution, although the rates of the anisyl and nitro compounds only differ ten-fold . Analysis of the range of AH and AS values indicates that inductive effects cannot be wholly responsible, and a small amount of aryl participation seems likely, although a singlet nitrene has been proposed ° that does show some discrimination towards available j8-linked groups, despite its great electrophilicity. 

As an example. Figure 1.6 shows the DSC measurement of triphenylmethyl azide (trityl azide) applying a linear heating rate of only l.OK/min (sample size 3.35mg, Argon atmosphere, A1 pan with pierced lid). Endothermic processes are displayed by negative... 

A concise synthesis of tetra-O-ethyl aldonolactam 83 starting from 1 has been reported [102]. After protection of its primary alcoholic moiety as a trityl ether, saponification and treatment with EtBr generated 80. Acidic hydrolysis liberated 81 that was esterified (tosylate). The latter was displaced with NaNs to give azide 82. Reduction of 82 resulted in lactam 83 (Scheme 24). 

Fig. 7 Plots of log k against pitR for nucleophilic reactions of water, azide ions and chloride ions (A) with benzhydryl and trityl cations.

As has been discussed elsewhere, Fig. 7 demonstrates the basis for using reactions with azide ion as a clock for determining values of log kH2o in the range pATR = -5 to —15. However, the discussion above cautions against too narrow an interpretation of this figure. The correlations apply to benzhydryl cations and trityl cations and, as we have seen, other families of cations can lead to less ideal dependences of kn2o and, presumably, kAz on p/fR. 

Choride ion is considerably less reactive than the azide ion. Thus, although values of kc 1/ kn2o have been quite widely available from mass law effects of chloride ion on the solvolysis of aralkyl halides, normally the reaction of the chloride ion cannot be assumed to be diffusion controlled and the value of kn2o cannot be inferred, except for relatively unstable carbocations (p. 72). Mayr and coworkers251 have measured rate constants for reaction of chloride ion with benzhydryl cations in 80% aqueous acetonitrile and their values of logk are plotted together with a value for the trityl cation19 in Fig. 7. There is some scatter in the points, possibly because of some steric hindrance to reaction of the trityl cations. However, it can be seen that chloride ion is more... 

The dilemma presented by these conflicting results was resolved by TaShma and Rappoport.265 They pointed out that the apparent dependence of kAz/ knl0 upon the reactivity of the carbocation arose because even the most stable cation reacting with azide ion did so at the limit of diffusion control. Thus while kn2o remained dependent on the stability of the cation in the manner illustrated in Fig. 7 the rate constant for the azide ion remained unchanged. Thus the most stable cation formed in the solvolysis reactions was the trityl ion, for which direct measurements of kn2o = 1 -5 x 105 s 1 and kAz = 4.1 x 109 now show that even for this ion the reaction with azide ion is diffusion controlled.22... 

Shikimic acid Sodium azide Dimethoxypropane Triethylamine Trityl chloride Triphenylphosphine Acetic anhydride Ethanol... 

Reaction of otfi-unsaturated acetals with silyl nucleophiles. This trityl salt is an efficient catalyst for reaction of the dimethyl acetal (2) of cinnamaldehyde with successive silyl nucleophiles to form y,5-unsaturated p-azido ketones. The azide group can be reduced to an amino group by the Staudinger reaction.1... 

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