Cyano group activating effects

A cyano group produces practical reactivity (methanolic CH30, 66°, < 3hr) by its presence in 2-chloro-3-cyano-6-methylpyridine, opposing the deactivating effect of a methyl group, and on other 2-chloropyridines (see references 3-6 in ref. 140). The cyano group activates 3-cyano-6,6-diphenyl-2-methoxypyrazine (168) (pre-... 

Vinylpyridine (23) came into prominence around 1950 as a component of latex. Butadiene and styrene monomers were used with (23) to make a terpolymer that bonded fabric cords to the mbber matrix of automobile tires (25). More recendy, the abiUty of (23) to act as a Michael acceptor has been exploited in a synthesis of 4-dimethylaminopyridine (DMAP) (24) (26). The sequence consists of a Michael addition of (23) to 4-cyanopyridine (15), replacement of the 4-cyano substituent by dimethylamine (taking advantage of the activation of the cyano group by quatemization of the pyridine ring), and base-cataly2ed dequatemization (retro Michael addition). 4-r)imethyl aminopyri dine is one of the most effective acylation catalysts known (27). 

As to the electron-withdrawing substituents, the activating effect of a nitro group in the piperidino-dechlorination of 2-chloropyridine involves factors of 7.3 x 10 and 4.6 x 10 from the para and ortho positions, respectively. An ortho-cyano group was found to be... 

Nucleophilic radical, R and activated alkyl iodides, R l, which have electron-withdrawing groups, react smoothly through a SOMO-LUMO (a ) interaction to form RI and stable R as shown in Table 1.17. Here, the formed Rf is stabilized through the resonance effect by an ester or a cyano group [74]. 

The position of the substituents on the pyridine moiety also affects the activity of the initiator. For example, p-MeO benzyl o-CN pyridinium salt 2k is 100 times more reactive than the corresponding p-CN derivative 2f. Thus, introduction of the o-cyano group into pyridine nucleo causes a large enhancement of the initiator activity. The reason for the activity enhancement by this modification can be accounted for by both electronic and steric effects of the o-cyano group of the pyridine group. In a typical comparison of the initiation activities of p-CN 2f and m-COOMe 21 substituted p-methoxy benzyl pyridinium salts in the polymerization of GPE, it was observed that p-substituted salt 2f is approximately 10 times more reactive than the corresponding o-substituted salt 21. In this case the steric effect of the substituents is negligible. A similar... 

It was also observed that the electronic effect seems to predominate over the steric effect on the activation by changing the cyano group from the para to the ortho position. 

The effect of activating and deactivating substituents is illustrated by the following 7,000-fold acceleration by a cyano group (Table VII, line 21) 2-5-fold deceleration by an alkyl group in chloropy-rimidines (Table III, lines 2 and 5-9) and in nitrochloropyridines (Table VII, lines 8 and 16) 12-18-fold acceleration by a 6-chloro group in 2,4-dichloro- vs. 2,4,6-trichloro-pyrimidine (Table V) cf. 

Aryl cyanates have activated cyano groups and undergo many reactions They are effective dehydrating and hydrogen sulfide-bonding agents in organic synthesis A-, 0-, and 5-nucleophiles (HX) add... 

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