Conjugation influence acid halides

The pKa of the methylene protons of 7 is close to that of cyanacetic ester. Thus, it was interesting to compare the reactions of these two species. We found that 7 can be acylated by various carboxylic acid halides, leading to compound 11. According to IR and NMR data 11 exists mostly as the enol-form, due to the influence of the carboranyl substituent, which strongly stabilizes conjugated double bonds.13 Compound 11 is a useful synthon for the preparation of heterocyclic compounds. It can be methylated, chlorinated and acylated twice ( compound 13). Compound 13 gives an adduct with phenylhydrazine (scheme 6). 

A study of the kinetics of nitrosation of iV,iV -dimethyl-A"-cyanoguanidine in acid media (Scheme 13) [where the substrate exists as its conjugate acid (130)] has established that the mechanism of the reversible reaction is similar to that found for nitrosation of amides and ureas, rather than amines (for which attack of the nitrosating agent on the free base is usually rate limiting).The reaction, which is subject to general-base catalysis but not influenced by halide ion, involves reversible rate-limiting proton transfer in the final step and exhibits solvent deuterium isotope effects of 1.6 and... 

A dissection of the influence of solvent and base should be possible from studies in dipolar aprotic solvents containing various bases in which the two reactants can be varied independently. Although bases whose conjugate acids have pATa values of less than 11 rarely induce elimination in protic media , halide ions have been used successfully in this connection in dipolar aprotic solvents . Of course in the latter solvents, which lack exchangeable hydrogens but possess atoms with lone pairs capable of solvating cations, pATa values may differ appreciably from those already derived in protic sol-vents . There is obviously ample scope for future research in this field. 

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