Conjugation influence nitriles

Conjugation has a great influence on the structure of aliphatic and alicyclic compounds. Thus, the existence of an amino form has been established (in addition to the extreme case of aromatic amines17) for all compounds where the double bond is conjugated with a carbonyl group (or its equivalent),12 with esters12,18 and nitriles of a,/8-un-saturated /8-amino acids,519,20 and with /8-amino-ketones. The /3-keto-esters ethyl 2-cyclopentanone- 1-carboxylate and ethyl 2-cyclo-hexanone-l-carboxylate exist as mixtures containing 95% of the keto... 

A way out may be found if the cycloaddition of diazomethane to 1 occurs in the reverse direction as represented in XVII. Now the newly introduced methylene will be in the appropriate position for ring expansion to a six-mem-bered ring. This requires that the first new C-C bond of I with diazomethane be formed at the /3 carbon of the cyano aciylate group as opposed to V. This is possible thanks to the inversion of polarity or umpolung of the double bond due to its conjugation with the nitrile. This effect along with the influence of the ester overrules the polarization pull of the lactam ring. 

The influence of cyclopropyl on the gas phase stability of carbocations as measured by ion cyclotron resonance is shown in Table 14, along with data for some reference compounds. The results are given as gas phase basicities, GB, and proton affinities, PA, defined as AG° and AH°, respectively, for dissociation of the protonated molecule, as in equation 11. In addition hydride affinities D(BH H ) for some cations defined as — AH° for equation 18 are included. For the gas phase basicities and proton affinities the products B are alkenes, amines, nitriles or carbonyl compounds, and thus for these values the stability of the cation is compared to a derivative where the substituent is conjugated with a carbon-carbon or carbon-oxygen double bond, or a nitrogen lone pair, whereas for hydride affinities the products are saturated. 

Rann et al. reported the dramatic influence of a new tailor-made, task-specific, and stable ionic liquid, butyl methyl imidazolium hydroxide ([bmim][OH]), in Michael addition. They have discovered that a task-specific ionic liqnid [bmim][OH] efficiently promoted the Michael addition of 1,3-dicarbonyl compounds, cyano esters, and nitro alkanes to a variety of conjugated ketones, carboxylic esters, and nitriles withont reqniring any other catalyst and solvent (Fig. 12.21) [16]. Very interestingly, all open-chain 1,3-dicarbonyl componnds such as acetylacetone, ethyl ace-toacetate, diethyl malonate, and ethyl cyanoacetate reacted with methyl vinyl ketone and chalcone to give the usual monoaddition products, whereas the same reactions with methyl acrylate or acrylonitrile provided exclusively bis-addition products. 

Ranu BC, Baneijee S (2005) Ionic liquid as catalyst and reaction medium. The dramatic influence of a task-specific ionic liquid, bmim][OH], in Michael addition of active methylene compounds to conjugated ketones, carboxylic esters, and nitriles. J Oig Lett 7 3049-3052... 

Although in both cases the steric situation is at least comparable, the triple bond directs the elimination completely in the conjugate system 498 and it certainly merits mentioning that with 496 a strong acceptor group such as nitrile practically has no influence on the product distribution [177]. 

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