Principle of vinylogy

Under the principle of vinylogy, the active hydrogen can be one in the y position of an a,P-unsaturated carbonyl compound ... 

The electron-withdrawal to the cyclic nitrogen atom can be transmitted to the y-position of pyridine (560) (illustrating the principle of vinylogy). Hence, y-substituents have properties similar to those of a-substituents. 3-Substituents in pyridine are not directly conjugated with the heteroatom usually the reactivity is intermediate between that of the same substituent attached to a benzene ring, and that of an a- or y-substituted pyridine. 

Additional conjugation may not change the system significantly (the principle of vinylogy. Section 1.9.2). Vinylogous paths are often denoted with a prime mark. 

This paper illustrates how the principle of vinylogy may serve to direct attention to possible structural similarities in a large number of diverse structures of herbicides with similar activity and mode of action which might otherwise appear unlikely. Structural information such as this on various classes of PS II herbicides in conjunction with intuitive-empirical or computer oriented approaches should facilitate the design of new inhibitors. 

The principle of vinylogy can also be applied to search for other C H acidic compounds as suitable candidates to undergo conjugate addition under iminium activation. This is the case of the vinylogous Michael addition of a,a-dicyanoolefins to a,p-unsaturated aldehydes catalyzed by diphenylprolinol... 

In concert with the principle of vinylogy, the phosphoramide/SiCLt system could be applied to silyl dienol ethers derived from a,(3-unsaturated esters, ketones [65],... 

Now let s consider 1,4-dicarbonyl compound 39. One polar disconnection leads to charged fragments A -I- B or C -l- D (Case 1). The C -I- D pair can easily be related to an acyl anion equivalent and methyl vinyl ketone (by apph-cation of the principle of vinylogy). The acyl anion equivalent can be generalized by structure 40 in which an A-fimction behaves as a N-fiinction. 

Explain why A can be deprotonated by lithium diisopropylamide (LDA) where as B cannot. Explain why this is not a breakdown of the principle of vinylogy. (Difiinctional Relationships-6)... 

Dienamine is a recent extension of the enamine concept to extended donors by using the principle of vinylogy. By extension of the enamine to conjugated dienamine starting from alkyl substituted enals or enones, it allows for the functionalization of a,p-unsaturated carbonyls in a- or 7-position using various electrophiles (Scheme 11.26). This potential of amine catalysts to promote extended functionalization is highly interesting, but because of its relative infancy, few synthetic applications of such activation have been reported to date. 

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