1 Classification reactions Enols

Building on a recently introduced reaction classification system that considers electronic effects, a descriptor for steric hindrance has been added.The expanded classification hierarchy has been applied to a range of representative reactions, including additions to carbonyl compounds, and enolate formation. 

To avoid this difficulty the words single-step and reactant are used. Clearly, the lactone is considered to be a starting material, but the enolate to be the reactant and therefore a diastereoface-differentiating reaction is said to have occurred. This example may illustrate another point, i.c.. that the product-based classification according to types of stereoselectivity and the Izumi-Tai classification (stereodifferentiation) are independent to a certain extent. Thus, the example can be classified as a diastereoface-differentiating, diastereoselective reaction. 

The foregoing classification is of fundamental significance for the understanding of enolate chemistry. For every pair of C,H acid and base, one needs to know whether the combination effects quantitative or partial enolate formation. If deprotonation is only partial, then the unreacted substrate may represent an electrophile that can react with the enolate nucleophile. In such a case, it depends on the specific circumstances whether an enolate reacts with any remaining substrate or whether it reacts only with an added different electrophile. The occurrence of a reaction between enolate and unreacted substrate is avoided if the C,H acid is deprotonated completely with a stoichiometric amount of a sufficiently strong base. 

To facilitate an analysis of enolate reactivity and as an aid to the rationalization of the stereochemical outcome of the aldol reaction, a consideration of the enolate structure is necessary. For convenience, the following classification of transition metal and lanthanide metal enoiates will be used here T) -0-bound metal enoiates (1) of carbonyl compounds T) -C-bound metal enoiates (2) and ij -metal enoiates (3) of... 

Claisen head adapter, 20, 26,134 Claisen-Schmidt reaction, 309-317 classification tests, 640-654. See also qualitative analysis alcohols, 640-642 aldehydes, 642-644 alkanes, 644-645 alkenes, 645 alkyl halides, 645-646 aUcynes, 645 amides, 647-648 amines, 648-649 ammonium salts, 647-648 aromatic hydrocarbons, 649-650 carboxylic acids, 650 cycloalkanes, 644-645 defined, 630 enols, 653-654 esters, 650-651 ethers, 651... 

---