Carbon family important reactions

Carbonates represent an important family of protecting groups of hydroxyl groups. All of the members of the carbonate family are easy to introduce by reaction of the free alcohol with chloroformates or mixed carbonate esters. In general, carbonates are less reactive than esters towards basic hydrolysis owing to the reduced electrophilicity of the carbonyl afforded by the resonance deactivation by two oxygens. However, the conditions that attack esters may also attack carbonates. 

The most important reactions in this group are the Beckmann rearrangement, which converts oximes to amides a family of reactions that convert carboxylic add derivatives to amines with loss of the carbonyl carbon and the reaction of ketones with hy dr azoic acid to give amides (the Schmidt reaction). 

Atom insertions constitute another important family of reactions. Insertion of single atoms into carbon-carbon cr-bonds change difunctional relationships from odd to even (or even to odd). Cyclohexanones (for example 121) are preparable from 1,5-dicarbonyls (see Functional Groups-11) or 1,7-dicarbonyls. Baeyer-Villiger and Beckman rearrangments convert cyclohexanones into 1,6-difunctional compounds. Conversely, cyclopentanones (for example 123) can be prepared from 1,4-dicarbonyls or 1,6-dicarbonyls vide supra) and can be similarly converted to 1,5-difunctional compounds. This is also true for acyclic compounds (127 —> 128 and 129 130). Carbon insertion reac-... 

Sigmatropic rearrangements clearly play an important role in synthesis. The in-depth study of these types of reactions has led to a fundamental mechanistic understanding, which generally allows for the accurate prediction of the stereochemical properties of the product. This fact, combined with the creation of a carbon-carbon bond from an easily accessed C—X bond, has rendered this family of reactions as valuable tools for the stereoselective synthesis of complex molecular architectures. 

One family of porphyrin complexes that will be treated in the review, even though they do not contain metal-carbon bonds, are metalloporphyrin hydride and dihydrogen complexes. As in classical organometallic chemistry, hydride complexes play key roles in some reactions involving porphyrins, and the discovery of dihydrogen complexes and their relationship to metal hydrides has been an important advance in the last decade. 

Fenimore had noted an earlier and smaller source of NO produced within the flame combustion region. This prompt NO (Fenimore-NO) was proposed to be generated by the reaction of N2 with methyne (HC), the parent of the monovalent carbon (carbyne) family, with the formation of HCN and N( S) atom as important intermediates. 

Another important family of elimination reactions has as its common mechanistic feature cyclic TSs in which an intramolecular hydrogen transfer accompanies elimination to form a new carbon-carbon double bond. Scheme 6.20 depicts examples of these reaction types. These are thermally activated unimolecular reactions that normally do not involve acidic or basic catalysts. There is, however, a wide variation in the temperature at which elimination proceeds at a convenient rate. The cyclic TS dictates that elimination occurs with syn stereochemistry. At least in a formal sense, all the reactions can proceed by a concerted mechanism. The reactions, as a group, are often referred to as thermal syn eliminations. 

In addition, there are many important nonantibiotic uses of 2-azetidinones in fields ranging from enzyme inhibition [15-21] to gene activation [22], Systems containing one carbon atom common to two rings, spirocyclic compounds, represent an important structural organization. Spirocyclic p-lactams (Fig. 3) behave as p-tum mimetics [23-26] as well as enzyme inhibitors [27, 28], they are precursors of a,a-disubstituted p-amino acids [29-32], and the spiranic p-lactam moiety is present in chartellines and chartelamides [33-38], a family of marine natural products. Synthetic studies and biosynthetic speculation inspired by an unexpected reaction on the marine alkaloid chartelline C have been described [38],... 

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