Rearrangements of ketones

Rearrangements of ketones and aldehydes to difluoro-substituted ethers in the presence of hydrogen fluoride could be explained by the formation of fluorohydrin and further transformation to xenon fluoride ether, which readily decomposed90 and rearranged, thus forming difluoro ethers (Scheme 41). 

McLafferty Rearrangement of Ketones and Aldehydes The mass spectrum of butyraldehyde (Figure 18-4) shows the peaks we expect at m/z 72 (molecular ion), m/z 57 (loss of a methyl group), and m/z 29 (loss of a propyl group). The peak at m/z 57 is from cleavage between the /3 and y carbons to give a resonance-stabilized carbocation. This is also a common fragmentation with carbonyl compounds like the other odd-numbered peaks, it results from loss of a radical. 

From several early calculations [65,66], it soon became evident that the rearrangement of ketone to enol radical cations is a slow process with activation... 

Sharghi, H., Hosseini, M. Solvent-free and one-step Beckmann rearrangement of ketones and aldehydes by zinc oxide. Synthesis 2002, 1057-1060. 

The rearrangement of ketone nitrones with tosyl chloride in pyridine has been described in full. The reaction has resemblances to the Beckmann rearrangement of oximes, but does not depend upon nitrone stereochemistry, and gives N-alkyl-(usually A-methyl) lactams. 

Review of literature Heinrich, P., Methoden der Organischen Chemie, Houben-Weyl-Muller, vol. IV/Sb. p. 891 ff., Thieme Verlag, Stuttgart, 1975 McLafferty-rearrangement of ketones and numerous further classes of compounds see e.g. Rose, M. E., Johnstone, R. A. W. Mass spectrometry for chemists and biochemists, Cambridge University Press, Cambridge, p. 222 ff. (1982)... 

Rearrangement of ketones to amides by heating with sulfur and ammonia or amines (see 1st edition). 

The tert-butoxide-catalyzed [2.3J Wittig rearrangement of ketone 10 has also been reported ... 

When a study of the thermal rearrangement of ketone (32) was undertaken, synthesis of (32) was completed via allylic alcohol (33) in order to ensure efficient cyclisation. Allylic alcohol (33) is best made by regioselective reduction (Chapter 14) of enone (34). 

See Baeyer-Villiger rearrangement of ketones by thallium(3 +), 136 of oximes to amides (Beckmann rearr 136-137... 

N-Methyl nitrones -> N-methylamides (4, 510-511). Details are now available for the rearrangement of ketonic nitrones. ... 

As distinct from the above rearrangements, in the rearrangement of ketones the above complicating factors seem to manifest themselves little if at all. Several examples have established the independence of the reaction rate constant of the acidity function Hq in sulphuric acid of more than 95 % concentration. The basicity of dialkylketones of similar structure is practically identical (for the discussion of ketone basicity see Ref. 

Methyl esters of a-arylalkanoic acids 907 can be prepared by oxidative rearrangement of ketones 906 via a 1,2-aryl shift using iodic acid in methanol in the presence of trimethyl orthoformate and sulfuric acid (Scheme 3.364) [1304]. 

When the fragmenting ion contains a heteroatom, abundant rearrangement ions are often formed in the spectrum via a transition state in which the charge is localized on the heteroatom. The McLafferty rearrangement of ketones may be used to illustrate this process ... 

---