Amines interconversions

The position of the equilibrium (equation 65) depends upon the nature of X, and the intramolecular hydrogen atom transfer can be monitored by H NMR magnetization transfer. This provides a model for the generalized imide-amide-amine interconversion by proton transfer. 

Owing to the reversible nature of the allylic sulfenate/allylic sulfoxide interconversion, the stereochemical outcome of both processes is treated below in an integrated manner. However, before beginning the discussion of this subject it is important to point out that although the allylic sulfoxide-sulfenate rearrangement is reversible, and although the sulfenate ester is usually in low equilibrium concentration with the isomeric sulfoxide, desulfurization of the sulfenate by thiophilic interception using various nucleophiles, such as thiophenoxide or secondary amines, removes it from equilibrium, and provides a useful route to allylic alcohols (equation 11). 

The chemical meaning of these mathematical equations is that the rate law is first order with respect to the amine base for each reaction (i.e. interconversion of la and Ih and hydrogen bromide elimination). 

The different reactivity mentioned above also proves the validity of inequality ki, k3> >k4 used in the simplification of our model. On the contrary, in the presence of CHA less than one equivalent the signals of both the la and Ih appear, a large extent of deuteration at C-3 is observed both in the cis and tram isomers and in the product flavone (2). Using an excess of amine both isomer gave 2 deuterated at C-3 to an extent ca. 80-85 %. Considering the kinetic profile of the interconversion we conclude that it takes place via an enolate where the rate determining step is the deprotonation at C-3. 

R = H, X = S, A = Et3N and Py). In solution the former is mainly in an ionic form the latter exists as a complex. The basicity of the amine is assumed to be important. Triethylamine is a stronger base than pyridine and the ionic form is stabilized. When the proton affinity is weak, the basicity in relation to the B(III) atom, a Lewis acid, plays an important role. This involves an equilibrium shift toward the complex. This assumption is confirmed by an easy displacement of pyridine by triethylamine. The reverse process demands more severe conditions. In the NMR spectra of the triethylamine complex the signal is shifted from 22 to 42 ppm as pyridine is added. The absence of signals of two separate forms is evidence in favor of their fast interconversion. The chemical shift of the signal in 3IP spectra is 22 ppm (EtOH), 26 ppm (Py, DMFA), and 42 ppm (EtOH, Py) for complexes with triethylamine and pyridine. 

The residue so obtained is immediately placed in solution with methanolic potassium hydroxide to effect interconversion of the stereoisomers. Amination and Transposition will proceed simultaneously, the first batch being transposed while the second is aminated. 

Fourth, the salt concentration in cheese also influences the production of biogenic amines (Kebary et al., 1999 Joosten, 1988). Gouda cheese contains 3.5 mmol histamine per kg with a salt water ratio of 0.048, and 2.1 mmol histamine with a salt water ratio of 0.026 (Joosten, 1988). Each cheese has its own characteristic free amino acid and biogenic amine profiles, resulting from its specific degradation, interconversion, and synthesis (Polo et al., 1985). 

There is a distinct relationship between keto-enol tautomerism and the iminium-enamine interconversion it can be seen from the above scheme that enamines are actually nitrogen analogues of enols. Their chemical properties reflect this relationship. It also leads us to another reason why enamine formation is a property of secondary amines, whereas primary amines give imines with aldehydes and ketones (see Section 7.7.1). Enamines from primary amines would undergo rapid conversion into the more stable imine tautomers (compare enol and keto tautomers) this isomerization cannot occur with enamines from secondary amines, and such enamines are, therefore, stable. 

This enzyme [EC 5.1.3.9], also known as A -acetylglucos-amine-6-phosphate 2-epimerase, catalyzes the interconversion of A -acylglucosamine 6-phosphate to A -acyl-mannosamine 6-phosphate. 

This enzyme [EC 5.4.2.S], also known as acetylglucos-amine phosphomutase and A -acetylglucosamine-phos-phate mutase, catalyzes the interconversion of M-acetyl-D-glucosamine 1-phosphate and A -acetyl-o-glucosamine 6-phosphate. The enzyme is activated by A -acetyl-o-glu-cosamine 1,6-bisphosphate. 

An effect observed with a number of compounds which have apparent chiral centers on elements other than carbon. Eor example, secondary and tertiary amines have a pyramidal structure in which the unshared pair of electrons is at the top of the pyramid. If the three substituents hnked to the nitrogen are all different, one might suspect that the tertiary amine would give rise to optical activity and be resolvable. However, rapid oscillation of the unshared pair of electrons on one side of the nitrogen to the other (hence, pyramidal inversion) in effect causes interconversion of the two enantiomers and prevents resolution. If the nitrogen is at a bridgehead, this umbrella effect is inhibited and optical isomers can be isolated. 

Non-geminal bis, tris, and tetrakis secondary amino derivatives are found to undergo reversible cis trans isomerisations in the presence of amine hydrochlorides [141-145]. It is reported that aluminium trichloride also acts as a catalyst for these interconversions (Eq. 26) [142]. 

In 2002, Winter and coworkers reported that aminoallenylidene complexes trans-[Cl(dppm)2Ru=C=C=C(NRR )(CH3)] were obtained from the regioselective addition of secondary amines to frans-[Cl(dppm)2Ru=C=C=C=CH2] [133]. They also found that unsymmetrically substituted amines gave rise to Z/E isomeric mixtures. To study the Z/E isomeric interconversion, they calculated the rotational barrier around the C—N bond of the model complex shown in Scheme 4.23. The orthogonal... 

The only four- - six-membered ring interconversions of any real synthetic significance are those involving diketene. Base-catalyzed dimerization of diketene is a long-established and efficient method for the preparation of dehydroacetic acid (equation 161), while mild treatment with water in the presence of tertiary amine bases gives 2,6-dimethyl-4-pyrone (equation 162). 1,3-Dioxins are obtained from the acid-catalyzed condensation of diketene with ketones (equation 163). 

Related to the above are the reactions of pyridinium ions with nucleophiles. It has been known for many years that pyridinium ions can undergo ring-opening reactions with primary amines (70JA5641). Studies on the mechanisms of these reactions indicate that the interconversion of the dihydropyridine (48) with the acyclic dianils (49) of glutacondialdehyde is a key step in these reactions. 

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