Bridgehead tertiary amine

The evidence for this mechanism includes the facts that nitrous oxide is a product (formed by 2 HNO —y H2O + N2O) and that quinuclidine, where the nitrogen is at a bridgehead, and therefore caruiot give elimination, does not react. Tertiary amines have also been converted to nitrosamines with nitric acid in Ac20 and with... 

Smaller macrobicycles and macrotricycles bearing less that six N-donors are also known. These ligands comprise tertiary or secondary amines and are derived from insertion of one or more straps between pairs of potentially bridgehead N-donors contained within a small ring macrocycle, and in this sense they may be considered analogs of the well-known azacryptands. The inability to offer six N-donors, and the presence of tertiary amines in these ligands leads to the preference for divalent over trivalent Co. 

A parallel library of optically active bicyclic tertiary amines 127 bearing N-chiral bridgehead nitrogen atoms was readily prepared by condensation of primary amines, cyclic amino acids 126, and aldehydes. This method gives access to a large variety of substituted hexahydro-l/7-pyrrolo[l,2-/ ]imidazol-l-ones of type 127 (Scheme 16). These... 

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. 

Some bridgehead amines [l,4-diazabicyclo-[2,2,2]octane (102), quinuclidine (103) and quinuclidine-3-ol] form 1 1 molecular complexes with quinones 104. Formation of 2 1 (amine/quinone) complexes was observed in solutions of DABCO (102) and chloranil (104, R = Cl). These tertiary amines are able to form complexes, while non-bridgehead amines (triethylamine, piperidine) cannot because of steric hindrance or nitrogen inversion183. Stable complexes may be predicted (by CNDO/2 calculations) for... 

It was from the study of the environment of the second nitrogen of aj maline that its unusual nature first became apparent. It was a carbinol-amine which had the nitrogen at a bridgehead hence it could not be converted into an iminium cation so that it showed many of the normal reactions of a tertiary amine and an unhindered alcoholic group. Other reactions were better interpreted as taking place via the ring-opened tautomeric amino aldehyde which we shall call cfomoajmaline. It should be mentioned here that ajmaline methiodide exists in the closed form at least in the solid state, since its Ilt-spectrum in a nujol dispersion con-... 

Consideration of the chemical properties of quinuclidine derivatives led to the conclusion that this type of compound was characterized both by the presence of unshielded free lone pair electrons attached to the bridgehead nitrogen atom and by the specific conformation of the molecule. In contrast to aliphatic tertiary amines and iV-substituted piperidines quinuclidine has a rigidly fixed structure, each of the two rings in the structure having a bath form. 

Much of the chemistry of strychnine is a consequence of two factors, the environment of the bridgehead basic nitrogen which makes it different from a simple tertiary amine and the possibility of base induced reactions made possible by the lactam carbonyl in ring G. For a proper understanding of strychnine chemistry its topology must be remembered. From a theoretical point of view... 

The stoichiometric enantioselective reaction of alkenes and osmium tetroxide was reported in 1980 by Hentges and Sharpless [17], As pyridine was known to accelerate the reaction, initial efforts concentrated on the use of pyridine substituted with chiral groups, such as /-2-(2-menthyl)pyridine but e.e. s were below 18%. Besides, it was found that complexation was weak between pyridine and osmium. Griffith and coworkers reported that tertiary bridgehead amines, such as quinuclidine, formed much more stable complexes and this led Sharpless and coworkers to test this ligand type for the reaction of 0s04 and prochiral alkenes. 

Oxyaminatkm.1 The ratio of amino alcohol to diol formed by reaction of alkenes with the reagent is considerably improved by the presence of tertiary alkyl bridgehead amines. Of these ligands, quinuclidine (I, 976 4, 417) is the most efficient. In this case DME is used in place of pyridine as solvent. 

Quinuclidine (1) is a saturated bicyclic system with a bridgehead nitrogen atom. It has, in contrast to tertiary aliphatic amines and -substituted piperidines, a rigid structure. The atoms forming the quinuclidine ring are incapable of changing their relative positions by rotation around bond axes. These bond axes are included in the bicyclic system with each ring in the boat form. 

Apart from the normal reactions of tertiary aliphatic amines, in-dolizidines undergo reactions at the carbon atoms adjacent to the nitrogen, and particularly at the bridgehead carbon. 

Another formamidine which allows facile removal of hindered tertiary hydrogens has been recmdy introduced (equation 27). The bridgehead position of a tricyclic amine has also been alkylated in good yields via the t-butylformamidine. ... 

Note that the tertiary bridgehead nitrogen atom is not protonated because its basicity is reduced dramatically as a consequence of its proximity to the protonated secondary amines in each case. 

The quinuclidine molecule is a saturated bicyclic system having a bridgehead nitrogen atom [1-3]. In contrast to tertiary aliphatic amines and AT-sub-... 

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