Nitrogen prevention

The reductive coupling of of dienes containing amine groups in the backbones allows for the production of alkaloid skeletons in relatively few steps [36,46,47]. Epilupinine 80 was formed in 51% yield after oxidation by treatment of the tertiary amine 81 with PhMeSiEh in the presence of catalytic 70 [46]. Notably, none of the trans isomer was observed in the product mixture (Eq. 11). The Cp fuMcTIIF was found to catalyze cyclization of unsubstituted allyl amine 82 to provide 83. This reaction proceeded in shorter time and with increased yield relative to the same reaction with 70 (Eq. 12) [47]. Substitution of either alkene prevented cyclization, possibly due to competitive intramolecular stabilization of the metal by nitrogen preventing coordination of the substituted olefin, and resulted in hydrosilylation of the less substituted olefin. 

This result may be explained by carbanion destabilization by the nitrogen preventing the alternative nucleophilic attack at the / -carbon atom of the multiple bond as shown below for the case of the six-membered heterocycle. 

C3-quatemised 3-prenyl indolenines are accessible in an enantioselective manner by Pd-catalysed 3-allylation of 3-prenylindoles, as reported by Trost and Quancard in 2006 (Scheme 28) [122]. In addition to the Pd-source and the anthracene-derived chiral ligand 139, an optimised bulky tertiary borane (9-BBN-CgHi3) is added, which coordinates to the indole nitrogen, prevents N-allylation and also enhances the enantioselectivity of the reaction. The reaction from 138 to 140 is especially suitable for electron-rich indoles and could be tried with prenol as allylic alcohol. 

If an ortho-substituted benzene ring is attached to the nitrogen, the self-condensation is minimized due to steric hindrance and the yield of imidoyl chlorides increases in this order CH3 < Cl < Br ( ). Likewise, lowering of the basicity of the nitrogen prevents condensation. For example, N-sulfonimidoyl chlorides of aliphatic carboxylic acids are obtained in excellent yield ( ). The carboxylic acid amides of a,j8-unsaturated acids also do not undergo tautomerization, because the formation of allenes is not favored under mild conditions... 

It has been known for many years that GABA levels in the brain rise rapidly after death (Baxter, 1972 Lovell et al., 1963 Shaw and Heine, 1965, Minard and Mushahwar, 1966, Shank and Aprison 1971). Levels of other amino acids are modified postmortem, but not to the same extent as GABA (Perry et al., 1981). Decapitation into liquid nitrogen prevents the postmortem rise in GABA, how-... 

Edidin A. A., J. Muth, S. Spiegelberg, and S.R. Schaffner. 2000. Sterilization of UHMWPE in nitrogen prevents oxidative degradation for more than ten years. Transactions of the 46th Orthopaedic Research Society 25 1. 

In the aromatic series, Nagy and Takacs-Novak [49] pointed out both theoretically and experimentally that the 3- and 4-COOH pyridine carboxylic acids (nicotinic and isonicotinic acids) form the zwitterionic species in aqueous solution. The distances of the -COOH groups from the pyridine nitrogens prevent the formation of a favorable dimeric form (except for the 3-COOH isomer with and anti carboxylic conformation) where a double-proton-relay... 

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