N-Quaternization

Quaternization is difficult benzofuroxan is unaffected by triethyl-oxonium fluoroborate. With methyl trifluoromethanesulfonate, an interesting rearrangement occurs, and l-hydroxybenzimidazole-3-oxide (39, R = H) is formed, probably via the N-quaternized derivative (38). Compound 39 (R = Ceils) has been prepared similarly. 

O-acylation, O-sulfanylation, O-triflation/Suzuki coupling followed by N-quaternization (six inputs) and Hofmann elimination to release a 3,042-member library of tertiary amino aryls. One advantage of small-molecule nonoligomeric libraries... 

Emphasis is placed on simply substituted free bases. The problems of conformational equilibria in /V-alkylpiperidinium salts and N-quaternization reactions and the relationships of these to conformational equilibria in the free bases are not covered, since this area is a large one requiring separate treatment. In other relevant previous reviews, the topics include heterocyclic conformational analysis,3-7 interactions in azacyclic systems,8 the conformational analysis of piperidine,9 hexahydropyrimidines,10,11 hexahydropyri-dazines,12 quinolizidines,13 the conformational analysis of bi- and polycyclic... 

N-Quaternization and the formation of N-oxides of alkaloids cause strong paramagnetic deshielding effects for the carbon atoms neighboring the nitrogen atom however the carbons located at /(-position usually become more shielded [600, 606, 634, 643],... 

In 2000, Rajanbabu et al. published the synthesis and coordination chemistry of the first chiral NHC containing a l.T-binaphthyl unit as the chiral element (Scheme 24) [69]. It contains two imidazolium rings linked to the l,T-binaphlhyl backbone in the 2 and 2 position through methylene bridges. This linkage was achieved by nucleophilic substitution and the imidazolium salts subsequently generated in an N-quaternization step with methyl iodide. 

Nucleophilic substitution in fused thiazoloazines proceeds with ease in the activated positions in either ring. N-Quaternization further enhances the ease of substitution, especially in the ring which carries the charge. 

The synthesis of AMPHOS, the prototype of cationic phosphines, known for almost 20 years, requires intermediate protection of the phosphorus in Ph2P -(CH2)2 -NMe2 by oxidation or coordination to a transition metal before N-quaternization [99, 100], In the case of the ligands 28a, 28b, and 30, borane was used as the protecting group. 

Compound (41) was prepared from 3-hydroxy-6-methylpyridine by sequential benzylation, N-quaternization with PhCOCHjBr, and intramolecular cyclocondensation <82JCR(S)245>. A series... 

Without additional reagents N-Condensed cyclimmonium salts by cyclo-N-quaternization... 

Sodium alcohol-dimethyl sulfoxide Selective 0-alkylation Prevention of N-quaternization... 

N-Quaternization of weakly basic N-heterocyclics Quaternary ammonium 2,4-dinitrobenzenesulfonates... 

Hydrogen bromide acetic acid N-Quaternized enolesters from eneheterocyclics... 

N-Quaternization (s. a. Ammonium salts, quaternary, Enolesters, N-quaternized,... 

Thiopurinium betaines from 6-chloropurines with preceding preferential N-quaternization... 

Increasing use of dimethylacetamide as a solvent has been noticed Tetramethylenesulfone has been used successfully as a solvent for N-quaternizations. It has a high dielectric constant and does not involve side reactions such as appear with nitrobenzene and dimethylformamide... 

N-quaternization s. under N-Quaternization radical addition 27, 600 reduction of ketones in Grignard syntheses 19, 46 suppl. 26 ring closure, intramolecular 27, 799... 

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