[Ring cleavage of N-arylpyridinium salts by nucleophiles--regioselectivity and stereochemistry of the products. 2].

Abstract

The reaction of quaternary 3-pyridinecarboxamide compounds 2, 7 and 14 with alkali does not--contrary to literature--result in regiospecific ring opening, but yields mixtures of position isomer penta-2,4-dienal derivatives. With increasing steric hindrance by the 3-substituent, the hydroxide ion prefers the attack at 6-position. Usually products with all trans configuration are obtained. Only the 2-substituted aldehydes from 2 and 14 additionally occur in the 2,3-cis configuration as 5b and 21b, explainable by a hydrogen bond between the formyl and carbamoyl group. Surprisingly the "ring opened" 5-aminopenta-2,4-dienals 5 and 6 resp. 21 and 22 in acetone solution show an equilibrium of the positional isomers in each case, which must be generated by recyclization via the intermediates 24 resp. 25. With hydroxylamine 2, 7 and 14 only react to the 4-substituted pentadienal derivatives, which represent E,Z oxime mixtures. This is proved by dehydration to uniform nitriles and the synthesis from the corresponding aldehydes by oximation.

• Authors: H Möhrle, R Niessen
• Journal: Die Pharmazie (Pharmazie) Vol. 56 Issue 6 Pg. 448-57 (Jun 2001) ISSN: 0031-7144 [Print] Germany
• Vernacular Title: Ringöffnung von N-Arylpyridiniumsalzen durch Nucleophile--Regioselektivität und Stereochemie der Produkte--2. Mitt.
• PMID: 11446163 (Publication Type: English Abstract, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Aldehydes
• Hydroxylamines
• Indicators and Reagents
• Pyridinium Compounds

Topics

• Aldehydes
• Cyclization
• Hydrogen Bonding
• Hydrogen-Ion Concentration
• Hydroxylamines
• Indicators and Reagents
• Magnetic Resonance Spectroscopy
• Molecular Conformation
• Pyridinium Compounds (chemistry)
• Spectrophotometry, Ultraviolet