2(1H)‐Pyridones and ‐thiones related to 1‐substituted nicotinic acid derivatives have been prepared via the corresponding l‐substituted‐3‐formyl‐2(1H)‐pyridones and ‐thiones. A number of synthetic procedures for the interconversion of functional groups in these nicotinic acid derivatives are given i.e. preparation of the aldoximes, nitriles, carboxamides and carboxylic acids as well as the 3‐ hydroxyalkyl derivatives. The course of the basic peroxide oxidation of the l‐substituted‐3‐formyl‐2(1H)‐pyridinethiones is found to be very dependent upon the electronegativity of the 1‐substituent. A preparation of ricinidine is also described.
Aldol condensation of 3‐formyl‐2(1H)‐pyridinethiones and the corresponding pyridones with ketones such as acetophenones in aqueous base yields 3‐hydroxy‐1‐propanones in high yields. Reaction with propiophenone showed this reaction to be highly diastereoselective as only the erythro‐isomer is formed at room temperature. This assignment was based on an X‐ray crystallographic investigation of the compound given in the title. Aldol condensations of a number of related 3‐acetyl‐2(1H)‐pyridinethiones with benzaldehyde yielded the corresponding trans‐vinyl ketones.
Zunächst wird die Aldol‐Kondensation zwischen den 3‐Formyl‐pyridin‐ Derivaten (I) und den Ketonen (II) hinsichtlich der Stereochemie der gebildeten Alkohole (III) bzw. (IV) untersucht; mit (IIb) werden ausschließlich die erythro‐Isomere (IV) gebildet.
Aus dem Thiopyridon‐3‐aldehyd (I) erhält man in bekannter Weise das Pyrido‐isothiazol (II), das mit Methylat zum Nitril (IIIa) gespalten und dann in die Derivate (IIIb) und (IIIc) übergeführt wird.
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