Rearrangements of quinolizinium-1-diazonium salts and related reactions

Abstract

The methods of synthesis and known properties of aminoquinolizinium compounds are reviewed.
A number of 1-aminoquinolizinium salts when treated
with aqueous nitrous acid undergo rearrangement. Investigation by degradation and synthesis showed the initial products are cis-3-(v-triazolo[l,S-a]pyridyl)acraldehydes. These are rapidly isomerised to the trans-isomers. The mechanism of the rearrangement is discussed and the synthesis and properties of other v-triazolo[l,5-a]pyridines are reviewed.
The thermal isomerisation and decomposition of
3-(v-triazolo[l,5-a]pyridyl)acraldehydes to 5-(2-pyridyl)­pyrazoles is reported and a mechanism for the rearrangement is suggested.
In the last section the photochemistry of a,B-unsaturated carbonyl compounds is briefly reviewed. The photochemical con­version of some heterocyclic acraldehydes to derivatives of propionic acid is described. Some limitations of the reaction
are reported and a mechanism proposed, support for which is provided by studies on suitably deuterium labelled compounds.