Abstract
Photolysis of pyridine N -oxide ( 1a ) in aqueous basic solution yields the anion of 5-hydroxypentadienenitrile ( 2a ). Kinetic data are obtained from flash photolytic measurements. The reaction is extended to twenty substituted pyridine N -oxides, including deuterated derivatives, as well as 10 other experimental conditions (amines as the base in organic solvents). The results can be rationalized as involving primary photorearrangement to open-chain nitrene 11 ( τ 63 msec in water for 11a ), which rearranges in low yield to 2-formylpyrrole or undergoes polymerization to tars. In the presence of bases, this intermediate is efficiently deprotonated to anion 2 (k = 690 M -1s -1 for the reaction of 11a with OH -). The relation of this new rearrangement to other photoprocesses of heterocyclic N -oxides is discussed.
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