Photolysis of methyl [6-2H]2-pyridylacetate. Selective distribution of deuterium labelling

Abstract

Photolysis of methyl [6-²H] 2-pyridylacetate (I) gave ring-deuteriated methyl anthranilate (II) in 20% yield together with recovered methyl 2-pyridylacetate (III)(6%). The isolated anthranilates were found by n.m.r. spectroscopy to contain approximately equal amounts of [4-²H]-(IV)(40–45%) and [6-²H]-isomers (V)(35–40%) with small amounts of the other two deuteriated positional isomers (20–10%). The recovered methyl 2-pyridylacetate (III) contains ca. 90% of the original deuterium at the 6-position. The labelling patterns are in accord with the formation of a diradical intermediate involving scission of the N (1)–C(6) bond of the pyridine ring and bond formation between C(4 or 6) and (7).