Photoisomerization of 4-pyridones to 2-pyridones

1‐Methoxycarbonyl‐substituiertes 2,3‐Dihydropyridin‐4(1H)‐on (= Methyl‐1,2,3,4‐tetrahydro‐4‐oxopyridin‐1‐carboxylat) als Chromophor für die photochemische [2 + 2]‐Cycloaddition

“…3 ) Methyl-1,2,3,4-tetrahydro-4 1-(4-Benzoylbenzoyl)-2,3-dihydropyridin-4(1H)-on (29). 1-(4-Benzoylbenzoyl)piperidin-4-on-ethylenmetal (26). Eine Lsg.…”

“…zu transoid-1,2-cis-2-8-azatricyclo[5.4.O.O2~6]undecan-8-curboxylat (158). DC M+), 222 (86), 206 (lo), 192 (14), 180 (15), 156 (IOO), 155 (66), 154 (37), 140 (lo), 121 (26), 107 (12), 91 (42).…”

Substituent effect on selectivity in photoisomerization of 4-pyrones and 4-pyridones

“…Mass spectra of the photoproduct obtained at low voltage bombardment were particularly relevant to determine which substituent (either the phenyl or para-substituted phenyl group) is located on C-6 of the 2-pyrone ring, because the favorable fragmentation of 2-pyrones involves loss of the substituent at C-6 of the 2-pyrone ring as acyl radical from the fragment ion [M -CO]+.12•13 Their mass spectra are sum-marized in Table I. At the low bombarding electron energies (15-30 eV) the presence of the fragment ion corresponding to [M -CO -Ph]+ indicates the presence of the phenyl group at C-6, whereas the formation of fragment ion corresponding (3), 105 (8) mb 65636-02-4 30 295 (5), 294 (M+, 29), 267 (15), 266 (100), 258 (9), 161 (13), 143 (5), 105 (21) IVb 65636-03-5 30 295 (4), 294 (M+, 26), 267 (16), 266 (100), 161 (3), 143 (19), 105 (5) IIIc 65636-04-6 24 312 (16), 311 (9), 310 (M+, 46), 285 (7), 284 (33), 283 (21), 282 (100), 179 (4), 177 (13), 143 (2), 105 Br 32°VUId/VIId = 3.0 a The prolonged irradiation decreased yield because of formation of a tarry material. b Estimated maximum analytical error was within 5% except for that in lb and lib ranging ±9%.c Although pure IVa was not isolated, the 220 MHz NMR spectra of the isomeric mixture showed the different chemical shift for the methyl protons and the integration then gave the relative ratio of the isomers.…”