6- pyridine-2-one

In contrast to the 4-hydroxy isomers, the thermally stable 5-hydroxy-THISs add to the C=C bond of cyclopropenylidenes (4. 18, 27. 28). The adducts eliminate carbonyl sulfide, and the strained bond breaks resulting in ring-expansion with formation of pyridin-4-ones. -thiones, or -imines. or 4-alkylidenedihydropvridines (20, X = 0. S.NR. or CRR ) (Scheme 19). 

Pyrazolo[3,4-b]pyridin-4-one, 1,3,6-trimetbyl- C NMR, 5, 332 <75JHC517) Pyrazolo[3,4-b]pyridin-6-one, 1,3,4-trimetbyl- C NMR, 5, 332 <75JHC517) Pyrazolo[l,5-a]pyrimidine electron density, 5, 306 <75CJC119) Pyrazolo[3,4-d]pyrimidine electron density, 5, 306 <58JCS2973, 69CJC1129) Pyrazolo[3,4-d]pyrimidine, 4-amino- C NMR, 5, 310 <58JCS2973) Pyrazolo[4,3- /]pyrimidine electron density, 5, 306 <58JCS2973)... 

Furo[3,4-d]pyridazine-1,4-diones synthesis, 4, 985 Furopyridazines, 4, 984 Furo[2,3-6]pyridine, 3-amino-synthesis, 4, 977 Furo[2,3-6]pyridine, 4-methyl-synthesis, 4, 976 Furo[2,3-6]pyridine, 6-methyl-synthesis, 4, 976 Furo[2,3-6]pyridine, 5-nitro-synthesis, 4, 977 Furo[3,2-c]pyridine, 4-allyl-synthesis, 4, 982 Furopyri dines H NMR, 4, 983 physical data, 4, 983 properties, 4, 982 synthesis, 4, 974-982 UV spectroscopy, 4, 983 Furo[6]pyri dines HMO data, 4, 975 Furo[2,3-6]pyri dines synthesis, 4, 974-977 7, 512 Furo[3,2-6]pyri dines C NMR, 4, 982 synthesis, 4, 648, 981 Furo[c]pyri dines HMO data, 4, 976 Furo[2,3-c]pyri dines synthesis, 4, 977 Furo[3,2-c]pyri dines nitration, 4, 983 synthesis, 4, 978-981 Furo[3,4-c]pyri dines synthesis, 4, 982 Furo[3,2-c]pyridin-3-ols synthesis, 4, 980 Furo[2,3-6]pyridin-6-ones synthesis, 4, 976 Furo[3,4-c]pyridin-4-ones synthesis, 4, 982... 

Pyridin-3-one, 3-cyano-6-hydroxy-4-methyl-azo dyes from, 1, 331 Pyridin-4-one, 2-amino-synthesis... 

Pyridin-4-one, 3,5-dichloro-2,6-dimethyl-tautomerism, 2, 111 Pyridin-4-one, 1,4-dihydro-polymers, 1, 297 Pyridin-4-one, 2-dimethylamino-synthesis, 2, 419... 

Pyridin-4-one, 1 -hydroxy-2,6-dimethyl-hydrogen-deuterium exchange reactions, 2, 196 Pyridin-4-one, 1-methyl-hydrogen-deuterium exchange, 2, 287 pK 2, 150 Pyridin-2-one imine tautomerism, 2, 158 Pyridin-2-one imine, 1-methyl-quaternization, 4, 503 Pyridin-4-one imine tautomerism, 2, 158 Pyridinone methides, 2, 331 tautomerism, 2, 158 Pyridinones acylation, 2, 352 alkylation, 2, 349 aromaticity, 2, 148 association... 

H-Pyrrolo[3,2-6]pyridin-2( 1 H)-ones synthesis, 6, 630 1 H-Pyrrolo[3,2-c]pyridin-4-ones synthesis, 4, 277... 

Thieno[3,2-c]pyridine-4(5H)-thione, 6,7-dihydro-synthesis, 4, 762 Thieno[2,3-c]pyridin-4-ones synthesis, 4, 1007, 1008 Thieno[2,3-c]pyridin-7-ones synthesis, 4, 1007 Thieno[3,2-c]pyridin-7-ones synthesis, 4, 1007... 

Pyridin-4-ones, from 5-hydroxy-THISs. 10 Pyridin-4-thiones, from 5-hydroxy-THISs. 

More versatile seemed the synthesis of 2,3-dihydro-lH-pyridin-4-ones 176, that starts from the acrylic /3-ketoester 174 (Scheme 63). This product, pre-... 

Another method much used in elucidation of these equilibria involves comparison of the pKn of the compound under investigation with those of the model methylated derivatives. Scheme 3 illustrates the situation for pyridin-4-one. Consideration of the various equilibria allow equations (6)—(8) to be written. 

In an important application of this method, Katritzky and coworkers (67JCS(B)758, 68JCS(B)556) have attempted to estimate the influence of substituent effects on the tautomeric equilibrium of pyridin-4-one. They utilized equation (8) in the form of equation (11), by considering the pjRTa values of the appropriate methylated model compounds in water. 

The influences at work on these interactions have been discussed in two important papers (80JOC1347, 80JOC1354). It is found that influences of media can be expressed in terms of two effects, differential stabilization of the different dipoles of the two tautomeric species by the dielectric constant of the medium, the dipole reaction field and by differential hydrogen bonding. For self-association pyridin-4-one is shown to form oligomers, in contrast to the well-known dimerization of pyridin-2-ones. This self-association can shift the position of apparent tautomeric equilibrium (hence the warnings previously noted about effect of concentration on Kr). 

In line with Beak s finding, pyridin-2-one was estimated to be 31 kJ mol-1 less aromatic than the pyridine, and a similar figure of 25 was estimated for pyridine-2-thione. Subsequent results (73JCS(P2)1080, 76AHC(S1)71) on the pyridin-4-one, quinolin-2-one and isoquinolin-1-one series showed that aromatic resonance energy difference for the pyridin-4-one/4-hydroxypyridine system was very similar to that for the 2-substituted compounds, in contrast to Beak s findings. 

The aromatic energy differences between the aminopyridine and pyridinone imine form (jE yridine -Epyridineimine) can be found as detailed previously (see Section 2.04.4.2) (72JCS(P2)1295). The pyridinone imine form retains much aromaticity, but less so than in the case of the oxygen compounds, as can be seen from the following figures for the above quantity 2-aminopyridine/pyridin-2-one imine, 42 4-aminopyridine/pyridin-4-one imine, 61 2-aminoquinoline/quinolin-2-one imine, 21 1-aminoisoquinolinone/isoquinolin-l-one imine, 26 kJ mol-1. 

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