Pyridine-substituted hydroxythiophenes. I. Preparation of o-(2-, 3- and 4-pyridyl)-3-hydroxythiophenes.
2-(2-, 3- and 4-pyridyl)-3-hydroxythiophenes and 4-(2-, 3- and 4-pyridyl)- 3-hydroxythiophenes have been prepared by hydrogen peroxide oxidation of the corresponding boronic esters. In the former case the boronic esters were obtained in three steps from 2,3-dibromothiophene via the corresponding 3-bromo-2-pyridylthiophenes synthesized by Pd(0)-catalyzed coupling between 3-bromo-2-trimethylstannylthiophene and the corresponding bromopyridines. In the latter case the known isomeric pyridylthiophenes were converted into the corresponding boronic esters in three steps via tribromo- and 3-bromo-4-pyridylthiophenes successively. 4-(3- and 4-pyridyl) thiophen-2(5H)-ones were also obtained in the syntheses of 4-(3- and 4-pyridyl)-3-hydroxythiophene. They are suggested to arise from rearrangement during the halogen-metal exchange. Spectroscopic investigations by 1H NMR and IR show that these hydroxythiophene systems exist exclusively as enol forms.
Gronowitz
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S
Organic Chemistry 1, University of Lund, Sweden.
Zhang
Y
Y
Hörnfeldt
A B
AB
D006861:Hydrogen Peroxide; D006900:Hydroxylation; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011725:Pyridines / Q000138:chemical synthesis / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D013876:Thiophenes / Q000138:chemical synthesis* / Q000737:chemistry
D011725:Pyridines; D013876:Thiophenes; D006861:Hydrogen Peroxide