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Furopyridines. II. Bromination and nitration of furo[2,3‐ b ]‐, furo[3,2‐ b ]‐, furo[2,3‐ c ]‐ and furo[3,2‐ c ]pyridine
Author(s) -
Shiotani Shunsaku,
Morita Hiroyuki,
Inoue Masatoshi,
Ishida Toshimasa,
Iitaka Yoichi,
Itai Akiko
Publication year - 1984
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570210319
Subject(s) - nitration , chemistry , acetic anhydride , halogenation , derivative (finance) , acetic acid , pyridine , sulfuric acid , sodium hydroxide , nitric acid , methanol , medicinal chemistry , organic chemistry , sodium acetate , catalysis , financial economics , economics
In order to reveal the reactivities of furopyridines, we undertook bromination and nitration of four furopyridines ( 1, 2, 3 and 4 ) whose chemical properties had been almost unknown. Bromination of 1, 2, 3 and 4 gave the corresponding trans ‐2,3‐dibromo‐2,3‐dihydro derivatives 6, 8, 10 and 12 , respectively, which were converted to 3‐bromofuropyridines 7, 9, 11 and 13 by treatment with sodium hydroxide in aqueous methanol. Nitration of 1 with a mixture of fuming nitric acid and sulfuric acid afforded a mixture of addition products 14a, 14b and 14c and 2‐nitro derivative 15 . Both 14a and 14b were easily converted to 15 by treatment with sodium bicarbonate. Compound 2 was nitrated to give a mixture of cis ‐ and trans ‐2‐nitro‐3‐hydroxy‐2,3‐dihydro derivative 16a and 16b and 2‐nitro derivative 17 . The cis isomer 16a was transformed to the trans isomer 16b by refluxing on silica gel in ethyl acetate. Compound 16b was dehydrated with acetic anhydride to give 17 . Nitration of 3 gave a nitrolic acid derivative 20 . Nitration of 4 gave a mixture of 2‐nitro derivative 22 and 3‐(trinitromethyl)pyridin‐4‐ol ( 23 ). The structures of 20 and 23 were established by single crystal X‐ray analysis. The differences of behavior observed in these reactions are discussed in connection with the results of the determination of p K a values and the relative reactivities of deuteriodeprotonation of these furopyridines.