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Free radical 4‐nitrophenylation of thieno[2,3‐ b ]pyridine. Part 2: Isolation and structural studies of three samples of mono (4‐nitrophenyl) products; relative yields of the five possible isomers
Author(s) -
Klemm Leroy H.,
Weakley Timothy J. R.,
Gilbertson Robert D.
Publication year - 2001
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.5570380128
Subject(s) - chemistry , pyridine , ternary operation , orange (colour) , nmr spectra database , stereochemistry , spectral line , crystallography , medicinal chemistry , physics , food science , astronomy , computer science , programming language
From the crude mixtures of isomeric 4‐nitrophenylthieno[2,3‐ b ]pyridines ( 3 ) previously reported [1] were isolated three analytically pure samples, viz. the 2‐isomer (yellow needles, mp 258°, 3a ), the 6‐isomer (red prisms, mp 182°, 3e ), and a ternary mixture of the 2‐, 3‐, and 4‐isomers (orange needles, mp 213°, 3a:3b:3c = 1.3:1.0:0.5). The 258° compound was identified as either 3a or 3b by its 1 H nmr spectrum and definitively as the former by its x‐ray crystallographic analysis. The isomeric identities of the 182° and 213° samples were established from their 1 H nmr spectra only. No 5‐isomer ( 3d ) was identified. Semi‐quantitatively, relative isomeric yields fit the pattern 2‐ (64%)>>6‐ (14%)≥3‐ (12%)>4‐ (6%)≥5‐(≤4%). Crystallographic data for 3a are presented.