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

✍ Scribed by Leroy H. Klemm; Timothy J. R. Weakley; Robert D. Gilbertson

• Publisher: Journal of Heterocyclic Chemistry
• Year: 2001
• Tongue: English
• Weight: 53 KB
• Volume: 38
• Category: Article
• ISSN: 0022-152X
• DOI: 10.1002/jhet.5570380128

✦ Synopsis

Abstract

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.