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Synthesis of dihydrothieno[2,3-b]pyridines based on titanium(IV) chloride-mediated michael reactions of 2-amino-4,5-dihydro-3-thiophenecarbonitriles with α,β-unsaturated ketones

✍ Scribed by Hiroshi Maruoka; Motoyoshi Yamazaki; Yukihiko Tomioka

Publisher: Journal of Heterocyclic Chemistry
Year: 2004
Tongue: English
Weight: 170 KB
Volume: 41
Category: Article
ISSN: 0022-152X
DOI: 10.1002/jhet.5570410428

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✦ Synopsis

Abstract

2‐Arnino‐4,5‐dihydro‐3‐thiophenecarbonitriles 1a‐c reacted with α,β‐unsaturated ketones (e.g. methyl vinyl ketone 2 and benzalacetone 3) in the presence of titanium(IV) chloride to give the corresponding Michael adducts 4a‐c and 5a‐c. Thermal treatment of compounds 4a‐c and 5a‐c with titanium(IV) chloride caused intramolecular cyclocondensation to yield the corresponding tetrahydrothieno[2,3‐b]pyridines 6a‐c and 7a‐c. Aromatization of 6a‐c and 7a‐c with potassium tert‐butoxide in refluxing tert‐butyl alcohol pro ceeded smoothly to afford the corresponding dihydrothieno[2,3‐b]pyridines 8a‐c and 9a‐c.

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