Critical assessment of two classical synthetic methods for preparation of thiophene-substituted isoxazoles

Critical assessment of two classical synthetic methods for preparation of thiophene-substituted... Formation of thiophene-substituted isoxazoles by reaction of chalcone dibromides and 1,3-diketones with hydroxylamine hydrochloride has been examined under different conditions. Use of KOH as base in the reaction of dibromide chalcone analogs with hydroxylamine hydrochloride yields mixtures of isomeric isoxazoles in modest yields. Replacement of KOH with pyridine affords negligible amounts of isoxazoles only, the intermediate 2-bromoprop-2-en-1-one being isolated from the reaction as the major product. Substitution of the β-bromine atom from a chalcone dibromides with a methoxy group by solvolysis occurred when no base was used. Mixtures of isomeric isoxazoles in which the isoxazole that had a 2-thienyl group at position 5 were always major components, were obtained in good yields from reaction of thiophene-containing 1,3-diketones with hydroxylamine hydrochloride, irrespective of reaction pH. At low pH, regioselectivity was poorer than that observed for reaction of chalcone dibromides with hydroxylamine hydrochloride, but yields were substantially better. At high pH, yields were comparable with those at low pH and regioselectivity for 3-aryl-5-(2-thiophenyl)isoxazole was slightly enhanced, but the dioxime corresponding to the initial 1,3-diketone was also produced in low yields as a mixture of stereoisomers. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Research on Chemical Intermediates Springer Journals

Critical assessment of two classical synthetic methods for preparation of thiophene-substituted isoxazoles

Loading next page...
 
/lp/springer_journal/critical-assessment-of-two-classical-synthetic-methods-for-preparation-IoxPVMOWHw
Publisher
Springer Netherlands
Copyright
Copyright © 2013 by Springer Science+Business Media Dordrecht
Subject
Chemistry; Catalysis; Physical Chemistry; Inorganic Chemistry
ISSN
0922-6168
eISSN
1568-5675
D.O.I.
10.1007/s11164-013-1101-8
Publisher site
See Article on Publisher Site

Abstract

Formation of thiophene-substituted isoxazoles by reaction of chalcone dibromides and 1,3-diketones with hydroxylamine hydrochloride has been examined under different conditions. Use of KOH as base in the reaction of dibromide chalcone analogs with hydroxylamine hydrochloride yields mixtures of isomeric isoxazoles in modest yields. Replacement of KOH with pyridine affords negligible amounts of isoxazoles only, the intermediate 2-bromoprop-2-en-1-one being isolated from the reaction as the major product. Substitution of the β-bromine atom from a chalcone dibromides with a methoxy group by solvolysis occurred when no base was used. Mixtures of isomeric isoxazoles in which the isoxazole that had a 2-thienyl group at position 5 were always major components, were obtained in good yields from reaction of thiophene-containing 1,3-diketones with hydroxylamine hydrochloride, irrespective of reaction pH. At low pH, regioselectivity was poorer than that observed for reaction of chalcone dibromides with hydroxylamine hydrochloride, but yields were substantially better. At high pH, yields were comparable with those at low pH and regioselectivity for 3-aryl-5-(2-thiophenyl)isoxazole was slightly enhanced, but the dioxime corresponding to the initial 1,3-diketone was also produced in low yields as a mixture of stereoisomers.

Journal

Research on Chemical IntermediatesSpringer Journals

Published: Feb 23, 2013

References

You’re reading a free preview. Subscribe to read the entire article.


DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Search

Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly

Organize

Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.

Access

Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

DeepDyve

Freelancer

DeepDyve

Pro

Price

FREE

$49/month
$360/year

Save searches from
Google Scholar,
PubMed

Create lists to
organize your research

Export lists, citations

Read DeepDyve articles

Abstract access only

Unlimited access to over
18 million full-text articles

Print

20 pages / month

PDF Discount

20% off