Issue 16, 2006
From the journal:

Organic & Biomolecular Chemistry

Intramolecular 1,3-dipolar cycloadditions of dihydroimidazolium ylides: synthesis of pyrrolo[1,2,3-de]quinoxalines and imidazo[1,2-a]indoles

Pedro M. J. Lory,a   Raymond C. F. Jones,*b   James N. Iley,*a   Simon J. Colesc  and  Michael B. Hursthousec  

* Corresponding authors

a Chemistry Department, The Open University, Walton Hall, Milton Keynes, UK
E-mail: j.n.iley@open.ac.uk
Fax: +44 1908 858327

b Chemistry Department, Loughborough University, Loughborough, Leics, UK
E-mail: r.c.f.jones@lboro.ac.uk
Fax: +44 1509 223926
Tel: +44 1509 222557

c EPSRC National Crystallography Service, School of Chemistry, University of Southampton, Highfield, Southampton, UK

Abstract

N-Alkylation of 4,5-dihydroimidazoles with alkene-containing bromomethyl ketones and treatment of the so-formed 4,5-dihydroimidazolium ions with DBU gives rise to an intramolecular 1,3-dipolar cycloaddition reaction that affords (via a reaction cascade involving eliminative ring-opening, recyclisation and prototropic tautomerism) unexpected hexahydropyrrolo[1,2,3-de]quinoxaline products. Steric bulk in both the dihydroimidazole and the dipolarophile allows isolation of an imidazo[1,2-a]indole, the initial product of cycloaddition. When the bromomethyl ketone contains no other functionality, or when cycloaddition is inhibited due to steric constraints, the dihydroimidazolium ion undergoes ring-opening hydrolysis followed by recyclization of the exposed amino ketone to afford either 3-alkyl-1-formylpiperazine-2-ones or 3-aryl-1-formyl-1,4,5,6-tetrahydropyrazines.

Graphical abstract: Intramolecular 1,3-dipolar cycloadditions of dihydroimidazolium ylides: synthesis of pyrrolo[1,2,3-de]quinoxalines and imidazo[1,2-a]indoles

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Article information

DOI
https://doi.org/10.1039/B605458G
Article type
Paper
Submitted
18 Apr 2006
Accepted
28 Jun 2006
First published
18 Jul 2006

Org. Biomol. Chem., 2006,4, 3155-3165

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Intramolecular 1,3-dipolar cycloadditions of dihydroimidazolium ylides: synthesis of pyrrolo[1,2,3-de]quinoxalines and imidazo[1,2-a]indoles

P. M. J. Lory, R. C. F. Jones, J. N. Iley, S. J. Coles and M. B. Hursthouse, Org. Biomol. Chem., 2006, 4, 3155 DOI: 10.1039/B605458G

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