University of York Department of Chemistry

Carbonyl Compounds as Radical Precursors: Approaches to Substituted Furans, Pyrrolidines, Chromanols and Quinolinones.


David Bebbington,a Jon Bentley,a Paul A. Nilssonb and Andrew F. Parsonsb

aVernalis Research Ltd, Oakdene Court, 613 Reading Road, Winnersh, Wokingham RG41 5UA, UK 
bDepartment of Chemistry, University of York, Heslington, York, YO10 5DD, UK

 Paul Nilsson


The use of organotin hydrides (HSnR3) in radical chemistry is well established and is still the most common method for performing radical cyclisations. The tributyltin radical reacts with a variety of functional groups (e.g. halides, alkenes, xanthates, selenides) to generate carbon-centred radicals. However, reaction of the tributyltin radical with carbonyl compounds to generate O-stannyl ketyls, and their application in heterocyclic synthesis, has received much less attention.1

This project has looked at the formation of substituted pyrrolidines utilizing a tributyltin hydride mediated 5-exo-trig radical cyclisation of amino aldehydes (Scheme 1).

Scheme 1
Scheme 1: Substituted pyrrolidine synthesis.
 

The application of this method to substituted furan (and pyran) synthesis has also been investigated (Scheme 2). Both O-stannyl ketyls and allylic O-stannyl ketyls (Scheme 3) have been shown to undergo cyclisation onto electron-rich double bonds.2

Scheme 2
Scheme 2: Radical approaches to hydroxyfurans.
Scheme 3
Scheme 3: Allylic O-stannyl ketyl radicals in substituted furan synthesis.
 

1. E. J. Enholm and G. Prasad, Tetrahedron. Lett., 1989, 30, 4939; E. J. Enholm and J. A. Burroff, Tetrahedron, 1997, 53, 13583; Y.-S. Hon, P.-P. Sun, H.-L. Lu and N.-C. Chang, J. Chin. Chem. Soc., 1994, 41, 445.

2. D. Bebbington, J. Bentley, P. A. Nilsson and A. F. Parsons, Tetrahedron. Lett., 2000, 41, 8941.

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