University of York Department of Chemistry

 

6 Lectures, Module 8
Radicals in Synthesis

For many years the chemistry of radicals was very much the province of mechanistic and physical organic chemists.  More recently the situation has changed and the realisation that radical methods are often compatible with a range of functional groups, without further protection, has led to an increased interest in the use of radicals in synthesis.  The aim of this course is to illustrate how radical reactions have grown in importance to the point where they are now routinely considered in synthetic planning.

The following books may be useful to you:-
"Radical Chemistry: The Fundamentals", M.J. Perkins (Oxford Primer, 2000).
"Reactive Intermediates", C.J. Moody and G.H. Whitham (Oxford, 1992).
"Free Radicals in Organic Chemistry", J. Fossey, D. Lefort and J. Sorba (Wiley-Interscience, 1995).
“An Introduction to Free Radical Chemistry”, A.F. Parsons (Blackwell Science, 2000).

1  Introduction to Radical Chemistry
 (a) Radical detection and observation. (b) Radical stability. (c) Chain reactions. ( Questions 1-3 )

2 Radical Initiation Reactions
(a) Thermolysis. (b) Photolysis. (c) Radiolysis. (d) Electron transfer. ( Questions 4-6 )

3 Main Types of Radical Reaction
(i) Propagation. (a) Abstraction reactions. (b) Addition reactions. (c) Fragmentation ( b -elimination).  (ii) Termination. (a) Recombination or coupling. (b) Disproportionation. (c) Electron transfer. ( Question 7 ) (iii) Reactivity and Selectivity. ( Questions 8-11 )

4 Applications in Synthesis: Intramolecular Cyclisation Reactions
(a) Advantages of radicals in synthesis. (b) Introduction to tributyltin hydride: the synthesis of hirsutene (1) . (c) Tributyltin hydride: good and bad points. (d) A formal synthesis of morphine (2) . (e) An approach towards the preparation of lysergic acid (3) .

5 Intermolecular Reactions
(a) The synthesis of brevicomin (4) . (b) Radical polarity. (c) Prostaglandin F 2 a (5) synthesis: an intramolecular cyclisation-intermolecular alkylation.

6 Functional Group Interconversions
(a) Deoxygenation of alcohols via xanthates: analogues of taxol (6) . (b) Decarboxylation.

7 Atom Transfer Reactions: 1,5-Hydrogen Atom Transfer
 (a) Using tributyltin hydride. (b) Photolysis: carbonyls and nitrites.

8 Industrial Applications
 (a) Polymerisation. (b) Photochlorination. (c) Photonitrosation. (d) Autoxidation.

Molecules 1 to 6

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