Consecutive Radical Reactions

As far as the use of silanes as mediators in consecutive radical reactions is concerned, the knowledge of their hydrogen donor abilities coupled with the steric hindrance given by the silicon substituents has contributed substantially in this area, with interesting results in terms of reactivity and stereoselectivity. 

The general concepts of stereoselectivity in radical reactions have been illustrated in a number of recent books. Readers are referred to those books for a thorough treatment [1,2]. The following sections deal with a collection of applications where silanes act as mediators for smooth and selective radical strategies, based on consecutive reactions. 

Distinction between Consecutive Atom and Radical Reactions with... 

The consecutive reactions of the addition radical (R-CH-CH2R)- follow the same pattern as the reaction of the Kolbe radicals. At Pt anodes they undergo radical-radical reactions forming either dimers (4Id) or bisubstituted monomers (41e),... 

Care must be taken in order to ensure that the effective rates of the consecutive radical reactions are higher than the rate of hydrogen abstraction from (TMS)3SiH. Apart from the standard synthetic planning based on known rate constants, this is usually effected either by controlling the concentration of the reducing agent in the reaction medium... 

Auto-oxidation processes consist of a very large number of simultaneous and consecutive radical reactions. Most of these reactions can be categorized into three basic types, and these are shown by 8.11 to 8.15. Note that for these reactions an organic radical initiator In2 and no metal complex is used. The role of a metal ion in autoxidation processes is that of a catalyst for the initiation steps. 

A major focus of our research program has been the development of synthetically useful radical-mediated methodologies in recent years. Our interest in this area was partly initiated by asking how to generate five- and six-membered ring radicals from acyclic radical precursors. This problem has been unsolved in radical chemistry due to a disfavored 5-endo cyclization in pentenyl radical cyclizations. This simple but intriguing curiosity led us to study radical reactions of yV-aziridinylimines. The outcome of this research is the development of a novel consecutive carbon-carbon bond formation approach, which has tremendous synthetic potential. This review provides a full account of radical cyclizations of V-aziridinylimines and their applications to sesquiterpene natural products. 

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