A wide mechanistic spectrum observed in three different reactions with organometallic reagents

Abstract

The halogen-lithium exchange reaction is of one of the most powerful method for the preparation of organolithium compounds, but its mechanism is still controversial. To afford some new elements, we synthesized a new suitable fast radical clock, bearing a phenyl group at the alkene C-terminal. The examination of some mechanistic clues, as well as the identification of the unexpected by-products allowed the conclusion that the reaction proceeds by a polar mechanism and no evidence for radicals were found. The second reaction discussed is the insertion of NO in the N-Li bond of lithium amides. Evidence for the involving of paramagnetic and nitrosonium intermediates, as well as equilibria between different reactive species were essential for the proposal of a whole complex mechanism, which was confirmed by theoretical calculations. Finally, results on the addition of heteroaromatic organocuprates to a,b-unsaturated substrates are presented. Several reaction conditions were looked for to lead the reaction toward the more interesting 1,4-conjugated addition. Thus, addition of up to 6 equivalents of TMSCl to the reaction with arylcuprates leads to a clean addition yielding more than 95% of the 1,4-addition product. A further objective of the paper is to show how the search of unexpected routes of reaction allowed developing original pathways to lead them toward the formation of appealing functionalized compounds. Copyright © 2010 John Wiley and Sons, Ltd.