High-pressure-promoted electron transfer

Three cases of Type la activations illustrate a class of reactions expected to give positive results. The first one is provided by SrnI or ETC processes. Figure 1 shows the chain mechanism of the reaction of lithium nitronate with 4-nitro-benzyl bromide established by Komblum and Russell. This reaction was expected to display sonochemical switching, which was indeed foimd. The mechanism suggests that the sonochemical activation should find its origin either in creating species 1 or 2 (no direct entry to 3 seems plausible). The creation of 1 within a cavitation bubble could result either from high-pressure-promoted electron transfer (activation volumes for some electron transfer reactions may be found in Ref. 9) or local conditions at the interface between the cavitation bubbles and the bxilk solution (Qi. 1). The creation of radical 2 could result from a direct sonolysis of the benzylic C-Br bond (p. 86) but... 

A variety of other reaction conditions promote the Diels-Alder reaction/ including high pressure, ultrasound, electron transfer, polar... 

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