Science of Synthesis

Bietti, M.; Dénès, F., Science of Synthesis: Free Radicals: Fundamentals and Applications in Organic Synthesis, (2021) 1, 547.

Toluene and related aromatic compounds possessing benzylic C—H bonds add to dimethyl fumarate, fumaronitrile, and 1,4-diphenylbut-2-ene-1,4-dione upon initiation with triethylborane (‌Scheme 73‌). The reaction is usually complete within 3 hours at 180 °C, in diluted solution (c = 0.01 M; to minimize the competing polymerization process), and requires only 0.3–1 equivalents of triethylborane. In the absence of triethylborane the adduct is still formed, albeit in very low yield (ca. 8%), indicating that the reaction can be initiated by traces of impurities, presumably peroxides or molecular oxygen.[‌182‌] Under these conditions, reactive oxygen-centered species generated by reaction between triethylborane and molecular oxygen are believed to initiate the reaction by abstracting a hydrogen atom from the benzylic position. The benzylic radical formed adds to the radical trap and the resulting electrophilic radical intermediate is proposed to propagate the chain by playing the role of the hydrogen-atom-abstracting species as it is not able to react with trialkylborane, unlike radicals resulting from the addition to enones.

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‌Meeeeeeeeee 88‌

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‌Meeeee 88‌ Meeeeeeee ee ee Meeeeee Meeeee eeee Meeeeeeeeeeeeeeeee[‌888‌]

M eeeeeeeee eeee eeeeeee ee eeee eeeeeeee ee eee eeee eeeeeee eee eee eeeeeeeee ee eeeeee eeeeee[‌888‌] (eee ‌Meeeee 88‌, Meeeeee ‌8.88.8.8‌) eeeeeeee eee eee eeeeeeeee ee eee eeeeeeee eeeeeee (‌Meeeee 88‌).

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References