Science of Synthesis

Clark, A. J., Science of Synthesis, (2003) 5, 260.

Radicals generated by tin hydride mediated homolyses may undergo rearrangement, H-translocation, or SH2[‌399‌] and SHi reactions depending upon the substrates employed.[‌40‌–‌50‌] Some examples of rearrangement reactions have already been described above and include the 1,2-rearrangement of the anomeric radical ‌14‌ to the secondary radical en route to ‌16‌ (see ‌Scheme 15‌).[‌106‌] Groups other than (β-acyloxyl)alkyl groups[‌400‌–‌402‌] undergo similar radical 1,2-migrations; included are (β-phosphatoxyl)alkyl[‌403‌] and silyl groups.[‌404‌] The mechanisms for these rearrangements have been studied in depth using a range of substrates, solvents, and 17O-labeled substituents.[‌399‌–‌403‌] Other known migrations mediated by tributylstannane include neophyl-type radical migrations as well as 1,2-aryl migrations.[‌405‌,‌406‌] Often ring expansion reactions can be mediated by radical-induced rearrangements.[‌407‌] In these reactions the overall rearrangement occurs either via a sequence of a reversible radical cyclization/fragmentation, or just a fragmentation reaction. An example of the former reaction type is the formation of the bicycle ‌257‌, through the fragmentation and reduction of the tricyclic radical ‌256‌ released by the cleavage of 7-(3-bromopropyl)-8-methylenebicyclo[4.2.0]octane (‌255‌) (‌Scheme 58‌).[‌408‌]

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