SYNTHESIS VIA VINYL SULFONES .73. FREE-RADICAL SELF-IMMOLATIVE 1,2-ELIMINATION AND REDUCTIVE DESULFONYLATION OF ARYL SULFONES PROMOTED BY INTRAMOLECULAR REACTIONS WITH ORTHO-ATTACHED CARBON-CENTERED RADICALS
Pc. Vandort et Pl. Fuchs, SYNTHESIS VIA VINYL SULFONES .73. FREE-RADICAL SELF-IMMOLATIVE 1,2-ELIMINATION AND REDUCTIVE DESULFONYLATION OF ARYL SULFONES PROMOTED BY INTRAMOLECULAR REACTIONS WITH ORTHO-ATTACHED CARBON-CENTERED RADICALS, Journal of organic chemistry, 62(21), 1997, pp. 7142-7147
Aryl sulfones bearing an o-(bromomethyl)dimethylsilyl moiety (1), when
heated with AIBN and tributyltin hydride, suffer radical elimination
under mild conditions to give olefins and stannyl sulfinate 7 in high
yield. The mechanism is shown to proceed via intramolecular beta-sulfo
nyl hydrogen abstraction by o-silylmethylene radical 2, This step also
shows a large deuterium isotope effect of 12:1. In contrast, radical
intermediate 24, generated by tris(trimethylsilyl)silane radical addit
ion to o-allylsilane 23, undergoes intramolecular attack on the sulfon
e, resulting in homolytic sulfone cleavage to afford reduced products
and cyclic sulfone byproduct 25.