INHIBITION OF REARRANGEMENTS IN STANNANE-MEDIATED RADICAL REDUCTION REACTIONS BY CATALYTIC QUANTITIES OF DIPHENYL DISELENIDE - AN EXAMPLE OF POLARITY REVERSAL CATALYSIS

The presence of only 10 mol % of PhSeH, PhSeSePh (reduced in situ to PhSeH), and, to a lesser extent, PhSH has a dramatic effect on the efficiency of stannane-mediated free radical rearrangement reactions owing to the superior hydrogen donating qualities of PhSeH and PhSH. Slow radical rearrangements can be prevented altogether, and the yields of even moderately rapid rearrangements significantly diminished. The addition of 10 mol % of PhSeSePh to stannane-mediated aryl radical cyclizations is advantageous as the initial, rapid, 5-hexenyl rearrangement is not impaired but the subsequent, slower neophyl rearrangement is effectively minimized, resulting in the formation of vastly improved 5-exo/6-endo ratios.