The preparation and use of polyHIPE-grafted reactants to reduce alkyl halides under free-radical conditions

PolyHIPE-supported tin hydride and thiol are synthesized to reduce alkyl br omides under free-radical conditions, taking advantage of the fully interco nnected polyHIPE structure. Radical reduction of 1-bromoadamantane, 6-bromo hex-1-ene and 1-allyloxy-2-bromobenzene are performed using two methodologi es: one using supported tin hydride as reducing agent, and another using su pported thiol as polarity-reversal catalyst in the presence of triethylsila ne as reducing agent. The polyHIPE-supported tin hydride is used either in catalytic or stoichiometric amounts depending on the bromo compound to be r educed. In the case of unsaturated bromides, both methodologies lead to red uctive cyclization, thus enabling radical rearrangement before hydrogen tra nsfer. PolyHIPE-supported organotin hydride is a good alternative to tribut yltin hydride to prevent tin contamination and facilitate product separatio n. PolyHIPE-supported thiol, in the presence of an excess of triethylsilane , shows good activity and selectivity toward reductive cyclization products . Results obtained by the two methodologies are compared and discussed.