The
enantioselective, vicinal diamination of alkenes represents one of the
stereocontrolled additions that remains an outstanding challenge in organic
synthesis. A general solution to this problem would enable the efficient and
selective preparation of widely useful, enantioenriched diamines for
applications in medicinal chemistry and catalysis. In this Article we describe
the first enantioselective, <i>syn-</i>diamination
of simple alkenes mediated by a chiral, enantioenriched organoselenium catalyst
together with a <i>N,N’-</i>bistosyl urea as
the bifunctional nucleophile and <i>N-</i>fluorocollidinium
tetrafluoroborate as the stoichiometric oxidant. Diaryl, aryl-alkyl, and
alkyl-alkyl olefins bearing a variety of substituents are all diaminated in
consistently high enantioselectivities selectivities but variable yields. The
reaction likely proceeds through a Se(II)/Se(IV) redox catalytic cycle
reminiscent of the <i>syn-</i>dichlorination
reported previously. Furthermore, the <i>syn</i>-stereospecificity
of the transformation shows promise for highly enantioselective diaminations of
alkenes with no strong steric or electronic bias.
Structural rearrangements of a polyketide synthase module during its catalytic cycle