Asymmetric halolactonisation reaction—4: Asymmetric synthesis of optically active α,β-epoxyaldehydes from α,β-unsaturated acids

The bromolactones (5) stereoselectively produced by the asymmetric bromolactonisation of (S)-N-(α,β-unsaturated) acylprolines(3), were elaborated to highly optically active 2(R),3(S)-epoxyaldehydes(8)(84–98% ee) by successive epoxide formation and reductive cleavage of the proline moiety. The overall process constitutes a highly efficient asymmetric synthesis of 8 from α,β-unsaturated acids(1).