A new approach to (Z)-vinyloxyboranes via 1,4 hydroboration of (E)-α,β-unsaturated ketones. Synthesis of syn aldols

(Z)-Vinyloxy boranes are obtained via 1,4-hydroboration of acyclic disubstituted (E)-α,β-unsaturated ketones with dicyclohexylborane or diisopinocampheylborane in tetrahydrofuran, CH2Cl2 or CHCl3 at 20 °C; treatment of the hydroboration mixture with an aldehyde allows pure syn aldols to be synthesized in good yields, and in excellent enantiomeric excesses, using the latter borane.