Investigation of the active species in a Michael addition promoted by chirally modified tetrahydroborate

For the first time, asymmetric 1,4-addition of various malonates to enones has been carried out using tetrabutylammoniumtetrahydroborate (TBATB) in the presence of a chiral ligand. The Michael adducts were formed in reasonably good yields (61-67%) with moderate ee's at 0 °C. ¹¹B NMR spectroscopic studies explain this unexpected reactivity through the predominant formation of an aminodiol modified borate complex in the presence of a hydride acceptor.