Nonracemic 3°-carbamines from the asymmetric allylboration of N-trimethylsilyl ketimines with B-allyl-10-phenyl-9-borabicyclo[3.3.2]decanes

The simple and efficient asymmetric synthesis of 3°-carbamines 7 from N-TMS enamines (3) and either enantiomeric form of β-allyl-10-(phenyl)-9-borabicyclo[3.3.2]decane (1) is reported. The high reactivity (<1 h, -78 °C) and enantioselectivity (60-98% ee) of these substrates can be attributed to the fact that the complexation of 3 with 1 facilitates its isomerization to the corresponding syn-N-TMS ketimine complex from which allylation can occur. In addition to providing the homoallylic amines 7 with predictable stereochemistry, the procedure also permits the efficient recovery of the chiral boron moiety (50-65%) as air-stable crystalline pseudoephedrine complexes 8, which are directly converted back to 1 with allylmagnesium bromide in ether (98%). Copyright © 2006 American Chemical Society.