Highly Selective α-Acylvinyl Anion Additions to Imines

α-Hydroxypropargylsilanes undergo rearrangement to form reactive lithium allenolates. The resulting α-acylvinyl anion equivalents undergo highly selective additions to N-tert-butanesulfinyl imines generating β-substituted aza-MBH-type products. High yields are achieved for a wide range of α-hydroxypropargylsilanes as well as for a diverse selection of imines. The reactions proceed with good to excellent diastereoselectivity and regioselectivity (8−20:1 major/∑ minor) favoring the Z-isomer of the alkene.