Stereoselective Synthesis of Both syn- and anti-N-tert-Alkylamines Using Highly Stereospecific Crotylation of Ketone-Derived Acylhydrazones with Crotyltrichlorosilanes

Crotyltrichlorosilanes reacted with ketone-derived N-benzoylhydrazones in DMF without any catalyst. This is the first example of highly stereospecific crotylation of ketimine analogues leading to both syn- and anti-N'-tert-alkyl-N-benzoylhydrazines. Different reactivities between (Z)- and (E)-crotylsilanes in terms of yields and selectivities were observed. A kinetic study with both geometrically pure (Z)- and (E)-crotylsilanes was performed. These reactions are most likely to proceed via a cyclic chairlike transition state where the aromatic group of hydrazones takes an axial position. Both diastereomers of allylation products can be converted to the corresponding alpha,alpha-disubstituted homoallylic amines without epimerization.