Titanium-mediated reductive cross-coupling reactions of imines with terminal alkynes: An efficient route for the synthesis of stereodefined allylic amines

• Kebin Mao,
• Guoqin Fan,
• Yuanhong Liu,
• Shi Li,
• Xu You and
• Dan Liu

Beilstein J. Org. Chem. 2013, 9, 621–627, doi:10.3762/bjoc.9.69

• undergoes an unexpected 1,3-amino migration on silica gel during the column chromatography. Keywords: allylic amine; azatitanacyclopentene; reductive cross-coupling; regioselectivity; terminal alkyne; titanium-imine complex; Introduction Allylic amines are fundamental three-carbon building blocks in

• complex 3a was generated in situ by the reaction of imine 2a with 1.3 equiv of Ti(OiPr)4/2 c-C5H9MgCl at −30 °C. It was found that Ti-imine complex 3a could smoothly couple with 1.5 equiv of 1-heptyne to give allylic amine 5a in 77% NMR yield after hydrolysis of the resulting azatitanacyclopentene complex

• 4a with saturated aqueous NaHCO3 solution. In this reaction, azatitanacyclopentene 4a, rather than its regioisomer 4a’, was formed preferentially, in which the pentyl group is situated adjacent to titanium (Scheme 3, reaction 1). Accordingly, the allylic amine 5a could be obtained after hydrolysis