Amine-Catalyzed Asymmetric (3 + 3) Annulations of β'-Acetoxy Allenoates: Enantioselective Synthesis of 4H-Pyrans.
The asymmetric (3 + 3) annulations of β'-acetoxy allenoates with either 3-oxo-nitriles or pyrazolones have been realized by using 6'-deoxy-6'-[(l)-N,N-(2,2'-oxidiethyl)-valine amido]quinine (6h) as the catalyst. The three functions of catalyst 6h, including Lewis base (quinuclidine N), H-bond donor (amide NH), and Brønsted base (morpholine N), cooperatively take crucial roles on the chemo- and enantioselectivity, allowing for the construction of 4H-pyran and 4H-pyrano[2,3-c]pyrazole in high yields and enantioselectivity.
Jiangsu Key Laboratory of Advanced Catalytic Materials & Technology, School of Petrochemical Engineering, Changzhou University , 1 Gehu Road, Changzhou 213164, China.
Chunjie
C
Ni
Jiangsu Key Laboratory of Advanced Catalytic Materials & Technology, School of Petrochemical Engineering, Changzhou University , 1 Gehu Road, Changzhou 213164, China.
Xiaofeng
X
Tong