Amine-Catalyzed Asymmetric (3 + 3) Annulations of β′-Acetoxy Allenoates: Enantioselective Synthesis of 4H-Pyrans
摘要:
The asymmetric (3 + 3) annulations of beta'-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 Bronsted 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.
Efficient Highly Selective Synthesis of Methyl 2-(Ethynyl)alk-2(<i>E</i>)-enoates and 2-(1′-Chlorovinyl)alk-2(<i>Z</i>)-enoates from 2-(Methoxycarbonyl)-2,3-allenols
作者:Youqian Deng、Xin Jin、Chunling Fu、Shengming Ma
DOI:10.1021/ol9004273
日期:2009.5.21
Highly regio- and stereoselective reactions of readily available 2-(methoxycarbonyl)-2,3-allenols 1 with oxalylchloride in the presence of Et3N or DMSO afforded methyl 2-(ethynyl)alk-2(E)-enoates (E)-2 and 2-(1′-chlorovinyl)alk-2(Z)-enoates (Z)-3, respectively, in moderate to good yields.