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.
A flexible and functional group tolerant synthesis route to access a structurally diverse collection of bifunctional 6′-(thio)-urea containing Cinchona alkaloid-based chiral quaternary ammonium salts has been developed. This route gives access to more than 25 different novel urea- and thiourea-containing ammonium salt derivatives, which were not accessible so far.
Mix and go: The quinidine amide 1 catalyzed [2+2] cycloaddition between N‐sulfonylimines 2 and alkyl 2,3‐butadienoates 3 afforded the R‐configured azetidines 4 in excellent yields and enantioselectivities (M.S.=molecular sieve). The S enantiomer was obtained when a quinine amide catalyst, the pseudoenantiomer of 1, was used.