213137-46-3Relevant academic research and scientific papers
Highly Enantioselective Intermolecular Cu(I)-Catalyzed Cyclopropanation of Cyclic Enol Ethers. Asymmetric Total Synthesis of (+)-Quebrachamine
Temme, Oliver,Taj, Shabbir-Ali,Andersson, Pher G.
, p. 6007 - 6015 (2007/10/03)
A set of cyclic enol ethers derived from 2,3-dihydrofuran 35 and 3,4-dihydropyran 8 with a varying substitution pattern at the olefinic system were synthesized. Evans's ligand 5 with Cu(I)OTf was found to be an effective catalyst in the cyclopropanation reaction between cyclic enol ethers 14, 19, 28-31, and 33 and ethyl diazoacetate 6 to give diastereoselectivities up to exo/endo = 95:5 and enantioselectivities higher than 95% in nearly all cases. Because of the selective building of a quarternary carbon center and good yields in the formation of bicyclic structures 34c-h, the reaction was used as a key step in the asymmetric synthesis of (+)-quebrachamine 7, an indole alkaloid of the Aspidosperma family. After acid-induced ring opening of bicyclic compound 34f to lactone 40 followed by LiAlH4 reduction to the masked aldehyde 41, a reaction with tryptamine gave intermediate 42. This alcohol was efficiently converted into the indole alkaloid (+)-quebrachamine 7 in an overall yield of 37% starting from the chiral synthon 34f. Moreover it revealed the absolute configuration of the quarternary center of the cyclopropanation product 34f to be S.
