β-Selective Epoxidation of Cholesterol Derivatives with Molecular Oxygen and Aldehyde Catalyzed by Manganese(II) Complex
作者:Tohru Yamada、Kiyomi Imagawa、Teruaki Mukaiyama
DOI:10.1246/cl.1992.2109
日期:1992.11
In the presence of a catalytic amount of bis(dipivaloylmethanato)manganese(II) (= Mn(dpm)2), various cholesterol derivatives are smoothly converted into the corresponding β-epoxides in good to high yields with combined use of molecular oxygen and isobutyraldehyde. These stereoselectivities are the reversal of the cases using peracid such as mCPBA.
A Highly β-Stereoselective Catalytic Epoxidation of Δ<sup>5</sup>-Unsaturated Steroids with a Novel Ruthenium(II) Complex under Aerobic Conditions
作者:Venkitasamy Kesavan、Srinivasan Chandrasekaran
DOI:10.1021/jo980829k
日期:1998.10.1
6alpha-epoxides as the major products. The overall conformation of the steroid nucleus is nearly planar in the cholesteryl ester, while it is bent at the junction between the rings A and B in the 5beta,6beta-epoxide. This change from pseudo-trans- to cis-stereochemistry of the A-B ring junction provides more room for the catalyst to approach from the beta-face of the steroidal skeleton.
A novel and highly .beta.-selective epoxidation of .DELTA.5-unsaturated steroids with permanganate ion
作者:M. S. Syamala、Jagattaran Das、Sundarababu Baskaran、Srinivasan Chandrasekaran
DOI:10.1021/jo00032a059
日期:1992.3
MARCHON, JEAN-CLAUDE;RAMASSEUL, RENE, SYNTHESIS,(1989) N, C. 389-391
作者:MARCHON, JEAN-CLAUDE、RAMASSEUL, RENE
DOI:——
日期:——
A Convenient Synthesis of 5,6β-Epoxides of Some Cholesteryl Esters and Δ<sup>5</sup>-Ketosteroid Derivatives by Catalytic β-Stereoselective Epoxidation
作者:Jean-Claude Marchon、René Ramasseul
DOI:10.1055/s-1989-27261
日期:——
The epoxidation of a series of cholesteryl esters by air in the presence of a catalytic amount of a ruthenium tetramesitylporphyrin complex is described. The preparative procedure, which requires only 4 to 5 mol % of the catalyst, leads to high conversion (76 to 94 %) and very high β-stereoselectivity (> 99 %). Similar results are obtained in the epoxidation of 3β-acetoxyandrost-5-ene-17-one, 3β-acetoxypregn-5-ene-20-one, and 3,3-ethylenedioxycholest-5-ene.