566-88-1Relevant articles and documents
Direct organocatalytic stereoselective transfer hydrogenation of conjugated olefins of steroids
Ramachary, Dhevalapally B.,Sakthidevi, Rajasekar,Reddy, P. Srinivasa
, p. 13497 - 13506 (2013/09/02)
Kinetically controlled and organocatalytic syn-selective transfer hydrogenation has been successfully demonstrated for the reduction of the enone functional group of various steroids. Herein, diastereoselective synthesis of many 5β-steroids have been reported through organocatalysis, which have broad medicinal and pharmaceutical applications. The mechanistic studies and the selectivity of the products clearly indicated that the catalyst 1b·d-CSA is mild enough to activate the various chiral cyclic enones through iminium ion formation during the organocatalytic transfer hydrogenations with Hantzsch ester 2a as a hydrogen source. Further, clear evidence for the selective formation of intermediate iminium species [I]+ have been characterized through on-line monitoring of controlled experiments by NMR and ESI-HRMS analyses.
One-Pot Bi(OTf)catalyzed oxidative deprotection of tert -butyldimethyl silyl ethers with TEMPO and co-oxidants
Barnych, Bogdan,Vatèle, Jean-Michel
experimental part, p. 2048 - 2052 (2011/10/19)
A sequential one-pot synthesis for the oxidation of primary and secondary tert-butyldimethylsilyl (TBDMS) ethers, using catalytic amounts of metal triflates and TEMPO in combination with PhIO or PhI(OAc)in THF or acetonitrile, is described. Acid-sensitive protecting groups such as methylidene, isopropylidene, acetals, and Boc are unaffected under the reaction conditions. Another feature of this procedure is its high selectivity for TBDMS ethers over tert-butyldiphenylsilyl ethers and of aliphatic TBDMS groups over phenolic TBDMS groups. Georg Thieme Verlag Stuttgart - New York.
Application of the excited state meta effect in photolabile protecting group design
Wang, Pengfei,Hu, Ayou,Wang, Yun
, p. 2831 - 2833 (2008/02/07)
A novel photolabile protecting group for carbonyl compounds has been developed, based on the excited state meta effect.
Investigation on the regioselectivities of intramolecular oxidation of unactivated C-H bonds by dioxiranes generated in Situ
Wong, Man-Kin,Chung, Nga-Wai,He, Lan,Wang, Xue-Chao,Yan, Zheng,Tang, Yeung-Chiu,Yang, Dan
, p. 6321 - 6328 (2007/10/03)
We found that dioxiranes generated in situ from ketones 1-6 and Oxone underwent intramolecular oxidation of unactivated C-H bonds at δ sites of ketones to yield tetrahydropyrans. From the trans/cis ratio of oxidation products 1a and 2a as well as the retention of the configuration at the δ site of ketone 5, we proposed that the oxidation reaction proceeds through a concerted pathway under a spiro transition state. The intramolecular oxidation of ketone 6 showed the preference for a tertiary δ C-H bond over a secondary one. This intramolecular oxidation method can be extended to the oxidation of the tertiary γ′ C-H bond of ketones 9 and 10. For ketone 11 with two δ C-H bonds and one γ′ C-H bond linked respectively by a sp3 hydrocarbon tether and a sp2 ester tether, the oxidation took place exclusively at the δ C-H bonds. Finally, by introducing proper tethers, regioselective hydroxylation of steroid ketones 12-14 have been achieved at the C-17, C-16, C-3, and C-5 positions.
Controlling the reactive state through cation binding: Photochemistry of enones within zeolites
Uppili, Sundararajan,Takagi, Shinsuke,Sunoj,Lakshminarasimhan,Chandrasekhar,Ramamurthy
, p. 2079 - 2083 (2007/10/03)
The nature of the lowest triplet state of enones is altered by the cations present within Y zeolites. Alkali metal ions, such as Li+, are predicted to interact with the carbonyl unit of enones in a collinear fashion and significantly lower both the p-type n and π-2 orbitals. Excited state energies, estimated at the CIS(D)/6-31+G* level, show that the lowest triplet is n-π* in character for the enones, but switch to π-π* on coordination with Li+. Observed product distribution within zeolite is consistent with this theoretical prediction.
Palladium(II)-catalyzed oxidation of alcohols to aldehydes and ketones by molecular oxygen
Nishimura, Takahiro,Onoue, Tomoaki,Ohe, Kouichi,Uemura, Sakae
, p. 6750 - 6755 (2007/10/03)
A novel combination of Pd(OAc)2/pyridine/MS3A catalyzes the aerobic oxidation in toluene of a variety of primary and secondary alcohols into the corresponding aldehydes and ketones in high yields. Various substituents and protecting groups are compatible with this oxidation. The ca. 2:3 ratio of O2 uptake to product yield is observed, whereas in the absence of MS3A, the ratio is ca. 1:1, suggesting the in situ formation of H2O2 and its decomposition by MS3A into water and oxygen. A catalytic cycle including the formation of a Pd(II)-alcoholate followed by β-elimination of a Pd(II)H species and a carbonyl compound and then the formation of a Pd(II)OOH species is proposed.
Study of the reductive Cleavage of Selenides with Nickel Boride. A Convenient Deselenization Procedure
Back, Thomas G.,Birss, Viola I.,Edwards, Mark,Krishna, M. Vijaya
, p. 3815 - 3822 (2007/10/02)
The reductive deselenization of a variety of organoselenium compounds can be performed rapidly, conveniently, and in high yield by using nickel boride.The latter reagent was generated in situ by adding sodium borohydride to nickel chloride hexahydrate and the substrate selenide in THF-methanol at 0 deg C.Under these conditions, ca. 3-3.5 mol of borohydride was required to reduce all of the nickel salt to nickel boride and an excess of nickel boride was generally required to effect complete deselenization.Preformed nickel boride lost virtually all of its ability to cleave n-dodecyl phenyl selenide (2) after only 5 min, but continued to catalyze the decomposition of sodium borohydride.Deselenizing ability was not restored by the addition of hydrogen or further sodium borohydride to preformed nickel boride.Deuterium-labeling studies indicated that the hydrogen required for reductive deselenization originates from both the borohydride and the methanol solvent in a ratio of ca. 3:1.The use of sodium borodeuteride in methanol-d afforded 1-deuteriododecane of high isotopic purity, indicating that the procedure comprises a convenient method for preparing deuteriated products.The mechanism of nickel boride deselenization may involve transient nickel hydride or Ni(0) intermediates.The chemoselectivity of the reaction permits the cleavage of C-Se bonds in the presence of chlorides, nitriles, esters, sulfides, sulfones, ketones, and some olefins, but iodides and sulfinate esters undergo concomitant or preferential reduction.Electrochemical deselenization of 2 was studied and resulted in anodic oxidation of the selenide to 1-dodecene instead of cathodic reduction to n-dodecane.
Isomerization of Homoallyl Alcohols over Raney Nickel
Prasad, J. V. N. Vara,Pillai, C. N.
, p. 998 - 999 (2007/10/02)
Homoallyl alcohols undergo ready isomerization to the corresponding aldehydes or ketones when refluxed in a solvent with Raney nickel.Reaction pathways, based on identification of intermediates of the reactions, involve dehydrogenation-hydrogenation for the cyclic alcohols and double bond shift for the open chain alcohols.
