195625-74-2Relevant academic research and scientific papers
Rhodium-Catalyzed Methylenation of Aldehydes
Lebel, Helene,Paquet, Valerie
, p. 320 - 328 (2004)
The rhodium-catalyzed methylenation of aldehydes using trimethylsilyldiazomethane and triphenylphosphine produces a variety of terminal alkenes in excellent yields. These mild and nonbasic reaction conditions allow the conversion of enolizable substrates (keto aldehydes and nonracemic α-substituted aldehydes) to terminal alkenes without epimerization. Optimization of the reaction conditions led to the conclusion that a variety of rhodium(I) sources can be used as catalysts. The effect of the solvent on the reaction has also been studied, and it indicates that although the THF is the best solvent, other solvents may be used. The reactivity of the system is very much dependent on the nature of the phosphine reagent. The use of an easily removable phosphine is also described. Spectroscopic studies indicate that the reaction proceeds via an unusual mechanism which leads to the in situ formation of the salt-free phosphorus ylide, methylenetriphenylphosphorane.
The stereodirecting effect of the glycosyl C5-carboxylate ester: Stereoselective synthesis of β-mannuronic acid alginates
Codée, Jeroen D. C.,Van Den Bos, Leendert J.,De Jong, Ana-Rae,Dinkelaar, Jasper,Lodder, Gerrit,Overkleeft, Herman S.,Van Der Marel, Gijsbert A.
supporting information; experimental part, p. 38 - 47 (2009/04/07)
(Chemical Equation Presented) Glycosylations of mannuronate ester donors proceed highly selectively to produce the 1,2-cis-linked products. We here forward a mechanistic rationale for mis counterintuitive selectivity, based on the remote stereodirecting e
Stereoselective C-glycosylation reactions of pyranoses: The conformational preference and reactions of the mannosyl cation
Lucero, Claudia G.,Woerpel
, p. 2641 - 2647 (2007/10/03)
A systematic study of C-glycosylations of acetals related to mannose and other pyranoses was conducted. The C-5 alkoxyalkyl group provides only a modest influence on stereoselectivity. On the other hand, studies of pentopyranoses bearing alkoxy groups at
Multicatalytic processes using diverse transition metals for the synthesis of alkenes
Lebel, Helene,Paquet, Valrie
, p. 11152 - 11153 (2007/10/03)
A series of cascade processes for the synthesis of alkenes from alcohols is described. Each individual step is catalyzed with a specific transition metal complex. The oxidation-methylenation one-pot procedure took place in the presence of a palladium and a rhodium catalyst to produce the desired terminal alkenes in high yields. A methylenation-ring-closing metathesis allowed the synthesis of cyclic alkenes from carbonyl derivatives, using the second-generation metathesis catalyst. Finally, an oxidation-methylenation-RCM process that involves up to three different transition metal catalysts in the same vessel is presented. Copyright
Synthesis of aminocyclitols by intramolecular reductive coupling of carbohydrate derived δ- and ε-functionalized oxime ethers promoted by tributyltin hydride or samarium diiodide
Marco-Contelles, Jose,Gallego, Pilar,Rodriguez-Fernandez, Mercedes,Khiar, Noureddine,Destabel, Christine,Bernabe, Manuel,Martinez-Grau, Angeles,Chiara, Jose Luis
, p. 7397 - 7412 (2007/10/03)
The intramolecular reductive coupling of a series of simple or polyoxygenated oxime ethers δ- or ε-functionalized with bromide, α,β- unsaturated ester, aldehyde, or ketone groups is reported. The cyclization of a nitrile-tethered aldehyde is also studied. These reductive couplings are promoted by tributyltin hydride or samarium diiodide. The reactions proceed under mild conditions, in good chemical yield, and with high stereoselectivity. When applied to highly functionalized substrates derived from carbohydrates, this approach provides a selective entry to enantiomerically pure aminocyclitols of varying regio- and stereochemistry. In particular, the reductive coupling reaction of carbonyl-tethered oxime ethers promoted by samarium diiodide can be performed in a one-pot sequence, following a Swern oxidation step, allowing the direct transformation of hydroxyl-tethered oxime ethers into the corresponding aminocyclitols. Moreover, the resultant O-benzylhydroxylamine products of these cyclizations can be further reduced in situ with excess samarium diiodide, in the presence of water, to the corresponding amino alcohols in excellent yields. Some transformations of these compounds are discussed.
