10.1002/chem.201304675
This research investigates the asymmetric hydrogenation of α-acetamidocinnamates using an air-stable, readily available monodentate chiral H-phosphinate ligand, (R)-mentylbenzylphosphinate, which is prepared from PhCH2MgCl and (R)-menthylOPCl2. The study demonstrates that this ligand can efficiently induce high enantioselectivity (up to 99.6% ee) in the rhodium-catalyzed asymmetric hydrogenation of α-acetamidocinnamates. The research highlights the importance of intramolecular hydrogen bonding in the asymmetric induction process. The study also explores the effects of different R groups on the chiral phosphinates, various rhodium complexes, solvents, and reaction conditions on the enantioselectivity and yield of the hydrogenation products. Additionally, the formation of rhodium complexes 4a and 4b, which are key to the catalytic activity, is examined, and their structures are analyzed using X-ray crystallography. The findings show the potential of chiral H-phosphinates as efficient ligands for asymmetric hydrogenation reactions, offering a simpler and more accessible alternative to traditional chiral phosphine ligands.
10.3762/bjoc.10.202
The research presents an investigation into the Grignard reaction of carbohydrate aldehydes with benzylmagnesium halides, focusing on the unexpected rearrangement from benzyl to o-tolyl carbinols. The study was prompted by challenges encountered in synthesizing benzyl-branched sugar carbinols, which are precursors for phenylalanine-branched sugars. The main reactants were 2,3-O-isopropylidene-α-D-lyxo-pentodialdo-1,4-furanoside and benzylmagnesium chloride or bromide. The reaction yielded a mixture of diastereomeric benzyl and o-tolyl carbinols, with the ratio varying based on the reaction conditions. The research employed various methods (A-E) to manipulate these conditions, including changes in temperature, reactant ratios, solvents, and the sequence of reactant addition. The products were analyzed using NMR spectral data, X-ray crystallographic analysis, and other analytical techniques such as specific rotations, melting points, and mass spectrometry to confirm the structures of the resulting compounds and to propose a possible mechanism for the rearrangement. The study concluded that the rearrangement was specific to the starting sugar aldehyde and provided valuable insights for the synthesis of structurally modified iminosugars and other biologically active compounds.
10.1021/om701068h
The study investigates the synthesis and characterization of zwitterionic niobium and tantalum imido complexes, specifically focusing on their potential as catalysts for methyl methacrylate (MMA) polymerization. The researchers synthesized various complexes using trichloro derivatives [MCl3(NR)(py)2] (where M = Nb or Ta, R = tBu or aryl) and reacted them with lithium aryloxides (LiOAr) to obtain imido aryloxo complexes. They also employed benzyl magnesium chloride ([BzMgCl]) for alkylation, resulting in tribenzyl derivatives. Lewis acids such as B(C6F5)3 and Al(C6F5)3 were used to generate zwitterionic complexes from the tribenzyl derivatives, facilitating the exploration of their catalytic activity in MMA polymerization. The study highlights the role of these chemicals in modifying the reactivity and stability of high-valent metal complexes for potential applications in polymerization processes.
10.1021/jo00140a025
The research investigates the silver(1)-promoted rearrangement of cyclopropene derivatives, comparing these reactions to thermolysis and photolysis. Key chemicals involved include various cyclopropene compounds such as 1,3-diphenyl-2-methyl-3-benzylcyclopropene and 3-benzyl-1,2,3-triphenylcyclopropene, which undergo rearrangement to form indene derivatives under the influence of silver perchlorate. Other chemicals like benzylmagnesium chloride and phenylmagnesium bromide are used in the synthesis of intermediate compounds. The study also explores the effects of substituents on the cyclopropene ring, such as allyl and methyl groups, and how these influence the reaction outcomes. Silver perchlorate plays a crucial role as the catalyst for the rearrangement reactions, leading to the formation of products like bicyclo[3.1.0]hex-2-ene derivatives and indenes. The research provides insights into the regioselectivity and stereochemistry of these reactions, proposing mechanisms involving the formation of argentio- carbonium ions and subsequent cyclization or bond cleavage.
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