928-55-2Relevant articles and documents
Careful investigation of the hydrosilylation of olefins at poly(ethylene glycol) chain ends and development of a new silyl hydride to avoid side reactions
Shin, Hyunseo,Moon, Bongjin
, p. 527 - 536 (2018/01/27)
Hydrosilylation of olefin groups at poly(ethylene glycol) chain ends catalyzed by Karstedt catalyst often results in undesired side reactions such as olefin isomerization, hydrogenation, and dehydrosilylation. Since unwanted polymers obtained by side reactions deteriorate the quality of end-functional polymers, maximizing the hydrosilylation efficiency at polymer chain ends becomes crucial. After careful investigation of the factors that govern side reactions under various conditions, it was related that the short lifetime of the unstable Pt catalyst intermediate led to the formation of more side products under the inherently dilute conditions for polymers. Based on these results, two new chelating hydrosilylation reagents, tris(2-methoxyethoxy)silane (5) and 2,10-dimethyl-3,6,9-trioxa-2,10-disilaundecane (6), have been developed. It was demonstrated that the hydrosilylation efficiency at polymer chain ends was significantly increased by employing the internally coordinating hydrosilane 5. In addition, employment of the internally coordinating disilane species 6 in an addition polymerization with 1,5-hexadiene by hydrosilylation reaction yielded a polymer with high molecular weight (Mn = 9300 g/mol), which was significantly higher than that (Mn = 2600 g/mol) of the corresponding polymer obtained with non-chelating dihydrosilane, 1,1,3,3-tetramethyldisiloxane.
Total synthesis of (+)-azaspiracid-1. An exhibition of the intricacies of complex molecule synthesis
Evans, David A.,Kvaerno, Lisbet,Dunn, Travis B.,Beauchemin, Andre,Raymer, Brian,Mulder, Jason A.,Olhava, Edward J.,Juhl, Martin,Kagechika, Katsuji,Favor, David A.
supporting information; experimental part, p. 16295 - 16309 (2009/05/08)
The synthesis of the marine neurotoxin azaspiracid-1 has been accomplished. The individual fragments were synthesized by catalytic enantioselective processes: A hetero-Diels-Alder reaction to afford the E- and HI-ring fragments, a carbonyl-ene reaction to furnish the CD-ring fragment, and a Mukaiyama aldol reaction to deliver the FG-ring fragment. The subsequent fragment couplings were accomplished by aldol and sulfone anion methodologies. All ketalization events to form the nonacyclic target were accomplished under equilibrating conditions utilizing the imbedded configurations of the molecule to adopt one favored conformation. A final fragment coupling of the anomeric EFGHI-sulfone anion to the ABCD-aldehyde completed the convergent synthesis of (+)-azaspiracid-1.
Highly selective supramolecular catalyzed allylic alcohol isomerization
Leung, Dennis H.,Bergman, Robert G.,Raymond, Kenneth N.
, p. 2746 - 2747 (2007/10/03)
A supramolecular tetrahedral assembly Na12[Ga4L6] (L = 1,5-bis-catecholamide naphthalene) has been found to selectively encapsulate monocationic rhodium complexes of the appropriate size and shape. Encapsulation within the chiral environment of the host directly affects the symmetry of the rhodium guest and can be well characterized by NMR spectroscopy. The rhodium complexes were found to be catalytically active for the isomerization of allylic alcohols. Investigations into the catalytic activity of the encapsulated rhodium guests have shown that the constrained cavity of the host exerts a strong influence on the reactivity at the metal center. The supramolecular host prevents substrates of the wrong size and shape from entering the host cavity and reacting with the encapsulated metal center, while substrates of the correct dimensions are allowed ready access. These results suggest that the metal center remains in the active site of the host while reactants and products freely and rapidly access the host cavity. Copyright
