- Studies on a catalytic version of the Matteson asymmetric homologation reaction
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Studies of a catalytic asymmetric version of the Matteson reaction between dichloromethylboronates and organolithium reagents have been undertaken. From several different chiral catalytic systems studied, only one based on a mannitol derivative has given substantial asymmetric induction close to that previously achieved with a bis(oxazoline) derivative and ytterbium triflate. More detailed study of the latter reaction revealed that fresh ytterbium triflate actually reduced the level of asymmetric induction, while "aged"ytterbium triflate, or a fresh sample that had been treated with water, brought about improved induction. The implications of these findings are discussed.
- Smith, Keith,Saleh, Basil A.,Alshammari, Mohammed B.,El-Hiti, Gamal A.,Elliott, Mark C.
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supporting information
p. 4279 - 4284
(2021/05/31)
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- Asymmetric benzoylation of hydrobenzoin by copper(ii) bis(oxazoline) anchored onto ordered mesoporous silicas and their carbon replicas
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A copper(ii) complex with a commercial chiral bis(oxazoline) was anchored onto ordered mesoporous silica materials and their respective carbon replicas. The amount of transition metal complex loaded onto the mesostructured solids was determined by ICP-AES and the materials were also characterized by elemental analysis, FTIR, TG/DSC and isotherms of N2 adsorption at -196°C. For the first time the asymmetric benzoylation of a 1,2-diol was performed in the heterogeneous phase by using an anchored commercial bis(oxazoline) ligand. The effect of the type of mesoporous material on the catalytic parameters, as well as on the reutilization of catalysts in several catalytic cycles, was checked. All the composites prepared were active, selective and enantioselective in this asymmetric organic transformation. Using the two ordered mesoporous silicas as supports good selectivities, with comparable yields and TONs to the homogeneous phase reaction, were obtained. Furthermore these two heterogeneous catalysts are more stable upon reuse than the corresponding ordered carbon replica materials. One of the former heterogeneous catalysts, with mesoporous silica as a support, could be further reused for 4 consecutive cycles without significant loss of selectivity, the TON or enantioselectivity. The Royal Society of Chemistry 2013.
- Silva, Ana Rosa,Carneiro, Liliana,Carvalho, Ana P.,Pires, Joao
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p. 2415 - 2424
(2013/09/02)
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- An improved protocol for azole synthesis with PEG-supported Burgess reagent
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A polyethyleneglycol-linked version of Burgess reagent was developed and applied toward the cyclodehydration of β-hydroxy amides and thioamides. The desired oxazolines and thiazolines were obtained in high yields and excellent purities. The major advantag
- Wipf, Peter,Venkatraman, Srikanth
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p. 4659 - 4662
(2007/10/03)
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