Most lipases resolve secondary alcohols in accordance with the “Kazlauskas rule” to give the R enantiomers. In a similar manner to other lipases, Candida rugosa lipase (CRL) exhibits R enantioselectivity towards heptan‐2‐ol, although the enantiomeric ratio (E) is low (E=1.6). However, unexpected enantioselectivity (i.e., S enantioselectivity, E=58) of CRL towards 4‐(tert‐butoxycarbonylamino)butan‐2‐ol, which has a similar chain length to heptan‐2‐ol, has been observed. To develop a deeper understanding of the molecular basis for this unusual enantioselectivity, we have conducted a series of molecular modeling and substrate engineering experiments. The results of these computational and experimental analyses indicated that a hydrogen bond between the Ser450 residue and the nitrogen atom of the carbamate group is critical to stabilize the transition state of the S enantiomer. 相似文献
A three‐component reaction of 3‐(tri‐n‐butylstannyl)allyl acetates, aldehydes, and triorganoboranes in the presence of a palladium‐Xantphos catalyst system predominately gave (E)‐anti‐homoallylic alcohols with high diastereoselectivity and good to high levels of alkene stereocontrol. An efficient chirality transfer was observed when an enantioenriched substrate was employed. The reaction was initiated by the formation of an allylic gem‐palladium/stannyl intermediate, which subsequently underwent allylation of the aldehyde by an allyltributyltin followed by a coupling reaction of the in‐situ‐generated (E)‐vinylpalladium acetate with the triorganoborane.
Hydrogenation of esters to alcohols with a well‐defined iron iPr2PNP pincer complex has been recently reported by us and other groups. We now introduce a novel and sterically less hindered Et2PNP congener that provides superior catalytic activity in the hydrogenation of various carboxylic acid esters and lactones compared to the known complex. Successful hydrogenation proceeds under relatively mild conditions (60 °C) with lower catalyst loadings.
This paper reports the use of an immobilised ruthenium complex in a continuous flow process for the N-alkylation of morpholine with benzyl alcohol. The ruthenium-based catalyst was supported on a phosphine bound polymer. Screening experiments were first performed in a batch reactor, with a 16 vol% mixture of morpholine and benzyl alcohol (stoichiometric molar ratio of 1:1) in toluene as the solvent. Operating at 110 °C for 24 h, it was shown that high conversions (>99%) into the desired tertiary amine could be achieved. This reaction was then shown to be viable in a continuous flow reactor, where the catalytic polymer beads were retained in the bed. Operating at 150 °C and using p-xylene as a solvent, the conversion into the desired tertiary amine was shown to be as high as 98%. This approach is clearly very promising, as it provides a greener and more atom efficient route for the production of secondary and tertiary amines in the pharmaceutical industry. 相似文献
Visible light illumination of nitrogen-doped TiO2 brings about the selective oxidation of benzyl and cinnamyl alcohol to the corresponding aldehydes. The photocatalyst was prepared by a sol-gel method and characterised mainly by XRD, UV-vis diffuse reflectance and Raman spectroscopy. The conditions limiting the observation of visible light photoactivity are the use of dry nitriles as nonaqueous solvents and aromatic alcohols as the substrates. No visible light oxidation takes place in an aqueous medium. The efficiency of benzyl and cinnamyl alcohol photo-oxidation in nitrile solvents follows the order: CH3CN > CH3CH2CN > CH3(CH2)2CN. Conversely, since alcohol photo-oxidation occurs with 100% selectivity on electrodes in O2 saturated solutions at potentials close to Efb or under open-circuit conditions, suspensions of the photocatalyst can be advantageously employed. The process involves a relatively weak adsorption of the alcohol substrates which, however, do not readily capture the photogenerated holes. On the basis of the electrochemical and photoluminescence data, it appears that the solvent (e.g. acetonitrile), in addition to O2 has an active role in the reaction mechanism. 相似文献
The first procedure to access N‐tosylimines directly from alcohols under mild and neutral conditions is reported. The protocol involves saccharin‐lithium bromide‐catalyzed oxidation of alcohols to aldehydes/ketones with chloramine‐T followed by their condensation with the in situ generated oxidation by‐product p‐toluenesulfonamide in the same reaction vessel to afford N‐tosylimines in 40–90% overall yields. The present work opens up a new and efficient synthetic route to N‐tosyimines directly from alcohols in a one‐pot procedure. 相似文献