Conformationally restricted dynamic supramolecular catalysts for substrate-selective epoxidations
作者:Esmaeil Sheibani、Kenneth Wärnmark
DOI:10.1039/c2ob06859a
日期:——
A second generation of a substrate-selective dynamic supramolecular catalytic system consisting of a catalyst part and a receptor part, connected by a hydrogen-bonding motif, has been realized based on rational design. The results from analyses of the equilibrium mixture of the species generated by the components of the first generation system led us to selectively lock the cisoid conformation of the catalyst part to increase the amount of the substrate-selective catalytic cavity in the equilibrium mixture. This was realized by strapping the catalyst part by organic synthesis. This strapping led to an increase in substrate selectivity in the pair-wise competitive epoxidations of pyridyl- vs. phenyl-appended styrenes and pyridyl- vs. phenyl-appended stilbenes of both Z- and E- configuration compared to the first generation system, reaching 3.4 : 1 as the highest substrate selectivity for Z-mono-pyridyl-stilbene (27a) vs. the corresponding all-carbon analogue (28a) and for E-dipyridyl-stilbene (26b) vs. the corresponding all-carbon analogue (28b), respectively.
Modulation of the reactivity, stability and substrate- and enantioselectivity of an epoxidation catalyst by noncovalent dynamic attachment of a receptor functionality—aspects on the mechanism of the Jacobsen–Katsuki epoxidation applied to a supramolecular system
作者:Stefán Jónsson、Fabrice G. J. Odille、Per-Ola Norrby、Kenneth Wärnmark
DOI:10.1039/b518244a
日期:——
The synthesis of the components of the dynamic supramolecular hydrogen-bonded catalytic system 2 + 3 is described. The catalytic performance and substrate- and enantioselectivity of Mn(salen) catalyst 2 were investigated in the presence and absence of the Zn(porphyrin) receptor unit 3. The effects of pyridine and pyridine N-oxide donor ligands were also studied. Some aspects on the mechanism of the
Generation of oxiranyllithiums and oxiranyl Grignard reagents having a carbanion-destabilizing group from sulfinyloxiranes: Their property and an application to asymmetric synthesis of epoxides and alcohols
The first generation of oxiranyllithiums and oxiranyl Grignardreagents having a carbanion-destabilizing group (alkyl group) was realized from sulfinyloxiranes via the ligand exchange reaction of sulfoxides with tert-butyllithium or ethylmagnesium chloride in THF at −80 to −100°C. The generated oxiranyllithiums were found to be very unstable; however, these anions reacted with several electrophiles
Guanidine Bases in Synthesis: Extending the Scope of the Corey-Chaykovsky Epoxidation
作者:Andrew Graham、David Phillips
DOI:10.1055/s-0029-1219359
日期:2010.3
Guanidine bases, such as 1,5,7-triazabicyclo[4.4.0]dec-1-ene (TBD) or 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-1-ene (MTBD), are highly effective reagents for the in situ generation of sulfonium ylides from sulfonium salts in Corey-Chaykovsky epoxidation reactions of aldehydes. These reactions proceed rapidly to produce the corresponding epoxides in excellent yields and with high selectivity for the trans product. Significantly, this reagent combination is applicable to both nonenolizable and enolizable aldehydes and α,β-unsaturated aldehydes.
Synthesis of Epoxides from Alkyl Bromides and Alcohols with in Situ Generation of Dimethyl Sulfonium Ylide in DMSO Oxidations
作者:Zhi-Wei Zhang、Hai-Bo Li、Jin Li、Cui-Cui Wang、Juan Feng、Yi-Hua Yang、Shouxin Liu
DOI:10.1021/acs.joc.9b02621
日期:2020.1.17
the readily available alkyl bromides and alcohols to value-added epoxides using dimethyl sulfoxide (DMSO) under mild reaction conditions has been developed. Benzyl and allyl bromides, and activated and unactivated alcohols all proceeded smoothly to give epoxides in high to excellent yield. Dimethyl sulfide, generated by DMSO oxidations, was in situ elaborated to form the substituted dimethyl sulfonium