535967-34-1Relevant articles and documents
Asymmetric alternating copolymerization of cyclohexene oxide and CO2 with dimeric zinc complexes
Nakano, Koji,Nozaki, Kyoko,Hiyama, Tamejiro
, p. 5501 - 5510 (2003)
Dimeric zinc complex 2a [= Et2Zn2(1a)2] has been synthesized by the reaction of Et2Zn and (S)-diphenyl(pyrrolidin-2-yl)methanol (1a-H). X-ray crystallography revealed that the alkoxide ligand replaced one of the two ethyl groups of Et2Zn and formed a five-membered chelate ring through a Zn - N dative bond. Two zinc centers were bridged by oxygen atoms to form a Zn2O2 four-membered ring with a syn relationship between the two ethyl groups on the zinc centers. Dimeric zinc complex 2a was an active catalyst for asymmetric alternating copolymerization of cyclohexene oxide and CO2. An MALDI-TOF mass spectrum of the obtained copolymer showed that the copolymerization was initiated by the insertion of CO2 into Zn - alkoxide to give [(S)-diphenyl(pyrroridin-2-ly)methoxy] - [C(=O)O - (1,2-cyclohexylene) - O]n -H (copolymer I), including chiral ligand 1a as an initiating group. Complex 3a-OEt (= EtZn(1a)2ZnOEt), in which an ethoxy group replaced one of the two ethyl groups in 2a, also polymerized cyclohexene oxide and CO2 with higher catalytic activity and enantioselectivity than 2a and afforded EtO - [C(=O)O - (1,2- cyclohexylene) - O]n - H (= copolymer III), including an ethoxy group as an initiating group. Throughout the studies, dimeric zinc species are indicated to be the active species for the copolymerization. It is also depicted that the substituent on the aryl moiety in diaryl(pyrrolidin-2-yl)methanol 2b - e influenced the polymerization activity.
Intramolecular [2+2] Photocycloaddition of Cyclic Enones: Selectivity Control by Lewis Acids and Mechanistic Implications
Poplata, Saner,Bauer, Andreas,Storch, Golo,Bach, Thorsten
supporting information, p. 8135 - 8148 (2019/05/29)
The intramolecular [2+2] photocycloaddition of 3-alkenyl-2-cycloalkenones was performed in an enantioselective fashion (nine representative examples, 54–86 % yield, 76–96 % ee) upon irradiation at λ=366 nm in the presence of an AlBr3-activated oxazaborolidine as the Lewis acid. An extensive screening of proline-derived oxazaborolidines showed that the enantioface differentiation depends strongly on the nature of the aryl group at the 3-position of the heterocycle. DFT calculations of the Lewis acid–substrate complex indicate that attractive dispersion forces may be responsible for a change of the binding mode. The catalytic [2+2] photocycloaddition was shown to proceed on the triplet hypersurface with a quantum yield of 0.05. The positive effect of Lewis acids on the outcome of a given intramolecular [2+2] photocycloaddition was illustrated by optimizing the key step in a concise total synthesis of the sesquiterpene (±)-italicene.
CATALYST COMPOUNDS
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Page/Page column 25-26, (2013/06/27)
The present invention relates to compounds, particularly but not exclusively, compounds for use as catalysts, methods for producing said compounds and the use of said compounds as catalysts in catalytic processes including, but not limited to, the asymmetric reduction of imine and enamine compounds and/or the reductive amination of ketone compounds. The compounds have the formula 1 wherein: R1, R2, R3, R4 and R5 are each separately selected from the group consisting of hydrogen, alkyl and aryl; X is oxygen or sulfur; W is selected from the group consisting of – OR18,–SR18, –NR19R20, –PR19R20 where R18 is alkyl or aryl, and R19 and R20 are each separately selected from the group consisting of hydrogen, alkyl and aryl; and Z has the formula 2 wherein: R6 and R7 are each separately selected from the group consisting of hydrogen, alkoxy, nitro, halogen, alkyl and aryl, or R6 and R7 are linked to form a cyclic group; and Y is oxygen, sulfur or NR10 in which R10 is selected from the group consisting of hydrogen, alkyl and aryl.
