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Relevant academic research and scientific papers

Highly selective asymmetric Rh-catalyzed hydroformylation of heterocyclic olefins

A small family of new chiral hybrid, diphosphorus ligands, consisting of phosphine-phosphoramidites L1 and L2 and phosphine-phosphonites L3a-c, was synthesized for the application in Rh-catalyzed asymmetric hydroformylation of heterocyclic olefins. High-pressure (HP)-NMR and HP-IR spectroscopy under 5-10 bar of syngas has been employed to characterize the corresponding catalyst resting state with each ligand. Indole-based ligands L1 and L2 led to selective ea coordination, while the xanthene derived system L3c gave predominant ee coordination. Application of the small bite-angle ligands L1 and L2 in the highly selective asymmetric hydroformylation (AHF) of the challenging substrate 2,3-dihydrofuran (1) yielded the 2-carbaldehyde (3) as the major regioisomer in up to 68% yield (with ligand L2) along with good ees of up to 62%. This is the first example in which the asymmetric hydroformylation of 1 is both regio- and enantioselective for isomer 3. Interestingly, use of ligand L3c in the same reaction completely changed the regioselectivity to 3-carbaldehyde (4) with a remarkably high enantioselectivity of 91%. Ligand L3c also performs very well in the Rh-catalyzed asymmetric hydroformylation of other heterocyclic olefins. Highly enantioselective conversion of the notoriously difficult substrate 2,5-dihydrofuran (2) is achieved using the same catalyst, with up to 91% ee, concomitant with complete regioselectivity to the 3-carbaldehyde product (4) under mild reaction conditions. Interestingly, the Rh-catalyst derived from L3c is thus able to produce both enantiomers of 3-carbaldehyde 4, simply by changing the substrate from 1 to 2. Furthermore, 85% ee was obtained in the hydroformylation of N-acetyl-3-pyrroline (5) with exceptionally high regioselectivities for 3-carbaldehyde 8Ac (>99%). Similarly, an ee of 86% for derivative 8Boc was accomplished using the same catalyst system in the AHF of N-(tert-butoxycarbonyl)-3-pyrroline (6). These results represent the highest ees reported to date in the AHF of dihydrofurans (1, 2) and 3-pyrrolines (5, 6).

Rh-catalyzed asymmetric hydroformylation of heterocyclic olefins using chiral diphosphite ligands. Scope and limitations

(Chemical Equation Presented) We used a series of diphosphite ligands to study the effect of the ligand backbone, the length of the bridge, and the substituents of the biphenyl moieties and determine the scope of this type of ligand in the Rh-catalyzed asymmetric hydroformylation of several hetereocylic olefins. By carefully selecting the ligand components, we achieved high chemo-, regio-, and enantioselectivities in different substrate types. Unprecedentedly high enantioselectivities for five-membered heterocyclic olefins were therefore obtained. Note that both enantiomers of the hydroformylation products can be synthesized using the same ligand by a simple substrate change. For the seven-membered heterocyclic dioxepines, our results are among the best obtained. Also, both enantiomers of the hydroformylation products can be obtained by using pseudoenantiomer ligands or by carefully tuning the ligand parameters.

Asymmetric Hydroformylation of Heterocyclic Olefins Catalyzed by Chiral Phosphine-Phosphite-Rh(I) Complexes

Asymmetric hydroformylation of heterocyclic olefins catalyzed by phosphine-phosphite-Rh(I) complexes has been investigated. Hydroformylation of symmetrical heterocyclic olefins such as 2,5-dihydrofuran, 3-pyrroline derivatives, and 4,7-dihydro-1,3-dioxepin derivatives afforded the optically active aldehydes as single products in 64-76% ee. Unsymmetrical substrates such as 2,3-dihydrofuran and N-(tert-butoxycarbonyl)-2-pyrroline gave a mixture of regioisomers. From N-(tert-butoxycarbonyl)-2-pyrroline was obtained N-(tert-butoxycarbonyl)pyrrolidine-2-carbaldehyde in 97% ee. The hydroformylation products from 2,5-dihydrofuran and N-(tert-butoxycarbonyl)-3-pyrroline have the opposite configurations to those from 2,3-dihydrofuran and N-(tert-butoxycarbonyl)-2-pyrroline, respectively, with the same catalyst. The new phosphine-phosphite ligand (R,S)-3,3′-Me2-BINAPHOS [= (A)-2-(diphenylphosphino)-1,1′-binaphthalen-2′-yl (S)-3,3′-dimethyl-1,1′-binaphthalene-2,2′-diyl phosphite] was prepared and its hydridorhodium complex was characterized by NMR spectroscopy. Using (R,S)-3,3′-Me2-BINAPHOS as a ligand, the enantioselectivity was improved for some substrates. In addition, higher catalytic activity was observed with this ligand for most of the substrates employed.