The new hemilabile phosphorus ligand (II) is generated in situ by partial oxidation of the DIOP-type ligand (I) with RhCl3·H2O and found to be highly efficient for the asymmetric synthesis of diarylmethanols. The novel ligand can be isolated as stable borane complex (III) which exhibits similar catalytic activity. -(ARATO, T.; SUZUKI, K.; KONDO*, K.; AOYAMA, T.; Synthesis 2006, 22, 3809-3814; Grad. Sch. Pharm. Sci., Nagoya City Univ., Mizuho, Nagoya 467, Japan; Eng.) -Mais 13-090
A s y m m e t r i c S y n t h e s i s o f D i a r y l m e t h a n o l s Abstract: The asymmetric synthesis of diarylmethanols using a new hemilabile phosphorus ligand based on the concept of conformational control is described.We have been interested in developing novel chiral ligands based on the concept of conformational control. 1 In order to expand the scope of our concept, we planned to develop novel hemilabile phosphorus ligand 2 1 with both soft and hard coordinated centers within one molecule. Figure 1 shows the possible design of a novel hemilabile ligand 1, such that the soft diarylphosphino group (PAr 2 ) coordinates with a soft metal and the hard diarylphosphoryl group (POAr 2 ) coordinates with a hard metal. These two types of coordination allow conformational fix of a soft metal-hard metal-hemilabile ligand 1 complex, leading to the creation of a favorable reaction environment. Figure 1 Possible design of a soft metal-hard metal-hemilabile ligand 1 complexThere are two typical approaches to the catalytic asymmetric synthesis of diarylmethanols, reduction of the corresponding diaryl ketones 3 or arylation of aromatic aldehydes. 4 However, efficient methods for the catalytic asymmetric synthesis of optically active diarylmethanols are limited. We were interested in applying the novel hemilabile ligand 1 to the rhodium-catalyzed asymmetric phenylation of aromatic aldehydes with phenylboronic acids as follows: (1) No successful examples for this rhodium-catalyzed asymmetric phenylation of aromatic aldehydes have been reported. 4a-d (2) Some successful methods 4e for the arylation of aromatic aldehydes make use of air-sensitive organozinc reagents, which limit large-scale application. A solution could be the application of arylboronic acids, which are easy to handle and are commercially available or are straightforward to prepare, to the preparation of chiral diarylmethanols. 4g Miyaura 4a has reported rhodium-2-(diphenylphosphino)-2¢-methoxy-1,1¢-binaphthyl 5 (Rh-MOP) catalyzed asymmetric phenylation of 1-naphthaldehyde (3a) with phenylboronic acid giving 1-naphthyl(phenyl)methanol (4a) with 41% ee. We first chose 2 as a substrate and began to screen a variety of 4,5-bis[(diarylphosphino)methyl]-1,3-dioxolane derivatives 2 as the precursor of hemilabile phosphorus ligand 1. 6 Since hemilabile phosphorus ligand 1 was found to be very easily oxidized to bis-phosphine oxide 5 in air, it was initially decided to produce 1 in situ with a rhodium(III) complex. The results are shown in Table 1. Reactions were carried out with 2.0 equivalents of sodium tert-butoxide as a base and phenylboronic acid in 1,2-dimethoxyethane-water (5:1) at 100°C. First, the effects of the pendant diarylphosphino (PAr 2 ) group were examined. As shown in Table 1, entries 1 and 2, the pendant diarylphosphino group plays an important role: compare Ar = Ph (58% yield, 2% ee) and Ar = 4-MeO-3,5-Me 2 C 6 H 2 7 (97% yield, 75% ee). In the case of entry 2, only a fragment of the monophosphine oxide sodium salt 6 was observed in the reactio...
A s y m m e t r i c S y n t h e s i s o f D i a r y l m e t h a n o l s Abstract: Asymmetric synthesis of diarylmethanols by Rh(I)-catalyzed arylation of aromatic aldehydes with arylboronic acids, is described. A catalyst comprised of [RhCl(coe) 2 ] 2 and i-Pr-DuPHOS affords diarylmethanols with up to 66% ee. To the best of our knowledge this is the best enantioselectivity reported for Rh-catalyzed arylation of aldehydes.Optically active diarylmethanols are very important intermediates for the synthesis of some biologically active compounds. 1 Two typical approaches, reduction of the corresponding diaryl ketones 2 or arylation of the aromatic aldehydes, 3,4 exist for their catalytic asymmetric synthesis; however, efficient catalytic asymmetric synthesis of optically active diarylmethanols is rather limited. Despite many reports, only two successful examples have been reported by Bolm 4a and Shibasaki. 4b Since no successful example for asymmetric synthesis of optically active diarylmethanols in Rh(I)-catalyzed arylation of aromatic aldehydes with arylboronic acids has been reported, 5 despite the highly successful Rh(I)-catalyzed asymmetric 1,4-conjugate addition to electron-deficient alkenes 6 and imines 7 that have been reported, we were interested in developing the Rh(I)-catalyzed asymmetric arylation of aromatic aldehydes. Herein, we report our preliminary results on the Rh(I)-catalyzed asymmetric arylation of aromatic aldehydes with arylboronic acids. Figure 1We began by screening a range of ligands in the arylation of 1-naphthaldehyde (1) with PhB(OH) 2 and t-BuONa, and a catalytic amount of [RhCl(coe) 2 ] 2 (3 mol%; coe = cyclooctene). Miyaura reported that MeO-MOP 8 afforded moderate asymmetric induction (78%, 41% ee), while DIOP 9 and BINAP 10 were ineffective. 5a Both the Trost ligand 11 and BPPFA, 12 having a large P-Rh-P angle, were ineffective ligands (
Development of a new hemilabile P-P=O ligand based on the concept of conformational control is described. In Rh-catalyzed enantioselective phenylation of aromatic aldehydes with phenylboronic acid, MOD-DIOP monophosphine oxide is shown to function as a good ligand.We have recently been developing a novel chiral phosphine ligand and an N-heterocyclic carbene ligand based on the concept of conformational control. 1 In order to expand the scope of our concept, we planned to develop novel hemilabile P-P=O ligand 2 1 with both soft and hard coordinated centers within one molecule. Figure 1 shows the possible design of a novel hemilabile ligand 1, such that the soft Ar 2 P group coordinates with a soft metal and the hard Ar 2 P=O group coordinates with a hard metal. These two coordinations allow a fixed conformation of the complex between hemilabile ligand 1 and metals (soft and hard), leading to the creation of a favorable asymmetric environment. Figure 1 Possible designWe were interested in applying a novel hemilabile ligand 1 to Rh-catalyzed asymmetric phenylation 3 of aromatic aldehydes with phenylboronic acids, because no successful example for this Rh-catalyzed asymmetric phenylation of aromatic aldehydes has been reported, 4 although highly successful Rh-catalyzed asymmetric 1,4-conjugate addition to electron-deficient alkenes 5 and addition to tuned imines 6 have been reported. Miyaura 4a has reported Rh-MOP 7 -catalyzed asymmetric phenylation of 1-naphthaldehyde (2) with phenylboronic acid, giving (1-naphthyl)phenylmethanol (3) in 41% ee (Scheme 1). 8 We first chose 2 as a substrate and began to optimize reaction conditions with MOD-DIOP, 9 bisphosphine 4, as the precursor of hemilabile P-P=O ligand
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.