Hashimoto catalyst

The Hashimoto catalyst (9.101) has been used to give very high stereocontrol in the selective insertion into the enantiotopic aryl C-H bonds of substrate (9.102), to give the product (9.103) with a quaternary chiral centre in up to 98% ee. ... 

The intermolecular version of the above described reaction has also been reported [92]. In the first example the reaction of a rhodium catalyst carbonyl ylide with maleimide was studied. However, only low enantioselectivities of up to 20% ee were obtained [92]. In a more recent report Hashimoto et al. were able to induce high enantioselectivities in the intermolecular carbonyl ylide reaction of the... 

As shown in the previous two sections, rhodium(n) dimers are superior catalysts for metal carbene C-H insertion reactions. For nitrene C-H insertion reactions, many catalysts found to be effective for carbene transfer are also effective for these reactions. Particularly, Rh2(OAc)4 has demonstrated great effectiveness in the inter- and intramolecular nitrene C-H insertions. The exploration of enantioselective C-H amination using chiral rhodium catalysts has been reported by several groups.225,244,253-255 Hashimoto s dirhodium tetrakis[A-tetrachlorophthaloyl-(A)-/ r/-leuci-nate], Rh2(derived rhodium complex, Rh2(i -BNP)4 48,244 afforded moderate enantiomeric excess for amidation of benzylic C-H bonds with NsN=IPh. 

M., Mukai, S.R., Kawase, M., and Hashimoto, K. (2003) Methanol to olefins using ZSM-5 zeolite catalyst membrane reactor. Chem. Eng. Sci.,... 

Asymmetric activation of the C—H bonds in benzyl silyl ethers was achieved by using Hashimoto s A-phthaloyl-based Rh2((5)-PTTL)4 catalyst (Figure 5.6) in high diastereoselectivities and enantioselectivities (Scheme 5.15). The well-established dirhodium tetraprolinates such as Rh2((5)-DOSP)4 and Rh2((R)-DOSP)4 catalysts, which generally are excellent catalysts for asymmetric C—H bond activation, were not suitable catalysts in these reactions. 

Next to the above presented use of SiCl for the in situ preparation of a Lewis acid catalyst with a Lewis base for the aldol reaction, it is possible to apply this compound as a reagent in the ring opening of epoxides leading to chlorinated alcohols. Denmark [104] reported that the chiral phosphoramide 38 catalyzed the asymmetric ring opening reaction of meso-epoxides in the presence of tetrachlo-rosilane. Similar examples were provided by Hashimoto in 2002 [105], applying the A -oxide 39 as catalyst (Scheme 30). 

Later in 2005, Hashimoto [106] reported the asymmetric ring opening reaction of cyclohexane oxide with catalyst 30 and afforded the corresponding chlorohydrin in high yield and enantioselectivity (Scheme 31). 

With these results in hand, we turned our attention to the rational design of enantio-merically pure complexes [23, 24] that might direct the absolute sense of the cyclization of 47 to 48 (Eq. 2). The best catalyst reported to date for the cyclization of a /9-keto methyl ester such as 47 is that of Hashimoto [25], which effects C-H insertion with up... 

Hashimoto has noted improved enantioselectivities for C-H insertion of indane and tetralin substrates using dirhodium tetrakis(N-phthaloyl-tert-butylleucinate)-based catalysts (Scheme 17.9) ]49]. In the best of these examples, 84% ee was obtained with 1,1-dimethyltetrahn 9 (5 equiv) and NsN=IPh. Despite the modest enantiomeric ex-... 

After completing his initial intramolecular cycloaddition, Hodgson utilized conditions that had been optimized for the intermolecular cycloaddition of DMAD with simple cyclic carbonyl ylides used by Hashimoto and co-workers (139). Hodgson et al. (140) found that the reaction indeed gave excellent overall chemical yield, but the enantioselectivity dropped to 1%, giving essentially a racemic mixture. It appeared that ee ratios were sensitive to the electronic nature of the dipole. Hodgson chose to screen several binaphthol derived rhodium catalysts of the type developed by McKervey and Pirrung, due in part to the reports of... 

Hashimoto and co-workers (139) further looked at an intermolecular carbonyl ylide cycloaddition screening several different chiral rhodium catalysts. The Hashimoto group chose to study phthaloyl amino acid derivatives for enantiocon-trol of the cycloaddition reactions (Fig. 4.8). Using fluorinated or ethereal solvents with the phthaloyl catalysts gave ee ratios of 20-69%. 

To improve these selectivities, Hashimoto studied several catalysts that had been found highly effective for enantioselective C—H insertion reactions. The new catalysts incorporated an additional benzene in the naphthyl system to increase the steric bias of the catalyst. By using the second-generation catalysts in trifluorotoluene as solvent, at 0 °C, and short reaction times gave ee ratios of 68-92%. Lowered reaction temperature generally resulted in reduced chemical yields but did not erode the ee ratio. Tether lengths one smaller or one larger also tended to erode the ee ratio (Scheme 4.73). 

Hashimoto and co-workers (206,207) recently published enantioselectivities of up to 92% ee in carbonyl ylide cycloadditions to acetylenic esters in the presence of a chiral rhodium catalyst (Scheme 11.58). 

Hashimoto and co-workers, on the other hand, studied the intramolecular reaction between cyclic carbonyl yield and dimethyl acetylenedicarboxylate (DMAD) (Equation (14)). With dirhodium(ii) tetrakis[A-benzene-fused phthaloyl-(A)-valinate] [Rh2(WBPTV)4] 104, high enantioselectivity (68-92% ee) was achieved over a range of diazo substrates.The high level of enantiocontrol provided conclusive evidence that chiral Rh(ii) catalyst is associated with the ylide in the cycloaddition step. 

S. Hashimoto, M. Hayashi, and R. Noyori, Glycosylation using glucopyranosyl fluorides and silicon-based catalysts. Solvent dependency of the stereoselection, Tetrahedron Lett. 25 1379 (1984). 

Hashimoto has shown that the the valine-derived catalyst Rh2(S-BPTV)4 (5) is effective in intermolecular tandem cyclization/intermolecular cycloaddition resulting in the formation of 46 in 92% ee (Eq. (26) [10]. More recent studies have broadened the range of substrates that can be used in the reaction although the enantioselectivity is variable [38,39],... 

About the same time McKervey reported A-sulfonamidoprolinate catalysts [53] (17), and later Ikegami, Hashimoto, and co-workers described uses of dirhodium(II) catalysts with ligands that were phthalimide derivatives of phenylalanine [54] (18a), fer/-leucine [55] (18b), and alanine (18c), but they were similarly unselective in intermolecular cyclopropanation reactions of ethyl diazoacetate. Only when Davies applied chiral prolinate 17a and those that he reported for the first time (17c, X = rBu, C12H25) to cyclopropanation reactions of vinyldiazocarboxylates (Eq. 5.12) did the value of these catalysts for cyclopropanation reactions become fully expressed (Table 5.6) [56,57], The advantage of 17c (X = C12H25) is its solubility in pentane, even at -78°C. 

Enantiocontrol with 21-23 is lower than that achieved with chiral copper catalysts for reactions of diazoacetates with styrene and a few other alkenes examined thus far [68], but the carboxamidates display far greater stereocontrol than do the dirhodium(II) carboxylates for the same reactions [69]. However, Hashimoto has reported the use of chiral piperidinonate 24 and found exceptional enantiocontrol in the cyclopropanation of styrene and both mono- and... 

Since the early reports by the research groups led by McKervey and Hashimoto and Ikegami, major advances have been made in the applications of these catalysts. McKervey has reported [117] a highly diastereoselective synthesis of chromanones with enantiocontrol up to 82% ee (Eq. 5.26), and Hashimoto [118] recently reported a clever asymmetric synthesis of [3-lactams (Eq. 5.27), previously prepared by Ponsford and Southgate with Rh2(OAc)4 as the First published... 

For the production of higher-fructose syrup, Hashimoto and co-workers proposed a three-section SMB containing two different kinds of columns [11] first, separation columns included in the simulated solid-phase movement, which are filled with a stationary phase possessing only adsorptive properties, and second, reaction columns filled with a heterogeneous catalyst which remain stationary relative to the outlet ports, as shown in Fig. 6.6. 

---