Inoue’s catalyst

The Strecker reaction is defined as the addition of HCN to the condensation product of a carbonyl and amine component to give a-amino nitriles. Lipton and coworkers reported the first highly effective catalytic asymmetric Strecker reaction, using synthetic peptide 43, a modification of Inoue s catalyst (38), which was determined to be inactive for the Strecker reactions of aldimines (see Scheme 6.5) [62], Catalyst 43 provided chiral a-amino nitrile products for a number of N-benzhydryl imines (42) derived from substituted aromatic (71-97% yield 64->99% ee) and aliphatic (80-81% yield <10-17% ee) aldehydes, presumably through a similar mode of activation to that for hydrocyanations of aldehydes (Table 6.14). Electron-deficient aromatic imines were not suitable substrates for this catalyst, giving products in low optical purities (<10-32% ee). The a-amino nitrile product of benzaldehyde was converted to the corresponding a-amino acid in high yield (92%) and ee (>99%) via a one-step acid hydrolysis. 

Scheme 30.1 Asymmetric hydrocyanation using Inoue s catalyst 2.

Inoue s cyclic dipeptide 17 had been shown to catalyze the addition of HCN to aldehydes to form optically active cyanohydrins [70]. Lipton found that this same catalyst was unable to catalyze the mechanistically related Strecker reaction... 

Inoue,S., Tsukuma.I., Kawaguchi,M., Tsuruta,T. Synthesis of optically active polymers by asymmetric catalysts. VI. Behavior of organozinc catalyst systems in the stereoselective polymerization of propylene oxide. Makromol. Chem. 103,151 (1967). 

The first report of the copolymerization of an epoxide, namely, ethylene oxide and C02 is contained in a patent by Stevens [6]. However, this process, when carried out in the presence of polyhydric phenols, provided polymers which were viscous liquids or waxes possessing copious polyether linkages with only a few incorporated C02 units. The earliest metal-catalyzed copolymerization of epoxides and C02 was reported in 1969 by Inoue and coworkers, who employed a heterogeneous catalyst system derived from a 1 1 mixture of diethylzinc and H20 [7, 8], Subsequently, Kuran and coworkers investigated a group of related catalysts prepared from diethylzinc and di- and triprotic sources such as pyrogallol, with a slight improvement over Inoue s system for the production of polypropylene carbonate) from PO and C02 [9],... 

Fig. 18 Representative examples of homogeneous catalysts for CO epoxide copolymerization Inoue s tetraphenylporphyrin aluminium chloride complex (a), zinc hw-2,6-fluorophenoxide complex (b), zinc (3-diiminate complex (c) and chromium-salen complex (d)...

Inoue, S. and Aida, T., Catalysts for Living and Immortal Polymerization , in Ring-Opening Polymerization, Carl Hanser Publishers, Munich, 1993, pp. 197-215. 

The first homogeneously catalysed example was demonstrated by Inoue et. al. in 1976 . They used Rhodium(I) phosphane complexes such as Wilkinson s catalyst... 

Inoue s group pioneered studies on the cyclic peptide (diketopiperazine) 7 (Figure 10.9), which is readily available from L-histidine and L-phenylalanine, and used it as a catalyst for the addition of hydrogen cyanide to benzaldehyde with up to 97% (Equation 10.20) [42]. 

Inoue, S., Novel Zine Carboxylates as Catalysts for the Copolymeryzation of C02 With Epoxides, Makromol. Chem. Rapid Commun., 1980,1, 775. 

A breakthrough in the asymmetric synthesis of cyanohydrins with the use of small-molecuie catalysts was disclosed with Inoue s discovery in 1981 that the cyclic dipeptide 256 (R= Ph) as an organic catalyst mediates the addition of HCN to a variety of aldehydes to yield the corresponding (R)-cyanohydrins in high optical purity (up to 97 % (x) [169]. The structurally similar dipeptide 257 (R = i-Pr), in contrast, furnishes (S)-cyanohydrins, albeit in lower enantiomeric excess (38-81% ee) (170). Even higher enantioselectivity was obtained by Jackson with the Inoue catalyst 256 after careful freeze-drying or recrystallization of the dipeptide catalyst under anhydrous conditions (Scheme 2.33) [171]. In this manner, cyanohydrin 259 could be obtained in 98 % yield and >99 % ee and subsequently utilized in a synthesis of the insecticide (-)-tembamide (260). 

Takahashi, M Nakatani, T Iwamoto, S Watanabe, T Inoue, M. Effect of the composition of spinel-type Ga203-Al203-Zn0 catalysts on activity for the CH4-SCR of NO and optimization of catalyst composition, Ind. Eng. Chem. Res., 2006, Volume 45, Issue 10, 3678-3683. 

Oi and Inoue recently described the asymmetric rhodium-catalyzed addition of organosilanes [35]. The addition of aryl- and alkenyltriaUcoxysilanes to u,y9-unsaturated ketones takes place, in the presence of 4 mol% of a cationic rhodium catalyst generated from [Rh(COD)(MeCN)2]BF4 and (S)-B1NAP in dioxane/H20 (10 1) at 90°C, to give the corresponding conjugate addition products (Eq. 3). The enantioselectivity is comparable to that observed with the boronic acids, as the same stereochemical pathway is applicable to these reactions (compare Scheme 3.7). 

The Inoue-catalyst 1 tolerates exchange of phenylalanine for leucine, affording the catalytically active diketopiperazine cyclo-(S)-His-(S)-Leu (2, Scheme 6.3) [33], As shown in Scheme 6.3, addition of HCN to benzaldehyde and derivatives can be catalyzed by both 1 and 2. It should, however, be noted that the configurations of the cyanohydrins obtained were opposite, depending on whether 1 or 2 was employed as catalyst. With aliphatic aldehydes the diketopiperazine 1 generally affords rather poor enantioselectivity (< 50% ee) [19]. In contrast, catalyst 2 afforded ee as high as 81% for aliphatic aldehydes (Scheme 6.3) [33], The absolute configuration of the product cyanohydrin was determined only for n-butyraldehyde as substrate (not shown in Scheme 6.3) and found to be R [33],... 

The Inoue laboratory reported the first asymmetric hydrocyanation of an aldehyde using a synthetic peptide, cydo[(S)-Phe-(S)-His] (38), to give the cyanohydrin of benzaldehyde in high optical purity (up to 90% ee at 40% conversion). The ee-value of the product was found to diminish with increased reaction time (Scheme 6.5) [57]. The catalytic activity of 38 is presumed to arise from the bifunctional character of the catalyst, wherein aldehyde activation occurs through hydrogen-... 

S. Morita and T. Inoue, Allowable concentrations of organic sulfur compounds for various methane-reforming catalysts. Int. Chem. Eng., 5(1965) 180. 

Furthermore, the same a mmetric addition reaction in chloroform was studied by Ueyanagi and Inoue (22) using as catalyst the terminal amino group of poly(S-alanine), insoluble in chloroform, prepared by the polymerization of the NCA initiated with butylamine in acetonitrile. As Table 5 ows, the optical rotation of the addition product obtained by poly(S-alanine) as catalyst was larger than that obtruned by its terminal model, ethyl S-alaninate or S-alaninepropylamide, similarly to the case of PBLG. When poly(S-alanine) was used as catalyst, however, the largest optkal rotation of the product was obtained when n-3,n being the ratio of the NCA to the initiator in the preparation of the polymer (Table 5). 

T. Shiomura, M. Kohno, N. Inoue, Y. Yokote, M. Akiyama, T. Asanuma, R. Sugimoto, S. Kimura, M. Abe, Catalyst Design for Tailor-Made Polyolefins (Eds. K. Soga, M. Terano), Kodanska, Tokyo, 1994, p. 327. 

Yokata, K. Inoue, T. Naganuma, S. Shozaki, H. Tomotsu, N. Kuramoto, M. Ishihara, N. In Metalorganic Catalysts for Synthesis and Polymerization Springer-Verlag Berlin, 1999 435-445. 

The classical work of Inoue et al. [8] is an early example of a highly enantioselec-tive chiral synthesis effected by a fairly simple chiral catalyst, cydo-[(S)-Phe-(S)-His], which is shown in Fig. 6. 

As a final example of organic catalysis it is interesting to mention the catalytic addition of HCN to an aromatic aldehyde [89]. This old reaction of hydrocyana-tion of benzaldehyde, pioneered by Bredig in 1912 [10], was revisited in 1981 by Inoue et al. [89]. Impressive enantioselectivities (of up to 90% ee) could be reached by using a cyclic dipeptide as the catalyst. The catalyst is the diketopi-perazine formed between (S)-histidine and (S)-phenylalanine. The mechanistic details of this remarkable reaction are still not well understood, but it has been demonstrated by Danda et al. at Sumitomo that the high enantioselectivity is associated with the colloidal state of the catalyst in the organic solvent [90]. 

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