Corey catalyst

Cope rearrangement 17, 213 f., 643 Corey catalysts 74 f., 80 -, aldol condensations with 74 -, carbonyl allylations with 74 -, carbonyl reductions with 74 f. 

Some of the above-mentioned catalysts or precursors are commercially available, such as the Corey catalyst (,S) - 3,3 - d i p h e n yI -1 - met h y 1 tctralr yd ro- 3 H - py r-rolo[l,2-c] [l,3,2]oxazaborole (Me-CBS). The amino alcohol (5)-(—)-2-amino-3-methyl-l,l -diphenylmethan-l-ol, used as the ligand in the Itsuno catalyst is also readily available. The ligand used to prepare the oxazaphospholidine or oxazaphosphinamide complex (from Wills) can be synthesized easily from commeri-cally available material. The preparation of the Bolm (3-hydroxysulfoximine catalyst will be described in this chapter (Figure 11.2). 

A similar approach was reported by Lygo and co-workers who applied comparable anthracenylmethyl-based ammonium salts of type 26 in combination with 50% aqueous potassium hydroxide as a basic system at room temperature [26, 27a], Under these conditions the required O-alkylation at the alkaloid catalyst s hydroxyl group occurs in situ. The enantioselective alkylation reactions proceeded with somewhat lower enantioselectivity (up to 91% ee) compared with the results obtained with the Corey catalyst 25. The overall yields of esters of type 27 (obtained after imine hydrolysis) were in the range 40 to 86% [26]. A selected example is shown in Scheme 3.7. Because the pseudo-enantiomeric catalyst pairs 25 and 26 led to opposite enantiomers with comparable enantioselectivity, this procedure enables convenient access to both enantiomers. Recently, the Lygo group reported an in situ-preparation of the alkaloid-based phase transfer catalyst [27b] as well as the application of a new, highly effective phase-transfer catalyst derived from a-methyl-naphthylamine, which was found by screening of a catalyst library [27c],... 

Figure 5.6. Chiral catalysts for the Mukaiyama aldol reaction (a) Kiyooka catalyst [112,113] (b) Masamune catalyst [114] (c) Corey catalyst [115] (d) Yamamoto catalyst [116,117] (e-f) Kobayashi-Mukaiyama catalysts [118-120].

A modified Corey catalyst in which the boron atom is attached to the benzene ring of polystyrene has been prepared and evaluated. ... 

In an intramolecular aldol condensation of a diketone many products are conceivable, since four different ends can be made. Five- and six-membered rings, however, wUl be formed preferentially. Kinetic or thermodynamic control or different acid-base catalysts may also induce selectivity. In the Lewis acid-catalyzed aldol condensation given below, the more substituted enol is formed preferentially (E.J. Corey, 1963 B, 1965B). 

Epoxidation of aldehydes and ketones is the most profound utility of the Corey-Chaykovsky reaction. As noted in section 1.1.1, for an a,P-unsaturated carbonyl compound, 1 adds preferentially to the olefin to provide the cyclopropane derivative. On the other hand, the more reactive 2 generally undergoes the methylene transfer to the carbonyl, giving rise to the corresponding epoxide. For instance, treatment of P-ionone (26) with 2, derived from trimethylsulfonium chloride and NaOH in the presence of a phase-transfer catalyst Et4BnNCl, gave rise to vinyl epoxide 27 exclusively. ... 

An ingenious application of Corey s ylide (1) was discovered by the Shea group in 199 7 51,52 ugjj g trialkylboranes as initiator/catalyst and 1 as the monomer, a living... 

Another chiral titanium reagent, 11, was developed by Corey et al. [17] (Scheme 1.24). The catalyst was prepared from chiral ris-N-sulfonyl-2-amino-l-indanol and titanium tetraisopropoxide with removal of 2-propanol, followed by treatment with one equivalent of SiCl4, to give the catalytically-active yellow solid. This catalyst is thought not to be a simple monomer, but rather an aggregated species, as suggested by NMR study. Catalyst 11 promotes the Diels-Alder reaction of a-bro-moacrolein with cyclopentadiene or isoprene. 

Corey et al. reported that the catalyst 19, prepared from trimethylaluminum and the bis-trifluorosulfonamide of stilbenediamine (stien), with generation of methane, is a suitable catalyst for the Diels-Alder reaction of 3-acryloyl, and 3-crotonoyl-l,3-oxazo-lidin-2-ones, giving the cycloadducts in high optical purity [28] (Scheme 1.35, Table 1.14). X-ray structure analysis of the catalyst and and NMR studies revealed that... 

Corey et al. synthesized a chiral bis(oxazoline)Fe(III) catalyst 30, the ligand of which was prepared from chiral phenylglycine. The catalyst was formed by the reaction of the ligand with Fel3 in the presence of I2.12 greatly enhances the Lewis acidity of the catalyst owing to the formation of a cationic species [39] (Scheme 1.49). 

Among the many chiral Lewis acid catalysts described so far, not many practical catalysts meet these criteria. For a,/ -unsaturated aldehydes, Corey s tryptophan-derived borane catalyst 4, and Yamamoto s CBA and BLA catalysts 3, 7, and 8 are excellent. Narasaka s chiral titanium catalyst 31 and Evans s chiral copper catalyst 24 are outstanding chiral Lewis acid catalysts of the reaction of 3-alkenoyl-l,2-oxazolidin-2-one as dienophile. These chiral Lewis acid catalysts have wide scope and generality compared with the others, as shown in their application to natural product syntheses. They are, however, still not perfect catalysts. We need to continue the endeavor to seek better catalysts which are more reactive, more selective, and have wider applicability. 

I would like to thank Professors E. J. Corey and K. Narasaka for giving me a chance to work with super-reactive chiral catalyst 9 and TADDOL-based chiral titanium catalyst 31, respectively. 

A series of chiral boron catalysts prepared from, e.g., N-sulfonyl a-amino acids has also been developed and used in a variety of cycloaddition reactions [18]. Corey et al. have applied the chiral (S)-tryptophan-derived oxazaborolidine-boron catalyst 11 and used it for the conversion of, e.g., benzaldehyde la to the cycloaddition product 3a by reaction with Danishefsky s diene 2a [18h]. This reaction la affords mainly the Mukaiyama aldol product 10, which, after isolation, was converted to 3a by treatment with TFA (Scheme 4.11). It was observed that no cycloaddition product was produced in the initial step, providing evidence for the two-step process. 

The catalyst played an important role in the asymmetric synthesis of Corey lactone based on high diastereofacial selective Diels-Alder reaction between chiral acrylate 37 and 5-benzyloxymethylcyclopentadiene [41] (Equation 3.9). The cycloadduct 38 was then converted into chiral Corey lactone [42] by a three-step procedure. 

Cationic oxazaborinane 59 (Figure 3.10) is a chiral super-Lewis-acidic catalyst recently described by Corey and coworkers [61]. The catalyst is in equilibrium with 59a and the oxazaborinane system 59 59a is unstable and undergoes... 

These ligands can readily be obtained by a Grignard reaction of aziridine esters, followed by an acidic detritylation (see Scheme 40) [19,55]. These aziridine carbinol-derived catalysts are equally efficient as the Corey ligand 55 derived from proline carbinols (Fig. 4) [55,56]. 

Corey, E.J. Helal, C.J. (1998) Reduction of Carbonyl Compounds with Chiral Oxazaborolidine Catalysts A New Paradigm for Enantioselective Catalysis and a Powerful New Synthetic Method. Angewandte Chemie International Edition, 37, 1986-2012. 

Corey et al.66 have developed a bidentate chiral ligand 93 for asymmetric dihydroxylation of olefins. As shown in Table 4-13, asymmetric dihydroxylation of a series of olefins using 93 as a chiral catalyst and OsCU as the oxidant gives good to excellent yield as well as good enantioselectivity in most cases. 

Corey and Ishihara29 report the synthesis of a new bis(oxazoline). This catalyst effects Diels-Alder reaction via a tetracoordinated metal complex. Ligand (.S )-8I is synthesized from (iS )-phenylglycine, as depicted in Scheme 5-25. Treatment of 81 with Mgl2 L gives a dark solution of complex 82, which can be utilized as a Diels-Alder reaction catalyst. Thus, reaction of cyclopentadiene with 71 in the presence of 82 yields product 72a with an enantiomeric ratio of over 20 1 (Scheme 5-26). 

Oxazaborolidine catalysts behave like an enzyme in the sense of binding with both ketone and borane, bringing them close enough to undergo reaction and releasing the product after the reaction. Thus these compounds are referred to as chemzymes by Corey.78 The oxazaborolidines listed in Figure 6-6 are representative catalysts for the asymmetric reduction of ketones to secondary alcohols. 

Addition of triethylamine to the oxazaborolidine reaction system can significantly increase the enantioselectivity, especially in dialkyl ketone reductions.79 In 1987, Corey et al.80 reported that the diphenyl derivatives of 79a afford excellent enantioselectivity (>95%) in the asymmetric catalytic reduction of various ketones. This oxazaborolidine-type catalyst was named the CBS system based on the authors names (Corey, Bakshi, and Shibata). Soon after, Corey s group81 reported that another fi-methyl oxazaborolidine 79b (Fig. 6-6) was easier to prepare and to handle. The enantioselectivity of the 79b-catalyzed reaction is comparable with that of the reaction mediated by 79a (Scheme 6-36).81 The -naphthyl derivative 82 also affords high enantioselectivity.78 As a general procedure, oxazaborolidine catalysts may be used in 5-10 mol%... 

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