Ytterbium catalyst

Nakagawa and coworkers reported a chiral ytterbium catalyst 34 which was prepared from l,l -(2,2 -bisacylamino)binaphthalene and Yb(OTf)3 in the presence of diisopro-pylethylamine by a method similar to that used for Kobayashi s chiral ytterbium reagent [52] (Scheme 1.65, Table 1.66). The amine also plays an important role in this reaction, because racemic cycloadducts were obtained without the tert-amine. Reduc-... 

In 1997 the application of two different chiral ytterbium catalysts, 55 and 56 for the 1,3-dipolar cycloaddition reaction was reported almost simultaneously by two independent research groups [82, 83], In both works it was observed that the achiral Yb(OTf)3 and Sc(OTf)3 salts catalyze the 1,3-dipolar cycloaddition between nitrones 1 and alkenoyloxazolidinones 19 with endo selectivity. In the first study 20 mol% of the Yb(OTf)2-pyridine-bisoxazoline complex 55 was applied as the catalyst for reactions of a number of derivatives of 1 and 19. The reactions led to endo-selective 1,3-dipolar cycloadditions giving products with enantioselectivities of up to 73% ee (Scheme 6.38) [82]. In the other report Kobayashi et al. described a... 

The 2-pyrones can behave as dienes or dienophiles depending on the nature of their reaction partners. 3-Carbomethoxy-2-pyrone (84) underwent inverse Diels-Alder reaction with several vinylethers under lanthanide shift reagent-catalysis [84] (Equation 3.28). The use of strong traditional Lewis acids was precluded because of the sensitivity of the cycloadducts toward decarboxylation. It is noteworthy that whereas Yb(OTf)j does not catalyze the cycloaddition of 84 with enolethers, the addition of (R)-BINOL generates a new active ytterbium catalyst which promotes the reactions with a moderate to good level of enantio selection [85]. 

A combination of cat. Ybt and A1 is effective for the photo-induced catalytic hydrogenative debromination of alkyl bromide (Scheme 28) [69]. The ytterbium catalyst forms a reversible redox cycle in the presence of Al. In both vanadium- and ytterbium-catalyzed reactions, the multi-component redox systems are achieved by an appropriate combination of a catalyst and a co-reductant as described in the pinacol coupling, which is mostly dependent on their redox potentials. 

Recently the primary amine 39 was transformed into indolizidine 40 using an ytterbium catalyst. After a regio-specific C=C bond insertion of the internal olefin into the Ln-N bond, a second insertion is accomplished as illustrated in the proposed mechanism <2004JOC1038> (Scheme 15). 

Huang YJ, Yang FY, Zhu CJ (2005) Highly enantioseletive biginelli reaction using a new chiral ytterbium catalyst Asymmetric synthesis of dihydropyrimidines. J Am Chem Soc 127 16386-16387... 

Kobayashi and co-workers exploited the use of lanthanide in a variety of achiral reactions and extended them into several catalytic asymmetric reactions. Their work commenced with catalytic asymmetric Diels-Alder reactions [32], The reaction was performed with a chiral ytterbium catalyst prepared from Yb(OTf)3, binaphthol and a tertiary amine. The amine significantly influenced reaction selectivity. When triethyl-amine was used in the preparation of the catalyst, the desired product was obtained in moderate ee (33%) (Table 8, entry 1). After screening several reaction conditions, they found that, in general, bulky amines gave better results (entries 2-6). They suggested interesting explanations of this experimental result on the basis of investigations into catalyst structure. Consequently, the use of cw-l,2,6-trimethylpiperidine combined with 4 A molecular sieves (4A MS) was found to produce the best result (yield 77%, endolexo = 89/11, endo = 95% ee) (entry 6). 

Catalytic Asymmetric Aza Diels-Alder Reactions Promoted by Chiral Ytterbium Catalysts... 

An approach to the synthesis of dihydroxyvitamine D3 and analogs involves the Diels-Alder reaction of the simple unsubstituted 2-pyrone with benzyl vinyl ether (Scheme 10.7). It is well known that the reaction progresses with extreme difficulty under normal conditions. Temperature is precluded as the potential cycloadduct easily decarboxylates. The biactivation mode induces sufficient reactivity as demonstrated by Posner et al. [35]. In the presence of the chiral ytterbium catalyst... 

High ees in the nitrone cycloaddition with oxazolidinone (8.51) have been achieved by Kobayashi and Kawamura using the ytterbium catalyst (8.194). The... 

The well known, D-mannitol-derived bis-aziridine 37 has been used to prepare 6-amino-6-deoxy-2,5-imino-D-glucitol and -1,5-imino-D-mannitol derivatives 38 and 39 as potential glycosidase inhibitors. Treatment of 37 with acetic add, or alternatively allyl alcohol in the presence of an ytterbium catalyst, afforded mono-O-acetylated or -allylated glucitol/mannitol mixtures in 2 1 and 1 2 ratios respectively. ... 

Small particules (15-20 nm) of samarium or ytterbium metal are obtained by vaporization on a THF matrix (14). Samarium readily catalyzes reduction of olefins but not of triple bonds. The corresponding ytterbium catalyst is less active. Methylacetylene is rapidly converted by the Sm catalyst into allene at 0°C. 

The aqueous layer remaining in the separatory funnel contains the ytterbium catalyst. Pour the aqueous layer from the top of the separatory funnel into a preweighed 50-mL Erlenmeyer flask. Completely evaporate the water on a hot plate. Weigh the flask to determine how much catalyst you were able to recover. Place the catalyst in a container that holds the recycled catalyst that will be reused in other classes. 

Y. Huang, F. Yang, C. Zhu, J. Am. Chem. Soc. 2005, 127, 16386-16387. Highly enantioselective Biginelli reaction using a new chiral ytterbium catalyst asymmetric synthesis of dihydropyrimidines. 

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