BINAP catalysis addition

Annual Volume 71 contains 30 checked and edited experimental procedures that illustrate important new synthetic methods or describe the preparation of particularly useful chemicals. This compilation begins with procedures exemplifying three important methods for preparing enantiomerically pure substances by asymmetric catalysis. The preparation of (R)-(-)-METHYL 3-HYDROXYBUTANOATE details the convenient preparation of a BINAP-ruthenium catalyst that is broadly useful for the asymmetric reduction of p-ketoesters. Catalysis of the carbonyl ene reaction by a chiral Lewis acid, in this case a binapthol-derived titanium catalyst, is illustrated in the preparation of METHYL (2R)-2-HYDROXY-4-PHENYL-4-PENTENOATE. The enantiomerically pure diamines, (1 R,2R)-(+)- AND (1S,2S)-(-)-1,2-DIPHENYL-1,2-ETHYLENEDIAMINE, are useful for a variety of asymmetric transformations hydrogenations, Michael additions, osmylations, epoxidations, allylations, aldol condensations and Diels-Alder reactions. Promotion of the Diels-Alder reaction with a diaminoalane derived from the (S,S)-diamine is demonstrated in the synthesis of (1S,endo)-3-(BICYCLO[2.2.1]HEPT-5-EN-2-YLCARBONYL)-2-OXAZOLIDINONE. 

One of the landmark achievements in the area of enantioselective catalysis has been the development of a large-scale commercial application of the Rh(I)/BINAP-catalyzed asymmetric isomerization of allylic amines to enamines. Unfortunately, methods for the isomerization of other families of olefins have not yet reached a comparable level of sophistication. However, since the early 1990s promising catalyst systems have been described for enantioselective isomerizations of allylic alcohols and aUylic ethers. In view of the utility of catalytic asymmetric olefin isomerization reactions, I have no doubt that the coming years will witness additional exciting progress in the development of highly effective catalysts for these and related substrates. 

Since the pioneering studies of asymmetric catalysis with core-functionalized dendrimers reported by Brunner (88) and Bolm (89), several noteworthy investigations have been described in this field. Some examples of the dendritic effects observed in enantioselective catalysis with dendrimers having active sites in the core were discussed in Section II, such as the catalytic experiments with TADDOL-cored dendrimers described by Seebach et al. (59) the asymmetric addition of Et2Zn to aldehydes catalyzed by core-functionalized phenylacetylene-containing dendrimers reported by Hu et al (42)-, the asymmetric hydrogenation investigations with (R)-BINAP core-functionalized dendrimers synthesized by Fan et al. (36) or the results... 

The mechanism involving simple nitrogen-coordinated complexes also accounts for reactivities of certain sterically constrained systems. For instance, 3-(diethyamino)cyclohexene undergoes facile isomerization by the action of the BINAP-Rh catalyst (Scheme 18). The atomic arrangement of the substrate is ideal for the mechanism to involve a three-centered transition state for the C—H oxidative addition to produce the cyclometalated intermediate. The high reactivity of this cyclic substrate does not permit any other mechanisms that start from Rh-allylamine chelate complexes in which both the nitrogen and olefinic bond interact with the metallic center. On the other hand, fro/tt-3-(diethylamino)-4-isopropyl-l-methylcyclohexene is inert to the catalysis, because substantial I strain develops during the transition state of the C—H oxidative addition to Rh. 

Shibasaki has examined catalysis of a complex, prepared in situ from PdCl2, AgOTf, (R)-or (S)-BINAP, 4 A molecular sieves, and H20, in the aldol addition reaction of enolsilanes by (Eq. 8B2.5) [13]. Under these conditions, aryl methyl ketone-derived trimethylsilyl enolates add to benzaldehyde and hydrocinnamaldehyde, affording adducts with up to 73% ee. 

Noyori s BINAP catalysts deserve special attention because their chirality is based on the bulkiness of the naphthalene groups, rather than on carbon or phosphorus asymmetric centers (Figure 3.28, inset) [77]. One of the many examples of asymmetric catalysis using BINAP is the synthesis of (—)-menthol, an important additive for flavors, fragrances, and pharmaceuticals. Starting from myrcene, the process is carried out by Takasago International on a multi-ton scale. The key step is the isomerization of geranyldiethylamine to (R)-citronellal enamine [78], which is then hydrolyzed to (R)-citronellal with nearly 99% ee. 

Very recently, Fan et al. [13] reported on the use of a water-soluble PEO-substitut-ed first- and second-generation Frechet-type dendrimer with a chiral BINOL (1,1 -bi-2-naphthol) unit in catalysis. The enantiomeric excess in asymmetric hydrogenation of 2-[p-(2-methylpropyl)phenyl]acrylic acid with [RuCl(BINAP)(cymene)]Cl in an aqueous system was reported to increase upon addition of the dendritic... 

In addition to rhodium phosphane complexes, ruthenium phosphane complexes have also been successfully applied as catalysis for enantioseleetive hydrogenation of 2-acylamino-2-alkenoic acids and esters1 71,72b 3, enol acetates 18 (R = i-Pr E = COOEt X = OCOCH3 98% ee with BINAP)137, and itaeonic acid138. The absolute configuration of the products from the ruthenium-catalyzed reactions shown below is opposite to that obtained with the corresponding rhodium catalysts. 

During an examination of the use of substituted maleimides 100, Hayashi discovered that the regioselectivity in the addition was a function of the ligand employed (Scheme 8.24) [89]. Whereas, rhodium/BINAPquaternary stereocenter, rhodium/ diene-catalysis led to ds/trans-iraxtaies of 102. 

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