Desymmetrization catalytic

Scheme 9 Catalytic desymmetrization of meso compounds using 56...

Formal hydration of the double bond appeared by the hydroboration-oxidation sequence. Desymmetrization reactions with catalytic asymmetric hydroboration are not restricted to norbornene or nonfunctionalized substrates and can be successfully applied to meso bicyclic hydrazines. In the case of 157, hydroxy derivative 158 is formed with only moderate enantioselectivity both using Rh or Ir precatalysts. Interestingly, a reversal of enantioselectivity is observed for the catalytic desymmetrization reaction by exchanging these two transition metals. Rh-catalyzed hydroboration involves a metal-H insertion, and a boryl migration is involved when using an Ir precatalyst (Equation 17) <2002JA12098, 2002JOC3522>. 

Recently, Krische and co-workers developed an effective protocol for the catalytic desymmetrization and parallel kinetic resolution of enone-diones via tandem conjugate addition-aldol cyclization (Scheme 66).150 This transformation, involving enantioselective rhodium-catalyzed conjugate addition methodology, enabled the formation of two C-G bonds and four contiguous stereogenic centers from simple precursors with high diastereo- and enantiocontrol. 

Unlike kinetic resolution, catalytic desymmetrization and asymmetrization can afford enantiopure products in theoretical yields of 100 % and are more generally applicable than DKR or deracemization techniques. 

A number of workers have made progress on this front. Asami and coworkers have anchored the stoichiometric base on the solid phase to realize a catalytic desymmetrization using lithiated diamine 135. Andersson has shown that slow addition of LDA results in an improvement in enantioselectivity when using his bicyclic base 136, while Ahlberg has illustrated that a stoichiometric base such as lithiated 1,2-dimethylimidazole results in an efficient catalytic system using diamine 137. Alexakis has published a smdy involving a number of chiral ethane-and propane-diamines in the catalytic deprotonation of cyclohexene oxide. Enan-tioselectivities observed are moderate, with diamine 138 providing the desired product in 59% ee and 80% yield. ... 

The catalytic desymmetrization shown in Scheme 5 involves a meso-tetraene substrate optically pure unsaturated siloxane 23 is obtained in >99% ee and 76% yield [16]. The unreacted siloxy ether moiety is removed to afford optically pure 24. Mo-alkylidenes derived from both enantiotopic terminal alkenes in 22 are likely involved. Since the initial metal-alkylidene generation is rapidly reversible, the major product arises from the rapid RCM of the matched segment of the tetraene. If any of the mismatched RCM takes place, a subsequent and more facile matched RCM leads to the formation of meso-bicycle. Such a byproduct is absent from the unpurified mixture containing 23, indicating the exceptionally high degree of stereodifferentiation induced by the chiral Mo com-... 

BINOL-Ti catalysis is also applicable to carbonyl-ene reaction with formaldehyde or vinylogous and alkynylogous analogs of glyoxylates in the catalytic desymmetrization (vide infra) approach to the asymmetric synthesis of isocarbacycline analogs (Scheme 8C.7) [24],... 

In the mid-1980s Oda et al. reported that of a series of alkaloids screened for catalytic desymmetrization of cyclic meso-anhydrides with methanol, (+)-cinchonine (1) performed best [4-6]. As shown in Scheme 13.2, 10 mol% of this catalyst was... 

For a recent summary of developments in the metal-based and metal-free catalytic desymmetrization of meso anhydrides with alcohols, see A. P. Spivey, B. I. Andrews, Angew. Chem. 2001, 113, 3227-3230 Angew. Chem. Int. Ed. 2001, 40, 3131-3134. 

The enantiomerically enriched 4-hydroxyenones 32 are an important class of chiral building blocks. This class of molecules has generally been obtained by the enzymatic or nonenzymatic catalytic desymmetrization of meso-cyclic diols 31 (or their derivatives) that can be prepared from the meso-endoperoxides 30 [32]. It is also well known that achiral bases such as NEt3 can promote the Kornblum-DeLaMare rearrangement of the meso-endoperoxides 30 [33]. This process is believed to proceed via the E2... 

Highly enantioselective catalytic desymmetrization of meso-epoxides through nucleophihc ring opening was first effectively demonstrated by Nugent, who found that a zirconium trialkanolamine complex catalyzed the addition of azi-dosilanes to meso-epoxides (Scheme 1) [3]. Azide has been the most widely explored nitrogen nucleophile [4,5,6,7], in part due to its utiHty as an amine sur-... 

Oestreich, M., Sempere-Culler, F. and Machotta, A.B. (2005) Catalytic desymmetrizing intramolecular Heck reaction evidence for an unusual hydroxy-directed migratory insertion. Angew. Chem. Int. Ed., 44, 149-52. 

A classical example of catalytic desymmetrization is a regioselective oxidation of polyoles, in particular 1,2-diols to form the corresponding... 

Typical Procedure for the Catalytic Desymmetrization of meso-Epoxides [120]... 

Y. Chen, S. Tian, L. Deng, A highly enantioselective catalytic desymmetrization of cyclic anhydrides with modified cinchona alkaloids, J. Am. Chem. Soc. 122 (39) (2000) 9542-9543. 

In comparison with the asymmetric epoxide-opening reactions described above in Section 9.4, catalytic desymmetrizations of meso-aziridines have relatively limited precedence [151]. Kanai and Shibasaki have disclosed a number of promising results obtained with lanthanide complexes of the chiral phosphinoxide ligand 193 (Scheme 9.24) [152, 153]. These efforts were showcased in the desymmetrization of meso-aziridine 192 with TMSN j to provide azide 194 in 96% yield and 91 % ee. Adduct 194 was subsequently converted into the anti-influenza drug oseltamivir phosphate (Tamiflu, 195) [153]. 

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