Heterocycle asymmetric ring opening

Ogawa, C. Azoulay, S. Kobayashi, S. (2005) Bismuth triflate-chiral bipyridine complex catalyzed asymmetric ring opening reactions of meso-epoxide in water., Heterocycles, 66 201-206. 

Recently, Floveyda and Schrock have developed molybdenum-based catalysts (i.e. 744a,b) for an asymmetric ring-opening metathesis (AROM) reaction (Scheme 121) (98JA4041, 98JA9720, 99JA11603). Using a tandem AROM/RCM sequence, they examined the asymmetric synthesis of several heterocyclic compounds. For example,... 

Gillingham DG, Hoveyda AH (2007) Chiral N-Heterocyclic Carbenes in Natural Product Synthesis Application of Ru-Catalyzed Asymmetric Ring-Opening/Cross-Metathesis and Cu-Catalyzed Allylic Alkylation to Total Synthesis of Baconipyrone C. Angew Chem Int Ed 46 3860... 

Heterocycles may also be carbonylated, to give either ring-expanded heterocycles, or ring-opened products. These include epoxides (Scheme 4.29), aziridines (Scheme 4.30), ° oxetanes (Scheme 4.31) and azetidines (Scheme 4.32). The cobalt-catalysed carbonylation of epoxides provides a short route to (3-hydroxyesters 4.73 (Scheme 4.29). These useful synthetic building blocks are often obtained in enan-tiomerically enriched form by the asymmetric reduction of P-ketoesters. As many epoxides are readily available in very high e.e., the carbonylation chemistry provides a useful alternative route. 

Blechert et al. successfully introduced a desymmetrization approach. An asymmetric ring-opening cross metathesis of norbornenedicarboxylic anhydride was rendered possible by a Hoveyda- Blechert type ruthenium- carbene complex with a chiral N-heterocyclic carbene (NHC) ligand (Scheme 5.6). The chiral iirforma-tion of the NHC backbone was translated into ruthenium s active coordination sphere by the steric repulsion of an isopropyl group with a skewed ort/ro-biphenyl substituent [17]. 

Gillingham DG, Hoveyda AH. Chiral N-heterocyclic car-benes in natural product synthesis application of Ru-catalyzed asymmetric ring-opening/cross-metathesis and Cu-catalyzed allylic alkylation to total synthesis of baconipyrone C. Angew. Chem. Int. Ed. 2007 46(21) 3860-3864. 

Palladium remains the most widely recognized transition metal to effect stereoselective allylic alkylation reactions. Consequently, diastereoselective and enantioselective Pd-catalyzed processes are extensively discussed in Sections 14.2 and 14.3. More recent advances in the field of metal-catalyzed al-lylation reactions include the use of chiral iridium complexes, dealt with in Section 14.4 [33, 34]. Section 14.5 describes selected stereoselective copper-catalyzed SN2 -allylation reactions [33, 35-37], while a brief presentation of allylation reactions with other transition metals including Mo and Rh is given in Section 14.6 [8, 13, 33, 38, 39]. The closing Section 14.7 deals with selected methods for asymmetric ring-opening reactions of unsaturated heterocycles [38, 40, 41]. 

Asymmetric Ring-Opening Reactions of Unsaturated Heterocycles... 

Lastly, Antilla has disclosed a novel asymmetric desymmetrization of a wide range of aliphatic, aromatic, and heterocyclic meso-aziridines with TMS-N3 promoted by 11 and related 12 (Scheme 5.31) [56]. Uniquely, this is one of only several reports of electrophilic activation of nonimine substrates by a chiral phosphoric acid. Mechanistic studies suggest that silylation of 11 or 12 by displacement of azide generates the active catalytic species A. Consequently, the aziridine is activated through coordination of it carbonyl with chiral silane A to produce intermediate B. Nucleophilic ring opening by azide furnishes the desymmetrized product and regenerates 11 or 12. 

Higashiyama K, Matsumura M, Kurita E, Yamauchi T. Asymmetric syntheses of pyrrolidine and piperidine derivatives via regio- and stereo-selective ring-opening reactions of chiral zone. Heterocycles 2012 86(1) 371-80. 

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