Aerobic oxidative desymmetrization

Chiral (nitrosyl)ruthenium(salen) complexes have been found to be efficient catalysts for aerobic oxidative desymmetrization of mc.vo-diols under photoirradiation to give optically active lactols. With the suitable catalysts, high enantioselectivities up to 93% has been achieved. The kinetics of the oxidation depend on the nature of the ligand. On the basis of kinetic parameters and the kinetic isotope effect, it has been suggested that when a ligand with an apical hydroxy group is used, the hydrogen atom... 

Shimizu, H., Onitsuka, S., Egami, H., et al. (2005). Ruthenium(Salen)-Catalyzed Aerobic Oxidative Desymmetrization of Meso-Diols and its Kinetics, J. Am. Chem. Soc., 127, pp. 5396-5413. 

Suzuki T, Morita K, Matsuo Y, Hiroi K. Catalytic asymmetric oxidative lactonizations of meso-diols using a chiral iridium complex. Tetrahedron Lett. 2003 44 2003—2006. Moritani J, Hasegawa Y, Kayaki Y, Ikariya T. Aerobic oxidative desymmetrization of meso-diols with bifunctional amidoiridium catalysts bearing chiral N-sulfonyldiamine ligands. Tetrahedron Lett. 2014 55 1188-1191. 

Subsequent to the development of the (salen)Cr-catalyzed desymmetrization of meso-epoxides with azide (Scheme 7.3), Jacobsen discovered that the analogous (salen)Co(n) complex 6 promoted the enantioselective addition of benzoic acids to meso-epoxides to afford valuable monoprotected C2-symmetric diols (Scheme 7.15) [26], Under the reaction conditions, complex 6 served as a precatalyst for the (salen) Co(iii)-OBz complex, which was fonned in situ by aerobic oxidation. While the enantioselectivity was moderate for certain substrates, the high crystallinity of the products allowed access to enantiopure materials by simple recrystallization. 

Kinetic resolution of secondary alcohols and desymmetrization of diols were reported by asymmetric oxidation using chiral (nitrosyl)Ru(salen) chloride (31) (Eq. (7.42)) [97] in addition to the aerobic oxidation reaction [97d]. 

Aerobic Alcohol Oxidations. The combination of PdCl2(CH3CN)2 (5-10 mol%) with (—(-sparteine (20 mol%) constitutes an effective catalyst system for the oxidative kinetic resolution of secondary alcohols with molecular oxygen as the terminal oxidant, with enantiomeric excesses t)q)ically above 90% ee (eq 45). This enantioselective aerobic oxidation has been successfully extended to the desymmetrization of meso-1,3-diols. 

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