Methyltrioxorhenium‐Catalyzed Epoxidation‐Methanolysis of Glycals under Homogeneous and Heterogeneous Conditions

Abstract

Abstract:The efficient and high yielding domino epoxidation-methanolysis of glycals 8 -15 has been achieved by oxidation with UHP in MeOH catalyzed by MTO. The products have been conveniently isolated as 2-acetoxy derivatives 16 -23a, b by direct acetylation of the crude mixtures. Homogeneous MTOamine complexes 5 -7, heterogeneous poly(4-vinylpyridine)/MTO compounds I -III, and microencapsulated polystyrene/MTO systems IV -VII were also tested and demonstrated their effectiveness as catalysts for the oxidation step. The facial diastereoselectivity of the oxidation ranged from satisfactory to excellent depending on the substrate and could be optimized by ample screening of catalysts. Complete conversions of substrates and nearly quantitative yields of products were obtained under environmentally friendly experimental conditions and with the use of simple work-up procedures.

Synthesis of l-Hexoses

“…Epoxidation of 6-deoxy- l -glycals followed by opening of the epoxide has been shown to lead to the preparation of 6-deoxy- l -glycosides. The epoxidation has been accomplished with DMDO, methyltrioxorhenium/urea hydrogen peroxide complex, or RuCl 3 /CeCl 3 /NaIO 4 (Scheme ). − Opening of the epoxide in situ or afterward with various nucleophiles resulted in 6-deoxy- l -glucosides 619 having different anomeric functionalities (methyl, uridine diphosphate, dibutyl phosphate, and acetate).…”

Remarkable Oxidation Stability of Glycals: Excellent Substrates for Cerium(IV)-Mediated Radical Reactions

“…Importantly, epoxidation of glycals, discovered in the seminal work of Danishefsky, resulted in many examples from the synthesis of biologically interesting oligosaccharides and glycoconjugates . While dimethyldioxirane (DMDO) is a convenient reagent for this transformation, other oxidants such as methyltrioxorhenium (MTO) have received growing attention recently . These reactions work remarkably well with glycals 1 , whereas simple cyclic enol ethers such as 2,3-dihydropyran are easily cleaved under acidic conditions or in the presence of manganese(III) .…”

MoO 2 (acac) 2 anchored on organic copolymer-inorganic hybrid zirconium phosphonate-phosphate functionalized by pyridines as highly efficient, reusable catalysts for alkene epoxidation

“…Molybdenum-based catalysts used in homogeneous phase had shown remarkable catalytic activity and efficient use of oxidant in olefin epoxidation processes but display industrial problems associated with corrosion and deposition of the catalyst as well as difficulty in catalyst recovery [25][26][27][28][29][30]. Therefore, there is a need to develop improved strategies for recycling of catalysts for economical and environmental concerns [31][32][33][34][35][36][37].…”