Rhenium(V)-Catalyzed Synthesis of 2-Deoxy-α-glycosides

Abstract

A mild method for the synthesis of 2-deoxysugars from the coupling of glycals with a range of nucleophiles is described. The method employs 1 mol % of an air- and moisture-tolerant rhenium-oxo complex [ReOCl3(SMe2)(Ph3PO)] as a catalyst for the formation of O-, N-, and S-alpha-glycosides. The catalytic system tolerates a number of commonly employed protecting groups, including isopropylidene acetals, alkyl and silyl ethers, acetates, and benzoates. Furthermore, the high-oxidation-state complex selectively catalyzes the coupling with the glycal acceptor in preference to oxidation of the glycals, alcohols, and even thiols.

Oxidorhenium(V) Complexes with Tridentate and Tetradentate Phenol‐Based Ligands

“…[20] The metal precursors [ReOX 3 -(OPPh 3 )(SMe 2 )] [35,36] (X = Cl or Br) and [ReOBr 3 -(PPh 3 ) 2 ] [37] were prepared essentially according to known procedures.…”

Palladium‐Catalyzed Direct Stereoselective Synthesis of Deoxyglycosides from Glycals

“…Pleasingly, high yields (68–86 %) and excellent selectivity for α‐linked glycosides (α/β ratio of >10:1 to >30:1 ) were obtained in all examples, with the exception of peracetylated galactal 1 e (entry 4). Although we show that ester groups are tolerated elsewhere in the glycal donor (Table 3, entry 1), the presence of a deactivating ester group at C‐3 in close proximity to the reacting double bond is known to significantly decrease the reactivity of the donor 2a, 7. Encouragingly, the reaction was also applicable to glycosylations with glucal substrates, and reactions of 3,4‐ O ‐siloxane‐protected 4 a 2c and 4 b 2c with primary and secondary OH nucleophiles 2 a or 2 f afforded the corresponding glycosides 7 a , 7 b , and 7 f with high α‐stereocontrol (α/β from >30:1 to α only) and good yields (68–86 %, entries 6–8).…”

Direct Reductive Deoxygenation of Aryl Ketones Catalyzed by Oxo‐Rhenium Complexes

“…Ketones, silanes, and catalysts were obtained from commercial suppliers and were used without further purification. [ReIO 2 (PPh 3 ) 2 ], [18] [ReOBr 3 (PPh 3 ) 2 ], [28] [ReOCl 3 (PPh 3 ) 2 ], [28] [ReOCl 3 (SMe 2 )(OPPh 3 )], [29] PhSiD 3 , [30] and PhMe 2 SiD [31] were prepared according to literature procedures. Flash chromatography was performed on MN Kieselgel 60 M 230-400 mesh.…”