We herein described the design, synthesis and application of two recyclable benzyl-type fluorous tags with double fluorous chains. The benzyl-type fluorous tags were prepared in 3 steps from a commercially available fluorous alcohol. The glycosylation of the benzyl-type tags with imidate donors proceeded smoothly to provide the corresponding fluorous-tagged carbohydrates in good to excellent yields, which were readily purified by fluorous solid-phase extraction (FSPE). Efficient removal of the tags from tag-tethered carbohydrates were conducted under the common catalytic hydrogenation condition and the initial benzyl-type fluorous tags could be regenerated via a 2-step simple procedure in 69%–93% yields. The utility of the new benzyl-fluorous tag was demonstrated via the FSPE-assisted synthesis of oligosaccharides Gb3.Download high-res image (130KB)Download full-size imageTwo recyclable benzyl-type fluorous tags with double fluorous chains were designed, synthesized and applied to the synthesis of oligosaccharide Gb3.

We have developed an easy and practical method for the synthesis of α,β-unsaturated oximes and nitriles from readily available propargylic alcohols with hydroxylamine hydrochloride (NH2OH·HCl) under metal-free conditions. By using or not using p-toluenesulfonyl chloride (p-TsCl) as the dehydrating promoter, the desired nitriles or oximes could be obtained, respectively via a three-step one-pot or two-step one-pot process in moderate to excellent yields with good functional group compatibility.

An efficient method to rapidly synthesize 3-deoxy-d-manno-2-octulosonic acid (Kdo) and its derivatives in large scale has been developed. Starting from d-mannose, the di-O-isopropylidene derivative of Kdo ethyl ester was prepared in three steps on a scale of more than 40 g in one batch in an overall yield of 75–80% without any intermediate purification. Kdo, Kdo glycal, and 2-acetylated Kdo ester were synthesized quickly in high yield from a di-O-isopropylidene derivative of Kdo ethyl ester. 2-Deoxy-β-Kdo ester was obtained with high stereoselectivity via the epimerization of the α-isomer using t-BuOH as a proton source.

An efficient method was developed to synthesize ferrocene-based bifunctional amine–thioureas bearing multiple hydrogen-bonding donors. Asymmetric Michael addition of acetylacetone to nitroolefins catalyzed by these novel bifunctional catalysts affords the Michael adducts in high yield and moderate to excellent enantioselectivities. Multiple hydrogen-bonds play an important role in accelerating the reaction.

This Letter described the synthesis of the first diarylprolinol silyl ether-derived bifunctional thiourea organocatalysts. The catalysts were applied to the asymmetric Michael addition of aldehydes to nitroalkenes to give the desired adducts in good yields (up to 99%) with excellent enantioselectivities (up to 99% ee) and excellent diastereoselectivities (up to 99:1). The spatial placement of C-4 substituent is of importance to the reaction activity and stereoselectivity.

An efficient method was developed to synthesize ferrocene-based bifunctional amine–thioureas bearing multiple hydrogen-bonding donors. Asymmetric Michael addition of acetylacetone to nitroolefins catalyzed by these novel bifunctional catalysts affords the Michael adducts in high yield and moderate to excellent enantioselectivities. Multiple hydrogen-bonds play an important role in accelerating the reaction.