HClO4·SiO2 catalysed synthesis of alkyl 3-deoxy-hex-2-enopyranosides from 2-hydroxy glucal ester: application in the synthesis of a cis-fused bicyclic ether and a 4-amino-C-glucoside
作者:Preeti Gupta、Nitee Kumari、Aditi Agarwal、Yashwant D. Vankar
DOI:10.1039/b810654a
日期:——
A variety of alcohols react with 2,3,4,6-tetra-O-acetyl-1,5-anhydro-D-arabino-hex-1-enopyranose 1 in the presence of a catalytic amount of HClO4 supported on silica gel to give the corresponding alkyl 3-deoxy-hex-2-enopyranosides 2 in high yield, with short reaction times (10–45 mins) and good α-selectivity. Work-up merely involves filtration of the reagent, followed by chromatographic purification of the crude product. This methodology has also been employed in the synthesis of a bicyclic ether, a useful precursor for cyclic polyethers, and a 4-amino-C-glucoside.
The title compound was divided into three retrosynthetic segments, A, B and C, by disconnecting two C-C bonds at C- and C-. Synthesis of the segment C in the optically active natural form starting from a D-glucose derivatives is described. The key features are stereochemical control which includes a methodology named heteroconjugate addition involving carbon chain extension using carbanion stabilized
Sequential Norrish Type II Photoelimination and Intramolecular Aldol Cyclization of α-Diketones: Synthesis of Polyhydroxylated Cyclopentitols by Ring Contraction of Hexopyranose Carbohydrate Derivatives
作者:Dimitri Alvarez-Dorta、Elisa I. León、Alan R. Kennedy、Angeles Martín、Inés Pérez-Martín、Concepción Riesco-Fagundo、Ernesto Suárez
DOI:10.1002/chem.201301230
日期:2013.7.29
nono‐2,3‐diulose derivatives by irradiation with visible‐light initiates a sequential Norrish type II photoelimination and aldol cyclization process that finally gives polyfunctionalized cyclopentitols. The rearrangement has been confirmed by the isolation of stable acyclic photoenol intermediates that can be independently cyclized by a thermal 5‐(enolexo)‐exo‐trig uncatalyzed aldol reaction with high diastereoselectivity
One of the three spiro-segments in the synthesis of okadaic acid was synthesized under a new heteroconjugate addition strategy. Successive coupling of this spiro-segment with two tautomycin-synthetic segments afforded a hybrid molecule between okadaic acid and tautomycin.