Simple and efficient syntheses, catalysed by a mixed Lewis acid system (ZrCl(4)/ZnI(2)), of enantiomerically pure 2- and 2,3-disubstituted furan derivatives--including important synthons such as 3-iodofuran and 3-(hydroxymethyl)furan derivatives--from commercially available 3,4,6-tri-O-acetyl-D-glucal are described. The transformation is achieved through a synergistic interaction between ZrCl(4) and ZnI(2) in catalytic amounts.
The development of an innovative method to access enantiopure 2,4-disubstituted 6-hydroxy-1,6-dihydro-2H-pyridin-3-ones starting from D-glucal via the aza-Achmatowicz transformation has been described. These highly functionalized pyridin-3-ones have been utilized for the synthesis of contiguously substituted pyridines through a rapid and efficient Et(3)N/Ac(2)O promoted cyclo-elimination, aromatization cascade, allowing the facile assembly of important pyridine-based building blocks like 2-substituted 3-acetoxy-4-iodopyridines and enantiopure 2-substituted 3-acetoxy-4-pyridinemethanols possessing benzylic stereogenic centers, whose synthesis otherwise would be tedious. The utilization of commercially available sugars as starting materials, mild reaction conditions, catalytic transfer hydrogen (CTH) of α-furfuryl azide derivatives, transfer of chiral aryl/alkyl methanols from enulosides to pyridin-3-ones and pyridines, high yields, and short reaction times are key features of this method. The utility of the method has been further exemplified by demonstrating the usage of the 2-substituted 3-acetoxy-4-iodopyridine for the construction of biologically significant molecules like 2,7-disubstituted furo[2,3-c]pyridines and 7,7'-disubstituted 2,2'-bifuro[2,3-c]pyridines.
Furan derivatives R 0060Facile Synthesis of Enantiomerically Pure 2-and 2,3-Disubstituted Furans Catalyzed by Mixed Lewis Acids: An Easy Route to 3-Iodofurans and 3-(Hydroxymethyl)furans. -A synthesis, catalyzed by mixed Lewis acids (ZrCl4/ZnI2), of enantiomerically pure 2-and 2,3-disubstituted furan derivatives in good to very good yields from commercially available 3,4,6-tri-O-acetyl-D-glucal is described. Key features of this method are the use of inexpensive reagents in catalytic amounts, mild reaction conditions and an easy workup procedure. -(SAQUIB, M.; HUSAIN, I.; KUMAR, B.; SHAW*, A. K.; Chem. Eur. J. 15 (2009) 24, 6041-6049; Div. Med. Process Chem., Cent. Drug Res. Inst., Lucknow 226 001, India; Eng.) -Bartels 41-094
Sugar‐based Morita–Baylis–Hillman (MBH) acetates easily obtained from commercially available D‐glucal underwent rapid reaction with 1,2‐benzenediamines to give, in good yields, a series of enantiomerically pure tricyclic pyrano‐fused 1,5‐benzodiazepines with multiple points of diversity, which could serve as potential drug scaffolds. The driving force behind this reaction seemed to be the high stability associated with the conjugated tricyclic system. The reaction involved an unprecedented amine–carbonyl condensation/[3,3]‐sigmatropic rearrangement/cyclization cascade.
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