title: Gold(III) chloride catalyzed synthesis of chiral substituted 3-formyl furans from carbohydrates: application in the synthesis of 1,5-dicarbonyl derivatives and furo[3,2-c]pyridine.
abstract: This report describes a gold(III)-catalyzed efficient general route to densely substituted chiral 3-formyl furans under extremely mild conditions from suitably protected 5-(1-alkynyl)-2,3-dihydropyran-4-one using H2 O as a nucleophile. The reaction proceeds through the initial formation of an activated alkyne-gold(III) complex intermediate, followed by either a domino nucleophilic attack/anti-endo-dig cyclization, or the formation of a cyclic oxonium ion with subsequent attack by H2 O. To confirm the proposed mechanistic pathway, we employed MeOH as a nucleophile instead of H2 O to result in a substituted furo[3,2-c]pyran derivative, as anticipated. The similar furo[3,2-c]pyran skeleton with a hybrid carbohydrate-furan derivative has also been achieved through pyridinium dichromate (PDC) oxidation of a substituted chiral 3-formyl furan. The corresponding protected 5-(1-alkynyl)-2,3-dihydropyran-4-one can be synthesized from the monosaccharides (both hexoses and pentose) following oxidation, iodination, and Sonogashira coupling sequences. Furthermore, to demonstrate the potentiality of chiral 3-formyl furan derivatives, a TiBr4 -catalyzed reaction of these derivatives has been shown to offer efficient access to 1,5-dicarbonyl compounds, which on treatment with NH4 OAc in slightly acidic conditions afforded substituted furo[3,2-c]pyridine.
authors: Chemistry Division, CSIR-Indian Institute of Chemical Biology, 4, Raja S. C. Mullick Road, Jadavpur, Kolkata 700032 (India), Fax: (+91) 33-2473-5197.
authors: Kanchan
authors: K
authors: Mal
authors: Abhinandan
authors: A
authors: Sharma
authors: Indrajit
authors: I
authors: Das
mesh_terms: D002241:Carbohydrates / Q000737:chemistry*; D005663:Furans / Q000138:chemical synthesis* / Q000737:chemistry; D017612:Gold Compounds / Q000737:chemistry*; D015394:Molecular Structure; D011725:Pyridines / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D002241:Carbohydrates; D005663:Furans; D017612:Gold Compounds; D011725:Pyridines; C038016:gold chloride
keywords: carbohydrates; chirality; furans; gold; homogeneous catalysis