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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
Author(s) -
Mal Kanchan,
Sharma Abhinandan,
Das Indrajit
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201402286
Subject(s) - chemistry , nucleophile , furan , pyridinium , pyridine , medicinal chemistry , alkyne , pyran , sonogashira coupling , catalysis , organic chemistry , palladium
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 H 2 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 H 2 O. To confirm the proposed mechanistic pathway, we employed MeOH as a nucleophile instead of H 2 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 TiBr 4 ‐catalyzed reaction of these derivatives has been shown to offer efficient access to 1,5‐dicarbonyl compounds, which on treatment with NH 4 OAc in slightly acidic conditions afforded substituted furo[3,2‐ c ]pyridine.