Montmorillonite K-10 clay-catalyzed Ferrier rearrangement of 2-C-hydroxymethyl-d-glycals, 3,4,6-tri-O-alkyl-d-glycals, and 3,4-(dihydro-2H-pyran-5-yl)methanol: a few unexpected domino transformations |
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Authors: | Kumaran Elumalai Santhi Meenakshisundaram Balasubramanian Kalpattu K Bhagavathy Shanmugasundaram |
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Institution: | Shasun Research Centre, Chennai, Tamil Nadu, India. |
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Abstract: | Montmorillonite K-10 clay-catalyzed substitution reactions of 3,4,6-tri-O-alkyl-2-C-hydroxymethyl-d-glycals, 3,4,6-tri-O-acetyl-d-glycals, 3,4,6-tri-O-alkyl-d-glycals, and 3,4-(dihydro-2H-pyran-5-yl)methanol with a few alcohols and phenols are described. The reactions of 2-C-hydroxymethyl-d-glycals with phenols were similar to those of 2-C-acetoxymethyl-d-glycals and afforded pyrano2,3-b]benzopyrans. This montmorillonite K-10 clay-catalyzed transformation is facile both under ambient (Method 1) and microwave conditions (Method 2). Ferrier rearrangement of 3,4-(dihydro-2H-pyran-5-yl)methanol with p-cresol, 2,6-xylenol, and ethanol led to totally unexpected transformations. Reaction of 2-C-hydroxymethyl-d-galactal with 2,6-dimethylphenol in the presence of montmorillonite K-10 led to a novel domino transformation affording 4-(5',6'-dihydro-4H-pyran-3'-ylmethyl)-2,6-dimethylphenol. In contrast, 3,4,6-tri-O-acetyl-d-glucal furnished the Ferrier rearrangement product, 2,6-dimethylphenyl 4,6-di-O-acetyl-2,3-dideoxy-α-d-erythro-hex-2-enopyranoside. Also, isomerization of 3,4,6-tri-O-alkyl-d-glycals to products of allylic rearrangement, 2,3-unsaturated-O-glycosides in good yields is reported. |
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