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

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 pyrano[2,3-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-Oacetyl-2,3-dideoxy-alpha-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. (C) 2011 Elsevier Ltd. All rights reserved.