Proton-catalyzed addition of alcohols

The chemistry of 1,3-dioxins containing four double bonds is poorly developed. A few examples of nucleophilic additions have been demonstrated. The proton-catalyzed addition of alcohol or carboxylic acid nucleophiles to anhydro derivatives of acetylsalicylic acid - new prodrugs of aspirin - was reported to give the C-2 O-substituted 1,3-dioxanes in 41-60% yield (Equation 19) <2001TL5231, 2003CRC265>. 

Proton-Catalyzed Addition of Alcohols to Glycals Glycals as Glycosyl Donors... 

The proton-catalyzed addition of alcohols to glycals is shown not to be trans diaxial addition. Bollitt et al. [83] reported that triphenylphosphine hydrobromide (TPP-HBr) was the catalyst of choice for mild and high-yield protonation and subsequent glycosidation of glycals (Fig. 5.44). 

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