Acid-free, organocatalytic acetalization

The acid-free, organocatalytic acetalization of various aldehydes and ketones with NN-bis[3,5-bis(trifluoromethyl)phenyl] thiourea is presented. The neutral, double hydrogen bonding thiourea catalyst can be used at very low loadings of 0.01-1 mol% at room temperature to furnish the respective acetals in 65-99% yield at turnover frequencies around 600 h(-1). Acid-labile TBDMS-protected as well as unsaturated aldehydes can be converted efficiently into their acetals utilizing this very mild and highly practical method. (c) 2005 Elsevier Ltd. All rights reserved.