An efficient, continuous flow technique for the chemoselective synthesis of thioacetals

By optimizing a reagent’s residence time within a packed-bed reactor, it is possible to overcome selectivity issues frequently encountered in stirred reaction vessels. This important feature is demonstrated for the chemoselective protection of 4-acetylbenzaldehyde whereby 1-[4-1,3-dithian-2-yl-phenyl]ethanone is obtained in excellent yield and purity. In addition, the generality of the technique is highlighted via the protection of numerous aldehydes and ketones affording the respective thioacetal/ketal in excellent yield (>99.1%) and purity (>99.9%), with space-time yields in the range of 0.44-1.10 g h⁻¹.