Aldehydes and acetals were very efficiently converted to acyclic and cyclic dithioacetals in 5 M lithium perchlorate/diethyl ether (LPDE) medium at ambient temperature in high yields. Spectroscopic and other experimental evidences strongly suggest the formation of oxocarbenium ion intermediates from acetals in 5 M LPDE which subsequently reacted with thiols to give the dithioacetals. Under the same conditions ketones and their acetals also reacted, albeit very slowly compared to aldehydes and acetals, to yield dithioacetals. The difference in their reactivity was successfully employed in the chemoselective dithioacetalization of aldehydes and acetals in the presence of ketones and their acetals. The chemoselective dithioacetalization of keto aldehydes has been realized with the keto group remaining intact. The present method offers a convenient, efficient, and neutral medium for the deprotection of acetals to aldehydes and also the chemoselective protection of aldehydes to dithioacetals. © 1994, American Chemical Society. All rights reserved.