Antimony pentachloride

Abstract

(A) Chlorination of aromatic compounds by antimony pentachloride has received relatively little attention, except as a route to polychlorinated compounds. An investigation of the reaction of SbCl5 with halobenzenes and toluene indicated that chlorination proceeds by electrophilic substitution, involving an attacking species of low activity. This was evidenced by the almost exclusive ortholpara orientation. (Diagram presented). (B) Tetrasulfur tetranitride (S4N4) reacts in inert solvents with a wide variety of Lewis acids to give isolable adducts. The interest in exploiting the potential synthetic utility of the adduct S4N 4·SbCl5 led to a preliminary result in which treatment of α-bromomethyl ketones 1 with the adduct in toluene at reflux gave the corresponding chloro compounds 3 in good to excellent yields, regardless of the bulkiness of the groups at the α′-position of ketones 1. (Diagram presented). (C) Improved regioselectivity in catalyzed Diels-Alder cycloadditions between non-symmetrical benzoquinones and mono-substituted butadienes can be achieved with SbCl5. (Diagram presented). (D) SbCl5 in sub-stoichiometric quantity, in moist acetonitrile, is an efficient and mild system for the deprotection of TBS derivatives of amines, phenols, primary alcohols and aryl carboxylic acids. Yields for this deprotection are good to excellent. High selectivity for OTBS cleavage is noted in the presence of a ketal group. (Diagram presented). © Georg Thieme Verlag Stuttgart.