Preparation of Pyrylium Tetrafluoroborate (Pyry‐BF 4 )

Abstract This chapter presents the procedure for the preparation of pyrylium tetrafluoroborate (Pyry‐BF 4 ). A facile synthesis of Pyry‐BF 4 is developed to enable the chemoselective activation of aminoheterocycles and sulfonamides, which upon addition of different nucleophiles, permit direct modification of such scaffolds. Capitalizing on the high reactivity of Pyry‐BF 4 with NH 2 groups, a method is developed to enable the activation of the NH 2 groups in aminoheterocycles, to forge the corresponding pyrdinium salts. The use of Pyry‐BF 4 in combination with cheap and available MgCl 2 permits a mild substitution of the NH 2 group in primary sulfonamides to forge the corresponding sulfonyl chloride. Due to the mild conditions of the protocol, sulfonyl fluoride also enables the derivatization of complex sulfonamides as exemplified by the multitude of functional groups tolerated by the protocol.