Generation and NMR studies of stable cations derived from monothia[3.2]- and dithia[3.3]metacyclophanes

Abstract

Monothia[3.2]- and dithia[3.3]metacyclophanes 1–5 are S-protonated in FSO₃H·SbF₅ (4 ∶ 1)–SO₂ (or SO₂ClF) superacids to give their corresponding acidic mono- and bis(sulfonium) cations. A detailed NMR study of the resulting cations and their precursors is provided; conformational aspects are also addressed via NOE measurements. PM3 calculations are used in selected cases as a guiding tool to identify preferred conformations. A remarkable deactivation of the aryl rings occurs upon S-protonation, whereby further ring protonation to form disulfoniomonoarenium trications does not occur, even though positive charge delocalization into the phenyl rings is limited.