B(C_6F_5)_3 promoted cyclisation of internal propargyl esters: structural characterisation of 1,3-dioxolium compounds

摘要

The reactions of internal propargyl esters with B(C_6F_5)_3 provide access to stable zwitterionic 1,3-dioxolium compounds which are characterised by X-ray diffraction. These 6n-etectron systems show no significant aromatic stabilisation. The 1,2-addition of the Lewis acid B(C_6F_5)_3 and a Lewis base to alkynes is well precedented. Recendy, we have extended this methodology to generate zwitterionic oxazolium borate species via B(C_6F_5)_3 promoted intramolecular cyclisation reactions of a range of propargyl amides.