Abstract A novel general method for the synthesis of oxindoles, namely the 'azirine/oxindole ring enlargement via amidinium-intermediates' has been established: the reaction of 2H- azirin-3-amines 1 with BF 3⋅ OEt 2 in THF solution at− 78 leads to 1, 3, 3-trialkyl-2-amino- 3H-indolium tetrafluoroborates 14 in good yields (Scheme 5). Treatment of aqueous solutions of 14 at 0 with aqueous NaOH (30%) and extraction with CH 2 Cl 2 gives oily ...
