Electrophile induced addition reactions of bis-phosphonio-isophosphindolide cations

Bis-triphenylphosphonio-isophosphindolide cations 1 react with triflic acid to give C-protonated products 4, 5 which show an enhanced reactivity to un dergo addition of H2O or MeOH to the cyclic pi-system. This reaction is the first step of the hydrolytic decomposition of the heterocycle which was mo nitored by NMR spectroscopic studies. No evidence for direct P-protonation or P-alkylation (which had been postulated in a previous study) was obtaine d. Addition of H2O or H2S to the cyclic pi-system of 1 is also promoted by oxidizing agents such as I-3(-) or sulfur and affords novel zwitterionic (t hio)-phosphinates 11, 13. (C) 1999 Published by Elsevier Science Ltd. All r ights reserved.