Structure and reactivity of tautomeric forms of zwitterionic species from the reaction of phosphorus(iii) compounds with electron deficient alkenes and alkynes

Abstract

Synthesis and reactivity of tautomeric forms of the zwitterions proposed in the phosphine catalysed transformations of electron-deficient alkenes/alkynes using the heterocycles [(t-BuNH)PN-t-Bu]2 (1) and Ph2P(NH-t-Bu) (2) are discussed. Thus, compounds (t-BuNH)P(N-t-Bu)2P(N-t-Bu)CHCH(CO2Me) (3), (t-BuNH)P(N-t-Bu)2P(N-t-Bu)CH2CH2(CN) (4) and Ph2P(N-t-Bu){C(Ph)CH(CO2Et)} (5) are isolated. A novel heterocycle [(t-BuNH)P(N-t-Bu)2P[C(CO2Me)–CH(OMe)–C(O)–N(t-Bu)–] (6) obtained by utilizing 1 and MeO2CCCCO2Me is described. The structural proof for the second stage intermediate after the addition of phenols/carboxylic acids to the zwitterions formed in the reaction of electron deficient alkenes with PIII compounds [e.g. {(t-BuNH)P(N-t-Bu)2P(NH-t-Bu)CH2CH2(CN)}+{X}− where X = PhO− + PhOH (7·Ph–O–H⋯OPh), 4-NO2–C6H4–CO2− + H2O (8·H2O)] is also provided for the first time. X-Ray structural characterisation of 3–8 has also been accomplished.