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

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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.
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