Reactive species formed from N-benzyloxycarbonyl α-aminophosphonochloridates and triethylamine: probable identity and implications for synthesisElectronic supplementary information (ESI) available: NMR data for compounds 4 and 5 (X = Cl) and the products formed by them with Et3N. See http://www.rsc.org/suppdata/cc/b1/b109231f/