Synthesis of 9-Acetyl-8,9-diaza-1-phosphabicyclo[4.3.0]nona-3,7-dienes by Regioselective Diels-Alder Reaction of 2H-1,2,3-Diazaphospholes with Isoprene - Chen, Ruyu; Cai, Baozhong; Li, Guowei (Synthesis, 1991)