Both phosphine oxides and phosphites gave ring-opening to afford allylic phosphine oxides and allylic phosphonates, respectively. At the start of our studies, there was only one transformation, using phosphine oxides and cyclopropenes that provided the ring-retained cyclopropyl phosphine product, albeit as a racemic mixture. 14l Coinciding with our efforts, the Wang group was independently pursuing the enantioselective addition of phosphines to cyclopropenes by Pd-catalysis; their asymmetric version occurs by Pd-H insertion into the cyclopropene. 4h While promising, the scope is limited strictly to ester-bearing cyclopropenes and requires precious metal.