Density functional theory (DFT) calculations were carried out to investigate the [2+2], [3+2] and [4+2] cycloadditions of the phosphaethynolate anion (PCO−). The results reveal that the electronic properties of different unsaturated compounds play a crucial role in reactivity and regioselectivity.

http://pubs.rsc.org/en/Content/ArticleLanding/2014/CC/C4CC04610B#!divAbstract