“…27 Subsequently, we reported on an elusive 1,2s 4 l 5 -oxaphos-phetane P-oxide (VI) and also on a stable P-sulfide and a P-selenide, formerly unknown. 29 Fig. 1 Oxetane (I), phosphetanes (s 3 l 3 IIa, s 5 l 5 IIb), 1,3-oxaphosphetanes (s 3 l 3 IIIa, s 5 l 5 IIIb), 1,2-oxaphosphetanes (s 3 l 3 IVa, s 5 l 5 IVb), 1,2s 3 l 3 -oxaphosphetane metal complexes (V), 1,2s 4 l 5 -oxaphosphetanes (VI) and 1,2 s 4l 4 -oxaphos-phetan-2-ium (VII).…”