Small Organophosphorus-Selenium Heterocycles from the Selenation of Conjugated Ketones and Enals

Reaction of 2,4-bis(phenyl)-1,3-diselenadiphosphetane-2,4- diselenide [Woollins' reagent, WR] with equimolar amount of alpha,beta-unsaturated ketones [(RC)-C-1(O)C=CR2 (R-1 = aryl or alkyl; R-2 = aryl)] leads to a series of novel five-membered C3P(Se)Se heterocycles 1-8 in 48-95% isolated yields. Furthermore, WR reacts with one equivalent of aromatic conjugated enals [RC=CC=O, R = Ph and 2-MeOC6H4] to give five-membered C3P(Se) Se heterocycles 9 and 10 via the cleavage/cyclic extension of WR molecular ring. All new compounds have been characterised spectroscopically (P-31 NMR, Se-77 NMR, H-1 NMR, C-13 NMR, IR and mass spectroscopy) and one representative X-ray structure is reported.