is not active as an acetylcholinesterase inhibitor in either mammals or insects, in mammals the animals metabolism tends to remove lipophilic side groups from the phosphorus atom while an insect tends to oxidise the compound so removing the terminal sulfur and replacing it with a terminal oxygen which causes the compound to be more able to act as an acetylcholinesterase inhibitor. The dithiophosphine ylides of LR and related compounds can react with strained alkenes, for example the bicyclic norbornadiene reacts with FcPS to form a compound with a PSC ring. Unlike small rings containing only first row elements such as carbon, nitrogen and oxygen the small rings containing more heavy elements such as sulfur and selenium are more stable with regards to ring opening. Hence, the rings such as PSC are much more stable than things like epoxides. A selenium version of this ring type has been made, one notable example has been named Woollins' reagent and is PhPSe, this is made by the reaction of (PhP) with selenium metal. The solubility of this compound is very low but the group of Prof John Derek Woollins have published some reactions of this compound. For instance the reaction of Woollins' reagent with a dialkyl cyanamide has been found to form a bicyclic PCNSe system. References Organophosphorus compounds Phosphorus compounds Four-membered rings