SULFUR AND SELENIUM DERIVATIVES OF 2-PHOSPHAINDOLIZINES

The 2-phosphaindolizines 1 react with hydrogen sulfide and elemental s ulfur to give the new, zwitterionic heterocyclic systems 2 of the N-py ridiniomethyl dithiophosphinate type. In contrast, no reaction is obse rved with sulfur alone. Mel methylates 2e,f at sulfur. The analogous p yridiniodiselenophosphinate 5 results from the reaction of 1a with 1,3 ,2,4-diselenadiphosphetane-2, 4-diselenide, 4a, in the absence of an a dditional base. As a further product, the perselenophosphinic anhydrid e 6 is identified. in the presence of triethylamine, la reacts with ea ch of the diselenides 4a-c to give the new triethylammonium diselenoph osphinates 7a-c, respectively. This reaction can be extended to 1-aza- 2-phosphaindolizine, 8, which yields with each of 4a,b and NEt3, the d iselenophosphinates 9a,b, respectively. The anhydride 6 and the disele nophosphinates 7 and 9 result from an electrophilic substitution at th e phosphaindolizine ring. (C) 1998 John Wiley & Sons, Inc.