445 Heteroatom Chemistry Volume 9, Number 4, 1998 Sulfur and Selenium Derivatives of 2-Phosphaindolizines Raj K. Bansal, 1 Neelima Gupta, 1 Neela Bharatiya, 1 Geetika Gupta, 1 Anushka Surana, 1 Gabriele Hackenbracht, 2 and Konstantin Karaghiosoff 2 1 Department of Chemistry, University of Rajasthan, Jaipur-302004, India 2 Institut fu ¨ r Anorganische Chemie der Universita ¨ t Mu ¨nchen, Meiserstr. 1, D-80333 Mu ¨ nchen, Germany Received 16 March 1998; revised 3 April 1998 ABSTRACT: The 2-phosphaindolizines 1 react with hydrogen sulfide and elemental sulfur to give the new zwitterionic heterocyclic systems 2 of the N-pyridi- niomethyl dithiophosphinate type. In contrast, no re- action is observed with sulfur alone. MeI methylates 2e,f at sulfur. The analogous pyridiniodiselenophos- phinate 5 results from the reaction of 1a with 1,3,2,4- diselenadiphosphetane-2,4-diselenide, 4a, in the ab- sence of an additional base. As a further product, the perselenophosphinic anhydride 6 is identified. In the presence of triethylamine, 1a reacts with each of the diselenides 4a–c to give the new triethylammonium diselenophosphinates 7a–c, respectively. This reaction can be extended to 1-aza-2-phosphaindolizine, 8, which yields with each of 4a,b and NEt 3 the diseleno- phosphinates 9a,b, respectively. The anhydride 6 and the diselenophosphinates 7 and 9 result from an elec- trophilic substitution at the phosphaindolizine ring.  1998 John Wiley & Sons, Inc. Heteroatom Chem 9:445–452, 1998 Dedicated to Prof. Dr. Dr. mult. h.c. Heinrich No ¨th on the oc- casion of his seventieth birthday. Correspondence to: Raj K. Bansal and Konstantin Karaghiosoff.  1998 John Wiley & Sons, Inc. CCC 1042-7163/98/040445-08 INTRODUCTION In azaphospholes, the center of reactivity is repre- sented by the dicoordinate phosphorus atom. A large number of 1,1-addition reactions to the phosphorus atom and 1,2-addition reactions of various reagents to the PC or PN double bond have been reported [1–4]. The 1,2-additions may or may not be accom- panied by an oxidation of the phosphorus atom. In some cases, the 1,2-addition may be followed by a 1,2-elimination, resulting in an overall substitution at the position adjacent to the phosphorus atom in the azaphosphole ring. As many azaphospholes are readily available, this reactivity offers a considerable synthetic potential, which has been used only little so far. 2-Phosphaindolizines have become recently ac- cessible through the [41]cyclocondensation of 1,2- dialkylpyridinium bromides with phosphorus tri- chloride in the presence of triethylamine [5–7]. In- vestigating the reactivity of these heterocycles, we reported their bromination and dichlorophosphiny- lation at the 1-position [8]. Hydrolysis caused an opening of the azaphosphole ring with formation of zwitterionic phosphinates [5]. Here, we report on the reaction of 2-phosphaindolizines with hydrogen sul- fide and elemental sulfur, as well as with 1,3,2,4-di-