Synthesis of novel heterocyclic systems. 2,3-dihydropyrido[1,2-b][1,4,2]oxaselenazin-5-ium

Abstract

We have recently proposed a method for the synthesis of the novel 2,3-dihydropyrido[1,2-b][1,4,2]-oxathiazinium-5 heterocyclic system based on the heterocyclization of 2-chlorosulfenyl-1-pyridine 1-oxide with unsaturated compounds [1][2][3][4]. As far as we known, analogous selenium containing heterocycles have not been prepared to this time. In this connection, we have now synthesized 2-chloroselanyl-1-pyridine 1-oxide (1) and studied its reaction with styrene (2a) and trans-stilbene (2b). We have found that the reaction of the selanyl chloride 1 with the alkenes 2a,b in nitromethane in the presence of an equimolar amount of lithium perchlorate occurs by a polar cycloaddtion [5] to give the 2,3-dihydropyrido[1,2-b][1,4,2]oxaselenazin-5-ium derivatives 3a,b in 76 and 82% yield respectively. Se O N Ph R N SeCl O R Ph MeNO 2 LiClO 4 1 2a,b 3a,b + 2, 3 a R = H, b R = PhClO 4 -+ + 1 H NMR spectroscopy was used to show that the reaction studied is regio-and stereospecific. IR spectra were recorded on a Shimadzu IR-Prestige-21 spectrometer for KBr tablets. 1 H NMR spectra were taken on a Bruker AM-300 instrument (300 MHz) using DMSO-d 6 and with TMS as internal standard.2-Chloroselanyl-1-pyridine 1-Oxide (1). A solution of sulfuryl chloride (0.27 g, 2 mmol) in dichloromethane (15 ml) was added to a solution of 2-selanyl-1-pyridine 1-oxide (0.35 g, 2 mmol) (prepared by method [6]) in dichloromethane (20 ml) at 20ºC. After 1 h it was filtered to give compound 1 (0.33 g, 80%) and the filtrate was evaporated in vacuo. Recrystallization of the residue from dichloromethane gave a further 0.06 g (15%) of compound 1; mp 160-162ºC.

Pathways of reactions of 3,4-dihydropyran with hetareneselanyl chlorides

“…2-Pyridineselanyl chloride (2) was obtained according to Toshimitsu et al [4], while 2-chloroselanyl-1-pyridine 1-oxide was obtained according to our previous procedure [3].…”