Reaction of selenium dichloride with methacrylic acid

Abstract

Selenium dichloride and dibromide in solution undergo disproportionation, so that they could not be isolated as individual substances [1]. Freshly prepared (in situ) selenium dichloride and dibromide are effective electrophilic reagents which are immediately involved in various transformations leading to organoselenium compounds [2–6]. We perform systematic studies on reactions of selenium dichloride and dibromide with compounds containing a double bond [3–5]. Reactions of selenium dihalides with divinyl sulfide [3] and divinyl selenide [4] give the corresponding Markovnikov addition products, 2,6-dihalo-1,4-thiaselenanes and -diselenanes, which undergo rearrangement into thermodynamically more stable 1,3-thiaselenolanes and -diselenolanes. Unlike vinyl sulfides and vinyl selenides, the double bond in vinyl sulfones is deactivated toward addition of electrophiles due to strong electron-withdrawing effect of the sulfonyl group. Selenium dihalides react with divinyl sulfone at a much lower rate as compared to divinyl sulfide, leading to fourand fivemembered heterocycles [6]. Methacrylic acid is a compound whose molecule contains a double bond and a strong electron-withdrawing group. Reactions of selenium halides with methacrylic acid were not studied. We examined the reaction of selenium dichloride with methacrylic acid at a molar ratio of 1 : 2 in acetonitrile at room temperature. Instead of expected 1 : 2 adduct we isolated in high yield (92%) a compound containing a diselenide moiety, previously unknown 2,2′-diselanediylbis(3-chloro-2-methylpropanoic acid) (I), whereas no analogous monoselenide was detected. Diselenide I was also obtained when Se2Cl2 was used instead of SeCl2; in this case, the reaction was accompanied by liberation of an equimolar amount of elemental selenium. The structure of diselenide I was confirmed by the H, C, and Se NMR and mass spectra and elemental analysis. It was isolated as two diastereoisomers at a ratio of 8 : 1. The observed coupling constant between the selenium atom and quaternary carbon atom (JSeC = 77 Hz for the major diastereoisomer) corresponds to direct coupling (JCSe) [7]. Thus the reaction of selenium dichloride with methacrylic acid is chemo-, regio-, and stereoselective, and it leads to the formation of diselenide I. Probable mechanism of this transformation is now under study. 2,2′-Diselanediylbis(3-chloro-2-methylpropanoic acid) (I). White powder, mp 121–122°C. H NMR spectrum, δ, ppm: major diastereoisomer: 1.52 s (6H, CH3), 3.85 d and 4.14 d (2H each, CH2Cl, J = 10.6 Hz); minor diastereoisomer: 1.53 s (6H, CH3), 3.81 d and 4.11 d (2H each, CH2Cl, J = 10.6 Hz). C NMR spectrum, δC, ppm: major diastereoisomer: 20.74 (CH3, JSeC = 16.2 Hz), 49.11 (CCH3, JCSe = 77 Hz), 51.29 (CH2Cl, JSeC = 15.1 Hz), 172.21 (C=O); minor diastereoisomer: 20.65 (CH3), 49.21 (CCH3), 51.29 (CH2Cl), 172.05 (C=O). Se NMR spectrum: major diastereoisomer: δSe 545 ppm; minor diastereoisomer: δSe 544 ppm. Mass spectrum (electron impact, 70 eV), m/z (Irel, %): 402 (4) [M] , 236 (10), 200 (7), ISSN 1070-4280, Russian Journal of Organic Chemistry, 2011, Vol. 47, No. 12, pp. 1889–1890. © Pleiades Publishing, Ltd., 2011. Original Russian Text © V.A. Potapov, S.V. Amosova, A.G. Khabibulina, L.I. Larina, 2011, published in Zhurnal Organicheskoi Khimii, 2011, Vol. 47, No. 12, pp. 1853–1854.