Mendeleev Communications Electronic Version, Issue 5, 2001 1 Interaction of trimethylsilyl isocyanate with xenon difluoride and fluoroxenonium triflate in the presence of alkenes Namig Sh. Pirkuliev,a,b Valery K. Brel,*a Novruz G. Akhmedov,b Nikolai S. Zefirova,b and Peter J. Stangc a Institute of Physiologically Active Compounds, Russian Academy of Sciences, Chernogolovka, 142432 Moscow Region, Russian Federation.Fax: +7 095 913 2113; e-mail: brel@ipac.ac.ru b Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation c Department of Chemistry, University of Utah, Salt Lake City, UT 84112, USA 10.1070/MC2001v011n05ABEH001492 The title reactions lead to the corresponding â-fluoroisocyanates and â-isocyanatotriflates with the formation of the intermediates FXeNCO and OCNXeOSO2CF3.Xenon difluoride and its derivatives have been used in organic synthesis for fluorination,1 oxidative decarboxylation,2 fluorodeiodination, 3 generation of nitrenes,4 mono-2 and biradicals5 and intermolecular rearrangements,6 as well as for the oxidation of organoelement compounds. The last direction is of great interest since it opens up possibilities for the synthesis of novel xenon compounds.In particular, the cleavage reactions of the Si–C, Si–Cl and Si–N bonds with XeF2 were studied in detail.1(a),7 These reactions are assumed to occur through the formation of intermediates with Xe–N and Xe–C bonds.7 We studied the interaction of trimethylsilyl isocyanate with XeF2 and FXeOSO2CF3 in the presence of unsaturated compounds.The initial fluoroxenonium triflate as a solution in CH2Cl2 was obtained from xenon difluoride and triflic acid (or trimethylsilyl triflate) in accordance with a well-known procedure. 8 The subsequent addition of trimethylsilyl isocyanate to the resulting solution afforded a solution of OCNXeOSO2CF3 1. If at the first step XeF2 was treated with trimethylsilyl isocyanate, highly reactive intermediate FXeNCO 2 was generated.Intermediates 1 and 2 were obtained at –40 to –30 °C as clear solutions in CH2Cl2. Our attempts to isolate intermediates 1 and 2 resulted in their fast decomposition at –20 °C with the formation of, presumably, Xe, CO and N2. The formation of a homogeneous solution during a metathetical reaction at –30 °C indicated the end of the reaction, and the resulting solution of compounds 1 and 2 can be used for further transformation in situ.The conclusions concerning the structure of 1 and 2 were made on the basis of published data1(a),9 and the results of the subsequent chemical transformations, particularly, the reactions with alkenes. The reactions of compounds 1 and 2 with cyclohexene and hex-1-ene were investigated.† The addition of an alkene to a solution of fluoroxenonium isocyanate 2 in CH2Cl2 at –78 °C resulted in rapid darkening of the reaction mixture.However, xenon evolution and concomitant reactions were observed only upon warming the reaction mixture to –30 °C. The products were isolated by column chromatography on silica gel. The ratio of the regioisomers in the reaction mixture and their structure were determined by NMR spectroscopy.In general, â- fluoroisocyanate 3b–5b and â-isocyanotriflate 3a–5a were relatively unstable and slowly decomposed in storage at room temperature. The reactions of isocyanatoxenonium triflate 1 and fluoroxenonium isocyanate 2 with cyclohexene lead to only product 3. The cis configuration of 3 was established by the vicinal H–H and H–F couplings in the 1H NMR spectra.The sum of JHH for H1 and H2 is 13–14 Hz, which is typical of cis substituted cyclohexanes. 10 The reactions of xenonium compounds 1 and 2 with hex- 1-ene resulted in the mixture of products 4 and 5 with domination of regioisomers 4. Each of the regioisomers was isolated and identified by 1H and 19F NMR. The 19F NMR spectrum of regioisomer 4b has the F signal as a doublet of triplets (d 220.7 ppm) with a geminal proton coupling of 47 Hz and a vicinal coupling of JHF = 23 Hz, while regioisomer 5b exhibited an analogous signal as multiplets with a chemical shift of 183 ppm.[FXeNCO] XeF2 [CF3SO2OXeNCO] Me3SiNCO i, CF3SO2OH or CF3SO2OSiMe3 ii, Me3SiNCO 1 2 † General procedure for the interaction of OCNXeOSO2CF3 1 with alkenes: TMSNCO (5.52 mmol) was added to a suspension of FXeOTf8 (4.72 mmol) in methylene chloride (20 ml) at –78 °C with stirring.The reaction mixture was then stirred at –40 °C for 1 h until formation of a colourless solution. The solution was cooled down to –78 °C, and a solution of an appropriate alkene (8 mmol) in methylene chloride (5 ml) was added.The reaction mixture was heated to 10 °C, washed with 30 ml of ice water, extracted with CH2Cl2, dried with Na2SO4, and concentrated in a vacuum at 10 °C. Products 3a–5a were separated by column chromatography on silica gel with 2:1 petroleum ether–diethyl ether as an eluent. cis-1-Trifyloxy-2-isocyanatocyclohexane 3a: oil, yield 53%. 1H NMR (CDCl3) d: 1.2–2.3 (m, 8H, 4CH2), 4.4–4.7 [m, 2H, CH(OTf)CHNCO]. 19F NMR (CDCl3) d: –74.9 (CF3SO3). 1-Trifyloxy-2-isocyanatohexane 4a: unstable oil, yield 45%. 1H NMR (CDCl3) d: 0.9–1.8 (m, 9H, Bu), 4.1–4.7 [m, 3H, CH(NCO)CH2OTf]. 19F NMR (CDCl3) d: –73.9 (CF3SO3). 1-Isocyanato-2-trifyloxyhexane 5a: unstable oil, yield 11%. 1H NMR (CDCl3) d: 0.9–1.9 (m, 9H, Bu), 4.2–4.9 [m, 3H, CH(OTf)CH2NCO]. 19F NMR (CDCl3) d: –74.7 (CF3SO3). General procedure for reactions of FXeNCO 2 with alkenes: TMSNCO (5.52 mmol) was added to a suspension of XeF2 (4.72 mmol) in dichloromethane (20 ml) at –78 °C with stirring.The reaction mixture was then stirred at –40 °C for 1 h. The resulting solution was cooled down to –78 °C, and a solution of an appropriate alkene (8 mmol) in CH2Cl2 (5 ml) was added. The mixture was allowed to warm to 10 °C with stirring.When the evolution of xenon gas ceased (0.5–1 h), the mixture was poured into solution of ice water, then extracted three times with CH2Cl2, dried (MgSO4), and concentrated in a vacuum at 10 °C. Products 3b–5b were isolated by column chromatography on silica gel with 2:1 petroleum ether–diethyl ether as an eluent. cis-1-Fluoro-2-isocyanatocyclohexane 3b: oil, yield 47%. 1H NMR (CDCl3) d: 1.4–2.1 (m, 8H, 4CH2), 4.54 (m, 1H, CHNCO), 4.82 (dddd, 1H, CHF, 1JHF 48 Hz, 2JHH 8, 2.5 and 2.5 Hz). 19F NMR (CDCl3) d: –74.6 (CF3SO3), –193.4 (CHF). 1-Fluoro-2-isocyanatohexane 4b: unstable oil, yield 51%. 1H NMR (CDCl3) d: 1.2–2.1 (m, 9H, Bu), 4.2–4.8 [m, 3H, CH(NCO)CH2F]. 19F NMR (CDCl3) d: –74.8 (CF3SO3), –220.7 (dt, CH2F, 1JHF 47 Hz, 2JHF 47 Hz, 2JHF 23 Hz). 1-Isocyanato-2-fluorohexane 5b: unstable oil, yield 15%. 1H NMR (CDCl3) d: 1.0–2.1 (m, 9H, Bu), 4.2–4.8 (m, 3H, CHFCH2NCO). 19F NMR (CDCl3) d: –73.5 (CF3SO3), –183 (CHF). NCO Y YXeNCO BuCH CH2 Y NCO 4 1, 2 3 BuCH CH2 NCO Y 5 a Y = OSO2CF3 b Y = FMendeleev Communications Electronic Version, Issue 5, 2001 2 In the light of these observations, we can suggest a mechanism1( a) that involves the initial electrophilic addition of the xenonium ion to the double bond leading to an organoxenonium intermediate.At the second step, nucleophilic substitution of Xe with the neighbouring fluorine or triflate anion occurs. This is an SN2 type process, which is analogous to the reactions of iodine(III) with olefins.11 Thus, we found that the reactions of xenon difluoride and fluoroxenonium triflate with trimethylsilylisocyanate in the presence of alkenes lead to the corresponding â-fluoroisocyanates and â-isocyanatotriflates. This fact indirectly confirms the formation of the intermediates FXeNCO and OCNXeOSO2CF3.We are grateful to NIH, FIRCA (2R03 TW00437) for financial support. References 1 (a) V. K. Brel, N. Sh. Pirkuliev and N.S. Zefirov, Usp. 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