Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) Induced oxidative rearrangement of non-terminal alkynes by [fluoro(trifluoromethanesulfonyloxy) iodo]benzene to esters of 2-alkyl- and 2-arylalkanoic acids Namig Sh. Pirguliyev,a Valery K. Brel,*b Nikolai S. Zefirova,b and Peter J. Stangc a Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation.Fax: +7 095 939 0290; e-mail: prnmsh@org.chem.msu.su b Institute of Physiologically Active Compounds, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation. Fax: +7 095 913 2113; e-mail: brel@ipac.ac.ru c Department of Chemistry, University of Utah, Salt Lake City, UT 84112, USA. Fax: +1 801 581 8433 The oxidation of non-terminal acetylenes by [fluoro(trifluoromethanesulfonyloxy)iodo]benzene in methanol causes oxidative rearrangement to esters of 2-alkyl- and 2-arylalkanoic acids.Hypervalent iodine reagents react with alkynes to give various products depending upon the type of reagent, the structure of alkynes and the reaction conditions. Terminal alkynes react with [hydroxy(tosyloxy)iodo]benzene to yield alkynyl iodonium tosylates,1 which are important intermediates for the syntheses of alkynyl carboxylates,2 phosphates2 and triflates.3 Reactions of (perfluoroalkyl)phenyliodonium salts with terminal alkynes yield a mixture of substitution and addition products.4 Nonterminal alkynes are converted to a-diketones by oxidation with iodosobenzene in the presence of ruthenium,5 while terminal alkynes afford carboxylic acids.5 Oxidation of alkynyl ethers and alkynyl amines with PhIO in the presence of RuII catalysts yields a-ketoesters and a-ketoamides,6 respectively.Bis-trifluoroacetoxyiodobenzene (PIFA) reacts with non-terminal alkynes to give a-diketones,7 while terminal alkynes yield a-hydroxyketones. 7,8 The cleavage of alkynes to carboxylic acids has been accomplished using PIFA/C6H6/H2O under reflux conditions.9 Oxidative rearrangement of terminal and non-terminal alkynes by [hydroxy(tosyloxy)iodo]benzene affords carboxylic acid esters.10 Recently, a new approach was suggested for the one-pot generation of aryliodoso derivatives directly from iodoarenes.11 The iodonium triflate with the general formula [ArI+F–OTf] is assumed to result from the oxidation of iodoarenes upon treatment with xenon fluorotriflate.It was shown that the reactions of these reagents with terminal acetylenes are accompanied with anti-addition to afford (E)-[b-(trifyloxy)alkenyl]- (aryl)iodonium triflates in moderate to excellent yields.11 In a continuation of our investigation on hypervalent iodine chemistry, we now report the results of reaction of [fluoro- (trifluoromethanesulfonyloxy)iodo]benzene with non-terminal alkynes in methanol.It is interesting to note that this reaction is accompanied by oxidative rearrangement of non-terminal alkynes to esters of alkyl and arylalkanoic acids (Table 1). A great attention directs towards the synthesis of arylalkanoic acids due to their anti-inflammatory properties.10,12,13 A likely mechanism for these oxidative rearrangements entails the initial formation of 2-methoxy-1-alkenyl(phenyl)iodonium triflates A analogous to the production of (2-trifyloxy-1- alkenyl)iodonium salts from terminal alkynes with PhI+F–OTf in non-hydroxylic solvents.11 Michael addition followed by a 1,2-shift of the R group in B with dissociative reductive elimination of iodobenzene would ultimately afford 2a–g.† In summary, iodine(III)-induced oxidative rearrangement of non-terminal acetylenes by [fluoro(trifluoromethanesulfonyloxy) iodo]benzene offers an efficient procedure for the specific transformation of alkynes to alkyl- and arylalkanoic acids. This work was supported by FIRCA of NIH (grant no. 5RO-TW00437). XeF2 + HOTf FXeOTf [PhIF]+[TfO]– i ii iii iv – HF – Xe [PhIF]+[TfO]– + R R' R' R OMe O R' R OH O 1a–g 2a–g 3a–g Scheme 1 Reagents and conditions: i, CH2Cl2, –78 °C; ii, PhI, CH2Cl2; iii, MeOH; iv, aqueous NaOH, then 5% aqueous HCl.a R = Ph, R' = Me b R = Ph, R' = Et c R = R' = Ph d R = p-NO2C6H4, R' = Me e R = p-MeCOC6H4, R' = Me f R = R' = Et g R = Pr, R' = Me R R' [PhIF]+[TfO]– R C R' I Ph F OTf MeOH – HF R MeO I+Ph–OTf R' A MeOH MeO MeO R I+Ph–OTf R' R R' MeO MeO OTf B 1a–g R' R OMe O 2a–g Scheme 2 Table 1 Oxidative rearrangement of non-terminal acetylenes with [PhI+F–OTf] in methanol.Starting compound Reaction time/h Product Yield (%) Characteristic 1a 22 3a 52 nD 20 1.523114 1b 28 3b 42 mp 43–44 °C 1c 28 3c 47 mp 147 °C14 1d 28 3d 44 mp 89 °C14 1e 30 3e 53 mp 57 °C15 1f 25 3f 39 nD 20 1.412914 1g 25 3g 40 nD 20 1.414214Mendeleev Communications Electronic Version, Issue 5, 1999 (pp. 171–212) References 1 (a) F. M. Beringer and S. A. Galton, J. Org. Chem., 1965, 30, 1930; (b) G. F. Koser, L. Rebrovic and R. H. Wettach, J. Org. Chem., 1981, 46, 4324; (c) L. Rebrovic and G. F. Koser, J. Org. Chem., 1984, 49, 4700; (d) A. J. Margida and G. F. Koser, J. Org. Chem., 1984, 49, 4703. 2 P. J. Stang, M. Boehshar and J. Lin, J. Am. Chem. Soc., 1986, 108, 7832. 3 P. J. Stang, B.W. Surber, Z. C. Chen, K. A. Robert and A. G. Anderson, J. Am. Chem. Soc., 1987, 109, 228. 4 T. Umemoto, Y. Kuriu and O. Miyano, Tetrahedron Lett., 1982, 23, 3579. 5 P. Müller and J. Godoy, Helv. Chim. Acta, 1981, 64, 2531. 6 P. Müller and J. Godoy, Tetrahedron Lett., 1982, 23, 366.† Typical procedure. A solution of iodobenzene (1.3 mmol) in CH2Cl2 (5 ml) was added dropwise at –78 °C to a solution of FXeOTf (1.3 mmol)16 in dry CH2Cl2 (20 ml). The mixture was stirred for 0.5 h at –78 °C. Next, an appropriate alkyne (10 mmol) was added dropwise to a solution of [PhIF]+[TfO]– in CH2Cl2 at –78 °C. The mixture was allowed to warm to –30 °C, and the stirring was continued for 0.5–1 h.Then, the mixture was cooled to –78 °C, and methanol (15 ml) was added dropwise to the solution. After being warmed to room temperature over 3 h, the stirring was continued for 20–30 h. Next, the mixture was treated with a saturated NaHCO3 solution. Extraction with CH2Cl2 (3×15 ml) followed by drying (MgSO4) and concentration at a reduced pressure gave a mixture of ester 2a–g and iodobenzene.The ester was purified by column chromatography on silica gel using heptane–diethyl ether (6:1) as an eluent. Hydrolysis in a 2 M NaOH solution yielded corresponding carboxylic acids 3a–g in good yields. All known products were identified by the IR and 1H NMR spectral data (Table 1). 7 E. B. Merkushev, L. G. Karpitskaya and G. I. Novosel’tseva, Dokl. Akad.Nauk SSSR, 1979, 245, 607 (Chem. Abstr., 1979, 91, 39072d). 8 Y. Tamura, T. Yakura, J.-J. Haruta and Y. Kita, Tetrahedron Lett., 1985, 26, 3837. 9 R. M. Moriarty, R. Penmasta, A. K. Awasthi and I. Prakash, J. Org. Chem., 1988, 53, 6124. 10 R. M. Moriarty, R. K. Vaid, M. P. Duncan and B. K. Vaid, Tetrahedron Lett., 1987, 28, 2845. 11 T. M. Kasumov, N. Sh. Pirguliyev, V. K. Brel, Yu. K. Grishin, N. S. Zefirov and P. J. Stang, Tetrahedron, 1997, 53, 13139. 12 J. Rieu, A. Boucherle, H. Cousse and G. Mouzin, Tetrahedron Lett., 1986, 27, 4095. 13 T. Yamauchi, K. Hattori, K. Nakao and K. Tamaki, Synthesis, 1986, 1044. 14 Dictionary of Organic Compounds, ed. J. Buckingham, Chapman and Hall, New York, 1982. 15 C. Giordano, G. Gastaldi, F. Uggeri and F. Guzzoni, Synthesis, 1985, 436. 16 M. Wechwsberg, P. A. Bulliner, F. O. Sladky, R. Mews and N. Bartlett, Inorg. Chem., 1972, 11, 3063. Received: 2nd February 1999; Com. 99/1435