ORGANIC LETTERS
Application of Trimethylvinylsilane as a Convenient Synthetic Precursor of (Perfluoroalkyl)ethenes: An Unusual Fluoride-Induced Elimination−Desilylation Coupled Reaction
2000 Vol. 2, No. 15 2347-2349
Zolta´n Szla´vik, Ga´bor Ta´rka´nyi,† AÄ gnes Go1 mo1 ry,‡ and Jo´zsef Ra´bai* Department of Organic Chemistry, Eo¨ tVo¨ s UniVersity, P.O. Box 32, H-1518 Budapest 112, Hungary
[email protected] Received May 25, 2000
ABSTRACT
A convenient and effective method for the preparation of perfluoroalkylated ethenes is described. First, the free radical addition of perfluoroalkyl iodides to trimethylvinylsilane in the presence of AIBN gave iodoethylsilane intermediates (F(CF2)nCH2CHISiMe3, n ) 4 (1), 6 (2), 8 (3), 10 (4); 94−99%). Then an unusual dehydrohalogenation−desilylation reaction was effected by tetrabutylammonium fluoride, and finally the product isolation (F(CF2)nCHdCH2 (5−8), 62−87%) was facilitated using a fluorous phase separation technique. This novel approach can also be applied to adjust short C2 hydrocarbon units to functionalized fluorinated segments (e.g., HOCH2(CF2)8CHdCH2 (11), 71%). All structures were verified by state-of-the-art multinuclear one- and two-dimensional NMR experiments involving both homo- (19F−19F) and heteronuclear (1H−13C, 19F−13C) correlations based on the GMQFCOPS and inverse 1H and/or 19F detected GHSQC, GHMQC sequences with broad-band adiabatic 13C decoupling.
The recent discovery of the concept of fluorous biphase systems (FBS)1 and fluorous synthesis2 based on the unique properties of perfluorocarbon fluids provides attractive alternatives for conventional organic synthesis. A more extensive application of this novel phase separation and immobilization concept requires designed fluorous catalysts, reagents, and labels. In the present work, we describe a convenient and effective laboratory-scale access to (perfluoroalkyl)ethenes RfnCHdCH2 (Rfn ) F(CF2)n, n ) 4 (5), 6 † Spectroscopic Research Division, Chemical Works of Gedeon Richter, Budapest, Hungary. ‡ Institute of Chemistry, Chemical Research Center, Hungarian Academy of Sciences, Budapest, Hungary. (1) (a) Horva´th, I. T.; Ra´bai, J. Science 1994, 266, 72. (b) Horva´th, I. T. Acc. Chem. Res. 1998, 31, 641. (2) Curran, D. P. Angew. Chem., Int. Ed. Engl. 1998, 37, 1175.
10.1021/ol006105o CCC: $19.00 Published on Web 06/28/2000
© 2000 American Chemical Society
(6), 8 (7), 10 (8)), useful building blocks of fluorous phase ligands having a wide range of applicability in the planning of fluorous synthesis.3 These compounds can be prepared industrially via the alkaline treatment of Rfn(CH2)2I,4 components of the telomerization reactions of perfluoroalkyl iodides with ethene.5 As a synthetic equivalent of ethene, (3) (a) Alvey, L. J.; Rutherford, D.; Juliette, J. J. J.; Gladysz, J. A. J. Org. Chem. 1998, 63, 6302. (b) Brown, H. C.; Chen, G.; Jennings, M. P.; Ramachandran, P. V. Angew. Chem., Int. Ed. 1999, 38, 2052. (c) Richter, B.; de Wolf, E.; van Koten, G.; Deelman, B.-J. J. Org. Chem. 2000, 65, 3885. (4) (a) Brace, N. O.; Marshall, L. W.; Pinson, C. J.; Wingerden, G. J. Org. Chem. 1984, 49, 2361. (b) Ame´duri, B.; Boutevin, B.; Nouiri, M.; Talbi, M. J. Fluorine Chem. 1995, 74, 191. (5) (a) Brace, N. O. U.S. Patent 3016406, 1962; Chem. Abstr. 1962, 57, 2078a. (b) Brace, N. O. U.S. Patent 3145222, 1964; Chem. Abstr. 1964, 61, 10589.
trimethylvinylsilane (TMVS) was used to react with a homologous series of F-alkyl iodides in the presence of azoisobutyronitrile (AIBN) to produce RfnCH2CHISiMe36 (n ) 4 (1), 6 (2), 8 (3), 10 (4)) with excellent yields.7 The tetrabutylammonium fluoride8 (TBAF) treatment of these adducts unexpectedly resulted in products 5-8 in one step,9 indicating that both dehydrohalogenation and cleavage of the C-Si bond occurred (Scheme 1). The applied polar aprotic
a shorter fluorinated chain (5 and 6) can be separated with a satisfactory result only from a more polar solvent with a higher boiling point, such as DMSO (Table 1). This way in
Table 1. Radical Addition to TMVS and Cleavage with TBAF, Yields of Isolated products and gas chromatographic purities RfnCH2CHI-SiMe3
Scheme 1
n 4 6 8 10
solvents (THF, DMSO) are readily miscible with water; therefore, the strongly hydrophobic products separate spontaneously from the diluted reaction mixture. In the case of the longer chain olefins 7 and 8 the less polar THF was used as solvent to provide homogeneous reaction conditions, and perfluorinated methylcyclohexane was applied as solvent during the workup procedure to increase the efficiency of fluorous phase separation. On the other hand, analogues with (6) Other methods for the preparation of (Rf)nCH2CHISiMe3 (n ) 6, 8): (a) Chen, Q. Y.; Yang, Z. Y.; Zhao, C. X.; Qiu, Z. M. J. Chem. Soc., Perkin Trans. 1 1988, 563. (b) Fuchikami, T.; Ojima, I. Tetrahedron Lett. 1984, 25, 303. (c) Beyou, E.; Babin, P.; Bennetau, B.; Dunogues, J.; Teyssie, D.; Boileau, S. Tetrahedron Lett. 1995, 11, 1843. (7) Typical procedure and analytical data for 4: a predried 25 mL glass tube was filled with F-decyl iodide (9.0 mmol), trimethylvinylsilane (10.0 mmol), and AIBN (0.2 mmol), sealed under a nitrogen atmosphere, and heated to 75 °C for 8 h. The crude product was purified by distillation (140-150 °C bath temperature, 0.1 mmHg). NMR (ppm; in acetone): 1H NMR, 0.24 s (9H) [SiMe3], 2.68-2.83 m (1H) and 2.90-3.03 m (1H) [H-2x and H-2y], 3.42 dd (1H) (3JH,H ) 10.5 Hz, 3JH,H ) 2.5 Hz) [H-1]; 13C NMR, -2.4 [SiMe3], 1.9 [C-1], 36.0 (2JC,F ) 21.9 Hz) [C-2], 109.5 [C-11], 111.3 [C-10], 111.8 and 111.9 [C-6 and C-9]*, 112.0 [C-7 and C-8], 112.2 [C-4], 112.4 [C-5], 118.2 [C-12], 119.4 [C-3]; 19F NMR, -80.5 (3F) [F-12], -112.7 d (1F) (2JF,F ) 267.4 Hz) and -114.6 d (1F) (2JF,F ) 267.4 Hz) [F-3x and F-3y], -120.8 (2F) [F-5], -120.9 (4F) [F-7 and F8], -121.1 (4F) [F-6 and F-9], -121.9 (2F) [F-10], -122.8 (2F) [F-4], -125.4 (2F) [F-11]. The asterisk (*) denotes interchangeable assignments. MS (EI, 70 eV; m/z, I (relative intensity), M• - X): 746,
