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Regio- and stereoselective allylic fluorination using chiral rhenium complexes
Journal of Fluorine Chemistry 93 (1999) 171±173
Regio- and stereoselective allylic ¯uorination using chiral rhenium complexes SteÂphanie Legoupy, Christophe CreÂvisy, Jean-Claude Guillemin, Rene GreÂe*
Laboratoire de SyntheÁses et Activations de BiomoleÂcules, associe au CNRS, ENSCR, Avenue du GeÂneÂral Leclerc, 35700, Rennes, France Received 14 September 1998; accepted 14 October 1998
Abstract The ®rst example of metal mediated regio- and stereoselective allylic ¯uorination using chiral rhenium complexes is reported. # 1999 Elsevier Science S.A. All rights reserved. Keywords: Fluorination; DAST; Rhenium complexes; Regioselectivity; Stereoselectivity
1. Introduction Fluorinated molecules are now important compounds both in material sciences and bioorganic molecules. In the latter ®eld, many mono¯uorinated derivatives have been reported already either as pharmacological tools or as drugs [1±9]. Thus, it is not surprising that many studies deal with the issues of the regio- and stereoselectivity during the ¯uorination step. However, this remains a challenging problem, especially for the reactions occurring in positions vicinal to unsaturated systems where isomerization and racemization processes occur easily particularly during nucleophilic ¯uorination [10]. A typical example is the reaction of diethylaminosulfur tri¯uoride (DAST) with either crotyl alcohol 1 or its isomer 2 to give about the same (1:2) mixtures of ¯uorinated derivatives 3 and 4 (Scheme 1) [11]. Such allylic transpositions are not limited to DAST but occur also with other ¯uorinating agents [12,13]. Furthermore they are observed with many allylic or polyenic alcohols even if, in some cases, the nature of the substituents on the double bonds exerts a regiochemical control [14±16]. A potentially general solution to such problems would be to inhibit the transposition by a temporary complexation of the -system with a transition metal complex. Furthermore, this should take advantage also of the chirality of such complexes to obtain stereoselective ¯uorinations. We have already demonstrated the potentialities of this approach in
*Corresponding author.
the DAST ¯uorination of dienyl or benzylic alcohols using respectively iron [17] or chromium tricarbonyl [18] complexes. To the best of our knowledge, this has never been done in the case of allylic systems. Thus, the purpose of this note is to report our preliminary results establishing that chiral rhenium complexes are good candidates for such selective ¯uorination process. In his pioneering studies, Gladysz described the preparation of chiral rhenium complexes [19], their resolution [20] and some synthetic applications [21]. We have reported recently the easy complexation of allylic alcohols leading to type 5 derivatives [22,23] and their nucleophilic substitution which occurs not only with a complete regiocontrol [24] but also stereospeci®cally [25]. Reaction of DAST with complex 5a occurs smoothly at room temperature to give ¯uorinated derivative 6a (40% isolated yield), easily characterized by spectral and analytical data1. The secondary alcohol 5b also reacts with DAST to give a single ¯uoride 6b (74% yield) while its stereoisomer 5c2 gives only the derivative 6c (76% yield) (Scheme 1 Selected spectroscopic data: 6a, Yield: 40%. 1 H NMR (400 MHz, CDCl3) d: 7.55±7.61 (m, 9H, PPh3); 7.33±7.42 (m, 6H, PPh3); 5.87 (s, 5H, C5H5); 5.13 (dm, 1H, J 48.3, CH2F); 4.56±4.75 (m, 2H, CH2F and =CH); 2.52±2.60 (m, 1H, H2C=); 2.36 (ddd, 1H, J 10.7, 10.7, 4.1, H2C=). 13 C NMR (100 MHz, CDCl3) d: 133.8 (d, J 9.9, o-Ph); 133.1 (d, J 2.7, p-Ph); 130.4 (d, J 59.5, i-Ph); 130.4 (d, J 11.4, m-Ph); 98.1 (s, C5H5); 87.4 (d, J 171.7, CH2F); 45.7 (d, J 20.6, =CH); 36.8 (dd, J 6.1, 6.1, =CH2). 31 P f1 Hg NMR (121 MHz, CDCl3) d: 10.4 (s). 19 F f1 Hg NMR (376 MHz, CDCl3) d: ÿ200.6 (s, CH2F); ÿ152.7 (m, BF4). 2 Diastereomers 5b and 5c were separated by chromatography and their stereochemistry established by X-ray analysis, see [25].
0022-1139/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved. PII: S0022-1139(98)00305-4
172
S. Legoupy et al. / Journal of Fluorine Chemistry 93 (1999) 171±173
Scheme 1.
2). The NMR data of these compounds3 clearly demonstrate that, in both cases, the ¯uorine is linked to the secondary carbon atom and that the bulky substituent is (as in the starting complex) on the side of the nitrosyl ligand4. The stereochemistry of 6b and 6c is attributed by analogy with previous results indicating that, in this type of complex, the nucleophilic substitution occurred with overall retention of con®guration [25]. It is important to point out that careful NMR analysis of the crude reaction mixture not only established the stereospeci®city of these reactions but also excluded any allylic transposition during ¯uorination: reaction of complexed crotyl alcohol with DAST yielded exclusively the corresponding primary ¯uoride5 and none of the secondary derivatives 6b and 6c (NMR analysis). By analogy with previous results, the regio- and stereoselectivity can be explained by a -allyl type intermediate with the chirality at the metal center [25]. In conclusion, we have described the ®rst example of metal mediated regio- and stereoselective allylic ¯uorination and this is a further con®rmation of the potentialities of transition metal complexes in ¯uorine chemistry. However, this keeps open several questions, including the exact nature of the ¯uorinating species since Fÿ is known to react readily with various organometallic complexes: Bu4NF, for 3
1
Selected spectroscopic data: 6b Yield: 74%. H NMR (400 MHz, CDCl3) d: 7.55±7.61 (m, 9H, PPh3); 7.33±7.41 (m, 6H, PPh3); 5.86 (s, 5H, C5H5); 4.57 (dm, 1H, J 49.8, CHF); 4.46±4.58 (m, 1H, =CH); 2.47 (ddd, 1H, J 11.2, 7.6, 4.1, H2C=); 2.26 (ddd, 1H, J 10.2, 10.2, 4.1, H2C=); 1.60 (dd, 3H, J 6.6 and 23.9, CH3). 13 C NMR (100 MHz, CDCl3) d: 133.9 (d, J 9.9, o-Ph); 133.0 (d, J 2.7, p-Ph); 130.4 (d, J 59.5, iPh); 130.3 (d, J 11.1, m-Ph); 98.0 (s, C5H5); 94.5 (d, J 171.7, CHF); 52.4 (d, J 20.9, =CH); 35.2 (dd, J 6.9 and 6.9, =CH2); 25.3 (d, J 24.4, CH3). 31 P f1 Hg NMR (121 MHz, CDCl3) d: 10.6. 19 F f1 Hg NMR (376 MHz, CDCl3) d: ÿ162.7 (s, CHF); ÿ152.8 (m, BF4). 6c: Yield: 76%. 1 H NMR (400 MHz, CDCl3) d: 7.54±7.60 (m, 9H, PPh3); 7.32±7.40 (m, 6H, PPh3); 5.84 (s, 5H, C5H5); 4.93 (dm, 1H, J 48.3, CHF); 4.50± 4.64 (m, 1H, =CH); 2.58 (ddd, 1H, J 11.2, 11.2, 4.1, H2C=); 2.10 (ddd, 1H, J 10.7, 6.6, 4.1, H2C=); 1.63 (dd, 3H, J 6.1 and 23.9, CH3). 13 C NMR (100 MHz, CDCl3) d: 133.8 (d, J 9.9, o-Ph); 132.9 (d, J 2.7, pPh); 130.5 (d, J 59.1, i-Ph); 130.3 (d, J 11.1, m-Ph); 98.0 (s, C5H5); 93.7 (d, J 173.9, CHF); 50.8 (d, J 22.5, =CH); 33.2 (dd, J 6.1, 6.1, =CH2); 24.6 (d, J 23.7, CH3). 31 P f1 Hg NMR (121 MHz, CDCl3) d: 12.0. 19 F f1 Hg NMR (376 MHz, CDCl3) d: ÿ168.3 (s, CHF); ÿ152.4 (m, BF4). IR of a mixture of 6b and 6c (cmÿ1, neat): nNO 1727 (vs). HRMS: for (C27H27FNOP187Re): found: 618.1370, requires: 618.1372. 4 This is established from the NMR data, in agreement with structural assignments reported by Gladysz (see [19]): JPH and JCP coupling constants are observed only for the atoms of the =CH2 group: 6b, JPH 7.6 and 10.2 Hz, JCP 6.9 Hz; 6c, JPH 11.2 and 6.6 Hz, JCP 6.1 Hz. 5 Selected spectroscopic data: 31 P f1 Hg NMR (121 MHz, CDCl3) d: 11.1 (s). 19 F f1 Hg NMR (376 MHz, CDCl3) d: ÿ180.6 (s).
Scheme 2.
instance, is an ef®cient reagent to decomplex alkyne-cobalt carbonyl clusters [26,27]6. Extension to asymmetric synthesis and development of ef®cient decomplexation methodologies are under active study7. Acknowledgements We thank Prof. J.A. Gladysz for fruitful discussions and P. Guenot (CRMPO) for performing the mass spectral experiments. References [1] R. Filler, Y. Kobayashi (Eds.), Biomedicinal Aspects of Fluorine Chemistry, Elsevier, Amsterdam, 1982. [2] J. Mann, J. Chem. Soc. Rev. 16 (1987) 381. [3] J.T. Welch, Tetrahedron 43 (1987) 3123. [4] J.T. Welch, S. Eswarakrishnan, Fluorine in Bioorganic Chemistry, Wiley/Interscience, New York, 1991. [5] J.T. Welch (Ed.), Selective Fluorination in Organic and Bioorganic Chemistry, ACS Symposium Series 456, Washington DC, 1991. [6] R.H. Abeles, T.A. Alston, J. Biol. Chem. 265 (1990) 16705. [7] T. Hayashi, V.A. Soloshonok, Tetrahedron Asymmetry 5 (1994) xiii±xiv. [8] I. Ojima, J.R. Mc Carthy, J.T. Welch (Eds.), Biomedical Frontiers of Fluorine Chemistry, ACS Symposium Series 639, Washington DC, 1996, and references cited therein. [9] D. O'Hagan, H.S. Rzepa, Chem. Commun. (1997) 645. [10] R. GreÂe, J.-P. Lellouche, in: V.A. Soloshonok (Ed.), EPC Synthesis of Fluoroorganic Compounds: Stereochemical Challenges and Biomedical Targets, Wiley, Chichester, UK, in press. [11] W.J. Middleton, J. Org. Chem. 40 (1975) 574. [12] F. Munyemana, A.M. Frisque-Hesbain, A. Devos, L. Ghosez, Tetrahedron Lett. 30 (1989) 3077. 6
Reaction with acyclic pentadienyl cations complexed to Fe(CO)3 leads also to a complete decomposition of the starting complexes, see [17]. 7 To the best of our knowledge, in the case of such cationic rhenium complexes, efficient decomplexation has been obtained only in the case of s-bonded derivatives; see for instance [21].
S. Legoupy et al. / Journal of Fluorine Chemistry 93 (1999) 171±173 [13] F. Munyemana, Ph.D. Thesis, University of Louvain La Neuve, Belgium, 1991. [14] D. GreÂe, R. GreÂe, A. Boukerb, M. Laabassi, Tetrahedron Lett. 35 (1997) 6209. [15] A. Boukerb, D. GreÂe, M. Laabassi, R. GreÂe, J. Fluorine Chem. 88 (1998) 23. [16] Y. Li, K. Luthman, U. Hacksell, Tetrahedron Lett. 33 (1992) 4487. [17] D.M. GreÂe, C.J.M. Kermarrec, J.T. Martelli, R.L. GreÂe, J.-P. Lellouche, L.J. Toupet, J. Org. Chem. 61 (1996) 1918. [18] C. Kermarrec, V. Madiot, D. GreÂe, A. Meyer, R. GreÂe, Tetrahedron Lett. 34 (1996) 5691. [19] J.A. Gladysz, B.J. Boone, Angew. Chem., Int. Ed. Engl. 36 (1997) 550. [20] F. Agbossou, E.J. O'Connor, C.M. Garner, N. Quiros Mendez, J.M. Fernandez, A.T. Patton, J.A. Ramsden, J.A. Gladysz, Inorg. Synth. 29 (1992) 211.
173
[21] G.B. Richter-Addo, D.A. Knight, M.A. Dewey, A.M. Arif, J.A. Gladysz, J. Am. Chem. Soc. 115 (1993) 11863. [22] S. Legoupy, C. CreÂvisy, J.-C. Guillemin, R. GreÂe, Tetrahedron Lett. 37 (1996) 1225. [23] S. Legoupy, C. CreÂvisy, J.-C. Guillemin, R. GreÂe, J. Organomet. Chem. 567 (1998) 75. [24] S. Legoupy, C. CreÂvisy, J.-C. Guillemin, R. GreÂe, Organometallics 16 (1997) 1822. [25] S. Legoupy, C. CreÂvisy, J.-C. Guillemin, R. GreÂe, Chem. Eur. J. 4 (1998) 2155. [26] S.L. Schreiber, T. Sammkia, W.E. Crowe, J. Am. Chem. Soc. 108 (1986) 3128. [27] G.B. Jones, J.M. Wright, T.M. Rush, G.W. Plourde II, T.F. Kelton, J.E. Mathews, R.S. Huber, J.P. Davidson, J. Org. Chem. 62 (1997) 9379.
Regio- and stereoselective allylic ¯uorination using chiral rhenium complexes SteÂphanie Legoupy, Christophe CreÂvisy, Jean-Claude Guillemin, Rene GreÂe*
Laboratoire de SyntheÁses et Activations de BiomoleÂcules, associe au CNRS, ENSCR, Avenue du GeÂneÂral Leclerc, 35700, Rennes, France Received 14 September 1998; accepted 14 October 1998
Abstract The ®rst example of metal mediated regio- and stereoselective allylic ¯uorination using chiral rhenium complexes is reported. # 1999 Elsevier Science S.A. All rights reserved. Keywords: Fluorination; DAST; Rhenium complexes; Regioselectivity; Stereoselectivity
1. Introduction Fluorinated molecules are now important compounds both in material sciences and bioorganic molecules. In the latter ®eld, many mono¯uorinated derivatives have been reported already either as pharmacological tools or as drugs [1±9]. Thus, it is not surprising that many studies deal with the issues of the regio- and stereoselectivity during the ¯uorination step. However, this remains a challenging problem, especially for the reactions occurring in positions vicinal to unsaturated systems where isomerization and racemization processes occur easily particularly during nucleophilic ¯uorination [10]. A typical example is the reaction of diethylaminosulfur tri¯uoride (DAST) with either crotyl alcohol 1 or its isomer 2 to give about the same (1:2) mixtures of ¯uorinated derivatives 3 and 4 (Scheme 1) [11]. Such allylic transpositions are not limited to DAST but occur also with other ¯uorinating agents [12,13]. Furthermore they are observed with many allylic or polyenic alcohols even if, in some cases, the nature of the substituents on the double bonds exerts a regiochemical control [14±16]. A potentially general solution to such problems would be to inhibit the transposition by a temporary complexation of the -system with a transition metal complex. Furthermore, this should take advantage also of the chirality of such complexes to obtain stereoselective ¯uorinations. We have already demonstrated the potentialities of this approach in
*Corresponding author.
the DAST ¯uorination of dienyl or benzylic alcohols using respectively iron [17] or chromium tricarbonyl [18] complexes. To the best of our knowledge, this has never been done in the case of allylic systems. Thus, the purpose of this note is to report our preliminary results establishing that chiral rhenium complexes are good candidates for such selective ¯uorination process. In his pioneering studies, Gladysz described the preparation of chiral rhenium complexes [19], their resolution [20] and some synthetic applications [21]. We have reported recently the easy complexation of allylic alcohols leading to type 5 derivatives [22,23] and their nucleophilic substitution which occurs not only with a complete regiocontrol [24] but also stereospeci®cally [25]. Reaction of DAST with complex 5a occurs smoothly at room temperature to give ¯uorinated derivative 6a (40% isolated yield), easily characterized by spectral and analytical data1. The secondary alcohol 5b also reacts with DAST to give a single ¯uoride 6b (74% yield) while its stereoisomer 5c2 gives only the derivative 6c (76% yield) (Scheme 1 Selected spectroscopic data: 6a, Yield: 40%. 1 H NMR (400 MHz, CDCl3) d: 7.55±7.61 (m, 9H, PPh3); 7.33±7.42 (m, 6H, PPh3); 5.87 (s, 5H, C5H5); 5.13 (dm, 1H, J 48.3, CH2F); 4.56±4.75 (m, 2H, CH2F and =CH); 2.52±2.60 (m, 1H, H2C=); 2.36 (ddd, 1H, J 10.7, 10.7, 4.1, H2C=). 13 C NMR (100 MHz, CDCl3) d: 133.8 (d, J 9.9, o-Ph); 133.1 (d, J 2.7, p-Ph); 130.4 (d, J 59.5, i-Ph); 130.4 (d, J 11.4, m-Ph); 98.1 (s, C5H5); 87.4 (d, J 171.7, CH2F); 45.7 (d, J 20.6, =CH); 36.8 (dd, J 6.1, 6.1, =CH2). 31 P f1 Hg NMR (121 MHz, CDCl3) d: 10.4 (s). 19 F f1 Hg NMR (376 MHz, CDCl3) d: ÿ200.6 (s, CH2F); ÿ152.7 (m, BF4). 2 Diastereomers 5b and 5c were separated by chromatography and their stereochemistry established by X-ray analysis, see [25].
0022-1139/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved. PII: S0022-1139(98)00305-4
172
S. Legoupy et al. / Journal of Fluorine Chemistry 93 (1999) 171±173
Scheme 1.
2). The NMR data of these compounds3 clearly demonstrate that, in both cases, the ¯uorine is linked to the secondary carbon atom and that the bulky substituent is (as in the starting complex) on the side of the nitrosyl ligand4. The stereochemistry of 6b and 6c is attributed by analogy with previous results indicating that, in this type of complex, the nucleophilic substitution occurred with overall retention of con®guration [25]. It is important to point out that careful NMR analysis of the crude reaction mixture not only established the stereospeci®city of these reactions but also excluded any allylic transposition during ¯uorination: reaction of complexed crotyl alcohol with DAST yielded exclusively the corresponding primary ¯uoride5 and none of the secondary derivatives 6b and 6c (NMR analysis). By analogy with previous results, the regio- and stereoselectivity can be explained by a -allyl type intermediate with the chirality at the metal center [25]. In conclusion, we have described the ®rst example of metal mediated regio- and stereoselective allylic ¯uorination and this is a further con®rmation of the potentialities of transition metal complexes in ¯uorine chemistry. However, this keeps open several questions, including the exact nature of the ¯uorinating species since Fÿ is known to react readily with various organometallic complexes: Bu4NF, for 3
1
Selected spectroscopic data: 6b Yield: 74%. H NMR (400 MHz, CDCl3) d: 7.55±7.61 (m, 9H, PPh3); 7.33±7.41 (m, 6H, PPh3); 5.86 (s, 5H, C5H5); 4.57 (dm, 1H, J 49.8, CHF); 4.46±4.58 (m, 1H, =CH); 2.47 (ddd, 1H, J 11.2, 7.6, 4.1, H2C=); 2.26 (ddd, 1H, J 10.2, 10.2, 4.1, H2C=); 1.60 (dd, 3H, J 6.6 and 23.9, CH3). 13 C NMR (100 MHz, CDCl3) d: 133.9 (d, J 9.9, o-Ph); 133.0 (d, J 2.7, p-Ph); 130.4 (d, J 59.5, iPh); 130.3 (d, J 11.1, m-Ph); 98.0 (s, C5H5); 94.5 (d, J 171.7, CHF); 52.4 (d, J 20.9, =CH); 35.2 (dd, J 6.9 and 6.9, =CH2); 25.3 (d, J 24.4, CH3). 31 P f1 Hg NMR (121 MHz, CDCl3) d: 10.6. 19 F f1 Hg NMR (376 MHz, CDCl3) d: ÿ162.7 (s, CHF); ÿ152.8 (m, BF4). 6c: Yield: 76%. 1 H NMR (400 MHz, CDCl3) d: 7.54±7.60 (m, 9H, PPh3); 7.32±7.40 (m, 6H, PPh3); 5.84 (s, 5H, C5H5); 4.93 (dm, 1H, J 48.3, CHF); 4.50± 4.64 (m, 1H, =CH); 2.58 (ddd, 1H, J 11.2, 11.2, 4.1, H2C=); 2.10 (ddd, 1H, J 10.7, 6.6, 4.1, H2C=); 1.63 (dd, 3H, J 6.1 and 23.9, CH3). 13 C NMR (100 MHz, CDCl3) d: 133.8 (d, J 9.9, o-Ph); 132.9 (d, J 2.7, pPh); 130.5 (d, J 59.1, i-Ph); 130.3 (d, J 11.1, m-Ph); 98.0 (s, C5H5); 93.7 (d, J 173.9, CHF); 50.8 (d, J 22.5, =CH); 33.2 (dd, J 6.1, 6.1, =CH2); 24.6 (d, J 23.7, CH3). 31 P f1 Hg NMR (121 MHz, CDCl3) d: 12.0. 19 F f1 Hg NMR (376 MHz, CDCl3) d: ÿ168.3 (s, CHF); ÿ152.4 (m, BF4). IR of a mixture of 6b and 6c (cmÿ1, neat): nNO 1727 (vs). HRMS: for (C27H27FNOP187Re): found: 618.1370, requires: 618.1372. 4 This is established from the NMR data, in agreement with structural assignments reported by Gladysz (see [19]): JPH and JCP coupling constants are observed only for the atoms of the =CH2 group: 6b, JPH 7.6 and 10.2 Hz, JCP 6.9 Hz; 6c, JPH 11.2 and 6.6 Hz, JCP 6.1 Hz. 5 Selected spectroscopic data: 31 P f1 Hg NMR (121 MHz, CDCl3) d: 11.1 (s). 19 F f1 Hg NMR (376 MHz, CDCl3) d: ÿ180.6 (s).
Scheme 2.
instance, is an ef®cient reagent to decomplex alkyne-cobalt carbonyl clusters [26,27]6. Extension to asymmetric synthesis and development of ef®cient decomplexation methodologies are under active study7. Acknowledgements We thank Prof. J.A. Gladysz for fruitful discussions and P. Guenot (CRMPO) for performing the mass spectral experiments. References [1] R. Filler, Y. Kobayashi (Eds.), Biomedicinal Aspects of Fluorine Chemistry, Elsevier, Amsterdam, 1982. [2] J. Mann, J. Chem. Soc. Rev. 16 (1987) 381. [3] J.T. Welch, Tetrahedron 43 (1987) 3123. [4] J.T. Welch, S. Eswarakrishnan, Fluorine in Bioorganic Chemistry, Wiley/Interscience, New York, 1991. [5] J.T. Welch (Ed.), Selective Fluorination in Organic and Bioorganic Chemistry, ACS Symposium Series 456, Washington DC, 1991. [6] R.H. Abeles, T.A. Alston, J. Biol. Chem. 265 (1990) 16705. [7] T. Hayashi, V.A. Soloshonok, Tetrahedron Asymmetry 5 (1994) xiii±xiv. [8] I. Ojima, J.R. Mc Carthy, J.T. Welch (Eds.), Biomedical Frontiers of Fluorine Chemistry, ACS Symposium Series 639, Washington DC, 1996, and references cited therein. [9] D. O'Hagan, H.S. Rzepa, Chem. Commun. (1997) 645. [10] R. GreÂe, J.-P. Lellouche, in: V.A. Soloshonok (Ed.), EPC Synthesis of Fluoroorganic Compounds: Stereochemical Challenges and Biomedical Targets, Wiley, Chichester, UK, in press. [11] W.J. Middleton, J. Org. Chem. 40 (1975) 574. [12] F. Munyemana, A.M. Frisque-Hesbain, A. Devos, L. Ghosez, Tetrahedron Lett. 30 (1989) 3077. 6
Reaction with acyclic pentadienyl cations complexed to Fe(CO)3 leads also to a complete decomposition of the starting complexes, see [17]. 7 To the best of our knowledge, in the case of such cationic rhenium complexes, efficient decomplexation has been obtained only in the case of s-bonded derivatives; see for instance [21].
S. Legoupy et al. / Journal of Fluorine Chemistry 93 (1999) 171±173 [13] F. Munyemana, Ph.D. Thesis, University of Louvain La Neuve, Belgium, 1991. [14] D. GreÂe, R. GreÂe, A. Boukerb, M. Laabassi, Tetrahedron Lett. 35 (1997) 6209. [15] A. Boukerb, D. GreÂe, M. Laabassi, R. GreÂe, J. Fluorine Chem. 88 (1998) 23. [16] Y. Li, K. Luthman, U. Hacksell, Tetrahedron Lett. 33 (1992) 4487. [17] D.M. GreÂe, C.J.M. Kermarrec, J.T. Martelli, R.L. GreÂe, J.-P. Lellouche, L.J. Toupet, J. Org. Chem. 61 (1996) 1918. [18] C. Kermarrec, V. Madiot, D. GreÂe, A. Meyer, R. GreÂe, Tetrahedron Lett. 34 (1996) 5691. [19] J.A. Gladysz, B.J. Boone, Angew. Chem., Int. Ed. Engl. 36 (1997) 550. [20] F. Agbossou, E.J. O'Connor, C.M. Garner, N. Quiros Mendez, J.M. Fernandez, A.T. Patton, J.A. Ramsden, J.A. Gladysz, Inorg. Synth. 29 (1992) 211.
173
[21] G.B. Richter-Addo, D.A. Knight, M.A. Dewey, A.M. Arif, J.A. Gladysz, J. Am. Chem. Soc. 115 (1993) 11863. [22] S. Legoupy, C. CreÂvisy, J.-C. Guillemin, R. GreÂe, Tetrahedron Lett. 37 (1996) 1225. [23] S. Legoupy, C. CreÂvisy, J.-C. Guillemin, R. GreÂe, J. Organomet. Chem. 567 (1998) 75. [24] S. Legoupy, C. CreÂvisy, J.-C. Guillemin, R. GreÂe, Organometallics 16 (1997) 1822. [25] S. Legoupy, C. CreÂvisy, J.-C. Guillemin, R. GreÂe, Chem. Eur. J. 4 (1998) 2155. [26] S.L. Schreiber, T. Sammkia, W.E. Crowe, J. Am. Chem. Soc. 108 (1986) 3128. [27] G.B. Jones, J.M. Wright, T.M. Rush, G.W. Plourde II, T.F. Kelton, J.E. Mathews, R.S. Huber, J.P. Davidson, J. Org. Chem. 62 (1997) 9379.