One step synthesis of 7metacyclophanediyne complexes from bis(propargyldicobalt) dication equivalents Richard Guo and James R. Green* Chemistry and Biochemistry, School of Physical Sciences, University of Windsor, Windsor, Ontario, Canada N9B 3P4. E-mail: jgreen@uwindsor.ca Received (in Covallis, OR, USA) 1st October 1999, Accepted 4th November 1999 The BF3middot;OEt2 mediated addition reactions of electron-rich arenes to 1,3-dialkoxyhepta-2,5-diyne(dodecacarbonyl)- tetracobalt complex 1 directly afford 7metacyclophanediyne( dodecacarbonyl)tetracobalt complexes.The chemistry of small cyclophanes has been the focus of much attention, due to their structural and electronic properties, and their ability to include either metal ions or neutral or charged organic molecules.1ndash;3 Syntheses of these classes of compounds, however, are rarely straightforward. Access to the smaller nmetacyclophanes (n @ 8), for example, is most often accomplished by rearrangement of propellanes or spirocycloalkadienones, intramolecular Dielsndash;Alder reactions of dienynes, or extrusion reactions of sulfoxides.1,2 Direct intermolecular cycloaddition approaches towards these systems have not been efficient ones.4 The use of hexacarbonyldicobalt alkyne complexes has become important in organic synthesis.5ndash;7 Among the noteworthy features of these complexes is their ability to serve as protected versions of alkynes that would be severely or prohibitively strained.8 This property has seen application as a tactic in the chemistry of cyclohexynes and cycloheptynes,9 Bergman cyclization precursors,10 and other polyacetylenic macrocycles.11 We have begun a program on the investigation of the chemistry of dodecacarbonyltetracobalt complexes of hepta- 2,5-diynyl 1,7-diethers 1 and closely related compounds as latent 1,4-diynes, dienes, or enynes, based on the known ability of hexacarbonyldicobalt complexes of propargyl alcohols and their derivatives to form cations readily.5 The diether complex 1 underwent ready reaction with electron-rich arenes in the presence of BF3middot;OEt2, but did not stop cleanly at the monoarylation products.When 1 was subjected to equimolar amounts of BF3middot;OEt2 and 1,3,5-trimethoxybenzene at 0 deg;C (at 1022 M each in CH2Cl2), only a 24 yield of 2 could be isolated. The predominant product (26) proved to be 7metacyclophanediyne complex 3a, stemming from two substitution reactions by trimethoxybenzene on 1.The yields of 3a realized could be improved considerably by increasing the amounts of both BF3middot;OEt2 and trimethoxybenzene to 2 equiv; 3a was then obtained in 92 yield after 5 h at 0 deg;C.dagger; Other electron-rich benzenes also gave 7metacyclophanediyne complexes under analogous conditions (Table 1). 1,2,3-Trimethoxybenzene gave 3b in a more modest yield (34), while 1,3-dimethoxybenzene gave two separable cyclophanes, 3c and 3d, in 78 combined yield (63 3c + 15 3d).Among heterocycles tested, furan gave 7(2,5)furanocyclophane complex 3e in 30 yield. Pyrrole, unlike the other electron rich arenes, afforded monocondensation product 4 as the only tractable product in 51 yield. Subsequent addition of 4 to excess BF3middot;OEt2 (4 equiv.) at 0 deg;C in CH2Cl2 (24 h, 1022M) then gave 7(2,5)pyrrolophane 3f in 40 yield. Thiophene proved insufficiently reactive to give any condensation product with 1. Conducting the reactions at lower concentration (1023 M) increased the necessary reaction time considerably (3 d at 0 deg;C), but gave some improvement in the yields of 3c (68 3c + 15 3d) and 3e (43).The yield of 3b was actually inferior (19) at the lower concentration. The 1H NMR spectra of these 7metacyclophanediyne complexes possessed characteristics that fell into two distinctly different groups. Those which contained a methoxy function between the two termini of the bridge (3a and 3d) revealed highly diastereotopic methylene groups; the bispropargylic methylene function of 3a, for example, gave resonances at d 4.99 and 4.31, whereas the benzylic methylene function gave resonances at d 4.34 and 4.09.The other cyclophanediyne complexes (3b, 3c, 3e, 3f) showed methylene groups whose protons were isochronous. The number of alkyne containing cyclophanes is relatively modest,11,12 and dominated by cases where the alkyne function serves simply as a spacer,13 but there is much interest in the demonstrated coordinating ability of the alkyne function of Table 1 Additions between diyne complexes 1 or 4 with arenes Diyne Nucleophile Product ( yield) 1 1,3,5-trimethoxybenzene 3a (92) 1 1,2,3-trimethoxybenzene 3b (34) 1 1,3-dimethoxybenzenea 3c (68) 3d (15) 1 Furana 3e (43) 1 Pyrrole 4 (51) 4 mdash; 3f (40) a Conducted at 1 = 1023 M.This journal is copy; The Royal Society of Chemistry 1999 Chem. Commun., 1999, 2503ndash;2504 2503cyclic polyynes.14 As a result, we deemed it of interest to determine whether or not decomplexation of 3 could be accomplished.In fact, attempted removal of the hexacarbonyldicobalt units from 3a by the usual reagents Me3NO, (NH4)2Ce(NO3)6, CuCl2, FeCl3 resulted in complete destruction of the cyclophanediyne unit. On the other hand, stirring complex 3a in a pyridinendash;Et2O solvent mixture (1+1, in air) over a 10 d period resulted in the formation of 5 in 56 yield. The 1H NMR spectrum of 5 also showed the presence of diastereotopic methylene groups; the resonances for the benzylic hydrogen atoms appeared at d 3.48 and 3.41, while the bispropargylic hydrogen atoms gave resonances at d 2.92 and 2.61.Compound 5 gave crystals suitable for X-ray diffraction, which revealed the structure represented in Fig. 1.Dagger; It is apparent that there is strain in this molecule, which is reflected in several ways. Among the most notable of these are the bond angles at the alkynyl carbon atoms, which have been bent to 164 (at C-11 and C-15) and 163deg; (at C-12 and C-14).The arene ring also shows these effects, as the benzylic carbon atoms are pulled out of the plane of the C-1, C-3, C-4, C-6 arene ring carbons by 32.9deg; (b), and the benzene ring itself deviates slightly from planar at both C-2 (a = 11.2deg;) and at C-5 (g = 5.5deg;) (Fig. 2). Nevertheless, compound 5 has good thermal stability. The structural data also suggest strongly that the diastereotopic methylene groups in 3a, 3d and 5 are consequences of the ring inversion represented in Fig. 2 at the slow exchange limit (Fig. 2, shown for 5). The singlets observed for 3b, 3c, 3e and 3f stem from molecules at the fast exchange limit of the analogous inversion process.15 The 7metacyclophanediyne 5 is the smallest nmetacyclophane containing a triple bond reported to date. Nevertheless, a small number of reported metacyclophanes have larger deformation angles (a, b, g),16 and a number alkynes with smaller bond angles also exist.17 These data suggest that smaller alkyne containing nmetacyclophanes may be accessible. We are grateful to NSERC (Canada) for support of this research.We wish to thank Professor Doug Stephan and Professor Stephen Loeb (WINMOL) for the crystallographic structural work on 5. Notes and references dagger; The use of the theoretically required 1 equiv. of 1,3,5-trimethoxybenzene with 2 equiv. of BF3-OEt2 afforded 3a in 86 yield. Dagger; Crystal data for 5: C16H16O3, with Mo-Ka radiation, M = 256.30, triclinic, a = 7.836(3), b = 7.925(4), c = 11.378(7) Aring;, a = 101.66(4), b = 98.03(3), g = 95.35(5)deg;, U = 679.8(6) Aring;3, T = 293 K, space group P�1, Z = 2, Dc = 1.252 Mg m23, m = 0.086 mm21, q range 1.85ndash;25.0deg;.GOF on F2 1.003 for 2338 unique observed data on 172 parameters, R1 = 0.0476, wR2 = 0.1355. CCDC 182/1476. See http://www.rsc.org/suppdata/cc/ 1999/2503/ for crystallographic data in .cif format. 1 Cyclophanes, ed. P. M. Klein and S.M. Rosen, Academic Press, New York, 1983, vol. 1 and 2; F. Diederich, Cyclophanes, Royal Society of Chemistry, Cambridge, 1991. 2 V. V. Kane, W. H. de Wolf and F. Bickelhaupt, Tetrahedron, 1994, 50, 4575; Y. Tobe, Top. Curr. Chem., 1994, 172, 1. 3 J. Schulz and F. Vouml;gtle, Top. Curr. Chem., 1994, 172, 41. 4 For an exception in 8paraclophane chemistry, see T. Tsuji, T. Shibata, Y. Hienuki and S. Nishida, J. Am. Chem. Soc., 1978, 100, 1806. 5 M. J. Went, Adv. Organomet. Chem., 1997, 41, 69 6 A.J. M.Caffyn and K. M. Nicholas, in Comprehensive Organometallic Chemistry II, ed. E. W. Abel, F. G. A. Stone and G. Wilkinson, vol. ed. L. S. Hegedus, Pergamon, Oxford, 1995, vol. 12, ch. 7.1; K. M. Nicholas, Acc. Chem. Res., 1987, 20, 207. 7 N. E. Schore, in Comprehensive Organometallic Chemistry II, ed. E. W. Abel, F. G. A. Stone and G. Wilkinson, vol. ed. L. S. Hegedus, Pergamon, Oxford, 1995, vol. 12, ch. 7.2; N. E. Schore, Org. React., 1991, 40, 1.N. E. Schore, in Comprehensive Organic Synthesis, ed. B. M. Trost, vol. ed. L. A. Paquette, Pergamon, Oxford, 1991, vol. 5, ch. 9.1; N. E. Schore, Chem. Rev., 1988, 88, 1081. 8 W. M. Jones and J. Klosin, Adv. Organomet. Chem., 1998, 42, 147. 9 M. M. Patel and J. R. Green, Chem. Commun., 1999, 509; S. L. Schreiber, M. T. Klimas and T. Sammakia, J. Am. Chem. Soc., 1986, 108, 3128; T. Nakamura, T. Matsui, K. Tanino and I. Kuwajima, J. Org. Chem., 1997, 62, 3032; N. E. Schore and S.D. Najdi, J. Org. Chem., 1987, 52, 5296; C. Yenjai and M. Isobe, Tetrahedron, 1998, 54, 2509 and references therein; N. Iwasawa and H. Satoh, J. Am. Chem. Soc., 1999, 121, 7951. 10 P. Magnus, Tetrahedron, 1994, 50, 1397; M. E. Maier, Synlett, 1995, 13; J. W. Grissom, G. U. Gunawardena, D. Klingberg and D. Huang, Tetrahedron, 1996, 52, 6453. 11 M. M. Haley and B. L. Langsdorf, Chem. Commun., 1997, 1121. 12 G. J. Bodwell, T. J. Houghton and D. Miller, Tetrahedron Lett., 1998, 39, 2231; T.Kawase, N. Ueda and M. Oda, Tetrahedron Lett., 1997, 38, 6681 and references therein; H. Ueda, C. Katayama and J. Tanaka, Bull. Chem. Soc. Jpn., 1981, 54, 891 and references therein; H. Hopf, P. G. Jones, P. Bubenitschek and C. Werner, Angew. Chem., 1995, 107, 2592, Angew. Chem., Int. Ed. Engl., 1995, 34, 2367. 13 D. Orsquo;Krongly, S. R. Denmeade, M. Y. Chang and R. Breslow, J. Am. Chem. Soc., 1985, 107, 5544. 14 T. Nishinaga, T. Kawamura and K. Komatsu, Chem. Commun., 1998, 2263; J. D. Ferrara, A. Djebli, C. Tessier-Youngs and W. J. Youngs, J. Am. Chem. Soc., 1988, 110, 647; D. Solooki, J. D. Bradshaw, C. A. Tessier and W. J. Youngs, Organometallics, 1994, 13, 451; D. Zhang, D. B. McConville, J. M. Hrabusa III, C. A. Tessier and W. J. Youngs, J. Am. Chem. Soc., 1998, 120, 3506. 15 For a discussion of conformational properties of cyclophanes, see R. H. Mitchell, in Cyclophanes, ed. P. M. Klein and S. M. Rosen, Academic Press, New York, 1983, vol. 1, ch. 4. 16 J. L. Pierre, P. Baret, P. Chautemps and M. Armand, J. Am. Chem. Soc., 1981, 103, 2986. 17 A. Krebs and J. Wilke, Top. Curr. Chem., 1983, 109, 189; H. Meier, Adv. Strain Org. Chem., 1991, 1, 215. Communication 9/07991B Fig. 1 ORTEP drawing of 5 (30 probability). H atoms not shown. Selected bond lengths (Aring;) and angles (deg;): C(1)ndash;C(2) 1.398(3), C(14)ndash;C(15) 1.186(3), C(13)ndash;C(14)ndash;C(15) 164.0(2), C(14)ndash;C(15)ndash;C(16) 162.9(2), C(12)ndash;C(14) 106.1(2), C(2)ndash;C(3)ndash;C(16) 117.2(2). Fig. 2 Distortion angles and fluxional process for 5. 2504 Chem. Commun., 1999, 2503ndash;2504
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