First [4 + 3] Annulation of Alkynyl Fischer Carbene Complexes and Azadienes. X-ray Structure of a Metalated Zwitterionic Intermediate Jose ´ Barluenga,* ,† Miguel Toma ´s, † Eduardo Rubio, † Jose ´ A. Lo ´pez-Pelegrı ´n, † Santiago Garcı ´a-Granda, ‡ and Pilar Pertierra ‡ Instituto UniVersitario de Quı ´mica Organometa ´ lica “Enrique Moles”, Unidad Asociada al CSIC, and Departamento de Quı ´mica Fı ´sica y Analı ´tica UniVersidad de OViedo, Julia ´ n ClaVerı ´a, 8 E-33071, OViedo, Spain ReceiVed August 9, 1995 Recently, R,-unsaturated Fischer carbene complexes have been recognized to play an important role in transition-metal- mediated organic synthesis. 1 Although alkynyl Fischer carbene complexes are less versatile intermediates than their alkenyl counterparts, a number of useful reactions have been reported; for instance, 1,2- and 1,4-nucleophilic additions 2 as well as [2 + 2], 3 [3 + 2], 4 [3 + 3], 5 [4 + 2] 6 and Pauson-Khand type 7 cyclization reactions. On the other hand, the [4 + 3] cycload- dition of alkenyl carbenes with electron-rich dienes, which may involve a tandem cyclopropanation/Cope rearrangement, has recently emerged as an attractive entry into seven-membered carbocycles; 8 in contrast, no examples of this type of process involving alkynyl complexes are known, perhaps because of the required involvement of a strained cumulene ring. 9 In an extension of this reaction we found that activated 1-azadienes, like 4-amino-1-azadienes and N-hydroxy-1-azadienes, readily undergo [4 + 3] annulation with alkenyl Fischer carbene complexes leading to the azepine ring; interestingly, NMR studies proved that the cycloaddition involves nucleophilic addition of the imine nitrogen to the carbene carbon and cyclization rather than consecutive [2 + 1] cycloaddition and [3,3] rearrangement. 10 On working with alkynyl carbene complexes and nitrogen- containing substrates one can anticipate that either 1,4- or 1,2- addition might take place and therefore different reaction pathways should be observed. 11 Reported here is the achieve- ment of a [4 + 3] cycloaddition reaction of alkynyl Fischer carbene complexes with R,-unsaturated imines as well as the isolation of an η 1 -azepine chromium complex intermediate. 12 The reaction of azadienes 1 with pentacarbonyl methoxy (phenylethynyl)chromium carbene complex 2 (R 3 ) Ph) in hexane at 20 °C was complete in 3 h affording a precipitate that consisted essentially of the [4 + 3] cycloadducts 3a-c (Scheme 1, Table 1, entries 1-3). When chromium alkynyl complexes 2 having bulky groups at the -carbon (R 3 ) SiMe 3 , tert-Bu; entries 4-6) were employed, the cyclization became much more sluggish and therefore required the reaction to be † Instituto Universitario de Quı ´mica Organometa ´lica “Enrique Moles”. ‡ Departamento de Quı ´mica Fı ´sica y Analı ´tica (X-ray service). (1) (a) Wulff W. D. In ComprehensiVe Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon: New York, 1991; Vol. 5, p 1065. (b) Do ¨tz, K. H. Angew. Chem., Int. Ed. Engl. 1984, 23, 587. (2) For nitrogen nucleophiles, see, for instance: (a) Funke, F.; Duetsch, M.; Stein, F.; Noltemeyer, M.; de Meijere, A. Chem. Ber. 1994, 127, 911. (b) Stein, F.; Duetsch, M.; Pohl, E.; Herbst-Irmer, R.; de Meijere, A. Organometallics 1993, 12, 2556. (c) Pipoh, R.; van Eldik, R.; Henkel, G. Ibid. 1993, 12, 2236. (d) Pipoh, R.; van Eldik, R. Ibid. 1993, 12, 2668. (e) Aumann, R.; Jasper, B.; La ¨ge, M.; Krebs, B. ibid. 1994, 13, 3502. (f) Rahm, A.; Wulff, W. D.; Rheingold, A. L. Ibid. 1993, 12, 597. (g) Duetsch, M.; Lackmann, R.; Stein, F.; de Meijere, A. Synlett 1991, 324. (h) Aumann, R. Chem. Ber. 1994, 127, 725. (i) Aumann, R.; Hinterding, P. Ibid. 1993, 126, 421. For oxygen nucleophiles, see: (j) Stein, F.; Duetsch, M.; Lackmann, R.; Noltemeyer, M.; de Meijere, A. Angew. Chem., Int. Ed. Engl. 1991, 30, 1658. (k) Camps, F.; Llebaria, A.; Moreto ´, J. M.; Ricart, S.; Vin ˜as, J. M. J. Organomet. Chem. 1991, 401, C17. (l) Aumann, R.; Jasper, B.; La ¨ge, M.; Krebs, B. Chem. Ber. 1994, 127, 2475. (m) Segundo, A.; Moreto ´, J. M.; Vin ˜as, J. M.; Ricart, S.; Molins, E. Organometallics 1994, 13, 246. (n) Aumann, R. Chem. Ber. 1992, 125, 2773. For phosphorus nucleophiles, see: (o) Aumann, R.; Jasper, B.; Fro ¨hlich, R. Organometallics 1995, 14, 231. For carbon nucleophiles, see: (p) Aumann, R.; Kosmeier, M.; Roths, K.; Fro ¨hlich, R. Synlett 1994, 1041. For the ene reaction with electron-rich alkenes, see ref 3a. (3) (a) Faron, K. L.; Wulff, W. D. J. Am. Chem. Soc. 1990, 112, 6419. (b) Faron, K. L.; Wulff, W. D. Ibid. 1988, 110, 8727. (c) Aumann, R.; Roths, K.; La ¨ge, M.; Krebs, B. Synlett 1993, 667. (d) Pipoh, R.; van Eldik, R.; Wang, S. L. B.; Wulff, W. D. Organometallics 1992, 11, 490. (e) Camps, F.; Moreto ´, J. M.; Ricart, S.; Vin ˜as, J. M.; Molins, E.; Miravitlles, C. J. Chem. Soc., Chem. Commun. 1989, 1560. (f) Camps, F.; Llebaria, A.; Moreto ´, J. M.; Ricart, S.; Vin ˜as, J. M. Tetrahedron Lett. 1990, 31, 2479. (4) (a) Kreissl, F. R.; Fischer, E. O.; Kreiter, C. G. J. Organomet. Chem. 1973, 57, C9. (b) Chan, K. S.; Wulff, W. D. J. Am. Chem. Soc. 1986, 108, 5229. (c) Chan, K. S.; Yeung, M. L.; Chan, W.; Wang, R.; Mak, T. C. W. J. Org. Chem. 1995, 60, 1741. (d) Chan, K. S. J. Chem. Soc., Perkin Trans. 1 1991, 2602. (5) (a) Wang, S. L. B.; Wulff, W. D. J. Am. Chem. Soc. 1990, 112, 4550. (b) Merlic, C. A.; Xu, D. Ibid. 1991, 113, 9855. (c) Aumann, R.; Roths, K.; Grehl, M. Synlett 1993, 669. (d) Reference 2p. (6) (a) Wulff, W. D.; Yang, D. C. J. Am. Chem. Soc. 1984, 106, 7565. (b) Wulff, W. D.; Yang, D. C. Ibid. 1984, 106, 7656. (c) Bao, J.; Dragisich, V.; Wenglowsky, S.; Wulff, W. D. Ibid. 1991, 113, 9873. (d) Bao, J.; Wulff, W. D.; Dragisich, V.; Wenglowsky, S.; Ball, R. G. Ibid. 1994, 116, 7616. (e) Wulff, W. D.; Tang, P. C.; Chan, K. S.; McCallum, J. S.; Yang, D. C.; Gilbertson, S. R. Tetrahedron 1985, 41, 5813. (f) Barluenga, J.; Aznar, F.; Barluenga, S. J. Chem. Soc., Chem. Commun. 1995, 1973. (7) (a) Do ¨tz, K. H.; Christoffers, J. J. Organomet. Chem. 1992, 426, C58. (b) Camps, F.; Moreto ´, J. M.; Ricart, S.; Vin ˜as, J. M. Angew. Chem. Int., Ed. Engl. 1991, 30, 1470. (8) (a) Wulff, W. D.; Yang, D. C.; Murray, C. K. J. Am. Chem. Soc. 1988, 110, 2653. (b) Barluenga, J.; Aznar, F.; Martı ´n, A.; Garcı ´a-Granda, S.; Salvado ´ , M. A.; Pertierra, P. J. Chem. Soc., Chem. Commun. 1993, 319. (c) Barluenga, J.; Aznar, F.; Martı ´n, A. Organometallics 1995, 14, 1429. (d) Barluenga, J.; Aznar, F.; Valde ´s, C.; Martı ´n, A.; Garcı ´a-Granda, S.; Martı ´n, E. J. Am. Chem. Soc. 1993, 115, 4403. (e) Harvey, D. F.; Grenzer, M. E.; Gantzel, P. K. Ibid. 1994, 116, 6719. (9) For cycloheptaallenic species, see: (a) Dolbier, W. R., Jr.; Garza, O. T.; Al-Sader, B. H. J. Am. Chem. Soc. 1975, 97, 5038. (b) Manisse, N.; Chuche, J. Ibid. 1977, 99, 1272. (c) Manisse, N.; Chuche, J. Tetrahedron 1977, 33, 2399. (d) Chapman, O. L.; Johnson, J. W.; McMahon, R. J.; West, P. R. J. Am. Chem. Soc. 1988, 110, 501. (10) Barluenga, J.; Toma ´s, M.; Ballesteros, A.; Santamarı ´a, J.; Lo ´pez- Ortiz, F.; Carbajo, R. J.; Garcı ´a-Granda, S.; Pertierra, P. Chem.sEur. J. 1996, 2, 180. (11) The 1,2- and 1,4-addition of amines (see refs 2b-i) and imines (see ref 2a) to alkynyl carbene complexes is well documented. (12) For previous work on Fischer carbene complexes and simple 1-azadienes, see: (a) Barluenga, J.; Toma ´s, M.; Lo ´pez Pelegrı ´n, J. A.; Rubio, E. J. Chem. Soc., Chem. Commun. 1995, 665. (b) Danks, T. N.; Velo- Rego, D. Tetrahedron Lett. 1994, 35, 9443. (13) Running the reaction of azadiene 1 (R 1 ) Ph; R 2 ) n-Pr) with carbene 2 (R 3 ) Ph) in THF at 20 °C resulted in the formation of 3a (55%) along with a second compound (28%) resulting from the [4 + 2] cycloaddition of the azadiene to the alkynyl function of the carbene complex. Unpublished results. (14) This metal migration has been independently invoked by Fischer and Do ¨tz to rationalize the cyclodimerization of alkynyl carbenes of chromium and tungsten that occurs on reaction with organolithium and organozinc reagents. See: (a) Do ¨tz, K. H.; Christoffers, C.; Knochel, P. J. Organomet. Chem. 1995, 489, C84. (b) Fischer, H.; Meisner, T.; Hofmann, J. Chem. Ber. 1990, 123, 1799. Scheme 1 695 J. Am. Chem. Soc. 1996, 118, 695-696 0002-7863/96/1518-0695$12.00/0 © 1996 American Chemical Society