Metal-mediated trandem [6 + 2],homo[6 + 2] cycloadditions of alkynes to cycloheptatriene. Generation of novel tetracycloundecadienes

Full text of DOI:10.1021/ja961436a

9980
J. Am. Chem. Soc. 1996, 118, 9980-9981
Communications to the Editor
Scheme 1. Tandem [6π + 2π],homo[6π + 2π] Alkyne
Cycloadditions
Metal-Mediated Tandem [6 + 2],homo[6 + 2]
Cycloadditions of Alkynes to Cycloheptatriene.
Generation of Novel Tetracycloundecadienes
Weichun Chen, Karen Chaffee, Hyei-Jha Chung, and
John B. Sheridan*
Department of Chemistry
Rutgers, The State UniVersity of New Jersey
UniVersity Heights, Newark, New Jersey 07102
ReceiVed May 1, 1996
manganese19,20 and chromium21 cyclodienyl species forming four
new C-C bonds and two rings in a single step with high degrees
of stereo- and regiocontrol. In early work, Green, Woodward,
and co-workers briefly described a novel tetracyclic complex 3
derived from 2 equiv of hexafluorobut-2-yne and [(η6-C7H8)-
Fe(CO)3],22,23 although no further details were reported. It is
now clear that all of these double-addition reactions are
variations of a general metal-assisted [6π + 2π],homo[6π +
2π] cycloaddition process, and a schematic representation for
the dienyl and triene manifolds is shown in Scheme 1.
Transition metal-mediated cycloaddition reactions continue
to attract interest for the efficient and stereoselective syntheses
of a variety of ring systems.1,2 Metal-promoted higher-order
processes that generate medium size rings (e.g., [6 + 2] and [6
+ 4]) were first reported in the 1970s,3,4 have been extensively
studied by Rigby and co-workers, and used in a number of
natural product syntheses.5-8 The [6 + 2] cycloaddition of
alkynes to coordinated polyene manifolds has been reported by
a number of groups,3,9-13 and we have previously described a
[6 + 2] coupling of internal alkynes and [(η6-triene)Cr(CO)3]
complexes under photochemical conditions that gives bicyclo-
[4.2.1]nonatriene derivatives (eq 1).14,15
We now report that this double-addition protocol can be
extended to the chromium complex 1 forming the decomplexed
tetracyclic species 4, in which fiVe new C-C bonds are formed
in a single step. The reaction proceeds in up to 80% yield with
2-butyne and can be performed in a tandem reaction sequence
that couples two different alkyne partners with 1 allowing access
to a range of new tetrasubstituted tetracycloundecadienes.
UV irradiation of toluene or n-hexane solutions of [(η6-C7H8)-
Cr(CO)3] (1) and 2 equiv or more of 2-butyne at room
temperature for 4-8 h followed by chromatographic workup
gave an 80% isolated yield of 4,5,6,11-tetramethyltetracyclo-
[8.1.0.03,704,11]undeca-5,8-diene (4a) as a colorless oil (eq 2).24,25
Higher-order cycloadditions have been extended to the η5-
dienyl manifold,16-18 and we have recently reported novel [5
+ 2],homo[5 + 2] double-alkyne cycloadditions to both
(1) Lautens, M.; Klute, W.; Tam, W. Chem. ReV. 1996, 96, 49.
(2) Schore, N. E. Chem. ReV. 1988, 88, 1081.
(3) Davis, R. E.; Dodds, T. A.; Hseu, T.; Wagnon, J. C.; Devon, T.;
Tancrede, J.; Mckennis, J. S.; Pettit, R. J. Am. Chem. Soc. 1974, 96, 7562.
(4) O¨ zkar, S.; Kurz, H.; Neugebauer, D.; Kreiter, C. G. J. Organomet.
Chem. 1978, 160, 115.
(5) Rigby, J. H. Acc. Chem. Res. 1993, 26, 579.
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K. M.; Sugathapala, P. M. Tetrahedron 1993, 49, 5495.
(7) Rigby, J. H.; Pigge, F. C. J. Org. Chem. 1995, 60, 7392.
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1995, 60, 7720.
(9) Brammer, L.; Dunne, B. J.; Green, M.; Moran, G.; Orpen, A. G.;
Reeve, C.; Schaverien, C. J. J. Chem. Soc., Dalton Trans. 1993, 1747.
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G.; Reeve, C.; Schaverien, C. J. J. Chem. Soc., Chem. Commun. 1985, 1409.
(12) Mach, K.; Antropiusova, H.; Petrusova, L.; Hanus, V.; Turecek,
F.; Sedmera, P. Tetrahedron 1984, 40, 3295.
A trace of hexamethylbenzene (GC/MS) is also formed via
cyclotrimerization of the alkyne substrate, but this contrasts with
the previously reported titanium-mediated triene-alkyne cy-
(13) Nagashima, H.; Matsuda, H.; Itoh, K. J. Organomet. Chem. 1983,
258, C15.
(14) Chaffee, K.; Huo, P.; Sheridan, J. B.; Barbieri, A.; Aistars, A.;
Lalancette, R. A.; Ostrander, R. L.; Rheingold, A. L. J. Am. Chem. Soc.
1995, 117, 1900.
(19) Wang, C.; Sheridan, J. B.; Chung, H.-J.; Cote´, M. L.; Lalancette,
R. A.; Rheingold, A. L. J. Am. Chem. Soc. 1994, 116, 8966.
(20) Chung, H.-J.; Sheridan, J. B.; Cote´, M. L.; Lalancette, R. A.
Organometallics 1996, 15, 4575.
(21) Chen, W.; Chung, H.-J.; Wang, C.; Sheridan, J. B.; Cote´, M. L.;
Lalancette, R. A. Organometallics 1996, 15, 3337.
(22) Bottrill, M.; Goddard, R.; Green, M.; Hughes, R. P.; Lloyd, M. K.;
Lewis, B.; Woodward, P. J. Chem. Soc., Chem. Commun. 1975, 253.
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(15) Chaffee, K.; Sheridan, J. B.; Aistars, A. Organometallics 1992, 11,
18.
(16) Kreiter, C. G.; Lehr, K.; Leyendecker, M.; Sheldrick, W. S.; Exner,
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Chem. 1995, 490, 133.
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S0002-7863(96)01436-9 CCC: $12.00 © 1996 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 118, No. 41, 1996 9981
cloadditions12,26 which almost exclusively gave arene products
with nonsterically demanding alkynes. Compound 4a consists
of four rings, cyclopropane, -pentane, -pentene, and -heptene,
and possesses six chiral centers. A single diastereomer is
isolated since bond formation occurs at the metal face of the
triene precursor.
alkyne group of the eneyne adds to 1, although [6 + 2]
cycloadditions of both alkynes14,15 and olefins27 to 1 have been
previously reported by us and Rigby et al., respectively.
Subsequent UV irradiation of 2b and 2-butyne results in a single
regioisomer of the highly functionalized tetracyclic product 4e.
The reaction is not confined to 2-butyne and can be extended
to terminal alkynes. Thus, reaction of phenylacetylene and 1
under identical conditions to those used for 2-butyne gave
moderate yields of 4b as well as some triphenylbenzene (ca.
25%). Significantly, 4b is a single regioisomer of the four
possibilities that can form from the addition of two unsym-
metrical alkynes to 1 and presumably arises from the various
insertion preferences of particular alkyne termini during the
stepwise coupling reaction. Similar regioselectivity has been
observed in the related alkyne insertions into dienyl ligands.19-21
The synthetic potential of the new double-cycloaddition
reaction is highlighted by the fact that the tandem addition of
two different alkynes to 1 is possible. Thus, reaction of 1 with
diphenylacetylene gives the bicyclo[4.2.1]nonatriene complex
2a,14,15 which can then be reacted with either 2-butyne or
phenylacetylene to give single regioisomers of the mixed double
adducts 4c and 4d, respectively (eq 3). More elaborate
functionality can be introduced into the tetracyclic species by
reaction of 1 with the eneyne PhCtC(CH2)3CHdCH2 giving
bicyclic 2b in 55% yield. Noteworthy is the fact that only the
In summary we have demonstrated the facile construction of
complex tetracyclic species via the tandem addition two alkynes
to cycloheptatriene utilizing Cr(CO)3 derivatives and UV light.
The [6 + 2],homo[6 + 2] cycloadditions described herein
complement the [5 + 2],homo[5 + 2] processes we have
discovered for Mn and Cr dienyl species and appear to be
general for the reactions of alkynes with coordinated noncyc-
lically conjugated 6π-polyene and 6π-polyenyl manifolds.
Thus, through the use of different organometallic precursors,
access to novel fused C5,C5,C6;19,20 C5,C6,C7;21 or C3,C5,C5,C7
ring systems is possible. Further studies to fully discern the
synthetic potential of the new cycloadditions are planned.
(24) Satisfactory spectroscopic data (1H, 13C, and 1H-1H 2D (COSY)
NMR spectra and high-resolution MS) were obtained for all new compounds
reported (see supporting information).
(25) General Procedure for the Preparation of 4a-e. A solution of [(η6-
C7H8)Cr(CO)3] (1, 1-2 mmol) or 2 (1-2 mmol)) and the appropriate alkyne
(3-5 mmol) in n-hexane (100-200 mL) was irradiated with UV light from
a 450 W Hanovia Hg vapor lamp through Pyrex at a distance of ca. 5 cm
until all of 1 or 2 had been consumed (IR, 4-48 h). Removal of the solvent
in vacuo and purification of the residue on a silica gel column or by TLC
gave the products 4a-e as clear colorless oils or white solids. The reactions
proceed in good yields when higher concentrations of substrates are used,
however the more intense color of these solutions necessitates longer reaction
times.
Acknowledgment. We are grateful to the Rutgers Research Council
for financial support.
Supporting Information Available: Characterization data for 4a-e
and the 1D and 2D COSY 1H NMR spectra of 4c (3 pages). See any
current masthead page for ordering and Internet access instructions.
JA961436A
(26) Klein, R.; Sedmera, P.; Cejka, J.; Mach, K. J. Organomet. Chem.
1992, 436, 143.
(27) Rigby, J. H.; Henshilwood, J. A. J. Am. Chem. Soc. 1991, 113,
5122.