Co₂(CO)₈ Catalyzed Pauson-Khand Reaction under Microwave Irradiation [1]

Abstract

Microwave irradiation is used to accelerate Pauson-Khand reactions. The conditions for the Pauson-Khand reaction, catalytic in Co₂(CO)₈ under microwave irradiation, were optimized. It is possible to obtain various types of [2+2+1] cycloaddition products in 5 minutes without additional carbon monoxide.

Key words

microwave - Pauson-Khand reaction - catalysis - cobalt - cycloaddition

References

• 1 Transition metal catalyzed reactions in organic synthesis, part 2. For part 1, see: Jung M. Groth U. Synlett  2002,  12:  2015 
• 2a Khand IU. Knox GR. Pauson PL. Watts WE. J. Chem. Soc., Chem. Commun.  1971,  36 
• 2b Khand IU. Knox GR. Pauson PL. Watts WE. J. Chem. Soc., Perkin Trans. 1  1973,  975 
• 2c Khand IU. Knox GR. Pauson PL. Watts WE. J. Chem. Soc., Perkin Trans. 1  1973,  977 
• For reviews, see:
• 3a Pauson PL. Tetrahedron  1985,  41:  5855 
• 3b Schore NE. Chem. Rev.  1988,  88:  1081 
• 3c Geis O. Schmalz HG. Angew. Chem. Int. Ed.  1998,  37:  911 
• 3d Chung YK. Coord. Chem. Rev.  1999,  188:  297 
• 3e Brummond KM. Kent JL. Tetrahedron  2000,  56:  3263 
• 3f Buchwald SL. Hicks FA. In Comprehensive Asymmetric Catalysis   Vol. II:  Jacobsen EN. Pfaltz A. Yamamoto H. Springer-Verlag; Berlin, Heidelberg: 2000.  Chap. 15. p.1-20  
• 4a Jamison TF. Shambayati S. Crowe WE. Schreiber SL. J. Am. Chem. Soc.  1997,  119:  4353 
• 4b Kerr WJ. McLaughlin M. Pauson PL. Robertson SM. J. Organomet. Chem.  2001,  630:  104 
• 4c Murray A. Hansen JB. Christensen BV. Tetrahedron  2001,  57:  7383 
• 4d Velcicky J. Lex J. Schmalz H.-G. Org. Lett.  2002,  4:  565 
• 5a

  See ref. 2c.

• 5b Jeong N. Hwang SH. Lee Y. Chung YK. J. Am. Chem. Soc.  1994,  116:  3159 
• 5c Pagenkopf BL. Livinghouse T. J. Am. Chem. Soc.  1996,  118:  2285 
• 5d Jeong N. Hwang SH. Lee YW. Lim JS. J. Am. Chem. Soc.  1997,  119:  10549 
• 5e Sugihara T. Yamada M. Ban H. Yamaguchi M. Kaneko C. Angew. Chem., Int. Ed. Engl.  1997,  36:  2801 
• 5f Sugihara T. Yamaguchi M. J. Am. Chem. Soc.  1998,  120:  10782 
• 5g Kim JW. Chung YK. Synthesis  1998,  142 
• 5h Belanger DB. O’Mahony DJR. Livinghouse T. Tetrahedron Lett.  1998,  39:  7637 
• 5i Krafft ME. Bonaga LVR. Hirosawa C. Tetrahedron Lett.  1999,  40:  9171 
• 5j Krafft ME. Bonaga LVR. Hirosawa C. Tetrahedron Lett.  1999,  40:  9177 
• 5k Krafft ME. Bonaga LVR. Synlett  2000,  959 
• 5l Krafft ME. Bonaga LVR. Angew. Chem. Int. Ed.  2000,  39:  3676 
• 5m Sughihara T. Yamaguchi MN. Nishizawa M. Chem.-Eur. J.  2001,  7:  1589 
• 6 Gedye RN. Smith F. Westawya K. Ali H. Baldisera L. Laberge L. Rousell J. Tetrahedron Lett.  1986,  27:  279 
• For reviews, see:
• 7a Gabriel C. Gabriel S. Grant HG. Halstead BSJ. Mingos DMB. Chem. Soc. Rev.  1998,  27:  213 
• 7b Perreux L. Loupy A. Tetrahedron  2001,  57:  9199 
• 7c Lidström P. Wathey B. Westman J. Tetrahedron  2001,  57:  9225 
• 7d Kuhnert N. Angew. Chem. Int. Ed.  2002,  42:  1863 
• 7e Larhed M. Moberg C. Hallberg A. Acc. Chem. Res.  2002,  35:  717 
• See ref. 5e. For reactivity of Co₂(CO)₆-alkyne complexes, see:
• 8a Nicholas KM. Acc. Chem. Res.  1987,  20:  207 
• 8b Melikyan GG. Nicholas KM. In Modern Acetylene Chemistry   Stang PJ. Diederich F. Wiley VCH; Weinheim: 1995.  Chap. 4. p.99-138  
• 8c Fischer S. Synlett  2002,  1558 
• 10 All experiments were preformed using a Smith Synthesizer from Personal Chemistry. For a detailed instrument description, see: Stadler A. Kappe CO. Comb. Chem.  2001,  3:  624 
• 11 Deposition of a metal film has recently also been observed in a Pd(OAc)₂ catalyzed C-P cross-coupling reaction: Stadler A. Kappe CO. Org. Lett.  2002,  4:  3541 
• All spectral data were in full accordance with those reported in literature:
• 14a Entry 1: Devasagayaraj A. Periasamy M. Tetrahedron Lett.  1989,  30:  595 
• 14b Entry 3: Hayakawa K. Schmid H. Helv. Chim. Acta  1977,  60:  2160 
• 14c Entry 4: Grossman RB. Buchwald SL. J. Org. Chem.  1992,  57:  5803 
• 14d

  Entry 2: ¹H (CDCl₃, 400 MHz): δ = 7.00 (d, J = 2.4 Hz, 1 H), 2.54 (sept., J = 6.6 Hz, 1 H), 2.48 (m, 1 H), 2.30 (m, 1 H), 2.08 (m, 2 H), 1.58 (m, 1 H), 1.51 (m, 1 H), 1.21 (m, 2 H), 1.01 (d, J = 6.6 Hz, 6 H), 0.86 (m, 2 H). ¹³C (CDCl₃, 100 MHz): δ = 210.7, 156.5, 155.4, 54.1, 47.7, 38.9, 37.9, 30.8, 29.0, 28.3, 24.5, 21.5, 21.2.

9

It should be stated that low boiling solvents usually cannot be heated to 200 °C but in our case the desired temperature could be reached in all cases except dichloromethane, which reached a maximum at 140 °C.

12

When conventional heating of the sealed vessel was provided under identical conditions the yield did not exceed 40% even after 4 h.

13

Typical Experimental Procedure: To a 10 mL glass vial 942 mg (10 mmol, 5 equiv) norbornene 1 and 137 mg (0.4 mmol, 0.2 equiv) Co₂(CO)₈ were added under an inert gas atmosphere in a glove box and sealed with a Teflon septum and an aluminum crimp top. After the addition of 2 mL toluene (freshly distilled from sodium), 220 µL (2 mmol) phenylacetylene 2 and finally 275 µL (2.4 mmol, 1.2 equiv) cyclohexylamine were added through the Teflon septum. The vessel was then heated to 100 °C under microwave irradiation using the Smith Synthesizer (monomode microwave cavity at 2.45 GHz; temperature control by automated adjustment of irradiation power in a range from
0 to 300 W). After 300 s the vial was cooled to r.t. by gas jet cooling. The reaction mixture was then subjected to a typical aqueous workup. The dried organic phase was then liberated from solvent and purified by flash chromatography on silica eluting with EtOAc/petroleum ether to give 363 mg (1.62 mmol, 81%) of exo-3.