ORGANIC LETTERS
Catalytic and Highly Efficient 1,4-Addition of Terminal Alkynes to Conjugated Enones by [RuCl2(p-cymene)]2/Pyrrolidine
2001 Vol. 3, No. 13 2089-2091
Sukbok Chang,*,† Youngim Na,† Eunjung Choi,† and Sunggak Kim‡ Department of Chemistry, Ewha Womans UniVersity, Seoul 120-750, Korea, and Center for Molecular Design and Synthesis, Department of Chemistry, Korea AdVanced Institute of Science and Technology, Taejon 305-701, Korea
[email protected] Received April 30, 2001
ABSTRACT
A wide range of terminal alkynes was added to conjugated enones in a 1,4-fashion by a ruthenium catalyst in the presence of catalytic amounts of an amine base, and the corresponding γ,δ-alkynyl ketones were obtained in good to excellent yields.
The excellent coordinating ability of alkynes for transition metal complexes makes transition metal catalyzed addition of various functional groups to activated alkynes a promising area for exploration (pathway a in Scheme 1).1 The insertion
Scheme 1
of a transition metal into spC-H bonds and the subsequent addition of the metal alkynilide, or its equivalents, into †
Ewha Womans University. Korea Advanced Institute of Science and Technology. (1) (a) Horn, K. A. Chem. ReV. 1995, 95, 1317. (b) Naota, T.; Takaya, H.; Murahashi, S.-I. Chem. ReV. 1998, 98, 2599. (c) Beletskaya, I.; Moberg, C. Chem. ReV. 1999, 99, 3435. ‡
10.1021/ol016047m CCC: $20.00 Published on Web 06/01/2001
© 2001 American Chemical Society
organic acceptors such as enones (pathway b in Scheme 1) would also be highly valuable due to the wide utility of the produced difunctional adducts in organic synthesis. Whereas numerous demonstrations of the reaction pathway a have been disclosed,2 metal-catalyzed transformations via pathway b are much more rare and only limited examples have been reported such as Zn-catalyzed addition of alkynes to CdN bonds3 or Pd-catalyzed addition to conjugated Cd C bonds.4 Trost et al. recently developed an elegant multicomponent reaction protocol in which Ru catalyzes coupling reactions between alkynes and conjugated enones in the presence of heteroatom nucleophiles that initially add to alkynes to yield alkenyl ketones as the final products.5 Although the first example of Ru-catalyzed Michael addition of terminal alkynes to butenone has recently been revealed,6 its synthetic scope is rather limited and yields are low (20(2) (a) Doucet, H.; Martin-Vaca, B.; Bruneau, C.; Dixneuf, P. H. J. Org. Chem. 1995, 60, 7247. (b) Hua, R.; Shimada, S.; Tanaka, M. J. Am. Chem. Soc. 1998, 120, 12365. (c) Ohmura, T.; Yamamoto, Y.; Miyaura, N. J. Am. Chem. Soc. 2000, 122, 4990. (3) Frantz, D. E.; Fa¨ssler, R.; Carreira, E. M. J. Am. Chem. Soc. 1999, 121, 11245. (4) (a) Trost, B. M.; Sorum, M. T.; Chan, C.; Harms, A. E.; Ru¨hter, G. J. Am. Chem. Soc. 1997, 119, 698. (b) Trost, B. M.; Frontier, A. J. J. Am. Chem. Soc. 2000, 122, 11727.
74%). We report here a highly efficient catalytic system for 1,4-addition of a wide range of terminal alkynes to conjugated enones to provide γ,δ-alkynyl ketones.7 A possible pathway based on NMR studies and a deuterium-incorporation experiment will be also presented. In a test reaction of 1-decyne and methyl vinyl ketone (MVK), we found that the transformation could be efficiently effected with the use of a dimeric ruthenium catalyst, [RuCl2(p-cymene)]2 (1),8 in the presence of catalytic amounts of certain bases (Table 1). A survey of various bases revealed
Table 1. Effect of Additives in the Ru-Catalyzed 1,4-Addition of 1-Decyne to Methyl Vinyl Ketone (MVK)a
entry
catalyst
additive (equiv)
GC yield,b %
1 2 3 4 5 6 7 8 9 10 11
[RuCl2(p-cymene)]2 [RuCl2(p-cymene)]2 [RuCl2(p-cymene)]2 [RuCl2(p-cymene)]2 [RuCl2(p-cymene)]2 [RuCl2(p-cymene)]2 [RuCl2(benzene)]2 RuH2(PPh3)4 RuCl2(PPh3)3 [RuCl2(p-cymene)]2 [RuCl2(p-cymene)]2
none Cs2CO3 (0.1) n-PrNH2 (0.1) piperidiine (0.1) pyrrolidine (0.1) pyrrolidine (1.0) pyrrolidine (0.1) pyrrolidine (0.1) pyrrolidine (0.1) 1-Me-pyrrolidine (0.1) 2,6-lutidine (0.1)
