5015
Organometallics 1995, 14, 5015-5016
Nickel-Catalyzed Tandem Coupling of Chlorotrimethylsilane,ad-Enones,Alkynes, and Dimethylzinc Shin-ichi Ikeda," Hiroaki Yamamoto, Kouji Kondo, and Yoshiro Sato* Faculty of Pharmaceutical Sciences, Nagoya City University, Tanabe-dori,Mizuho-ku, Nagoya 467, Japan Received September 6, 1995@ Scheme 1
Summary: A nickel and triphenylphosphine IPPhd system catalyzed a new tandem coupling of chlorotrimethylsilane ((TMS)Cl), a,P-enones 1, alkynes, and dimethylzinc (MezZn) to furnish the coupling products 2, Tandem (or one-pot) reactions, which permit the construction of complex molecules in a few steps, are important topics in organic We recently reported that the nickel-catalyzed tandem coupling of a,P-enones 1,alkynes, alkynyltins, and chlorotrimethylsilane ((TMS)Cl)gave regio- and stereoselective conjugated enyne compounds in high yield^.^ This result led us to search for other organometallics which could be used instead of alkynyltins. We report here a new nickel-catalyzed tandem coupling of dimethylzinc (MezZn), 1, alkynes, and (TMS)Cl to give coupling products 2 (reaction A in Scheme 1). The results of the coupling are summarized in Table l.4Typically, t o a THF (5 mL) solution of Ni(acac)z (5 mol %) and PPh3 (5 mol %) were added MezZn (1.2 mmol), 1-octyne (1.1mmol), 2-cyclopenten-1-one (la) (1.0 mmol), and (TMSlCl(1.2 mmol). The mixture was then stirred at 25 "C for 2 h. The coupling product 2 having the enol silyl ether function was converted into the corresponding carbonyl compound 3a by treatment with aqueous and product 3a was afforded in a yield of 89% by chromatography on a silica gel column (entry 1). The use of a Ni and PPh3 catalytic system was essential for this coupling. Although NiClz(PPh& (5 mol %) was also effective in this reaction (entry 21, Ni(acac)z in the absence of PPh3 did not catalyze the reaction (entry 4). Other additives gave the following yields: P(o-tolyl)a,56%;PBu3,11%;pyridine, 65%;EtsN, 0%. Although stereoisomers of the isolated products 3 were not detected by lH N M R or GC,the regioselectivity of 3 was dependent on the enones 1 and alkynes used. In the reaction with 1-octyne, a regioisomer of 3a was detected as a minor product (entries 1-3). The reaction of la with TMS-acetylene gave 3b as the sole product, and it was assigned an E geometry by NOE (entry 5 ) . Abstract published in Advance ACS Abstracts, October 15, 1995. (1)Hall, N. Science 1994,266, 32. (2) (a) Ho, T.-L.Tandem Organic Reactions; Wiley: Interscience: New York, 1992. (b) Tietze, L. F.; Beifuss, U. Angew. Chem., Int. Ed. Engl. 1993, 32, 131. (c) Ho, T.-L. Tactics of Organic Synthesis; Wiley-Interscience: New York, 1994; p 79. (3)(a)Ikeda, S.; Sato, Y. J. Am. Chem. SOC.1994, 116, 5975. (b) Ikeda, S.; Cui, D.-M.; Sato, Y. J. Org. Chem. 1994, 59, 6877. (4) All of the new compounds described herein gave spectral data @
and analytical results consistent with the assigned structures. (5)The methylation at the enol silyl ether position of 2a was not observed under the reaction conditions. See: Hayashi, T.; Katsuro,Y.; Kumada,M. Tetrahedron Lett. 1980,21,3951. Crouse, G. D.; Paquette, L.A. J. Org. Chem. 1981, 46, 4272.
OTMS
(reactionA)
OZnR (reaction B) 0
1
hydrolysis
//
1
hydrolysis
R'
3
5
..
Table 1. Results of the Nickel-Catalyzed Tandem Coupling of 1, Alkynes, MezZn, and (TMS)Cla entry no.
1 2
3 4 5 6
7 8 9 10
11
R' la
enone 1 R2 R3
-(CH2)2-(CH2)2-(CH2)2la -(CH2)2la -(CH2)2l a -(CH2)2l b Me H 1 c H H I d Me H le Me Me If Ph H la la
H H H H H H H
H H
H H
- alkyne R4 R R H H H H H H H Me Ph Me Ph
hexyl hexyl hexyl hexyl TMS Et hexyl hexyl hexyl Bu Bu
H
H H H H Et H H H H H
yield of 3,b % 3a, 89 (89) 3a, 82c (89) sa, 76d (89) 3a, W 3b, 69 (298) 3c, 70 3d, trace 3e, 60 ( > 98) 3f, 61 (84) 3g, trace 3h, 58d (48)
Reaction conditions: Ni(acac)z(0.05 mmol), PPh, (0.05 mmol), l ( 1 . 0 mmol), alkyne (1.1mmol), MezZn (1.0 M in hexane, 1.2 mL), (TMS)Cl (1.2 mmol), and THF (5 mL) at 25 "C for 2 h under N2 and then hydrolysis by 10%HCl(aq)at 25 "C for 10 min. Isolated yield; regioselectivity based on 'H NMR is in parentheses. PPh3 (0.2 mmol) was added. NiC12(PPh& (0.05 mmol) was used instead of Ni(acac)z and PPh3. e Only Ni(acac)z (0.05 mmol) was used.
While crotonaldehyde (IC)reacted with 1-octyneto give 3e regioselectively (entry 81, the reaction with Id reduced the selectivity of the corresponding 3f (entry 9). The product 3h obtained from the reaction of If with 1-hexyne did not show regioselectivity (entry 11). Reactions of both mesityl oxide (le)(entry 10) and methyl vinyl ketone (lb)(entry 7), which was an effective substrate for coupling with alkynyltins? gave little of the corresponding coupling products under these reaction conditions. It is well-known that the conjugate addition (Michaeltype addition) of organozincs to 1 is accelerated in the presence of nickel catalyst to produce adducts 4 (or hydrolyzed products 5) (reaction B in Scheme 1h6 The addition of MezZn to If occurred in the presence of NiCldPPh3)z a t 25 "C over 20 h to give 5a (R1 = R4 =
0276-733319512314-5015$09.00/00 1995 American Chemical Society
5016 Organometallics, Vol. 14, No. 11, 1995 Ph, R2 = R3 = H, R = Me) in 61% yield. However, the addition of (TMSIC1 to this reaction mixture resulted in a reduced yield of 5a under the same reaction On the other hand, the conditions (25% coupling reaction of lf, 1-hexyne, and MezZn did not occur in the absence of (TMS)Cl. Moreover, the carbozincation of MezZn to 1-octyne followed by conjugated addition to la did not proceed under these coupling condition^.^ These results suggest that reaction parts A and B differ from each other. The tandem coupling (6)Edrik, E.Tetrahedron 1992,44, 9577. (7)The conjugate addition of MezZn (1.2mmol) to If (1.0 mmol) in the presence of Ni(acac)z (0.05mmol) at 25 "C for 1 h followed by hydrolysis gave Sa in 299% GC yield. (8)In contrast, it is well-known that the conjugate addition with organocopper reagents is accelerated in the presence of (TMS)Cl. See: (b) Corey, (a) Corey, E. J.;Boaz, N. W. Tetrahedron Lett. 1985,26,6015. E.J.; Boaz, N. W. Tetrahedron Lett. 1985,26,6019.(c) Alexakis, A,; Berlan, J.; Besace, Y. Tetrahedron Lett. 1986,27,1047.(d) Horiguchi, Y.;Matsuzawa, S.; Nakamura, E.; Kuwajima, I. Tetrahedron Lett. 1986,27, 4025. (e) Nakamura, E.; Matsuzawa, S.; Horiguchi, Y.; Kuwaiima. I. Tetrahedron Lett. 1986.27.4029. (9)kor allylzincation to alkynes, see: 'Negishi, E.; Miller, J. A. J . Am. Chem. SOC.1983,105,6761.
Communications depicted in reaction A may proceed via the insertion of alkyne into 6,10911 followed by the transmetalation of MezZn and reductive elimination t o produce 2.3 In summary, the present tandem coupling reaction can be used to efficiently construct carbon-carbon bonds and may provide a versatile method for synthesizing trior tetrasubstituted alkenes. Further detailed studies on the scope of this reaction are in progress. Supporting Information Available: Text giving experimental details and spectral and analytical data for the obtained products ( 5 pages). This material is contained in many libraries on microfiche, immediately follows this article in the microfilm version of the journal, and can be ordered from the ACS; see any current masthead page for ordering information. OM950709S ~~
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(10)For preparation of complex 6, see: Johnson, J . R.; Tully, P. S.; Mackenzie, P. B.; Sabat, M. J. Am. Chem. SOC. 1991,113,6172. (11)The reaction did not give a product arising from insertion of the alkyne into the siloxy-substituted position of 6.
