· (MW 757.59)
(catalyst for the cross coupling1 of alkyl-, vinyl-, alkynyl-, and allylstannane groups with acyl chlorides,2 allyl halides,3 vinyl triflates, and iodides4)
Physical Data: mp 166-170 °C.
Solubility: sol THF, benzene, and other organic solvents.
Form Supplied in: crystalline; commercially available.
Preparative Methods: may be prepared from benzyl chloride and (Ph3P)4Pd in benzene at room temperature, washed with Et2O, and dried under vacuum.5
Handling, Storage, and Precautions: is an air-stable solid and remains stable in solution. Irritant.
Cross Coupling Reactions with Organostannane Compounds.
Palladium catalysis of cross coupling reactions is well established in organic chemistry.1 Benzylchlorobis(triphenylphosphine)palladium(II) (1), first reported in 1969,2 is used extensively for these reactions. Other palladium complexes, such as dichlorobis(triphenylphosphine)palladium(II) and Tetrakis(triphenylphosphine)palladium(0), catalyze cross coupling reactions; however, the title compound generally provides higher yields in shorter reaction times. Most common is the coupling of an organotin compound with an acyl halide to produce ketone products (eq 1), which has many advantages over existing methods of preparing ketones from acyl chlorides. The yields are high, and in many cases, nearly quantitative. Both the organotin compound and the catalyst are air stable. The reaction tolerates a wide variety of functional groups;
ester, alkene, nitro, nitrile, halo, methoxy, silyloxy, vinyl ether, and even aldehyde remain intact during the reaction. Sterically hindered acid chlorides will react, and conjugate addition with a,b-unsaturated acid chlorides does not occur. Further, if a vinyl-, aryl-, or alkynyl-trialkylstannane is used, only the vinyl, aryl, or alkynyl group is transferred. With stannanes as substituents on a stereogenic center, the reaction proceeds with stereochemical inversion of the stereogenic center.6 Acylstannanes can be prepared by the coupling of acyl halides and distannyl species.7
Aldehydes can be prepared from acid chlorides and Tri-n-butylstannane in the presence of (1).8 While this reduction can be performed by mixing the substrate and Bu3SnH, ester byproducts and other products resulting from radical reactions occur without the palladium catalyst. 1,2-Diketones can be made easily by the reaction of a 1-methoxyvinylstannane and an acid chloride, followed by hydrolysis (eq 2).9 A similar 2-methoxyvinylstannane was employed in the synthesis of agglomerin A and (±)-carolinic acid.10 Vinylstannanes and acyl chlorides have been coupled intramolecularly to provide 11-, 12-, 14-, 16-, and 20-membered macrocycles in 32-72% yields.11
Allylic halides can be coupled with organostannanes without allylic transposition.3b The reaction takes place with inversion of stereochemistry at the allylic carbon, and double bond geometry remains intact for acyclic substrates (eq 3).3c In addition, carbon monoxide can be inserted during the course of the reaction to provide ketone products.3a,12 Vinyl iodides couple in a similar fashion,4a and the coupling of vinyl triflates was used in the synthesis of pleraplysillin.4b
Ether Cleavage and Formation Reactions.
While the cross coupling reactions of organotin compounds in the presence of (1) tolerate a great deal of functionality, cyclic (5-membered or less), allylic and benzylic ethers can be cleaved upon reaction with an acid chloride catalyzed by the presence of trialkyltin chloride (eq 4).13 Aliphatic and phenolic ethers are not consumed. Complementary to this method of ether substrate cleavage, epoxides, oxetanes, and tetrahydrofurans can be formed by the reaction of bromo ketones and allylic stannanes or a-ketostannanes (eq 5).14 Other alkylstannanes fail to give cyclic ethers.
- 1. For reviews on metal catalyzed cross coupling reactions see: (a) Stille, J. K. AG(E) 1986, 25, 508. (b) Stille, J. K. PAC 1985, 57, 1771. (c) Negishi, E.-I. ACR 1982, 15, 340.
- 2. (a) Milstein, D.; Stille, J. K. JACS 1978, 100, 3636. (b) Milstein, D.; Stille, J. K. JOC 1979, 44, 1613. (c) Logue, M. W.; Teng, K. JOC 1982, 47, 2549. (d) Labadie, J. W.; Tueting, D.; Stille, J. K. JOC 1983, 48, 4634. (e) Verlhac, J.-B.; Pereyre, M. T 1990, 46, 6399. (f) Blanchot, V.; Fétizon, M.; Hanna, I. S 1990, 755. (g) Kang, K.-T.; Kim, S. S.; Lee, J. C. TL 1991, 32, 4341. (h) Degl'Innocenti, A.; Dembech, P.; Mordini, A.; Ricci, A.; Seconi, G. S 1991, 267. (i) Balas, L.; Jousseaume, B.; Shin, H.; Verlhac, J.-B.; Wallian, F. OM 1991, 10, 366.
- 3. (a) Milstein, D.; Stille, J. K. JACS 1979, 101, 4992. (b) Godschalx, J.; Stille, J. K. TL 1980, 21, 2599. (c) Sheffy, F. K.; Stille, J. K. JACS 1983, 105, 7173. (d) Liebeskind, L. S.; Wang, J. T 1993, 49, 5461.
- 4. (a) Stille, J. K.; Groh, B. L. JACS 1987, 109, 813. (b) Scott, W. J.; Stille, J. K. JACS 1986, 108, 3033. (c) Hinkle, R. J.; Poulter, G. T.; Stang, P. J. JACS 1993, 115, 11626.
- 5. (a) Fitton, P.; McKeon, J. E.; Ream, B. C. JCS(C) 1969, 370. (b) Lau, K. S. Y.; Wong, P. K.; Stille, J. K. JACS 1976, 98, 5832. (c) Lau, K. S. Y.; Stille, J. K. JACS 1976, 98, 5841.
- 6. Labadie, J. W.; Stille, J. K. JACS 1983, 105, 669.
- 7. Mitchell, T. N.; Kwetkat, K. S 1990, 1001.
- 8. Four, P.; Guibe, F. JOC 1981, 46, 4439.
- 9. Soderquist, J. A.; Leong, W. W.-H. TL 1983, 24, 2361.
- 10. Ley, S. V.; Trudell, M. L.; Wadsworth, D. J. T 1991, 47, 8285.
- 11. Baldwin, J. E.; Adlington, R. M.; Ramcharitar, S. H. CC 1991, 940.
- 12. Liebeskind, L. S.; Yu, M. S.; Fengl, R. W. JOC 1993, 58, 3543.
- 13. Pri-Bar, I.; Stille, J. K. JOC 1982, 47, 1215.
- 14. Pri-Bar, I.; Pearlman, P. S.; Stille, J. K. JOC 1983, 48, 4629.
Gregory R. Cook & John R. Stille
Michigan State University, East Lansing, MI, USA
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