· Benzyl 3-(Tributylstannyl)acrylate
· (MW 451.22)
(this reagent, along with the corresponding ethyl and methyl esters, are useful partners for Pd0-catalyzed coupling reactions with a variety of substrates including aryl triflates,1-3 aryl bromides4 and iodides,5,6 vinyl triflates,7,8 vinyl iodides,9-13 allylic chlorides,14 acyl chlorides,15-17 and sulfonyl chlorides18)
Physical Data: colorless oil.
Solubility: sol THF, CHCl3.
Preparative Methods: the benzyl acrylates (1) and (2) can be obtained by nonstereoselective hydrostannylation of benzyl propynoate (eq 1).15,20 Mixtures of substances (3) and (4)10 and of (5) and (6)13,21 have been prepared in similar fashion (eq 1). In each case the geometric isomers are chromatographically separable. The stereocontrolled synthesis of (3) can be achieved by sequential treatment of (E)-1,2-bis(tributylstannyl)ethene with an alkyllithium and ClCO2Et.22,23 On the other hand, stereospecific syntheses of (5) and (6) have been achieved by reaction of methyl (E)- and (Z)-3-chloro (or iodo)acrylates with Bu3SnCu24 (see Tri-n-butylstannylcopper).
Handling, Storage, and Precautions: since organotin compounds are toxic,19 reactions preparing and employing the reagent should be carried out and worked up in a fume hood.
Reaction with Aryl Triflates and Halides.
The Pd0-catalyzed couplings of reagents (1)-(6) with aryl triflates1-3 or halides4-6 constitute a useful method for the direct incorporation of a 2-(alkyoxycarbonyl)vinyl moiety into aromatic systems. Examples are shown in eqs 2-4.1,3,6 As indicated by eq 2, the couplings employing the (Z) reagents (2), (4), and (6) are generally more sluggish than those employing the corresponding (E) isomers. Furthermore, the reaction of (7) with (2) is not stereoselective.1 On the other hand, the interesting cross-coupling reaction involving tricarbonyl(iodo-h5-cyclopentadienyl)methyltungsten and the (Z) acrylate (6) (eq 4) proceeds in a completely stereoselective fashion, with retention of reagent stereochemistry.6
Reaction with Vinyl Triflates and Iodides.
The Pd0-mediated couplings of reagents (1)-(6) with vinyl triflates7,8 and iodides10-13 produce a valuable method for the stereocontrolled synthesis of substituted alkyl 2,4-alkadienoates (eqs 5-8).8,10,12 This carbon-carbon bond-forming process appears to be stereospecific (eqs 6-8). In contrast, formation of the unsymmetrical divinyl ketone (9) via cross-coupling of 1-iodocyclohexene with the (Z)-acrylate (2) in the presence of CO is not stereoselective (eq 9).9 The mechanism of this process has been discussed in detail.9
Reaction with Allylic Chlorides.
Reaction of allyl halides with vinylstannanes in the presence of a Pd0 catalyst provides, efficiently, cross-coupled products. An example of this process involving the (Z)-acrylate (2) is shown in eq (10).14 The substitution reaction takes place with overall inversion of configuration, while the stereochemistry of the acrylate moiety is retained.
Reaction with Acyl and Sulfonyl Chlorides.
Acyl and sulfonyl chlorides react with 3-tributylstannylacrylates in the presence of Pd0 to give alkyl 4-oxo-2-alkenoates15-17 and b-alkoxycarbonyl-a,b-unsaturated sulfones,18 respectively (eqs 11 and 12).16,18 In each case the configuration of the product is (E), regardless of the stereochemistry of the acrylate reagent.15,17,18 Intramolecular versions of the acyl chloride coupling process have been employed to prepare macrocyclic substances,25 including the macrodiolide (R,R)-(-)-pyrenophorin.25c
Reagent (3) has been used as a dienophile in Diels-Alder reactions22 and has been converted into the synthetically useful epoxide ethyl (E)-3-tributylstannyl-2,3-epoxypropanoate.26 The methyl acrylates (5) and (6) have been employed in effecting a highly stereoselective radical substitution process (eq 13),27 which played a key role in a total synthesis of the natural product bulgecin C.27
- 1. Echavarren, A. M.; Stille, J. K. JACS 1987, 109, 5478.
- 2. Krolski, M. E.; Renaldo, A. F.; Rudisill, D. E.; Stille, J. K. JOC 1988, 53, 1170.
- 3. Tilley, J. W.; Sarabu, R.; Wagner, R.; Mulkerins, K. JOC 1990, 55, 906.
- 4. Somei, M.; Sayama, S.; Naka, K.; Yamada, F. H 1988, 27, 1585.
- 5. Kondo, Y.; Watanabe, R.; Sakamoto, T.; Yamanaka, H. CPB 1989, 37, 2933.
- 6. Brehm, E. C.; Stille, J. K.; Meyers, A. I. OM 1992, 11, 938.
- 7. Peña, M. R.; Stille, J. K. TL 1987, 28, 6573; JACS 1989, 111, 5417.
- 8. (a) Crisp, G. T.; Flynn, B. L. TL 1990, 31, 1347. (b) Flynn, B. L.; Macolino, V.; Crisp, G. T. Nucleosides Nucleotides 1991, 10, 763.
- 9. Goure, W. F.; Wright, M. E.; Davis, P. D.; Labadie, S. S.; Stille, J. K. JACS 1984, 106, 6417.
- 10. Stille, J. K.; Groh, B. L. JACS 1987, 109, 813.
- 11. Crisp, G. T. SC 1989, 19, 2117.
- 12. Férézou, J. P.; Julia, M.; Li, Y.; Liu, L. W.; Pancrazi, A. SL 1991, 53.
- 13. Lai, M.; Li, D.; Oh, E.; Liu, H. JACS 1993, 115, 1619.
- 14. (a) Sheffy, F. K.; Stille, J. K. JACS 1983, 105, 7173. (b) Sheffy, F. K.; Godschalx, J. P.; Stille, J. K. JACS 1984, 106, 4833.
- 15. Labadie, J. W.; Tueting, D.; Stille, J. K. JOC 1983, 48, 4634.
- 16. Labadie, J. W.; Stille, J. K. TL 1983, 24, 4283.
- 17. Crisp, G. T.; Bubner, T. P. SC 1990, 20, 1665.
- 18. Labadie, S. S. JOC 1989, 54, 2496.
- 19. Pereyre, M.; Quintard, J.-P.; Rahm, A. Tin in Organic Synthesis; Butterworths: London, 1987; pp 6-7.
- 20. Labadie, J. W.; Stille, J. K. JACS 1983, 105, 6129.
- 21. See also Bew, S. P.; Sweeney, J. B. SL 1991, 109.
- 22. Johnson, C. R.; Kadow, J. F. JOC 1987, 52, 1493.
- 23. Renaldo, A. F.; Labadie, J. W.; Stille, J. K. OS 1989, 67, 86.
- 24. Seitz, D. E.; Lee, S.-H. TL 1981, 22, 4909.
- 25. Baldwin, J. E.; Adlington, R. M.; Ramcharitar, S. H. (a) CC 1991, 940. (b) T 1992, 48, 2957. (c) SL 1992, 875.
- 26. Chong, J. M.; Mar, E. K. JOC 1992, 57, 46.
- 27. Barrett, A. G. M.; Pilipauskas, D. (a) JOC 1990, 55, 5194. (b) JOC 1991, 56, 2787.
Edward Piers & Christine Rogers
University of British Columbia, Vancouver, BC, Canada
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