A flexible, stereoselective dimethylzinc-mediated radical-anionic cascade: Dramatic influence of additional Lewis acids

Organic Letters

Volumn 12, Issue 16, 2010, Pages 3590-3593

  Maury, Julien ^a   Feray, Laurence ^a   Perfetti, Patricia ^a   Bertrand, Michèle P ^a  

^a AIX MARSEILLE UNIVERSITY   (France)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 77955698635     PISSN: 15237060     EISSN: 15237052     Source Type: Journal    
DOI: 10.1021/ol101519w     Document Type: Article

References (34)

1. For a review, see: Bazin, S.; Feray, L.; Bertrand, M. P. Chimia 2006, 60, 260
2. Bertrand, M. P.; Feray, L.; Nouguier, R.; Perfetti, P. Synlett 1999, 1148
3. Bertrand, M. P.; Feray, L.; Nouguier, R.; Perfetti, P. J. Org. Chem. 1999, 64, 9189
4. Bertrand, M. P.; Coantic, S.; Feray, L.; Nouguier, R.; Perfetti, P. Tetrahedron 2000, 56, 3951
5. Bertrand, M. P.; Feray, L.; Gastaldi, S. C. R. Chim. 2002, 623
6. Bazin, S.; Feray, L.; Naubron, J.-V.; Siri, D.; Bertrand, M. P. J. Chem. Soc., Chem. Commun. 2002, 2506
7. Bazin, S.; Feray, L.; Vanthuyne, N.; Bertrand, M. P. Tetrahedron 2005, 61, 4261
8. Bazin, S.; Feray, L.; Vanthuyne, N.; Siri, D.; Bertrand, M. P. Tetrahedron 2007, 63, 77
9. Feray, L.; Bertrand, M. P. Eur. J. Org. Chem. 2008, 3164
10. Seyferth, D. Organometallics 2001, 20, 2940 and references cited therein
11. For a review, see: Akindele, T.; Yamada, K.-I.; Tomioka, K. Acc. Chem. Res. 2009, 42, 345
12. Yamada, K.-I.; Fujihara, H.; Yamamoto, Y.; Miwa, Y.; Taga, T.; Tomioka, K. Org. Lett. 2002, 4, 3509
13. Yamada, K.-I.; Yamamoto, Y.; Tomioka, K. Org. Lett. 2003, 5, 1797
14. Yamamoto, Y.; Maekawa, M.; Akindele, T.; Yamada, K.-I.; Tomioka, K. Tetrahedron 2005, 61, 379
15. Akindele, T.; Yamamoto, Y.; Maekawa, M.; Umeki, H.; Yamada, K.-I.; Tomioka, K. Org. Lett. 2005, 8, 5729
16. For dimethylzinc-mediated direct aminoalkylation of cycloalkanes, see: Yamada, K.-I.; Yamamoto, Y.; Maekawa, M.; Chen, J.; Tomioka, K. Tetrahedron Lett. 2004, 45, 6595
17. Yamada, K.-I.; Nakano, M.; Maekawa, M.; Akindele, T.; Tomioka, K. Org. Lett. 2008, 10, 3805
18. In Tomioka's article, triethylborane was preferred to dimethylzinc to achieve radical additions of acyloxymethyl radicals derived from 1a and 1b to N-tosylimines; see ref 8.
19. Acrylic esters are by far less reactive and more sensitive to polymerization than fumaric esters. They led to polymeric materials or to moderate yields in oxidized adducts depending on the nature of the Lewis acid.
20. Iyer, R. P.; Yu, D.; Ho, N.-H.; Agrawal, S. Synth. Commun. 1995, 25, 2739
21. Charette, A. B.; Beauchemin, A.; Francoeur, S. J. Am. Chem. Soc. 2001, 123, 8139
22. The reaction was tested also with chloromethyl pivalate. No evolution was observed in this case.
23. +]: 243.1227, found 243.1227.
24. The adduct of ethyl radical was detected with lactone 2a in a 24:76 NMR ratio.
25. 1H NMR spectra of the crude mixture. This result was not surprizing since α-alkoxycarbonyl radicals are known not to undergo homolytic substitution at boron, see: Ollivier, C.; Renaud, P. Chem. Rev. 2001, 101, 3415
26. The intermediacy of bis(pivaloyloxymethyl)zinc, formed through zinc-iodine exchange in the first step, can be ruled out since irradiation was shown to be required to preform this intermediate; see ref 11b.
27. A mechanism involving intramolecular acyl group transfer has been proposed recently for the bis(iodozincio)methane mediated 1,3-diketone synthesis, see: Sada, M.; Matsubara, S. J. Am. Chem. Soc. 2010, 132, 432
28. Such an intermediate has already been proposed to explain the formation of the major stereoisomer in diethylzinc-mediated radical-polar cascade leading to trisubstituted lactones; see ref 3b,3c. For their involvement in the syn selective aldol consensation of zinc enolates, see also: Lai, S.; Zercher, C. K.; Jasinski, J. P.; Reid, S. N.; Staples, R. J. Org. Lett. 2001, 3, 4169
29. In this case, the adduct of α-acyloxy radical, resulting from the hydrolysis of the corresponding zinc enolate intermediate before the acyl group transfer has occurred, was isolated in a 1:1 ratio with 2e while the starting material was recovered in 30% yield.
30. In order to determine which stereoisomer of the lactone 2 was formed during the process, epimerization reactions were conducted on lactones 2c and 2e in the presence of 1.2 equiv of DBU in DMF (0.1 M). After one night, no evolution was observed in both cases. This strongly suggested that the starting lactones were already in the most stable trans configuration. In addition, the coupling constants between H2 and H3 in lactones 2b -e were close to 6.8 Hz, and this is in agreement with a trans relationship, see
31. Yamauchi, S.; Sugahara, T.; Nakashima, Y.; Okada, A.; Akiyama, K.; Kishida, T.; Maruyama, M.; Masuda, T. Biosci. Biotechnol. Biochem. 2006, 70, 1934
32. Bennett, S. A.; Rickards, R. W. Tetrahedron Lett. 2003, 44, 6927
33. The presence in trace amount of the cis isomer could not be ascertained. A doublet (J = 8-9 Hz) was detected in the proton NMR spectra of the crude mixtures. However, no evolution of the spectra was observed when either 2c or 2e was treated with DBU.
34. During purification on silica gel, lactol 5e was partially dehydrated and degraded. Therefore, the signals of impurities appeared in the corresponding NMR spectra. This is the reason why complete transformation into 6e was preferred before purification.