Solvent-free, one-pot synthesis of β-lactams by the Sc(OTf) 3-catalyzed reaction of silyl ketene thiocetals with imines

European Journal of Organic Chemistry

Volumn , Issue 17, 2007, Pages 2865-2869

  Benaglia, Maurizio ^a   Cozzi, Franco ^a,b   Puglisi, Alessandra ^a  

^a UNIVERSITY OF MILAN   (Italy)

^b CNR   (Italy)

Author keywords

Catalysis; Lactams; Scandium triflate; Solvent free conditions; Synthetic methods

Indexed keywords

EID: 34250897964     PISSN: 1434193X     EISSN: 10990690     Source Type: Journal    
DOI: 10.1002/ejoc.200601127     Document Type: Article

References (22)

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2. For a review on the antibiotic activity of β-lactams, see: a) R. B. Morin, R. Gorman (Eds.), Chemistry and Biology of β-Lactam Antibiotics, Academic Press, New York, 1982, vols. 1-3. β-Lactam chemistry has witnessed a recent resurgence of interest since the discovery that some of these compounds have a strong activity as enzymatic inhibitors.
3. For a collection of papers on this subject, see: b) Recent Aspects of the Chemistry of β-Lactams, Part II, in Tetrahedron (Symposium-in-Print No. 80), 2000, 56, issue 31.
4. 2SiOTf), see: a) R. Annunziata, M. Cinquini, F. Cozzi, V. Molteni, O. Schupp, Tetrahedron 1996, 52, 2573-2582.
5. 3 as a catalyst in the solvent-free procedure.
6. For reviews, see: a) S. Kobayashi, Synlett 1994, 689-701, and references therein;
7. b) S. Kobayashi, H. Ishitani, Chem. Rev. 1999, 99, 1069-1094, and references therein.
8. cis = 5.0-6.0 Hz).
9. The yield was actually higher because β-lactams contaminated by β-amino thioesters were also obtained. Interestingly, NMR analysis of the crude product of the reaction carried out in dichloromethane showed the same β-lactams/β-amino thioester ratio as observed in the solvent-free process. The yield of isolated β-lactams was 72%.
10. When hydrolysis of the unreacted SKTA 1 was attempted to avoid chromatographic purification of the product, some β-lactam decomposition was also observed.
11. [3,4]), makes any attempts to rationalize its stereochemical behavior highly speculative.
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16. for a recent application of this catalyst to C-C bond forming reactions, see: b) S. Iimura, K. Manabe, S. Kobayashi, Tetrahedron 2004, 60, 7673-7678.
17. This supported catalyst also proved to be poorly active when the reaction was run for longer times (up to 96 h) or with a catalyst sample preswelled in organic solvents (dichloromethane, toluene). A more active, but commercially unavailable, supported scandium(III) catalyst has also been reported by professor Kobayashi: c) S. Kobayashi, S. Nagayama, J. Am. Chem. Soc. 1996, 118, 8977-8978.
18. 3 on silica gel or Celite to facilitate catalyst recycling was attempted without success. The possibility of recycling an aqueous solution containing different scandium(III) salts is currently under investigation.
19. It can be hypothesized that the Lewis acidic catalyst promotes the ring-closing step by coordinating the nitrogen atom of the 2-pyridylthiol residue of the thioester, making it a better leaving group. In agreement with this hypothesis is the observation that, when noncoordinating TMSOTf and TfOH were used to catalyze the reaction of 1 with 2, the β-amino ester precursors of 3t,c were isolated as the largely predominant products.
20. N. Miyachi, F. Kanda, M. Shibasaki, J. Org. Chem. 1989, 54, 3511-3513.
21. 3,3′ values for the 2,3-cis-3,3′- syn products range from 8.0 to 8.5 Hz.
22. B. K. Banik, M. S. Manhas, E. W. Robb, A. K. Bose, Heterocycles 1997, 44, 405-415.