Remarkable effect of basics ligands in the lanthanide-catalysed enantioselective cycloadditions of 3-carbomethoxy-2-pyrone (3-CMP)

Tetrahedron Letters

Volumn 38, Issue 24, 1997, Pages 4269-4272

  Markó, István E ^a   Chellé Regnaut, Isabelle ^a   Leroy, Bernard ^a   Warriner, Stuart L ^a  

^a UNIVERSITÉ CATHOLIQUE DE LOUVAIN   (Belgium)

Author keywords

[No Author keywords available]

Indexed keywords

PYRAN DERIVATIVE;

ARTICLE; CATALYSIS; CHIRALITY; DRUG SYNTHESIS; IN VITRO STUDY; MOLECULAR DYNAMICS; NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY; REACTION ANALYSIS;

EID: 0342981746     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0040-4039(97)00876-9     Document Type: Article

References (20)

1. (a) Markó, I.E.; Evans, G.R. Tetrahedron Lett., 1994, 35, 2771;
2. (b) Markó, I.E.; Evans, G.R.; Declercq, J.-P. Tetrahedron Special Issue, 1994, 50, 4557;
3. Markó, I.E.; Evans, G.R.; Declercq, J.-P.; Feneau-Dupont, J.; Tinant, B. Bull. Soc. Chim. Belg., 1994, 103, 295;
4. Markó, I.E.; Evans, G.R.; Declercq, J.-P.; Tinant, B.; Feneau-Dupont, J., Proceedings of the Chiral Synthesis Symposium and Workshop, Nice, France, 1994, 21;
5. (e) Markó, I.E.; Evans, G.R.; Declercq, J.-P.; Tinant, B.; Feneau-Dupont, J., Acros Organics Acta, 1995, 1, 63;
6. (f) Markó, I.E.; Evans, G.R.; Seres, P.; Chellé, I.; Janousek, Z., Pure & Appl. Chem. 1996, 68, 113. For the use of titanium complexes, in more than stoichiometric amounts, to promote some of these IEDDA reactions, see:
7. (a) Posner, G.H.; Carry J.-C.; Lee, J.K.; Bull, D.S.; Dai, H. Tetrahedron Lett., 1994, 35, 1321;
8. (b) Posner, G.H.; Eydoux, F.; Lee, J.K.; Bull, D.S. Tetrahedron Lett., 1994, 35, 7541.
9. 3 contains one residual water molecule. Water is also present in Shibasaki's catalyst (Sasai, H.; Suzuki, T.; Itoh, N.; Tanaka, K.; Date, T.; Okamura, K.; Shibasaki, M. J. Am. Chem. Soc., 1993, 115, 10372).
10. The influence of water on the enantioselectivity of the titanium-promoted cycloaddition of 3-CMP with two vinyl ethers was recently reported: Posner, G.H.; Dai, H.; Bull, D.S.; Lee, J.K.; Eydoux, F.; Ishihara, Y.; Welsh, W.; Pryor, N.; Petr, S. J. Org. Chem., 1996, 61, 671. According to the authors, the moisture modifies the surface of the sieves and allows more complete formation of the chiral titanium mediator. In our case, the sieves can be totally omitted and the water clearly plays a very different role.
11. 2. The role of the sieves thus appears to be that of a "water reservoir", adsorbing a large amount of water and gradually releasing it to the ytterbium complex.
12. For the replacement of inflate ligands on lanthanide complexes by water and THF, see: (a) Kobayashi, S. Synlett, 1994, 689;
13. (b) Hachiya, I.; Kobayashi, S. J. Org. Chem., 1993, 58, 6958.
14. Performing the ytterbium-catalysed reaction in neat THF resulted in the formation of racemic adduct 5. We believe that THF not only displaces the triflate substituents but also exchanges the binol ligand, generating an active though achiral complex that leads to racemic product 5.
15. We are currently studying the origin and scope of this peculiar effect.
16. (a) Kobayashi, S.; Ishitani, H.; Araki, M.; Hachiya, I. Tetrahedron Lett., 1994, 35, 6325;
17. (b) Kobayashi, S.; Ishitani, H.; Hachiya, I.; Araki, M. Tetrahedron, 1994, 50, 11623.
18. Leroy, B., Mémoire, Université catholique de Louvain, September 1994.
19. 1H NMR spectroscopy. The dynamic nature of this equilibrium is also evident from the titration curve of the Yb complex with 3-CMP, which shows no saturation kinetics.
20. This explanation is also consistent with the negligible variation in ee's observed when altering the structure of the amines. The steric size of the nitrogen bases is particularly important in the ytterbium-catalysed Diels-Alder reactions of cyclopentadiene (ref. 8).