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Facile Diels-Alder Reactions with Pyridines Promoted by Tungsten

Facile Diels-Alder Reactions with Pyridines Promoted by Tungsten. W. D. Harman * ,†. J. Am. Chem. Soc. 2005, 127, 10568. The Synthesis of Polycyclic Alkaloids via Diels-Alder Reactions. Pyridines are attractive as potential feedstocks. Tetrahedron 2002 , 58 , 8299-8305.

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Facile Diels-Alder Reactions with Pyridines Promoted by Tungsten

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  1. Facile Diels-Alder Reactions with Pyridines Promoted by Tungsten W. D. Harman*,† J. Am. Chem. Soc. 2005, 127, 10568

  2. The Synthesis of Polycyclic Alkaloids via Diels-Alder Reactions • Pyridines are attractive as potential feedstocks. Tetrahedron2002, 58, 8299-8305. TetrahedronLett.2000, 41, 8317-8321. Org.Lett.2001, 3, 3009-3012.

  3. Rhenium-Promoted Diels-Alder Cycloaddition Reaction with Benzene and a Maleimide M= J. Am. Chem. Soc. 2001, 123, 10756-10757

  4. The Cycloaddition of Benzene to The Powerful πbase {TpW(NO)(PMe3)} NMM＝ Organometallics 2003, 22, 4364-4366

  5. M＝ {TpW(NO)(PMe3)} pyridine has a substituent at the 2-position. Figure 1.A metal-mediated Diels-Alder reaction with pyridine to construct the isoquinuclidine core.

  6. Figure 2.η2-Lutidine complex (1) in equilibrium with lutidinyl hydride (1H).

  7. Oxidant : silver triflate

  8. Figure 5.Diels-Alder reaction of 3 with acrylonitrile.

  9. Figure 3.Crystal structure of 3 (30% ellipsoids). Selected bond lengths (Å): W-C4 2.229(4); W-C3 2.241(4); C4-C3 1.448(6); C3-C2 1.454(5); N1-C2 1.318(5); N1-C6 1.386(6); C6-C5 1.332(6); C5-C4 1.456(5); C2-N2 1.376(5).

  10. Figure 4.ORTEP diagram of 5 (30% ellipsoids).

  11. Table 1.Diels-Alder Reactions of Pyridine Complexes 1 and 3 N-methylmaleimide

  12. Figure 6.Pinene resolution of lutidine complex 1.

  13. Conclusions • The availability and diversity of commercially available pyridines, the exceptionally mild conditions under which cycloaddition occurs, and the ease with which the tungsten fragment can be resolved make the dearomatization of pyridines a potentially valuable new synthetic tool. • Although the preliminary data suggest that the methodology may be limited to 2-substituted pyridines, the authors are currently exploring a full range of pyridines and their proclivity to undergo cycloaddition reactions.

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