Pyridines via Fischer Carbene complexes.- W(CO)6-Mediated Cycloadditions of Enamines to AlkynesviaAlkynylcarbene and 1,2-Dihydropyridin-2-ylidene Complexes
- 1 January 1993
- journal article
- letter
- Published by Georg Thieme Verlag KG in Synlett
- Vol. 1993 (09) , 669-671
- https://doi.org/10.1055/s-1993-22566
Abstract
Pyridinium salts 6 and pyridines 7 are obtained by the W(CO)6-mediated cycloaddition of the alkyne LiC≡CPh 1 to 4-amino-pent-3-en-2-ones MeC(NHR)=CH-COMe 3a,b [R = H, Me] or the 4-amino-2-iminopent-3-ene 3c [R = Me, X = NMe]. The reaction involves the activation of 1 by formation of an alkynylcarbene complex (CO)5W=C(OEt)C≡CPh 2, which adds 3 to give 6-amino-1-tungstena-1,3,5-trienes 4. Compounds 4 cyclize spontaneously by the elimination of EtOH and form 1,2-dihydropyridin-2-ylidene complexes 5. Protonation of 5 takes place at the W,C bond and leads to the disengagement of pyridinium salts 6 and the recovery of W(CO)6. A pyridine 7 is generated from 6 (R = H) after treatment with a base. 1,2-Dihydropyridin-2-ylidene complexes 5 are also obtained by the aminolysis of pyran-2-ylidene complexes 8.Keywords
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