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Synlett 1993; 1993(9): 667-669
DOI: 10.1055/s-1993-22565
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Metathesis of Enamines by Alkynylcarbene Tungsten Complexes.- Formation of Aminobenzenesvia Pyranylidene Complexes

Rudolf Aumann* , Klaus Roths, Mechtild Läge, Bernt Krebs
  • *Organisch-Chemisches Institut der Universität Münster, Orléans-Ring 23, D-48149 Münster, Germany
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Publication Date:
19 March 2002 (online)

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4-Amino-pent-3-en-2-ones MeC(NR2)=CH-COMe 3 [NR2 = NMe2 (a), pyrrolidino (b), morpholino (c)] add to the alkynylcarbene carbene complex (CO)5W=C(OEt)C≡CPh 2 and give 1,3,5-trisubstituted aminobenzenes 6a-c and W(CO)6 in overall yields higher than 90%. The reaction involves the intermediate formation of open-chain 2-amino-6-oxo-hepta-2, 4-dien-3-yl carbene complexes 4a-c. These cyclize spontaneously by elimination of EtOH and give pyranylidene complexes 5a-c. The latter are stable and crystalline but undergo a fragmentation in solution with elimination of W(CO)6 and form 6a-c. The cycloaddition of 3 to 2 involves the insertion of the C≡C bond of the alkynyl carbene complex 2 into the C=C bond of the enamine 3 by a metathesis reaction. W(CO)6, which is initially introduced in order to activate the alkyne 1 by formation of the alkynyl carbene complex 2, is recycled in a high-yield process by which an oxygen atom of W(CO)6 is replaced by the oxygen atom of the acetyl group of 3.