INTERACTION OF DIHYDROPYRIDINES WITH ALKOXYCARBENE COMPLEXES OF TUNGSTEN - FORMATION AND USE AS CYCLOPROPANATION REAGENTS OF PYRIDINIUM YLIDE COMPLEXES

Alkoxycarbene complexes of tungsten, e.g. (CO)(5)W=C(CH3)OEt (13) reac t with 1,2- and 1,4-dihydropyridines, to give, upon transfer of a hydr ide to the carbene carbon, elimination of ethanol, and readdition of p yridine to an unstable alkylidene complex (CO)(5)W=C(H)CH3 (22), pyrid inium ylide complexes of the type (CO)(5)W--C(H)(CH3)Py+ (17). A secon d pyridinium ylide complex (CO)(5)W-C(H)(CH3)C5H7N (16), and a third d ihydropyridinium complex (CO)(5)W-C(H)(CH3)C8H11N (15), resulting from the interaction of respectively 2,5-dihydropyridine and 5-isopropylid ene-2,5-dihydropyridine with (CO)(5)W=C(H)(CH3) were also isolated and fully characterized by X-ray crystallography. The origin of the two l atter complexes could be established. The new N-ylide complexes react with olefins to give cyclopropanes. Especially interesting, as far as the yields are concerned, is the interaction of highly nucleophilic ol efins such as enamines with (CO)(5)W--C(H)PhPy+ (25) which leads to is omeric cyclopropylamines. The mechanism of their formation will be dis cussed. (C) 1998 Elsevier Science S.A. All rights reserved.