ORGANIC SYNTHESES VIA TRANSITION-METAL COMPLEXES .90. NOVEL ROUTE TO CYCLOPENTADIENES FROM (1-ALKYNYL)CARBENE COMPLEXES OF CHROMIUM AND TUNGSTEN VIA 2-AMINO METALLA-1,3,5-HEXATRIENES

1,5-Diamino cyclopentadienes 9a-c are obtained by thermally induced ri ng-closure of 2-amino-1-metalla-1,3,5-hexatrienes (CO)(5)M=C(NMe2)-CH= C(Ph)-C[=C(HNR)Me]COMe (Z)-7 in 50 - 58 % yields. The reaction involve s intermediate formation of novel type 1-metalla-cyclopentadienes 8, w hich were characterized by X-ray structure analyses. Starting compound s (2)-7 are easily available from (1-alkynyl)carbene complexes (CO)(5) M=C(OEt)C=CPh 1a,b (M = Cr, W) in two steps either via formation of 2- ethoxy-1-metalla-1,3,5-hexatrienes (2)-3b (addition of enamines to 1 a nd subsequent aminolysis) or of 2H-pyran-2-ylidene complexes 5 (conden sation of 1 with enolizable carbonyl compounds and subsequent aminolys is). Thus, the reaction leading from 1 to 9 involves an overall [3+2] cycloaddition, in which the (l-alkynyl)carbene complex functions as a C3 component, and the enamine, and the carbonyl compound, respectively , as a C2 component.