ORGANIC SYNTHESES VIA TRANSITION-METAL COMPLEXES .54. CYCLOPENTADIENES FROM 1-METALLA-1,3-DIENES AND ALKYNES BY CYCLIZATION OF INTERMEDIATE 1-METALLA-1,3,5-TRIENES (METAL = TUNGSTEN)

We report on first examples of the formation of cyclopentadienes from a 1-metalla-1,3-diene L(n)M = C-C = C [L(n)M = W(CO)5] and an alkyne in [3 + 2] cycloaddition multistep reactions. In a first step the alkyne Et2N-C = C-Me (2) adds to the 1-metalla-1,3-diene(CO)5W = C(OEt)-CH = CHPh (1b) to give 1-metalla-1,3,5-trienes(CO)5W = C(NEt2)-CMe = C(OEt)-CH = CHPh (3b) and (CO)5W = C(OEt)-CH = C(NEt2)-CMe = CHPh (4b). In a second step 3b cyclizes to thecyclopentadiene complex 5, which has an eta-1 ylide-type structure as established by an X-ray analysis. Hydrolysis of 5 leads to the formation of a 3-aminocyclopentenone 7. The 1-metalla-1,3,5-triene 4b yields a cyclopentadiene complex 8. In contrast to 5 the carbon skeleton of 8 has a connectivity different from that of the C3 unit of the 1-metalla-1,3-diene 1.