ORGANIC SYNTHESES VIA TRANSITION-METAL COMPLEXES .50. 2H-PYRROLE COMPLEXES BY A STEPWISE INSERTION OF ALKYNES AND ISOCYANIDES INTO M = C BONDS OF CARBENE CHROMIUM OR TUNGSTEN COMPLEXES

2H-Pyrrole complexes 6a, b are obtained in two steps by [1 + 2 + 2] cycloaddition reactions of the carbene complex (CO)5W = C(OEt)C6H5 (1d), the alkyne EtO - C = CH (2) and isocyanides R1 - NC 4a, b (R1 = CH3, c-C6H11). L(n)M = C(OEt)R 1 [L(n)M = Cr(CO)5, W(CO)5; R = C6H5, CH3] reacts with 2 to give 1-metalla-1,3-dienes 3a - d. (E)/(Z)-3d and 4 yield 6a, b via 1-aza-1,2,4-pentatriene complexes 5, which are open-chain precursors of 6. 2H-Pyrrole complexes 11 and 14 are synthesized in overall [2 + 1 + 2] cycloadditions with reversed connectivity, or formation of 1-chroma-1,3-dienes 10 and 13 by condensation of the methylcarbene complex 1a with acid amides, and cyclisation again with isocyanides 4.