Organische Synthesen mit Übergangsmetall‐Komplexen, 50 2 H ‐Pyrrol‐Komplexe durch stufenweise Insertion von Alkinen und Isocyaniden in MC‐Bindungen von Chrom‐ und Wolfram‐Carbenkomplexen

Organic Syntheses via Transition Metal Complexes, 50 1) . – 2 H ‐Pyrrole Complexes by a Stepwise Insertion of Alkynes and Isocyanides into MC Bonds of Carbene Chromium or Tungsten Complexes 2 H ‐Pyrrole complexes 6a, b are obtained in two step by [1+2+2] cycloaddition reactions of the carbene complex (CO) 5 WC(OEt)C 6 H 5 ( 1d ), the alkyne EtO‐CCH ( 2 ) and isocyanides R 1 ‐NC 4a, b [R 1 = CH 3 , c ‐C 6 H 11 ). L n C(OEt)R 1 [L n M = Cr(CO) 5 , W(CO) 5 ; R = C 6 H 5 , CH 3 ] 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 . 2 H ‐Pyrrole complexes 11 and 14 are synthesized in overall [2+1+2] cycloadditions withe 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 .