Organische Synthesen mit Übergangsmetall‐Komplexen, 58. Heptafulvenylcarben‐Komplexe von Chrom und Wolfram. – Azaspiro[4]‐Anellierung an 1‐Metalla‐1,3‐diene mit Isocyaniden; Liganden‐Abspaltung mit Pyridin oder durch Thermolyse

Organic Syntheses via Transition Metal Complexes, 58 [1] . – Heptafulvenylcarbene Complexes of Chromium and Tungsten. – Azaspiro[4] Anellation to 1‐Metalla‐1,3‐dienes with Isocyanides; Displacement of Ligands by Pyridine or by Thermolysis * (Cycloheptatrien‐1‐ylmethyl)carbene complexes L n M = C(OEt)CH 2 ‐c‐C 7 H 7 3 [L n M = Cr(CO) 5 ( a ), W(CO) 5 ( b )] are transformed into heptafulven‐8‐ylcarbene complexes L n M = C(OEt)CH = c‐C 7 H 7 5 in two steps. The first step involves the formation of (tropyliummethyl)carbene complexes [L n M = C(OEt)CH 2 ‐c‐C 7 H 6 ] + [BF 4 ] ‐ 4 by a hydride abstraction from the cycloheptatriene ring of 3 with [Ph 3 C] + [BF 4 ] ‐ ( 4a, 4b: 70%). 4 is deprotonated with Et 3 N to give 5 ( 5a : 89%; 5b : 92%). 5 adds one equivalent of cyclohexyl isocyanide ( 6 ) to the L n M = C – C = C unit via the intermediate ketenimine complexes L n M[c‐C 6 H 11 N = C = C(OEt) – CH = c‐C 7 H 6 ] 7 , which cyclize spontaneously and form the (thermolabile) azaspiro[4.6]undecatetraene complexes 8 ( 8a : 91%; 8b : 93%). The reaction of 8a, b with pyridine leads to the disengagement of a pyrrole 10 in almost quantitative yields. Thermolysis of 8a, b in the absence of pyridine gives an azulene 12 .