ORGANIC SYNTHESES VIA TRANSITION-METAL COMPLEXES .58. HEPTAFULVENYLCARBENE COMPLEXES OF CHROMIUM AND TUNGSTEN - AZASPIRO[4] ANNELATION 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)CH2-c-C7H7 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-C7H7 5 in two steps. The first step involves the formation of (tropyliummethyl)carbene complexes [L(n)M=C(OEt)CH2-C-C7H6]+ [BF4]- 4 by a hydride abstraction from the cycloheptatriene ring of 3 with [Ph3C]+ [BF4]- (4a, 4b: 70%). 4 is deprotonated with Et3N to give 5 (5 a: 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-C6H11N=C=C(OEt)-CH=c-C7H6] 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.