Formal [4+3], [4+2], [4+1] and [2+1] cycloadditions and acid-base reaction of 2-methyl-1,3-dimorpholino-1,3-butadiene with Fischer carbene complexes

2-Methyl-1,3-dimorpholino-1,3-butadiene 1 reacted with alpha,beta-unsaturated Fischer carbene complexes to give a wide range of different products depending on the substitution pattern. Thus, seven-membered rings (4, 5 and 6) could be obtained from chromium complexes 2 with aromatic or vinylic groups at the beta position. Similar results were observed when alpha-methyl-substituted carbene complex 7a was used. Six-membered carbocycles (derivatives of cycloadducts 12 and 13) were isolated after reaction with both chromium and tungsten complexes bearing one or two alkyl groups al the beta position (10 and 11). Moreover, cyclopentenones 20 were the main products when the starting carbene complexes were alkyl-substituted at both alpha and beta positions (19 a,b) or when aromatic (19 c, d) instead of vinylic complexes were used. A bicyclo[4.1.0]heptene system 18 has also been obtained in the special case of reaction with beta,beta-dimethylvinylchromium complex 13 b; its formation could be explained as a formal carbene insertion into a C-H bond. The behaviour of diene 1 towards alkoxymethylcarbene complexes 22 was unusual. The different reaction products (cyclopentadienes 23, bicyclo[3.1.0]hexenes 24, aromatic amine 25 and metallatrienes 26) imply a mechanism in which the deprotonation of the carbene complex by the diene is followed by Michael addition to the iminium salt formed.