Reactions of cobaltacyclopentadiene complexes with organic azides directed toward synthesis of highly substituted pyrroles

Article abstract of DOI:10.1016/0022-328X(89)85033-8

The reactions of the cobaltacyclopentadiene complexes (η⁵-C5H5)(PPH3)-Co(-CR¹=CR²-CR³=CR⁴)- (I) with organic azides were investigated.The complex Ia (R¹)=R²=R³=R⁴=Ph) reacts with phenyl azide at 80 degC to give 1,2,3,4,5-pentaphenylpyrrole in 73percent yeld.Similarly, the reactions of Ia with benzoyl and t-butoxycarbonyl azides give 1-benzoyl- and 1-(t-butoxycarbonyl)-2,3,4,5-tetraphenylpyrroles in 41 and 64percent yields, respectively, but reaction with p-toluenesulfonyl azide gives 2,3,4,5-tetraphenylpyrrole and 3,4,5,6-tetraphenylpyridazine in 35 and 45percent yields, respectively, in place of the expected 1-(p-toluenesulfonyl)-2,3,4,5-tetraphenylpyrrole.The reaction of Ic (R¹=R⁴=Ph, R²=R³=CO2CH3) with phenyl azide at 130 degC gives 1,2,5-triphenyl-3,4-bis(methoxycarbonyl)pyrrole (IIc)and 2,5-diphenyl-3,4-bis(methoxcarbonylpyrrole (Vb) in 22 and 15percent yields, respectively.The reaction of Ic with benzenesulfonyl azide gives only Vb in 57percent yield.In the reaction of Id (R¹=R³=Ph, R²=R⁴=CO2CH3) with benzenesulfonyl azide, Vb was unexpectedly obtained in 26percent yield, together with 2,4-diphenyl-3,5-bis(methoxycarbonyl)pyrrole (Vc, 30percent), which suggests that a skeletal rearrangement of the metallacycle IXd to IXc occurs during the reaction.The reaction of Ic or Id with benzoyl azide at 130 degC gives the 2(1H)-pyridinone derivatives VIIIa (82percent) and VIIIb (53percent), which are the products of the reaction of the corresponding cobaltacyclpentadiene with phenyl isocyanate generated by the rearrangement of benzoyl nitrene, in place of the expected, corresponding pyrrole.