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

Abstract

The reactions of the cobaltacyclopentadiene complexes (η 5-C 5H 5)(PPh 3)- Co(CR 1CR 2CR 3 C R 4) (I) with organic azides were investigated. The complex Ia (R 1  R 2  R 3  R 4  Ph) reacts with phenyl azide at 80°C to give 1,2,3,4,5-pentaphenylpyrrole in 73% yield. 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 64% yields, respectively, but reaction with p-toluenesulfonyl azide gives 2,3,4,5-tetraphenylpyrrole and 3,4,5,6-tetraphenylpyridazine in 35 and 45% yields, respectively, in place of the expected 1-( p-toluenesulfonyl)-2,3,4,5-tetraphenylpyrrole. The reaction of Ic (R 1  R 3  Ph, R 2  R 3 = CO 2CH 3) with phenyl azide at 130°C gives 1,2,5-triphenyl-3,4-bis(methoxycarbonyl)pyrrole (IIc) and 2,5-diphenyl-3,4-bis(methoxycarbonyl)pyrrole (Vb) in 22 and 15% yields, respectively. The reaction of Ic with benzenesulfonyl azide gives only Vb in 57% yield. In the reaction of Id (R 1  R 3  Ph, R 2  R 4  CO 2CH 3) with benzenesulfonyl azide, Vb was unexpectedly obtained in 26% yield, together with 2,4-diphenyl-3,5-bis(methoxycarbonyl)pyrrole (Vc, 30%), 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°C gives the 2(1 H-pyridinone derivatives VIIIa (82%) and VIIIb (53%), 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.