Nonacarbonyldiiron or Pentacarbonyliron Induced Decomposition of Organic Azides and an Azirine. Novel Reduction and Carbonyl Insertion of the Complexed Nitrene Intermediate in Protic Solvents

The thermal reactions of [Fe2(CO)9] or the photochemical reactions of [Fe(CO)5] with organic azides and an azirine in protic media have been investigated. The thermal reaction of azidobenzene (1) with [Fe2(CO)9] in methanol under mild conditions gave aniline and methyl phenylcarbamate, along with N,N′-diphenylurea, while in the presence of water, 1 afforded aniline and N,N′-diphenylurea, in good combined yield. Similarly, the thermal reaction of α-azidostyrene (4) with [Fe2(CO)9] in methanol gave methyl 1-phenylvinylcarbamate and acetophenone which could be derived from the corresponding enamine, while in the presence of water, 4 gave only acetophenone in good yield. The photoirradiation of [Fe(CO)5] with 1 or 4 also gave results similar to the [Fe2(CO)9]-induced reaction. However, the thermal reaction of 3-phenyl-2H-azirine (5) with [Fe2(CO)9] in methanol gave 2,5-diphenylpyrazine in low yield, in addition to acetophenone and methyl 1-phenyl-vinylcarbemate, although 5 afforded only acetophenone in the presence of water. The reaction pathways for the formation of the products are discussed on the basis of the formation of a complexed nitrene intermediate, reduction of which induces amine or enamine and carbonyl insertion to yield an organic isocyanate in protic media.