Organometallic diazoalkanes. Part II. Heterocyclic syntheses with the co-ordinated ligand CN22–; reactions of trimethylstannyl- and trimethylsilyl-diazoalkanes

Abstract

The reactions of organometallic diazoalkanes ZZ′CN₂[(Me₃Sn)₂CN₂, Me₃SiCHN₂, Me₃Si(Me₃Sn)CN₂, and Me₃SnC(CO₂Et)N₂] with 1,2-dipoles AB [AB = ArNCNAr, PhNCS, CS₂, MeO₂C·C⋮C·CO₂Me, CH₂:CH·CN, and CH₂:C(Me)·CN] to give, in the main, the pyrazolo- and related 1,3-cycloadducts ZZ′CN₂·AB are described. The results are compared with those for CH₂N₂. Clearly, the organometallic derivatives, and especially (Me₂Sn)₂CN₂, are more prone to 1,3-dipolar behaviour than is CH₂N₂, which often fragments with loss of nitrogen. The structures of the pyrazoles are established by spectroscopy and chemical reactions. In several instances cycloaddition is accompanied by a rearrangement involving migration of Z or Z′ from carbon to nitrogen; the relative migratory aptitudes decrease in the order Me₃Sn > Me₃Si > H > CO₂Et. The stannyl and related adducts afford the parent heterocycles (if stable) by treatment with cold 5M-HCl. Thus, a new general heterocyclic synthesis becomes available, which involves successively reaction of Me₃SnNMe₂ with CH₂N₂, addition of AB, and finally of 5M-HCl; Me₃Sn is thus a convenient protecting group.