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

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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.

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