Synthesis of Heterocycles Using Trimethylsilyldiazomethane

This review describes the recent application of trimethylsilyldiazomethane (Me3SiCHN2, TMSCHN2), its lithium and magnesium bromide salts [TMSC(Li)N2 and TMSC(MgBr)N2] to the synthesis of heterocycles. Reaction of TMSCHN2 with acyl isocyanates followed by Diels-Alder reaction with propiolates or N-phenylmaleimide affords furans or bicyclic pyridones in a one-pot process, respectively. In addition, TMSCHN2 is useful for the preparation of 2-azaazulenes, aziridines and indolizines. Meanwhile, TMSC(Li)N2 reacts with benzynes generated from halobenzenes to yield 3-trimethylsilylindazoles, which are easily converted to 1-arylindazoles or indazoles bearing 3-hydroxymethyl units. TMSC(Li)N2 is also applicable to the synthesis of indoles, benzofurans, pyrroles, thiophenes and 2,3-benzodiazepines. By using TMSC(MgBr)N2, α-substituted β-trimethylsilyl-α,β-epoxyesters can be synthesized from α-ketoesters in a one-pot process. Reaction of TMSC(MgBr)N2 with carbonyl compounds efficiently furnishes trimethylsilylated diazoalcohols, which react with propiolates to give di- or tri-substituted pyrazoles.