New Preparations of Heterocydes Using Trimethylsilyldiazomethane

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Synthesis of various heterocycles using trimethylsilyldiazomethane (TMSCHN_2), a stable and safe substitute for hazardous diazomethane, was investigated as follows.1) Vibsanol, a benzofuran-type lignan isolated from the wood of Viburnum awabuki, was synthesized by the tandem cyclization of o-tert-butyldimethylsiloxyarylalkynes with excess paraformal dehyde in the presence of tetrabutylammonium fluoride as the key step.2) Lithium salt of trimethylsilyldiazomethane (TMSC(Li)N_2), easily prepared from TMSCHN_2 with n-BuLi or LDA, smoothly reacted with γ-ketoaldehyde acetals to give 2-cyclopentenones via the 1,5-C-H insertion of alkyldene carbene in good yields. Using this method, the synthesis of trichodenone C, isolated from Trichoderma harzianum and exhibited cytotoxicity against cultured P388 cells, was accomplished.3) TMSCHN_2 easily reacted with N-sulfonylaldimines to give selectively cis-N-sulfonylaziridines in high yields.4) Reaction of TMSC(Li)N_2 with α-oxoketene dithioacetals gave thiophenes, homologous ketones, and homologous alkynes depending upon substrates used.5) TMSC(Li)N_2 reacted with o-aminoacetophenones to give indoles via the N-H insertion of alkyldene carbene in good yields.6) TMSC(Li)N_2 reacted with 4-aryl-2-oxobutanoic esters to give 2,3-dihydroazulenes via the alkyldene carbene intermediates which were easily converted to azulenes by oxidation with MnO_2 in good yields.