Elusive 2H-1,2-oxasiletes through reactions of an isolable dialkylsilylene with diazocarbonyl compoundsElectronic supplementary information (ESI) available: NMR spectra and X-ray crystallographic data of 2, 3, 8 and 11. CCDC 1056197, 1056194, 1063129 and 1405300. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5ob01224d

The reactions of isolable dialkysilylene 1 with 2-diazo-1,2-diphenylethanone and ethyl 2-diazo-2-phenylacetate gave elusive silacycles, 2 H -1,2-oxasiletes 2 and 3 , respectively, in high yields. Because these reactions occur at low temperatures of ca. −30 °C, initial complexation of the silylene to the carbonyl oxygen of the diazocarbonyl compounds is suggested to trigger dinitrogen elimination followed by cyclization. In contrast, a six-membered cyclic diazo compound 8 and 1-sila-2,3-diazabicyclo[3.3.0]oct-3-ene 10 were obtained in good yields by the reaction of 1 with less reactive ethyl 2-diazo-3-oxo-3-phenylpropanoate 7 and trimethylsilyldiazomethane 9 . Molecular structures of 2 , 3 , 8 and 10 were determined by X-ray crystallography. The reactions of isolable dialkysilylene 1 with compounds 5 and 6 gave elusive silacycles, 2 H -1,2-oxasiletes 2 and 3 , respectively, with releasing dinitrogen. In contrast, six-membered cyclic diazo compound 8 was obtained in a good yield by the reaction of 1 with less reactive 7 .