Unsaturated five-membered selenium–silicon containing heterocycles based on the reactions of selenium di- and tetrahalides with diorganyl diethynyl silanes

Reactions of SeBr2 and SeCl2 with diorganyl diethynyl silanes RR1Si(Ctriple bond; length of mdashCH)2 in CHCl3 at room temperature result in regio- and stereoselective formation of a new class of unsaturated five-membered heterocycles, 4,4-R,R1-3,6-dichloro(dibromo)-1,4-selenasilafulvenes (Z-isomers predominately), in preparative yields. Under similar conditions the reaction of SeBr4 and SeCl4 with diorganyl diethynyl silanes RR1Si(Ctriple bond; length of mdashCH)2 proceeds regioselectively to afford another new class of unsaturated five-membered heterocycles, 2-dichloro(dibromo)-methyl-2,4-dichloro(dibromo)-3,3-diorganyl-1-selena-3-silacyclopentenes-4. The structures of the heterocycles were proved by multinuclear (1H, 13C, 29Si, 77Se) NMR spectroscopy, 2D NOESY NMR spectroscopy and mass-spectrometry. A long-range spin–spin interaction of protons through five bonds lacking in E-isomers was revealed in Z-isomers of fulvene-type heterocycles. In the MS spectra heterocycles of cyclopentene structure were shown to manifest themselves as fragmentary ions [M−HX]+ or [M−X]+.