En Route to 7,7,8,8-Tetraethynyl-p-quinodimethane (TEQ)

摘要

The cross-conjugated 1,1-diethynylethylene derivatives 8b-10b were prepared from the corresponding bromides 16, 19, and 17 by Sonogashira coupling with trimethylsilylethyne and hydrolysis of the TMS-protected intermediates thus formed. Coupling of the tetrabromide 18 with (trimethylsilyl-ethynyl)magnesium bromide in the presence of 1,3-[bis(di-ethynyl)magnesium bromide in the presence of 1,3-[bis(di-phenylphosphanyl)propane]nickel(II) chloride yielded the protected tetraalkyne 32, from which the 7,7,8,8-tetraethyl-nyl-tetrahydro-p-quinodiumethane 33 was liberated by fluoride treatment. Although 33 is a highly unstable cross-conjug-ated hydrocarbon, it could be converted into its tetraphenyl derivative by Sonogashira coupling with phenyl iodide. Both 32 and the corresponding tetraphenyl derivative were oxidized to the 7,7,8,8-tetraethynyl-dihydro-p-quinodimethane derivatives 35 and 36, respectively, on treatment with DDQ in dioxane. Further dehydrogenation of 35 to 34 failed, how-ever. Alkylation of 9b with trimethylaminium in the presence of zirconocene dichloride as catalyst yielded the semicyclic dendralene 37, which on irradiation isomerized to the tricyclic diene 42, presumably via the vbicyclobutane 39 and a vinylcyclopropane rearrangement. Hydration of 9b furnished 43 and 44, the primary hydroation product 38 either undergoing ketene elimination (formation of 43) or a 1,5-hydrogen shift reaction (to 44) from its tautomer 41. Analogously, the still more highly unsaturated derivative 31 was alkylated to give the [5]dendralene derivative 45 and hydrated to give a mixture of the #beta#-diketones 46 and 49, the latter vbeing produced from 46 by 1,2-methyl migration. The thermal cyclization of 10b to the homoacepentalene derivative 51 failed.