125358-28-3Relevant articles and documents
Precursors to the cyclo[n]carbons: From 3,4-dialkynyl-3-cyclobutene-1,2-diones and 3,4-dialkynyl-3-cyclobutene-1,2-diols to cyclobutenodehydroannulenes and higher oxides of carbon
Rubin, Yves,Knobler, Carolyn B.,Diederich, Fran?ois
, p. 1607 - 1617 (2007/10/02)
A series of novel cyclobutenodehydro[n]annulenes (n = 18, 24, 30) have been prepared as precursors in an organic approach to the cyclocarbons C18, C24, and C30. On the way to these macrocycles, synthetic entries to three new classes of enediynes have been developed. Bis(1-propynyl)cyclopropenone was prepared in the reaction of 1-(trimethylsilyl)-1-propyne with trichlorocyclopropenylium tetrachloroaluminate. The 3,4-dialkynyl-3-cyclobutene-1,2-diones were prepared by the reaction of 3,4-dichloro-3-cyclobutene-1,2-dione either with (tri-n-butylstannyl)alkynes in the presence of catalytic amounts of Pd(PPh3)4 or with the soluble copper (I) acetylides of (trialkylsilyl)acetylenes. The peculiar downfield resonances of the terminal acetylenic carbon atoms in the 13C NMR spectra of the 3,4-dialkynyl-3-cyclobutene-1,2-diones are discussed. The stereospecific and regiospecific reduction of these diones with cerium trichloride-sodium borohydride afforded exclusively the cis-3,4-dialkynyl-3-cyclobutene-1,2-diols. The oxidative Hay coupling of the acetonide of 3,4-diethynyl-3-cyclobutene-1,2-diol or of the bis(ethylene ketal) of 3,4-diethynyl-3-cyclobutene-1,2-dione gave two series of cyclobutenodehydroannulenes with 18π-, 24π-, and 30π-electron perimeters. In both series, the unusually stable octahydro[24]annulene perimeter is formed with the highest yield. Deprotection of the trimer and the tetramer, obtained in the oxidative coupling of the bis(ethylene ketal) of 3,4-diethynyl-3-cyclobutene-1,2-dione, was best effected in concentrated sulfuric acid and yielded quantitatively the (3-cyclobutene-1,2-dione)-annelated dehydroannulenes 4 (C24O6) and 5 (C32O8), novel higher oxides of carbon and direct precursors to the cyclocarbons C18 and C24.
