Tetrahedron p. 1873 - 1882 (1986)
Update date:2022-08-03
Topics:
Dower, William V.
Vollhardt, K. Peter C.
The gas phase pyrolyses of variously labeled 1,5,9-decatriynes (1) and 1,5,9-cyclododecatriynes (2) were investigated to determine possible modes of thermal isomerizations.Conditions included temperatures in the range 400-600 deg C, pressures of 40 -10E-4 Torr, and contact times of ca 1 ms to 15 s.The labeling patterns in 1 and 2 were chosen such as to be able to distinguish direct intramolecular <2+2+2>cycloadditions of the alkyne units to form an aromatic ring (perhaps with subsequent rearrangements), and <3.3>sigmatropic shifts of the 1,5-diyne moieties.Methods for synthesizing the isotopically (particularly (13)C) labeled triynes were devised and implemented.The route to 5,6-(13)C2-1,5,9-decatriyne (1c) made use of a new procedure for the synthesis of symmetrically disubstituted alkynes involving coupling between two equivalents of an alkyl copper reagent and diiodoacetylene-(13)C2.The synthesis of 1,10-(13)C2-1,5,9-cyclododecatriyne (2b) was accomplished starting with K(13)CN, elaboration to labeled diethyl succinate, a crucial bis-Wittig condensation to labeled 1,5,9-cyclododecatriene 10, and bromination-dehydrobromination of the latter (NaOH-ethylene glycol).Products from the pyrolysis of unlabeled 1a included <1,2:4,5>dicyclobutabenzene, naphtalene and 3,4-dimethylidene-1-(but-3-ynyl)cyclobutene.Pyrolysis of 1b gave 3,6-dideuterio<1,2:4,5>dicyclobutabenzene and partially deuterated naphthalene, that of 1c produced 1,2-(13)C2-<1,2:4,5>dicyclobutabenzene and 9,10-(13)C2-naphthalene.While the pyrolysis of 2a resulted in hexamethylidenecyclohexane (hexaradialene), 2b furnished 1,4-(13)C2-hexaradialene.The results rule out the occurence of <2+2+2>cycloadditions of the alkyne units, but are consistent with the intervention of a series <3.3>sigmatropic shifts which connect starting materials with products.
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Doi:10.1016/0040-4020(82)80068-9
(1982)Doi:10.1021/jo00143a030
(1982)Doi:10.1016/0040-4020(82)80122-1
(1982)Doi:10.1016/S0040-4039(00)87195-6
(1982)Doi:10.1139/v82-254
(1982)Doi:10.1007/BF00577185
(1982)