181212-63-5Relevant articles and documents
New Diels-Alder reactions of 3-vinylindoles with an aryne: Selective access to functionalized [a]anellated carbazoles
Gonzalez, Eugenia,Pindur, Ulf,Schollmeyer, Dieter
, p. 1767 - 1771 (1996)
New results for the reactions of donor- and acceptor-substituted 3-vinylindoles with aryne and structurally related 3,4-pyridyne are described. Aryne reacts in Diels-Alder reactions as a dienophile to give rise to a variety of [a]anellated carbazoles in a one-step procedure. Additionally, aryne is involved in an ene or conjugate addition reaction with the initially formed [4 + 2]cycloadduct. Reaction of methyl (E)-3-(N-methylindol-3-yl)propenoate 6 in the presence of air gives besides the expected Diels-Alder product a new benzoxepino[b]indole derivative 14. The Diels-Alder reactions of the 3-vinylindoles with in situ generated 3,4-pyridyne are difficult to control and no cycloadducts with the required purity could be isolated.
Synthesis of phenanthrenes and polycyclic heteroarenes by transition-metal catalyzed cycloisomerization reactions
Mamane, Victor,Hannen, Peter,Fuerstner, Alois
, p. 4556 - 4575 (2007/10/03)
Readily available biphenyl derivatives containing an alkyne unit at one of their ortho-positions are converted into substituted phenanthrenes on exposure to catalytic amounts of either PtCl2, AuCl, AuCl3, GaCl3 or InCl3 in toluene. This 6-endo-dig cyclization likely proceeds through initial π-complexation of the alkyne unit followed by interception of the resulting η2-metal species by the adjacent arene ring. The reaction is inherently modular, allowing for substantial structural variations and for the incorporation of substituents at any site of the phenanthrene product. Moreover, it is readily extended to the heterocyclic series as exemplified by the preparation of benzoindoles, benzocarbazoles, naphthothiophenes, as well as bridgehead nitrogen heterocycles such as pyrrolo[1,2-a]quinolines. Depending on the chosen catalyst, biaryls bearing halo-alkyne units can either be converted into the corresponding 10-halo-phenanthrenes or into the isomeric 9-halo-phenanthrenes; in the latter case, the concomitant 1,2-halide shift is best explained by assuming a metal vinylidene species as the reactive intermediate. The scope of this novel method for the preparation of polycyclic arenes is illustrated by the total synthesis of a series of polyoxygenated phenanthrenes that are close relatives of the anticancer agent combretastatin A-4, as well as by the total synthesis of the aporphine alkaloid O-methyl-dehydroisopiline and its naturally occurring symmetrical dimer.
