Indoles Claisen rearrangements

That electrocyclic reaction is related to the Claisen rearrangement of phenyl vinyl ether. In a final step a cyclization takes place with subsequent elimination of ammonia to yield the indole 2 ... 

Cu-catalyzed domino reactions have been used for the synthesis of carbocycles, as well as for heterocycles such as indoles, benzoxazoles, and quinoxalines. A very useful process is also the combination of the formation of allyl vinyl ethers, followed by a Claisen rearrangement. 

Some other ring expansions involving the intramolecular amino Claisen rearrangement of vinylarylaziridine [ 123], the Diels-Alder reaction of indoles with acetylene derivative [124-127] and the dibromocarbene insertion into quinoline enol ethers [ 128] have been used to prepare 1-benzazepines. On the other hand, treatment of 3-chloro-3-phenyl-l,2,3,4,5,6-hexahydro-l-benz-azocin-2-ones with piperidine causes a ring contraction to give 2-phenyl-2-(l-piperidinylcarbonyl)-2,3,4,5-tetrahydro-l//-l-bcnzazepines in an excellent yield [23]. 

TV-Acetyl indolin-3-one 123 was converted to 3-cyanomethyl-3-(l,l-dimethylallyl) indol-2-one, 127, by a successive isomerization-Claisen rearrangement sequence (equation 63)91.7V-Acetylindolin-3-one 123 was converted in two steps to a mixture of E- and Z-isomers of 124. Isomerization of both isomers of 124 to 125 was accomplished with DBU. Claisen rearrangement of 125 afforded a 13% yield of 126, which was subsequently deprotected to give 3-cyanomethyl-3-(l,l-dimethylallyl)indol-2-one, 127, in 47% yield. 

Majumdar published several aza-Claisen rearrangements of 2-cyclohexenyl-1-anilines 39 (R -R =(CH2)3, Table 2, entries 22-28) [14]. The reaction was carried out upon heating the reactant in EtOH/HCl. The corresponding 2-cy-clohexenylanilines 41 were obtained with 50 to 90% yield. The cyclization to give indole derivatives 42 could be achieved in a separate step treatment of the rearrangement products 41 with Hg(OAc)2 in a suitable alcohol in the presence of acetic acid induced formation of the tetrahydrocarbazole 42. The tricyclic products 42 were synthesized with 70-85% yield. Finally, carbazoles could be obtained after DDQ dehydrogenation. 

The reactions of 2-hydroxy-2-(3-indolyl)ethanoamides and of ethyl 2-hydroxy-2-(2-pyrrolyl) ethanoates with trialkyl ortho-esters follow similar routes with the initial formation of the enol ethers (295) and (297), followed by an ortho- Claisen rearrangement to give the 2,3-disubstituted indoles (296) and pyrroles (298) (79JOC1885,80TL4335). 

Nitrogen heterocyclic systems, Claisen rearrangements in, 8, 143 Nomenclature of heterocycles, 20, 175 Nuclear magnetic resonance spectroscopy, application to indoles, 15, 277 Nucleophiles, reactivity of azine derivatives with, 4, 145... 

Sometimes, aldehydes obtained by TPAP oxidations suffer in situ intramolecular transformations in substrates with a great predisposition to do so. Examples found in the literature include retro-Claisen rearrangements,108 dipolar additions on enals,106a and attack of malonates109 and indole rings11 on aldehydes. 

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