Intramolecular ene reactions of 1,7-octenynes: The involvement of 1,2-cyclooctadiene intermediates

Strained cyclic cumulenes

“…Many cyclic cumulenes seem best considered as reactive intermediates. In the allene series, several 1,2-cyclohexadienes have been generated as reactive intermediates, while the current limit for isolability is a butressed 1,2-cyclooctadiene (45). There is convincing evidence that highly strained 1,2-cyclohexadiene (9) exists as a chiral allene.…”

“…46 This novel approach was also applied to the nondegenerate rearrangement of ether 48, albeit in low yield. 45 As noted in the Introduction, Favorski and co-workers believed they had synthesized 1,2-cycloheptadiene (10) around 1936 by treatment of 60 with sodium.9…”

New Reactions in Fullerene Chemistry

“…32 To the best of our knowledge, only two allene compounds formed by the thermal intramolecular ene reaction of enynes have been previously reported, and their synthesis involves the use of a high temperature (210 °C) to achieve a moderate yield in one case, 33 and the formation of a nonisolable allene intermediate in the other. 34 The first intermolecular ene reaction of arynes with alkynes to form a wide variety of symmetric and asymmetric allenes has been recently reported. 35 Our approach is the first example of the synthesis of allenes by simple and efficient thermal noncatalyzed intramolecular ene cyclization that involves a fullerene double bond as the ene moiety.…”

Ene Reaction of Arynes with Alkynes

“…Product 3a appears to further react with benzyne readily during the reaction, and it is essential to keep 1-hexyne in excess to inhibit this reaction. To the best of our knowledge, this is the first time that an alkyne was successfully used in the intermolecular ene reaction and the first detailed account of the synthesis of phenylallene from a benzyne and an alkyne in good yields under mild conditions.…”