A New Ru-Catalyzed Cascade Reaction Forming Polycyclic Cyclohexadienes from 1,6-Diynes and Alkenes

Abstract

Functionalized bicyclic 1,3-cyclohexadienes can be easily prepared by a new cascade reaction which involves the Ru-catalyzed addition of acyclic alkenes to 1,6-diynes to give (Z)-hexatrienes, followed by a pure thermal 6e-pi electrocyclization.

Recent Advances in “Formal” Ruthenium‐Catalyzed [2+2+2] Cycloaddition Reactions of Diynes to Alkenes

“…[6] As a further contribution to the above methodology, we recently described a new "formal" [2+2+2] cycloaddition of terminal 1,6-diynes 1 with acyclic alkenes 2 in the presence of 10 % of an equimolar amount of [RuA C H T U N G T R E N N U N G (CH 3 CN) 3 Cp*]PF 6 (Cp* = pentamethylcyclopentadienyl) and Et 4 NCl to give 1,3-cyclohexadienes 4 (Scheme 2). [7] We also found that cyclic alkenes 5 reacted with diynes 1 to afford tricyclic cyclohexadienes 6 (Scheme 3). [7] Unlike their acyclic alkene analogues 2, the double bonds in cyclohexadienes 6 are in the position expected for a [2+2+2] cycloadduct (as observed by Itoh).…”

“…[7] We also found that cyclic alkenes 5 reacted with diynes 1 to afford tricyclic cyclohexadienes 6 (Scheme 3). [7] Unlike their acyclic alkene analogues 2, the double bonds in cyclohexadienes 6 are in the position expected for a [2+2+2] cycloadduct (as observed by Itoh). [6f,g] Our mechanistic hypothesis for the Ru-catalyzed reaction of diynes and alkenes involves two possible pathways, depending on the alkene used (Scheme 4).…”

“…[12] Interestingly, this result clearly contrasts with that obtained between 5 a and 1 a (X = CA C H T U N G T R E N N U N G (CO 2 Me) 2 ) in which an excellent 92 % yield of cyclohexadiene 6 a was obtained. [7] The formation of the bis-cyclopropane 9 is probably due to the presence of the methyl group in 7 a, which inhibits the standard [2+2+2] cycloaddition mechanism from the corresponding ruthenabicyclocarbene IX favoring the reductive elimination to a cyclopropane ring; then, a second cyclopropanation of the resulting Ru-carbene species gives the observed bis-cyclopropane product 9.…”

CpRuCl- and CpCo-catalyzed or mediated cyclotrimerizations of alkynes and [2+2+2] cycloadditions of alkynes to alkenes: A comparative DFT study

“…The whole cascade process could be considered as a ''formal" [2+2+2] cycloaddition of alkynes to alkenes [24].…”

ChemInform Abstract: Dihydrobiphenylenes Through Ruthenium‐Catalyzed [2 + 2 + 2] Cycloadditions of ortho‐Alkenylarylacetylenes with Alkynes.

“…This process involves the [2+2+2] dimerization of the starting ortho-ethynylstyrene (1 a, a 1,5-enyne) instead of the expected Dixneuf product, the 1,4-diaryldiene 3 a, derived from head-to-head dimerization of arylacetylenes 1 with trapping of MeOH [Scheme 1, Eq. [11] The ruthenium-catalyzed dimerization of 1 a was optimized by systematically changing the reaction parameters (Table 1). [9] Even more strikingly, aromatization to naphthalene (4) was not detected in this case, despite it being the thermodynamically favored product often observed on reacting 1,5-arenynes 1 in the presence of other Ru II catalysts [Scheme 1, Eq.…”