Alkenes in [2+2+2] Cycloadditions

Abstract

Participation of alkenes and allenes in [2+2+2] cycloaddition reactions has attracted much attention recently. This version of the well-established alkyne cyclotrimerization renders interesting products, such as cyclohexadienes and other polycycles, through cascade processes. Many mechanistic variations are observed when using certain metal complexes as catalysts. The frequent generation of stereogenic centers has prompted the development of efficient asymmetric versions. This Minireview summarizes the efforts reported to date on the use of double bonds as partners in [2+2+2] cyclotrimerizations.

Expeditious Preparation of Open‐Cage Fullerenes by Rhodium(I)‐Catalyzed [2+2+2] Cycloaddition of Diynes and C60: An Experimental and Theoretical Study

“…On the other hand, transition-metal-catalyzed [2+ +2+ +2] cycloaddition reactions appear as the methodo fc hoice for the synthesis of sixmembered rings and enable the construction of cyclohexadiene scaffolds when the reactiont akes place between two alkynes and one alkene. [7] Given that the chemical reactivityo f C 60 is typicalo fa ne lectron-deficient olefin, it acts as av aluable candidate as ac o-substratei n[ 2 + +2+ +2] cycloadditions with alkynes. [7a] Furthermore, cycloaddition reactions with empty fullerenes show ar emarkable preference for the [6,6] ring junction over [5,6] bonds.…”

“…However,t his transformation operates on ad ifferent reactionm anifold, which is limited to Michael acceptors. Based on our previous experience in Rh-catalyzed [2+ +2+ +2] cycloaddition reactions between alkynesa nd both alkenesa nd allenes, [12,7] we envisaged the developmento facatalytic version of the [2+ +2+ +2] cycloaddition reaction between diynes and fullerene. Subsequent [4+ +4] photocycloaddition and retro-[2+ +2+ +2] reaction of the cyclohexadiene derivativesw ould provide, overall, av ersatile and efficient entry to open-cage fullerenes.…”

Synthesis of sinapine and its unprecedented ruthenium-catalyzed [2+2] photodimerization

“…These dimers were obtained by solid-state photodimerization. Photochemical transformations are of increasing importance for the synthesis of natural products as unique structures can be accessed otherwise being challenging to synthesize, and products can be obtained through high energy intermediates that remain unreachable by thermaldriven reactions 34 . As a consequence, in the last decades, the importance of light-induced reactions increased, and the introduction of LEDs presented a new state-of-the-art in science and technology 35 .…”

Unpredictable cycloisomerization of 1,11-dien-6-ynes by a common cobalt catalyst

“…Metal-catalyzed reactions of enynes represent an atom- and step-economical route to complex organic molecules with a broad range of functionalities [1–4]. In particular, cycloisomerization of enynes allows one to prepare compounds with exocyclic double bonds and cyclopropanes in a highly selective manner [5–7].…”