Back Cover: Rhodium(I)‐Catalyzed Cycloisomerization of Homopropargylallene‐Alkynes through C(sp³)−C(sp) Bond Activation (Angew. Chem. Int. Ed. 17/2018)

Abstract

The combination of an allenyne with an additional π‐component in the presence of a rhodium(I) catalyst constitutes a new approach for ring closure. In their Communication on page 4707 ff., C. Mukai and co‐workers report a rhodium(I)‐catalyzed cycloisomerization of homopropargylallene‐alkynes into six/five/five tricyclic frameworks that proceeds through migration of the alkyne moiety of the homopropargyl substituent. The cover picture shows the famous “Tsuzumi Gate” of Kanazawa station.

Rhodium(I)‐Catalyzed Ring‐Closing Reaction of Allene–Alkene–Alkynes: One‐Step Construction of Tricyclo[6.4.0.02,6] and Bicyclo[6.3.0] Skeletons from Linear Carbon Chains

“…The right‐sided double bond of the triene moiety of d ( n =1) would then selectively insert into Rh−H E bond, resulting in the formation of the intermediate e , which subsequently undergoes the reductive elimination to produce the final products 11 . It should be emphasized here that although homoallylallene–alkyne species 10 produced the six/five/five tricyclic derivatives 11 , whose structures are similar to 6 derived from homopropargylallene–alkynes 5 , the reaction mechanisms for those two transformations are quite different except for initial formation of the common rhodabicyclo[4.3.0]nonadiene intermediate A in Scheme . When RhCl(PPh 3 ) 3 was employed, 10 afforded 12 in a low yield.…”

“…We recently reported a unique transformation of homopropargylallene–alkynes 5 into the tricyclic six/five/five skeleton 6 via C(sp 3 )−C(sp) bond fission and migration of alkyne moiety of the homopropargyl group whereas the one‐carbon shortened allylallene–alkynes 7 efficiently afforded the [2+2+2]‐type cycloaddition products 8 . Both transformations ( 5 to 6 and 7 to 8 ) would be rationalized by initial formation of the common rhodabicyclo[4.3.0] intermediate A (Scheme ).…”