Metal-Catalyzed [4 + 2 + 2] Cycloadditions:  Cycloadducts of Substituted Norbornadienes and Their Opening with Zeise's Dimer

Synthesis of Isobenzofuranones by Cobalt Catalyzed [2+2+2] Cycloaddition

“…To evaluate this effect on the regioselectivity and catalyst performance, bi‐ and tridentate ligands were tested. Considering that optimal catalytic systems for this type of reaction employed bidentate biphosphine ligands,[6d], [17a], [17b], [17d], we started to explore the effect of diphenylphosphines ( DPPE and DPPP ) (Table , entries 1 and 2) in the reaction of diyne 1a , ethyl propiolate ( 2a ), Zn and ZnI 2 in the presence of 5 mol‐% CoCl 2 , however they resulted ineffective. The structures of the ligands employed are illustrated in Figure and the results are collected in Table .…”

“…In contrast, [4+2+2] cycloadditions required a bimetal catalytic system with the second metal being typically zinc serving as a Lewis acid. [17c], In the attempt to elucidate the role of ZnI 2 in this cycloaddition reaction, we tested different cobalt catalytic systems on the cycloaddition of 1a with ethyl 2‐butynoate ( 2b ), the results are shown in Table . When the reaction was performed in the presence of ZnI 2 with two different cobalt(II) sources, CoCl 2 /ZnI 2 (10/30 mol‐%) or CoI 2 /ZnI 2 (10/30 mol‐%) the desired product 3b was afforded in high yield with good regioselectivity (entries 1 and 2).…”

Metal-Mediated Synthesis of Medium-Sized Rings

“…Synder recently did a comprehensive study of the best conditions for the [4+2+2] cycloadditions of NBD ( 587 ) with 1,3-butadiene ( 592 ) to give cycloadduct 593 (Scheme ) . He found that cobalt(II) iodide with additives such as zinc iodide and phosphorus ligand, dppe, provided the best yields.…”

New Catalyzed Three‐Component Cycloadditions for the Synthesis of Eight‐Membered Carbocycles

“…the research groups of Evans and Gilbertson independently described new three‐component cycloadditions. Although both reactions are denoted as [4+2+2]‐type cycloadditions,7 they follow different pathways in assembling difficult‐to‐form eight‐membered carbocycles.…”