Zinc‐Catalyzed [4+3] Cycloaddition with Concomitant Furan Annulation: Formation of Cyclohepta[b]Furans

Abstract

A convenient zinc-promoted [4+3] cycloaddition of a carbonyl ene-yne with simple dienes was first achieved. This reaction provided an efficient strategy to prepare various cyclohepta[b]furan rings by cascade cycloadditions. Additionally, a multicomponent reaction of dione, alkynal, and diene was also reported, which exhibited a novel strategy for selective creations of C-O bonds and C-C bonds.

Zinc‐Catalyzed Multicomponent Reactions: Easy Access to Furyl‐Substituted Cyclopropane and 1,2‐Dioxolane Derivatives

“…To this end, we first performed the reaction with pentane‐2,4‐dione ( 1a ), 2‐octynal ( 2a ), 2,3‐dimethyl‐1,3‐butadiene ( 3o ) and ZnCl 2 (2 mol‐%). Stirring at room temperature for 12 h resulted in the formation of an almost 1:1 mixture of vinylcyclopropane 5a /cycloheptafuran 6a in moderate yield (Scheme ) 12. Similarly, 3‐phenylpropiolaldehyde ( 2j ) furnished a 1:2 mixture of 5b / 6b .…”

Recent Advances in Transition-Metal-Free (4+3)-Annulations

“…In 2014, Liang et al built a furan ring and a seven-membered ring in one step, using ZnCl 2 as a catalyst, by combining Knoevenagel adducts 5.1.4a and tert-butyldimethylsilyl-protected butadien-2-ol derivates 5.1.4b (Scheme 5.1.4). 80 Cyclohepta(b)furans 5.1.4c were isolated in moderate to good yields with ZnCl 2 , while other Zn II and Pt II salts gave lower yields.…”

Zinc reagents as non-noble catalysts for alkyne activation

“…51 Here, higher catalyst loadings as well as higher temperatures were required in order to obtain good yields. Making use of the inertness of stabilized diazocompounds toward zinc salts, López and Vicente use these compounds as nucleophiles to trap zinc carbenoids generated from enynones.…”