Fe-Catalyzed Allylic C–C-Bond Activation: Vinylcyclopropanes As Versatile a1,a3,d5-Synthons in Traceless Allylic Substitutions and [3 + 2]-Cycloadditions

Abstract

The low-valent iron complex Bu(4)N[Fe(CO)(3)(NO)] (TBAFe) catalyzes the allylic C-C-bond activation of electron-poor vinyl cyclopropanes to generate synthetically useful a1,a3,d5-synthons which are prone to undergo multiple consecutive reactions. The versatility of this approach is demonstrated by a traceless allylic substitution and a formal [3 + 2] cycloaddition to give either functionalized acyclic products or densely substituted cyclopentanes and pyrrolidines in high yields and regioselectivities.

Iron Catalysis in Organic Synthesis

“…759 Highly substituted cyclopentanes were obtained by this method (eq a). In addition, imines could be used instead of olefins leading to pyrrolidines (eq b).…”

The Evolution of Fe‐catalyzed Nucleophilic Activation of Acceptor‐substituted Vinyl‐ and Arylcyclopropanes

“…Based on the concept of activation of an acceptor‐substituted VCP, using an electron‐rich ferrate catalyst, we initially set out to develop a protocol for the traceless allylic substitution using different CH‐acidic pronucleophiles, and were pleased to find that in the presence of benzimidazole‐derived carbene ligand L1 , various substitution products were obtained in good to excellent yields. Importantly, this process is highly atom economical, since all atoms of the starting materials are fully conserved in the final product (Figure ) …”

“…In these reports, olefins, aldehydes, or isocyanates were employed as dipolarophiles. Indeed, we were able to employ allyl‐Fe complex 4 as an a 3 ,d 5 ‐synthon under slightly modified conditions using carbene ligand L2 (Figure ) …”

Iron Catalysis in Synthetic Chemistry

“…In 2012, Plietker and co-workers (7) reported an iron-catalyzed [3 + 2] cycloaddition of vinylcyclopropanes (VCP) and activated olefins or N-tosyl imines to generate functionalized vinylcyclopentanes and cyclopyrrolidines in high yields and regioselectivities. The activation of VCP by the electron-rich ferrate, Bu 4 N-[Fe(CO) 3 (NO)] (TBAFe) (TBA = tetrabutylammonium), resulted in the formation of an intermediate allyl-Fe complex, which can be regarded as an a1, a3, d5-synthon (Scheme 4).…”