Iron-Catalyzed Tunable and Site-Selective Olefin Transposition

Abstract

The catalytic isomerization of C−C double bonds is an indispensable chemical transformation used to deliver higher-value analogues and has important utility in the chemical industry. Notwithstanding the advances reported in this field, there is compelling demand for a general catalytic solution that enables precise control of the CC bond migration position, in both cyclic and acyclic systems, to furnish disubstituted and trisubstituted alkenes. Here, we show that catalytic amounts of an appropriate earthabundant iron-based complex, a base and a boryl compound, promote efficient and controllable alkene transposition. Mechanistic investigations reveal that these processes likely involve in situ formation of an iron-hydride species which promotes olefin isomerization through sequential olefin insertion/β-hydride elimination. Through this strategy, regiodivergent access to different products from one substrate can be facilitated, isomeric olefin mixtures commonly found in petroleum-derived feedstock can be transformed to a single alkene product, and unsaturated moieties embedded within linear and heterocyclic biologically active entities can be obtained.

Iron Catalyzed Double Bond Isomerization: Evidence for an FeI/FeIII Catalytic Cycle

“…More recently, Koh and co‐workers have reported an elegant regiodivergent isomerization process that uses B 2 pin 2 or PhMe 2 SiBpin in conjunction with an iron catalyst and LiO t Bu. Mechanistic studies revealed that the reaction is likely to proceed via an iron‐hydride with subsequent olefin insertion and β‐hydride elimination [12] . Pertinent to this study, Smith has employed an Fe I species, exploiting the propensity for spin crossover, to achieve iron catalyzed double bond isomerization via a two‐electron catalytic cycle [13] …”

“…Mechanistic studies revealed that the reactioni sl ikely to proceed via an iron-hydride with subsequent olefin insertion and b-hydride elimination. [12] Pertinent to this study, Smith has employed an Fe I species, exploiting the propensity for spin crossover, to achieve iron catalyzed double bond isomerization via at wo-electron catalytic cycle. [13] From the synthetic studies we have already disclosed in hydrofunctionalizationc hemistry, [14] we postulated that access to at wo-electron isomerization catalytic cyclew ould be possible by limiting the quantityo fh ydrides ource employed in order to access Fe I ,m eanwhilep reventing competitive Fe II hydroboration.…”

Base-Mediated Site-Selective Hydroamination of Alkenes

“…In recent years, there is growing interest in the field of remote functionalization as it allows for the formal activation of unreactive CH bonds distant from an initial reactive site without employing strongly coordinating directing groups 9 . In light of this, combining the present hydroamination protocol with our previously reported Fe-catalysed olefin migration methodology 10 , in a sequential fashion enables net remote hydroamination of terminal alkenes to afford the desired arylamines. This is noteworthy since the β position (vicinal to aryl groups) is typically less activated.…”

Selecting Double Bond Positions with a Single Cation-Responsive Iridium Olefin Isomerization Catalyst

“…The pincer-crown ether catalyst 2-18c6b is one of a select few catalysts capable of facilitating a single positional isomerization with exceptional stereoselectivity for the E-isomer. 5,[52][53][54][55][56] It is unique in selectively accessing either of two internal isomers in response to an external stimulus.…”