Contrasteric coupling of allenes and tetrahydroisoquinolines by iron-catalysed allenic C(sp2)-H functionalisation

Modern Organometallic C-H Functionalizations with Earth-Abundant Iron Catalysts: An Update

Iron-catalyzed C-H activation has recently emerged as an increasingly powerful synthetic method for the step- and atom- economical direct C-H functionalizations of otherwise inert C-H bonds. Iron's low-cost and toxicity along with its catalytic versatility have encouraged the scientific community to elect this metal for the development of new C-H activation methodologies. Within this review, we aim to present a collection of the most recent examples of iron-catalyzed C-H functionalizations with a particular emphasis on modern synthetic strategies and mechanistic aspects.

Iron-Mediated C-H Functionalization of Unactivated Alkynes for the Synthesis of Derivatized Dihydropyrrolones: Regioselectivity Under Thermodynamic Control

Cyclopentadienyliron dicarbonyl-based complexes present opportunities for underexplored disconnections in synthesis. Access to challenging dihydropyrrolone products is achieved by propargylic C-H functionalization of alkynes for the formation of cyclic organoiron species. Excellent regioselectivity for unsymmetrical alkynes is observed in many cases. Notably, regioselectivity under these stoichiometric conditions diverges from those observed previously under catalysis, occurring at the more-substituted terminus of the alkyne, allowing for methine functionalization and the formation of quaternary centers. Divergent demetallation of the intermediate organoiron complexes gives access to chemically diverse products which are amenable to further functionalization.

Designed Iron Catalysts for Allylic C-H Functionalization of Propylene and Simple Olefins

Propylene gas is produced worldwide by steam cracking on million-metric-ton scale per year. It serves as a valuable starting material for π-bond functionalization but is rarely applied in transition metal-catalyzed allylic C-H functionalization for fine chemical synthesis. Herein, we report that a newly-developed cationic cyclopentadienyliron dicarbonyl complex allows for the conversion of propylene to its allylic C-C bond coupling products under catalytic conditions. This approach was also found applicable to the allylic functionalization of simple α-olefins with distinctive branched selectivity. Experimental and computational mechanistic studies supported the allylic deprotonation of the metal-coordinated alkene as the turnover-limiting step and led to insights into the multifaceted roles of the newly designed ligand in promoting allylic C-H functionalization with enhanced reactivity and stereoselectivity.

Synthesis of 1,1-Disubstituted Allenylic Silyl Ethers Through Iron-Catalyzed Regioselective C(sp2)─H Functionalization of Allenes

We report a synthesis of allenylic silyl ethers through iron-catalyzed functionalization of the C(sp2)─H bonds of monosubstituted alkylallenes. In the presence of a cyclopentadienyliron dicarbonyl based catalyst and triisopropylsilyl triflate as a silylation agent, a variety of aryl aldehydes were suitable coupling partners in this transformation, furnishing a collection of 1,1-disubstituted allenylic triisopropylsilyl ethers as products in moderate to excellent yields as a single regioisomer. Lithium bistriflimide was identified as a critical additive in this transformation. The optimized protocol was scalable, and the products were amenable to further transformation to give a number of unsaturated, polyfunctional derivatives.

SbCl3 Initiated Aerobic Phosphorylation of sp3 C-H Bond: A Facile Approach to α-Phosphorylated Tetrahydroisoquinolines

An aerobic phosphorylation of N-aryltetrahydroisoquinolines was realized by SbCl 3 initiated sp 3 C-H bond functionalization, providing a series of α-aminophosphonates in high yields. This work reveals that SbCl 3 /O 2 is an efficient and facile catalyst system to enable the aerobic C-H functionalization, and antimony containing reagents might be potentially applied to more general transformations.

Synthetic applications of hydride abstraction reactions by organic oxidants

Carbon-hydrogen bond functionalizations provide an attractive method for streamlining organic synthesis, and many strategies have been developed for conducting these transformations. Hydride-abstracting reactions have emerged as extremely effective methods for oxidative bond-forming processes due to their mild reaction conditions and high chemoselectivity. This review will predominantly focus on the mechanism, reaction development, natural product synthesis applications, approaches to catalysis, and use in enantioselective processes for hydride abstractions by quinone, oxoammonium ion, and carbocation oxidants. These are the most commonly employed hydride-abstracting agents, but recent efforts illustrate the potential for weaker ketone and triaryl borane oxidants, which will be covered at the end of the review.