2-Diphenylphosphinomethyl-3-methylpyrazine

The lateral metalation-electrophilic trapping reaction of alkyl-substituted pyrazines has always been challenging and poorly regioselective, with the corresponding derivatives often being isolated in moderate yield. In this contribution, we first report on the preparation of an unsymmetrically-substituted pyrazine, that is 2-diphenylphosphinomethyl-3-methylpyrazine, by subjecting to metalation with n-BuLi the commercially available 2,3-dimethylpyrazine, followed by interception of the putative lithiated benzyl-type intermediate with Ph2PCl. Such a functionalization has been successfully carried out in the absence of additional ligands, working either in THF at −78 °C or in a more environmentally friendly solvent like cyclopentyl methyl ether at 0 °C, with the desired phosphine derivative being isolated in 70–85% yield. The newly synthesized adduct has been fully characterized by means of multinuclear magnetic resonance spectroscopic techniques, and also by preparing a selenium derivative, which furnished single crystals that were suitable for X-ray analysis.

Arylruthenium(III) Porphyrin-Catalyzed C-H Oxidation and Epoxidation at Room Temperature and [RuV(Por)(O)(Ph)] Intermediate by Spectroscopic Analysis and Density Functional Theory Calculations

The development of highly active and selective metal catalysts for efficient oxidation of hydrocarbons and identification of the reactive intermediates in the oxidation catalysis are long-standing challenges. In the rapid hydrocarbon oxidation catalyzed by ruthenium(IV) and -(III) porphyrins, the putative Ru(V)-oxo intermediates remain elusive. Herein we report that arylruthenium(III) porphyrins are highly active catalysts for hydrocarbon oxidation. Using catalyst [Ru^III(TDCPP)(Ph)(OEt₂)] (H₂TDCPP = 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin), the oxidation of C-H bonds of various hydrocarbons with oxidant m-CPBA at room temperature gave alcohols/ketones in up to 99% yield within 1 h; use of [ ⁿBu₄N]IO₄ as a mild alternative oxidant avoided formation of lactone from cyclic ketone in C-H oxidation, and the catalytic epoxidation with up to 99% yield and high selectivity (no aldehydes as side product) was accomplished within 5 min. UV-vis, electrospray ionization-mass spectrometry, resonance Raman, electron paramagnetic resonance, and kinetic measurements and density functional theory calculations lend evidence for the formation of Ru(V)-oxo intermediate [Ru^V(TDCPP)(O)(Ph)].

Chemoselective and stereoselective lithium carbenoid mediated cyclopropanation of acyclic allylic alcohols

A new method for the chemo- and stereoselective conversion of acyclic allylic alcohols into the corresponding substituted cyclopropane derivatives has been developed using lithium carbenoids.

“The Great Beauty” of organolithium chemistry: a land still worth exploring

This Frontier highlights and analyses, from the authors’ perspective, some recent selected contributions from the organolithium field with an eye towards new challenging research directions.

Dynamic resolution of lithiated ortho-trifluoromethyl styrene oxide and the effect of chiral diamines on the barrier to enantiomerisation

The first dynamic thermodynamic resolution of a racemic oxiranyllithium is described with selectivities of up to 82 : 18 from a selection of three types of chiral ligands (seven ligands in total). Both (-)-sparteine and its (+)-surrogate were surprisingly found to increase the enantiomerisation barrier.

2-Lithiated-2-phenyloxetane: a new attractive synthon for the preparation of oxetane derivatives

A valuable and direct method to access 2-substituted-2-phenyloxetanes by electrophilic quenching of the corresponding 2-lithiated derivative has, for the first time, been described. 2-Lithiated-2-phenyloxetane was found to be configurationally unstable. Evidence is presented to show that electron-transfer processes are also operative in the coupling reactions with electrophiles.

Anatomy of long-lasting love affairs with lithium carbenoids: past and present status and future prospects

After a long adolescence, the chemistry of lithium carbenoids has currently been entering its maturity bringing a dowry of a more in-depth and less empirical knowledge of the structure and configurational stability of such double-faced intermediates; this, thanks in particular to the synergistic and harmonic cooperation between calculations and the most modern NMR techniques now at our disposal. Such knowledge has stimulated the development of fruitful stereoselective applications in the field of organic synthesis, providing in addition a rationale to observed selectivities. Such aspects together with the role played by aggregation and solvation on the structure-reactivity relationship are highlighted throughout this Minireview with selected examples extracted from recent literature.