(Z)-Selective Takai olefination of salicylaldehydes

Chromium-catalyzed olefination of arylaldehydes with haloforms assisted by 2,3,5,6-tetramethyl-N,N'-bis(trimethylsilyl)-1,4-dihydropyrazine

Chromium-catalyzed olefination of arylaldehydes with haloforms was achieved using 2,3,5,6-tetramethyl-N,N'-bis(trimethylsilyl)-1,4-dihydropyrazine (1a) as an organic reducing agent, giving β-halostyrene derivatives in a trans-selective manner. The reaction required no metal powders, such as zinc and manganese, as reductants, thereby minimizing metal-based reaction waste.

Toward the Rational Design of Universal Dual Polarity Matrix for MALDI Mass Spectrometry

A series of novel anthranilic acid derivatives I-IV, of which COOH-NH₂ (I) and COOH-NHMe (IV) are endowed with acid and base bifunctionality, were designed and synthesized for matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry applications in dual polarity molecular imaging of biological samples, particularly for lipids. The heat of protonation, deprotonation, and proton transfer reaction as well as the capability of analyzing biomolecules in both positive and negative ion modes for I-IV were systematically investigated under standard 355 nm laser excitation. The results indicate correlation between dual polarity and acid-base property. Further, COOH-NHMe (IV) showed a unique performance and was successfully applied as the matrix for MALDI-TOF mass spectrometry imaging (MSI) for studying the mouse brain. Our results demonstrate the superiority of COOH-NHMe (IV) in detecting more lipid and protein species compared to commercially available matrices. Moreover, MALDI-TOF MSI results were obtained for lipid distributions, making COOH-NHMe (IV) a potential next generation universal matrix.

Unveiling the Takai Olefination Reagent via Tris( tert-butoxy)siloxy Variants

The elusive Takai olefination reagent, namely, the iodo-methylidene Cr(III) complex [Cr₂Cl₄(CHI)(thf)₄], has been isolated by careful handling of the reaction between CrCl₂ and CHI₃ in THF at -35 °C. Alternatively, treatment of [Cr(OSi(O tBu)₃)₂] with CHI₃ gave the mixed-valent dihalido-methanide complex [Cr^II/III₂I₂(OSi(O tBu)₃)₂(CHI₂)], featuring a Cr(III)-CHI₂ moiety. In the presence of TMEDA nucleophilic attack at CHI₂ occurred generating the zwitterionic species [Cr^III(OSi(O tBu)₃)₂(tmeda-CHI)][I]. Complexes [Cr₂Cl₄(CHI)(thf)₄] and [Cr^II/III₂I₂(OSi(O tBu)₃)₂(CHI₂)] were screened for their ability to induce monohalido olefination of benzaldehyde. Remarkably, both complexes promote olefination, with [Cr₂Cl₄(CHI)(thf)₄] accomplishing the same E selectivity as Takai 's original mixture. Complex [Cr^II/III₂I₂(OSi(O tBu)₃)₂(CHI₂)], however, appeared to give preferentially Z isomer, corroborating the monoiodo-methylidene species Cr(III)-CHI-Cr(III) as the active olefination component of the original in situ generated Takai reagent mixture.