Given the growing demand for green and sustainable chemical processes, the catalytic reductive alkylation of amines with main-group catalysts of low toxicity and molecular hydrogen as the reductant would be an ideal method to functionalize amines. However, such a process remains challenging. Herein, a novel reductive alkylation system using H is presented, which proceeds via a tandem reaction that involves the B(2,6-ClCH)( p-HCF)-catalyzed formation of an imine and the subsequent hydrogenation of this imine catalyzed by a frustrated Lewis pair (FLP). This reductive alkylation reaction generates HO as the sole byproduct and directly functionalizes amines that bear a remarkably wide range of substituents including carboxyl, hydroxyl, additional amino, primary amide, and primary sulfonamide groups. The synthesis of isoindolinones and aminophthalic anhydrides has also been achieved by a one-pot process that consists of a combination of the present reductive alkylation with an intramolecular amidation and intramolecular dehydration reactions, respectively. The reaction showed a zeroth-order and a first-order dependence on the concentration of an imine intermediate and B(2,6-ClCH)( p-HCF), respectively. In addition, the reaction progress was significantly affected by the concentration of H. These results suggest a possible mechanism in which the heterolysis of H is facilitated by the FLP comprising THF and B(2,6-ClCH)( p-HCF).
A solvent-controlled rhodium-catalyzed C6-selective alkenylation and alkylation of 2-pyridones with acrylates via a pyridine-directed CÀ H cleavage was developed. Using DMF as solvent, the CÀ H alkenylation with acrylates selectively occurs to deliver the corresponding C6-alkenylated 2-pyridones in good yields. On the other hand, the C6-alkylated products are predominantly formed in a more polar and protic solvent, HFIP. Thus, a single set of starting substrates can be divergently transformed to C6-functionalized 2-pyridones, which are of potent interest in medicinal and pharmaceutical chemistry.[a] S.
The first catalytic enantioselective total synthesis of (-)-podophyllotoxin is accomplished by a challenging organocatalytic cross-aldol Heck cyclization and distal stereocontrolled transfer hydrogenation in five steps from three aldehydes. Reversal of selectivity in hydrogenation led to the syntheses of other stereoisomers from the common precursor.
Direct synthesis of carboxylic-phosphinic mixed anhydrides has been achieved by treating carbon dioxide with N-phosphine oxide-substituted imidazolylidenes (PoxIms) that contain both nucleophilic carbene and electrophilic phosphorus moieties.T his novel mixed anhydride was efficiently derivatized into an ester,a na mide,a nd an unsymmetrical ketone via transformation into its corresponding imidazolium salt followed by ad ual substitution reaction. The presented work used well-designed multifunctional carbene reagents to establish anovel utility for carbon dioxide in organic synthesis.
Conjugated block copolymers consisting of poly(3hexyl thiophene) (P3HT) and a thermoresponsive polymer poly(N-isopropyl acrylamide) (PNIPAM) with varying composition have been synthesized by facile click reaction between alkyne terminated P3HT and azide terminated PNIPAM. The composition-dependent solubility, thermoresponsive property in water, phase behavior, electrochemical, optical, and electronic properties of the block copolymers were systematically investigated. The block copolymers with higher volume fraction of PNIPAM form thermoresponsive spherical micelles with P3HT-rich crystalline cores and PNIPAM coronas. Both X-ray and atomic force microscopic studies indicated that the blocks copolymers showed well-defined microphase separated nanostructures and the structure depended on the composition of the blocks. The electrochemical study of the block copolymers clearly demonstrated that the extent of charge transport through the block copolymer thin film was similar to P3HT homopolymer without any significant change in the band gap. The block copolymers showed improved or similar charge carrier mobility compared with the pure P3HT depending on the composition of the block copolymer. These P3HT-b-PNIPAM copolymers were interesting for fabrication of optoelectronic devices capable of thermal and moisture sensing as well as for studying the thermoresponsive colloidal structures of semiconductor amphiphilic systems.
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