Facile reduction of carboxylic acids to alcohols by zinc borohydride

Unravelling the underlying mechanism of the reduction of aldehydes/ketones with metal borohydride in an aprotic solvent

The reduction mechanism of aldehyde/ketones with M(BH4)n is not fully understood, even though the hydroboration mechanism of weak Lewis base borane complexes is known to involve a four-membered ring transition state. Herein, the reduction mechanism of M(BH4)n in aprotic solvents has been elucidated for a six-membered ring, in which hydride transfer to the C atom from the B atom, formation of an L·BH3 adduct, and disproportionation of (BH3(OR)-) borane are involved. The metal cations and solvents participate in and significantly influence the reaction procedure. We believe that this mechanistic study would provide a further reference for the application of M(BH4)n in organic reactions.

Reduction of liquid terminated-carboxyl fluoroelastomers using NaBH4/SmCl3

Using a simple one-pot method, the reduction of liquid terminated-carboxyl fluoroelastomers (LTCFs) by sodium borohydride and samarium chloride (NaBH₄/SmCl₃) was successfully realized and liquid terminated-hydroxyl fluoroelastomers (LTHFs) were obtained. The structure and functional group content of LTCFs and LTHFs were analyzed by FTIR, ¹H-NMR, ¹⁹F-NMR and chemical titration. The results showed that –C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C– and carboxyl groups of LTCFs were reduced efficiently, the reduction rate reached 92% under optimum reaction conditions. Compared with other frequently-used metal chlorides, SmCl₃ with a high coordination number could increase the reduction activity of NaBH₄ more effectively and the reduction mechanism was explored.

A facile method using NaBH₄/SmCl₃ allows for reduction of liquid terminated-carboxyl fluoroelastomers (LTCFs) in excellent yields and provides an attractive potential scheme for the reduction of other carboxyl organic compounds.

Mild and Convenient Method for Reduction of Aliphatic and Aromatic Carboxylic Acids and Anhydrides with (Pyridine)(Tetrahydroborato)Zinc Complex as a New Stable Ligand-Metal Tetrahydroborate Agent

Structurally different aliphatic and aromatic carboxylic acids and anhydrides are efficiently reduced to their corresponding alcohols with a new modified zinc tetrahydroborate agent, (pyridine)(tetrahydroborato)zinc complex, [(Py)Zn(BH4)2], in refluxing THF.

Facile reduction of carboxylic acids to primary alcohols under catalyst-free and solvent-free conditions

We report the development of a facile protocol for the deoxygenative hydroboration of aliphatic and aryl carboxylic acids to afford corresponding primary alcohols under solvent-free and catalyst-free conditions. The reaction proceeds under ambient temperature exhibits good tolerance towards various functional groups and generates quantitative yields. The plausible mechanism involves the formation of Lewis acid-base adducts as well as the liberation of hydrogen gas.

General Synthesis of the Nitropyrrolin Family of Natural Products via Regioselective CO2-Mediated Alkyne Hydration

The total synthesis of the 2-nitropyrrole natural products nitropyrrolins A and B and the formal synthesis of nitropyrrolin D are reported. The key 2-nitro-4-alkylpyrrole core was efficiently assembled by Sonogashira cross-coupling, with complete control of regioselectivity. An unusual carboxylative cyclization, sulfonylcarbamate formation, and base-promoted cleavage sequence enabled access to the key hydroxy ketone without affecting the protected 2-nitropyrrole unit. The total synthesis provides a general approach for preparation of the bioactive nitropyrrolin family of natural products.

Phenylsilane as an effective desulfinylation reagent

The reduction using phenylsilane in a KOH-catalyzed system was applied successfully to the conversion of sulfinyl-substituted cyclopropylcarboxylates into the corresponding alcohols. The presence of sulfinyl substituents in the α-position to the carboxylate group caused a desulfinylation product formation with full regio- and stereoselectivity, instead of a carbonyl group reduction. Investigations performed on different α-sulfinylcarbonyl compounds revealed that phenylsilane treatment constitutes a regiospecific method for the desulfinylation of a-sulfinylesters; for corresponding ketones the reaction course depends on the character of the carbonyl group.

Total synthesis of laidlomycin

The synthesis of laidlomycin is described. With an established stereocontrolled synthetic route to the aldehyde 5, the known β-keto phosphonate 4 was coupled with 5 and the resulting enone was subjected to a sequential hydrogenolysis/hydrogenation and equilibration process to effect the correct spiroketalization for the natural product. The stereogenic carbons were elaborated by desymmetrization for C12, allylation for C13, vanadyl-induced epoxidation for C16, Zn(BH4)2 reduction for C17, a chiral building block for C18 and C24, Shi epoxidation for C20 and C21, Myers' alkylation for C22, and thermodynamic control for C25.

A facile synthesis of Te nanoparticles with binary size distribution by green chemistry

Our work reports a facile route to colloidal Te nanocrystals with binary uniform size distributions at room temperature. The binary-sized Te nanocrystals were well separated into two size regimes and assembled into films by electrophoretic deposition. The research provides a new platform for nanomaterials to be efficiently synthesized and manipulated.

Synthesis of C-glycosyl compounds of N-acetylneuraminic acid from D-gluconolactone

A general strategy towards the synthesis of C-glycosyl compounds of N-acetylneuraminic acid (Neu5Ac) has been developed and successfully applied to the synthesis of C-methyl and C-phenyl derivatives. The key strategic elements are (i) chain extension of a D-gluconolactone derivative as C(6)-precursor with an allyl Grignard reagent as C(3)-precursor having in 2 position the C-linked aglycon moiety, (ii) stereoselective C-4/C-5 erythro-diol formation, (iii) 6-exo-trig selective heterocyclization, and (iv) installment of the 5-acetylamino and C-1 carboxylate functionalities. The efficiency and potential versatility of this approach was exemplified in the synthesis of C-methyl derivative 1 as target molecule.

De novo synthesis of a methylene-bridged Neu5Ac-alpha-(2,3)-gal C-disaccharide

A general strategy toward the synthesis of C-ketosides of N-acetylneuraminic acid (Neu5Ac) has been developed and successfully applied to the synthesis of methylene-bridged Neu5Ac-alpha-(2,3)-Gal C-disaccharide 2. The key strategic element of this novel approach is a stereoselective, 6-exo-trig selective, electrophilic cyclization of the appropriate open chain precursor 4 by means of phenylselenyl triflate. The open chain precursor was formed by the addition of lithiated iodide 18 accessible from D-galactose to open chain aldehyde 5a obtained from D-glucono-delta-lactone by chain elongation. Subsequent C1-incorporation using Tebbe-reagent, formation of a cyclic carbonate, and deprotection of the two isopropylidene ketals afforded tetrol 4 which, upon treatment with phenylselenyl triflate, was stereoselectively cyclized in a 6-exo-trig selective manner. A selena-Pummerer rearrangement, oxidation, and esterification readily led to methyl ester 37 which, after deacetylation, could be regioselectively tetrabenzoylated with benzoyl cyanide. Triflate activation of the axial hydroxyl group in 40 and nucleophilic displacement by azide ion with inversion of configuration afforded azide 41, which was reduced with hydrogen and Pearlman's catalyst. Concomitant removal of the benzyl ethers and subsequent saponification of all ester moieties successfully completed the de novo synthesis of the desired methylene bridged Neu5Ac-alpha-(2,3)-Gal C-disaccharide 2.