Synthesis of 5-Mercaptoalkylthiopyrazolyl-and 3-Mercaptoalkylthioisoxazolyl)-1,2,4-triazoles by Ring Chain Transformation

Cyclic α-oxo-α-(1,2,4-triazolyl)ketene S,S-acetals 1a-e react with hydrazine affording the substituted pyrazolyl-1,2,4-triazoles 3a-e. With hydroxylamine hydrochloride under basic conditions the substituted isoxazolyl-1,2,4-triazoles 5a-c are obtained.     

An Efficient One-Pot Synthesis of Nitriles from Carboxylic Acids Without Solvent Under Microwave Irradiation

Nitriles were prepared from alkyl and aryl carboxylic acids in dry media conditions, under microwave irradiation. Heating of the carboxylic acid, urea and amidosulfonic acid adsorbed on alumina support in a microwave oven affords nitriles in 20–93% yields.     

SiO2-NHC-CuI–Catalyzed N-Arylation of Imidazoles with Arylboronic Acids Under Base-Free Reaction Conditions

N-Arylation of imidazoles with arylboronic acids was efficiently carried out in the presence of a catalytic amount of SiO₂-NHC-Cu^I in methanol at room temperature under base-free reaction conditions. The reactions of a variety of arylboronic acids with imidazoles generated the corresponding products N-arylimidazoles in good to excellent yields. In addition, SiO₂-NHC-Cu^I could be recovered and recycled for six consecutive trials without significant loss of its reactivity.     

Expeditious Approach to Coumarins via Pechmann Reaction Catalyzed by Molecular Iodine or AgOTf

An efficient and facile route for the synthesis of coumarins via the Pechmann reaction catalyzed by molecular iodine or AgOTf was described.     

Efficient Green Procedure for the Synthesis of Coumarin Derivatives by a One‐Pot,Three‐Component Reaction under Solvent‐Free Conditions

A simple, efficient, and general method has been developed for the synthesis of coumarin derivatives through a one‐pot reaction of aromatic aldehydes, 2,2‐dimethyl‐1,3‐dioxane‐4,6‐dione and 5,5‐dimethyl‐1,3‐cyclohexanedione, in the presence of TEBA under solvent‐free conditions using grinding methods. The mild reaction conditions, simple protocol, high yields, and cleaner reaction make this protocol practical and economically attractive.     

Synthesis of 3-Trifluoromethyl-Substituted Benzo[f]chromene Derivatives in a One-Pot Reaction

In the presence of 1,8-diazabicycolo[5.4.0]undec-7-ene (DBU) and concentrated H₂SO₄, 2-naphthol reacted smoothly with α,β-unsaturated trifluoromethyl ketones in CH₂Cl₂ at room temperature, affording the 3-trifluoromethyl-substituted benzo[f]chromene derivatives in good to excellent yields in a one-pot reaction.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource: Full experimental and spectral details].     

Practical synthesis of C1–8 fragment of autolytimycin via a chelation-controlled diastereoselective addition of diisopropenylzinc to α-methoxy aldehyde

The C1–8 fragment of autolytimycin was synthesized via a reliable 10-step route capable of delivering 41% overall yield at multi-gram scale. As a key step, a chelation-controlled isopropenylation of α-oxygenated aldehydes was established with a reagent combination of diisopropenylzinc, magnesium halide, and a dichloromethane/toluene mixed solvent. Cram-chelate isopropenylation products dominated for aldehydes with a small α-substituents, such as –OMe and –OBn groups, while the Felkin product could be obtained with a bulky –OTBS group.     

Prins Cyclization of Styrenes or Acetophenone Catalyzed by DBSA in Water

Dodecylbenzenesulfonic acid (DBSA) was proved to be an efficient catalyst for Prins cyclization of styrenes and formaldehyde or acetaldehyde in water. A tandem dehydration/Prins cyclization reaction using a tertiary alcohol and formaldehyde as substrates proceeded very well by using DBSA as catalyst. Acetophenone, which is less reactive compared with styrene, can also react with formaldehyde when catalyzed by DBSA in water to afford 1,3-dioxan-5-ylphenylmethanone in good yield.     

Microstructural evolution during oxidative ablation in air for polyacrylonitrile based carbon fibers with different graphite degrees

Polyacrylonitrile‐based carbon fibers with different graphite degrees were oxidative ablated at 500 and 600 °C in air. By Thermal gravimetric (TG), Raman spectroscopy, X‐ray diffraction, and SEM, the mass loss, microstructure, and surface morphology of carbon fibers were investigated. The mass loss of carbon fiber increases linearly with increasing oxidative ablated time under 500 and 600 °C. The carbon fiber with higher graphite degree shows higher oxidative resistance, and the surface roughness increases gradually because of chemical ablation during the whole oxidation. A gloss morphology appears on the surface primarily because of physical denudation for carbon fibers with lower graphite degree and then burn off according to carbon and oxygen reaction. The crystallite size (La) decreases significantly, while interlayer spacing(d₀₀₂) remains nearly unchanged. SEM observation suggests the two kinds of ablation mechanisms for carbon fibers with different graphite degrees indicating that CC band in sp³ hybridization prefers to be attacked by oxygen molecule more than that in sp² hybridization during oxidation ablation in air. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis of poly(l-lactic acid) with improved thermal stability by sulfonic acid-catalyzed melt/solid polycondensation

Melt/solid polycondensation (MP/SSP) is deemed as an alternative synthetic route besides ring-opening polymerization (ROP) in synthesizing poly(l-lactic acid) (PLLA). However, it is found that PLLA synthesized by MP/SSP has much poorer thermal stability than that by ROP due to more residual Sn(II) metallic catalyst in the former, but sulfonic acids does not show any detrimental effect on the thermal stability of PLLA. To synthesizing PLLA with good thermal stability by MP/SSP, a variety of commercially available sulfonic acids were screened as catalysts in MP/SSP of PLLA. Among these nonmetallic catalysts, it was found that 1,3-propanedisulfonic acid (PSA) and 1,5-naphthalene disulfonic acid (NSA) exhibited satisfactory catalytic reactivity and PLLAs with excellent thermal stability, high molecular weight, little coloration and good optical purity were successfully synthesized by MP/SSP. The decomposition temperature was increased by 80–100 °C in comparison to SnCl₂-catalyzed PLLA, and the thermal stability is comparable to commercial PLLA produced by ROP.