Performance of clay soil reinforced with fly ash and lignin fiber subjected to freeze-thaw cycles

This paper aims to present the results of an experimental investigation related to the unconsolidated undrained triaxial compression behavior of finegrained soil as a function of freeze-thaw cycles, and fly ash–lignin fiber volume fractions. All the measurements were carried out for three selected fly ash fractions (0, 4, and 8%), and five selected lignin fiber fractions (0, 0.25, 0.5, 0.75, and 1%). The specimens were exposed to from 0 to 15 freeze-thaw cycles before testing. It has been observed that for the studied soil, the compression strength of unreinforced soil decreased with an increment the number of freeze-thaw cycles. Moreover, the fly ash–lignin fiber–reinforced soil specimens showed greater effect on compression strength after the 15th freeze-thaw cycle. The greatest amount of strength reduction was obtained on the maximum blend ratios of the lignin fiber. Also, the reduction trend of cohesion was declined for the reinforced soil and the resilient modulus of all soil specimens reduced after the 15th freeze-thaw cycle

Palladium-Catalyzed Cross-Coupling of Ethyl Bromodifluoroacetate with Aryl Bromides or Triflates and Cross-Coupling of Ethyl Bromofluoroacetate with Aryl Iodides

A palladium-catalyzed Negishi cross-coupling reaction of ethyl bromodifluoroacetate with aryl bromides or aryl triflates to construct C(sp2)–CF2 bonds is described. The reaction was conducted under mild reaction conditions, and no preparation of organozinc reagents is required. This is the first report encompassing the conversion of aryl triflates into products containing C–CF2 bonds. In addition, the construction of C(sp2)–CHF bonds was achieved under mild conditions via a cross-coupling of aryl iodides with ethyl bromofluoroacetate

Construction of pyridines and indoles via azide-imine tandem reactions

The abstract should briefly state the problem or purpose of the research, indicate the theoretical or experimental plan used, summarize the principal findings, and point out the major conclusions. Abstract length is one paragraph

Recent Progress in Radical Decarboxylative Functionalizations Enabled by Transition-Metal (Ni, Cu, Fe, Co or Cr) Catalysis

Aliphatic carboxylic acids are abundant in natural and synthetic sources and are widely used as connection points in many chemical transformations. Radical decarboxylative functionalization promoted by transition-metal catalysis has achieved great success, enabling carboxylic acids to be easily transformed into a wide variety of products. Herein, we highlight the recent advances made on transition-metal (Ni, Cu, Fe, Co or Cr) catalyzed C-X (X = C, N, H, O, B, or Si) bond formation as well as syntheses of ketones, amino acids, alcohols, ethers and difluoromethyl derivatives via radical decarboxylation of carboxylic acids or their derivatives, including, among others, redox-active esters (RAEs), anhydrides, and diacyl peroxides. 1 Introduction 2 Ni-Catalyzed Decarboxylative Functionalizations 3 Cu-Catalyzed Decarboxylative Functionalizations 4 Fe-Catalyzed Decarboxylative Functionalizations 5 Co- and Cr-Catalyzed Decarboxylative Functionalizations 6 Conclusions

Recent Progress in Methylation of (Hetero)Arenes by Cross-Coupling or C-H Activation

Owing to the 'magic methyl effect' on a compound's physical and biological properties, methylation is a strategy frequently used by medicinal chemists in structure-activity relationship studies or in lead optimization. This article highlights the most recent reported methods for the direct methylation of (hetero)arenes, which mainly involve either C-H functionalization or cross-coupling of methylating reagents with (hetero)aryl halides. Methylation of C-H bonds of (hetero)-arenes, which is atom economical, has been explored by several research groups in recent years. Given the unmatchable availability of (hetero)aryl halides, we believe that Ni-catalyzed methylation using iodomethane or deuterated iodomethane as the methyl source is one of the most convenient methods

Transition-Metal-Free Synthesis of N-Hydroxy Oxindoles by an Aza- Nazarov-Type Reaction Involving Azaoxyallyl Cations

Abstract: A novel transition-metal-free method to construct N-hydroxy oxindoles by an aza-Nazarov-type reaction involving azaoxyallyl cation intermediates is described. A variety of functional groups were tolerated under the weak basic reaction conditions and at room temperature. A one-pot process was also developed to make the reaction even more practical. This method provides alternative access to oxindoles and their biologically active derivative

Nickel-Catalyzed Cyanation of Aryl Halides and Hydrocyanation of Alkynes via C-CN Bond Cleavage and Cyano Transfer

We report the nickel-catalyzed cyanation and hydrocynation methods to prepare aryl nitriles and vinyl nitriles from aryl halides and alkynes, respectively. Using cheap and nontoxic 4-cyanopyridine N-oxide as the cyano shuttle, the methods provide an efficient approach to prepare aryl cyanides and vinyl nitriles under mild and operationally simple reaction conditions with a broad range of functional group tolerance. In hydrocyanation of alkynes, the method demonstrated good regioselectivity, producing predominantly E or Z-alkenyl nitriles in a controlled manner and exclusively Markovnikov vinyl nitriles when internal diaryl alkynes and terminal alkynes were applied as the substrates, respectively. The preliminary mechanistic investigation indicated that C-CN bond cleavage process is promoted by oxidative addition to nickel(I) complex in the cyanation of aryl halides, and the further studies via a series of deuterium exchange experiments indicated that water serves as the hydrogen source for the hydrocyanation of alkynes

Nickel-catalyzed enantioselective annulation/alkynylation and Sonogashira reaction to form C(sp3)-C(sp) and C(sp2)-C(sp) bonds, respectively

While traditional Sonogashira reaction requires a palladium catalyst and a copper co-catalyst, some recent variants were reported being promoted by single transition metals. Here we report a single nickel-catalyzed tandem Heck-Sonogashira annulation/alkynylation for enantioselectively constructing C(sp3)-C(sp) bond. In addition, using the same catalytic system, Sonogashira C(sp2)-C(sp) cross-coupling has also been achieved. The alkynylations described in this report are important for the three reasons: 1. C(sp3)/(sp2)-C(sp) bonds exist in many bioactive natural products and drug molecules as well as their key synthetic intermediates; 2. There was no precedent for single nickel-catalyzed Sonogashira reaction owing to the difficulties caused by strong coordination of nickel to the triple bond to inactivate the catalyst; 3. Isolation and characterization of single-crystal structure of a resting state intermediate, di-phosphine chelated σ-alkyl-NiII-I complex, which provided crucial evidence to support the mechanistic postulation and guided DFT calculations

Total Synthesis of (±)-Minfiensine via a Formal [3+2] Cycloaddition

(±)-Minfiensine (<b>1</b>) was synthesized in 10 steps in 26% overall yield with the 1,2,3,4-tetrahydro-9a,4a-iminoethanocarbazole core constructed through a [3+2] cycloaddition reaction between indole and an azaoxyallylic cation