Cationation of dimethylallyl alcohols by B(C6F5)3 as models of the (Re)initiation reaction in the bio‐inspired cationic polymerization of isoprene

The polymerization of isoprene initiated by dimethylallyl alcohols (DMAOH) in the presence of Lewis acids (LAs) as coinitiators has been selected as a potential model of the proposed cationic mechanisms involved in natural rubber (NR) biosynthesis. In view to investigate the activation/ionization mechanism of the allyl alcohol chain terminus (PIAllOH), which was shown to exist in NR, different isomers of DMAOH were used as simple models of polyisoprene chain‐end structures in the presence of tris(pentafluorophenyl)borane (BLA) as a LA. It is shown that cationation of 3,3‐DMAOH by BLA proceeds by direct OH abstraction. However, this process is strongly retarded in the presence of 2,6‐di‐tert‐butylpyridine (d^tBP), due to the formation of different BLA complexes, one with 3,3‐DMAOH, active for cationation, and a dormant one involving its ionized form 3,3‐DMAO^?. The monomer generated in situ by ionization/proton elimination steps subsequently adds on the primary allylic carbocation form, then resulting in the formation of oligoisoprenes, whereas the tertiary carbocation form of the allylic carbocation yields exclusively to proton elimination and isoprene formation, a possible mechanism of chain‐end termination. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Recent strategies in the synthesis of thiophene derivatives: highlights from the 2012–2020 literature

Molecular Diversity - Thiophene-based analogs have been fascinated by a growing number of scientists as a potential class of biologically active compounds. Furthermore, they play a vital role for...     

Enantioselective addition of diethylzinc to aryl aldehydes catalyzed by novel chiral imino alcohol ligands

The enantioselective alkylation of aryl aldehydes by diethylzinc in the presence of catalytic amounts of several novel chiral imino alcohol ligands, synthesized from the reaction of (R)-2-amino-1-butanol with aromatic aldehydes, was studied. The influence of temperature and ligand structure was investigated and enantioselectivity up to 81% was obtained.     

One-pot synthesis of 1,2,3-triazole linked dihydropyrimidinones via Huisgen 1,3-dipolar/Biginelli cycloaddition

The combination of the Biginelli reaction with click chemistry has been used for the one-pot synthesis of 1,2,3-triazole linked dihydropyrimidinones from azides, aromatic aldehydes containing a propargyl ether group, urea, and 1,3-dicarbonyl compounds using Cu(OAc)₂/sodium ascorbate as catalyst in acetic acid under mild reaction conditions.     

The method of upper and lower solutions and impulsive fractional differential inclusions

In this paper the concept of lower and upper solutions combined with the fixed point theorem of Bohnnenblust–Karlin is used to investigate the existence of solutions for a class of the initial value problem for impulsive differential inclusions involving the Caputo fractional derivative.     

Evaluation of antioxidant activities of the edible and medicinal Acacia albida organs related to phenolic compounds

This study compared phenolic contents and antioxidant activity in different organs of Acacia albida (leaves and bark) and focuses on identification of phenolic compounds of leaves by HPLC-DAD. The analysed organs exhibited differences in total polyphenol contents (100 and 59.5 mg GAE g^? 1 DW). Phenolic contents of leaves were two times higher than those in bark. Ethanolic extracts exhibited good antioxidant activities with IC₅₀ = 26 μg mL^? 1 for DPPH and EC₅₀ = 50 μg mL^? 1 for FRAP. Identification by HPLC-DAD revealed the presence of nine phenolic compounds known for their high antioxidant activity. The results suggested that this species can be used as source of natural antioxidants.