A new
class of biobased plasticizers is herein proposed as a replacement
of the currently used additives. The molecules were synthesized by
a selective protecting-group-free route, which was developed in order
to produce valuable asymmetrical ketal–diester derivatives
from the renewable levulinic acid, overcoming the typical drawbacks
of these types of reactions. Five molecules with different side chains
were successfully obtained and fully characterized by means of NMR
and FT-IR spectroscopies. These ketal–diester additives were
then tested in poly(vinyl chloride) (PVC) as the model polymer. Their
compatibility and plasticizing effect were evaluated by scanning electron
microscopy (SEM), differential scanning calorimetry (DSC), dynamic-mechanical
thermal analysis (DMTA), and thermogravimetric analysis (TGA). The
emerged trend showed a clear correlation between the structural features
of the ketal–ester and the thermal and mechanical properties
of the material. In particular, the best results in terms of glass
transition temperature reduction were achieved when the isobutyl-
and benzyl-terminated additives were used. Leaching tests in both
hydrophilic and hydrophobic environments were also performed. No significant
aqueous leaching was found; despite the aggressive treatment in hexane,
the extraction for all additives was remarkably low. Importantly,
when compared to commercial plasticizers such as di-2-ethylhexyl phthalate
(DEHP), 1,2-cyclohexane dicarboxylic acid diisononyl ester (Hexamoll
DINCH), acetyl tributyl citrate (ATBC), and diethylhexyl adipate (DEHA),
the proposed ketal–diester additives performed comparably and,
in some cases, even better. In particular, it was observed that the
plasticizing effect already starts at lower concentrations, permitting
one to use significantly less additive to obtain a similar effect
to the one achieved with the nowadays available plasticizers.
The
catalytic enantioselective dearomatization of pyridines with
nucleophiles represents a direct and convenient access to highly valuable
dihydropyridines. Available methods, mostly based on N-acylpyridinium salts, give addition to the C-2/C-6 of the pyridine
nucleus, rendering 1,2-/1,6-dihydropyridines. Herein, we present an
alternative approach to this type of dearomatization reaction, employing
activated N-benzylpyridinium salts in combination
with a bifunctional organic catalyst. Optically active 1,4-dihydropyridines
resulting from the addition of the nucleophile (indole) to the C-4
of the pyridine nucleus are obtained as major products, rendering
this method for nucleophilic dearomatization of pyridines complementary
to previous approaches.
PHB has been engineered by incorporating different levulinic acid-based bioplasticizers, which enhance flexibility and thermal processability of the neat biopolymer, while retaining excellent biocompatibility and biodegradability.
Catalytic addition of chiral enamines to azinium salts is a powerful tool for the synthesis of enantioenriched heterocycles. An unprecedented asymmetric dearomative addition of aldehydes to activated N-alkylpyridinium salts is presented. The process exhibits complete C-4 regioselectivity along with high levels of diastereo- and enantiocontrol, achieving a high-yielding synthesis of a broad range of optically active 1,4-dihydropyridines. Moreover, the presented methodology enables the synthesis of functionalized octahydropyrrolo[2,3-c]pyridines, the core structure of anticancer peptidomimetics.
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