The curing behaviour of the composition of a liquid-crystalline diepoxy monomer (LCEM) with the central triaromatic mesogenic group was studied using differential scanning calorimetry, conventional DSC and temperature-modulated TMDSC and nuclear magnetic resonance 1 H-NMR spectroscopy. The stoichiometric amount of primary aromatic diamine, 4,4 0-diaminodiphenylmethane (DDM), was used as a curing agent. TMDSC TOPEM Ò allowed the separation of the thermal effects related to reversible processes (e.g. phase transitions) from irreversible processes (cross-linking reaction) and determining that irreversible curing reaction occurs at the same time as reversible transition of the LCEM from crystal to the liquid-crystalline nematic phase. Additionally, 1 H-NMR analysis of the LCEM/DDM mixture preheated to a temperature from the temperature range of complex thermal changes was conducted. The obtained spectrum clearly showed the presence of partially cured products in the investigated samples and additionally proved that during the endothermic phase transition of the LCEM monomer an exothermic cross-linking reaction was occurring.
A new, convenient, and efficient method for the synthesis of homoallylic aromatic thioethers was developed. The present method consists of the formation of arylthionium intermediates from aromatic dithioacetals, which are trapped by a π-nucleophile. Screening of diverse aromatic substrates, selected Lewis acids, and allylstannane and allylsilane were evaluated. The method was found suitable for the preparation of homoallylic aryl thioethers bearing electron donating o-and p-groups only, as substrates with electron withdrawing groups were found unreactive to this system. Keywords Aromatic dithioacetals • Allylation • Lewis acid • Homoallyl sulfides Addition of π-nucleophiles to Lewis acids (LA)-activated carbonyl compounds or oxonium cations is one of the fundamental methods of construction of a new carbon-carbon bond (Yamamoto and Asao 1993; Masse and Panek 1995; Marshall 1996). As such, in a highly regioselective manner, in case of chiral substrates or catalysts with strong asymmetric induction, it is possible to obtain relevant alcohols or homoallylic ethers which are applicative building blocks in the synthesis of natural and biologically active products (Yus et al. 2013). Allyl metal reagents used in such process are allylborons, allylstannanes, allylsilanes, allyl halides, allyl acetates, allylindium (Yus et al. 2013; Shen et al. 2013; Kaib et al. 2016), or allyl transition metal complexes (e.g., Pd and Pt) that feature η 1-allyl or η 3-allyl bonding mode, respectively (Sone et al. 1995). Introduction of allyl function to the organic compounds gives opportunity for further double-bond transformations such as ozonolysis, epoxidation, dihydroxylation, cycloaddition hydroformylation, and olefin metathesis.
Synthesis of a new building block of symmetrically substituted pyrrole derivative, which is useful intermediate in the synthesis of known alkaloids and their marine analogues, is described. The substrate is anisaldehyde, which in six steps with the use of Knoevenagel condensation, hydrogenation of the aliphatic double bond and the key titanium(IV)-mediated oxidative dimerization of 2-azidocarboxylic ester allows to obtain the title derivative.
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