Lucia Veltri

Electrofluorochromism in π-conjugated ionic liquid crystals

Materials in which photoluminescence is modulated by redox processes are known as electrofluorochromic. Intrinsically switchable fluorophores, incorporating both redox and fluorescent moieties, could be ideal electrofluorochromic materials if they possess high fluorescence quantum yields in at least one of their redox states. Fluorescent liquid crystals with redox active centres could combine the above requirements with the advantage to work in bulk anisotropic phases. However, electrofluorochromic liquid crystals have not been reported yet because their synthesis is challenging due to aggregation-caused fluorescent quenching. Here we show the first examples of electrofluorochromic π-conjugated ionic liquid crystals based on thienoviologens. These ordered materials, combining ionic and electronic functions, are highly fluorescence in the bulk state (quantum yield>60%). Their direct electrochemical reduction leads to fast and reversible bulk electrofluorochromic response in both columnar and smectic phases allowing for fluorescence intensity modulation and colour tuning.

Recent Advances in the Synthesis of Indanes and Indenes

Indanes and indenes are among the most important carbocycles. Many indane and indene derivatives have shown important pharmacological activities, and the indane and indene nuclei are structural motifs present in several natural products of biological relevance. In spite of their importance, only a few reviews on their preparation methods have appeared so far in the literature, the most recent ones being published about ten years ago. The present Review is aimed at filling this gap, presenting some of the most important and innovative approaches to indanes and indenes that have been published in the course of the last ten years (coverage: from 2005 to May, 2015).

Stereoselective Synthesis of (E)‐3‐(Methoxycarbonyl)methylene‐1,3‐dihydroindol‐2‐ones by Palladium‐Catalyzed Oxidative Carbonylation of 2‐Ethynylanilines

A direct synthesis of (E)-3-(methoxycarbonyl)methylene-1,3-dihydroindol-2-ones 2 by palladium-catalyzed oxidative carbonylation of 2-ethynylanilines 1 is reported. Reactions were carried out in MeOH as the solvent at 50−70 °C in the presence of catalytic amounts of PdI2 in conjunction with KI under a 4:1 CO/air mixture (20 atm total pressure at 25 °C). When the reaction was applied to 2-alkynylanilines with internal triple bonds, the reaction course changed completely, with formation of carbamates 4.

Synthesis of 2-ynamides by direct palladium-catalyzed oxidative aminocarbonylation of alk-1-ynes

Abstract A novel synthesis of 2-ynamides (3) by palladium-catalyzed oxidative aminocarbonylation of alk-1-ynes (1) is reported. Reactions are catalyzed by PdI2/KI and are carried out at 100°C in dioxane as the solvent in the presence of dialkylamines (2) as nucleophiles (amine/alk-1-yne molar ratio=1/1) using a 4/1 CO/air mixture (20 atm total pressure at 25°C).

Synthesis of Benzothiophene Derivatives by Pd-Catalyzed or Radical-Promoted Heterocyclodehydration of 1-(2-Mercaptophenyl)-2-yn-1-ols

Novel and convenient approaches to benzothiophene derivatives 3 and 5 have been developed, based on heterocyclization reactions of 1-(2-mercaptophenyl)-2-yn-1-ols 2 or 4, respectively, readily available from alkynylation of 2-mercaptobenzaldehydes or 1-(2-mercaptophenyl) ketones 1. In particular, 1-(2-mercaptophenyl)-2-yn-1-ols 2, bearing a CH(2)R substituent on the triple bond (R = alkyl, aryl), were conveniently converted in fair to good yields (55-82%) into (E)-2-(1-alkenyl)benzothiophenes 3 when allowed to react in the presence of catalytic amounts (2 mol %) of PdI(2) in conjunction with KI (KI:PdI(2) molar ratio =10) at 80-100 °C in MeCN as the solvent, through a heterocyclodehydration process. On the other hand, 2-alkoxymethylbenzothiophenes 5 were selectively obtained in fair to excellent yields (49-98%) via a radical-promoted substitutive heterocyclodehydration process, by reacting 1-(2-mercaptophenyl)-2-yn-1-ols 4 (bearing an alkyl or aryl substituent on the triple bond) in alcoholic media at 80-100 °C in the presence of a radical initiator, such as AIBN.

A palladium iodide-catalyzed carbonylative approach to functionalized pyrrole derivatives.

A novel and convenient approach to functionalized pyrroles is presented, based on Pd-catalyzed oxidative heterocyclization-alkoxycarbonylation of readily available N-Boc-1-amino-3-yn-2-ols. Reactions were carried out in alcoholic solvents at 80-100 °C and under 20 atm (at 25 °C) of a 4:1 mixture of CO-air, in the presence of the PdI(2)-KI catalytic system (2-5 mol % of PdI(2), KI/PdI(2) molar ratio = 10). In the case of N-Boc-1-amino-3-yn-2-ols 3, bearing alkyl or aryl substituents, the carbonylation reaction led to a mixture of Boc-protected and N-unsubstituted pyrrole-3-carboxylic esters 4 and 5, respectively. This mixture could be conveniently and quantitatively converted into deprotected pyrrole-3-carboxylic esters 5 by a simple basic treatment. In the case of diastereomeric (3RS,4RS)- and (3RS,4SR)-N-Boc-3-amino-2-methyldec-5-yn-4-ol (syn-3f and anti-3f, respectively, whose relative configuration was determined by X-ray crystallographic analysis), no particular difference was observed in the reactivity of the two diastereomers between them and with respect to the diastereomeric mixture (3S,4S) + (3S,4R). Interestingly, N-Boc-2-alkynyl-1-amino-3-yn-2-ols 6, bearing an additional alkynyl substituent α to the hydroxyl group, spontaneously underwent N-deprotection under the reaction conditions and regioselective water addition to the alkynyl group at C-3 of the corresponding pyrrole-3-carboxylic ester derivative, thus directly affording highly functionalized pyrrole derivatives 7 in one step. In a similar manner, a novel functionalized dihydropyrrolizine derivative 9 was directly synthesized starting from (S)-7-(pyrrolidin-2-yl)trideca-5,8-diyn-7-ol 8.

Synthesis of Substituted Thiophenes by Palladium-Catalyzed Heterocyclodehydration of 1-Mercapto-3-yn-2-ols in Conventional and Nonconventional Solvents

A variety of readily available 1-mercapto-3-yn-2-ols 5 were conveniently converted into the corresponding thiophenes 6 in good to high yields in MeOH as the solvent at 50-100 °C in the presence of catalytic amounts (1-2%) of PdI(2) in conjunction with KI (KI:PdI(2) molar ratio = 10). The catalyst could be made recyclable employing an ionic liquid, such as BmimBF(4), as the solvent under suitable conditions.

Copper-catalyzed synthesis of substituted furans and pyrroles by heterocyclodehydration and tandem heterocyclodehydration-hydration of 3-yne-1,2-diols and 1-amino-3-yn-2-ol derivatives.

CuCl2-catalyzed heterocyclodehydration of readily available 3-yne-1,2-diols and 1-amino-3-yn-2-ol derivatives afforded substituted furans and pyrroles, respectively, in good to high yields (53-99%) under mild conditions (MeOH as the solvent, 80-100 °C, 1-24 h). In the case of 2,2-dialkynyl-1,2-diols, bearing an additional alkynyl substituent at C-2, a cascade process, corresponding to copper-catalyzed heterocyclodehydration followed by acid-catalyzed hydration of the triple bond, was realized when the reaction was carried out in the presence of both CuCl2 and TsOH, leading to 3-acylfurans in one step and high yields (75-84%). Under the same conditions, N-Boc-2-alkynyl-1-amino-3-yn-2-ols were converted into the corresponding N-unsubstituted 3-acylpyrroles in low to fair yields (19-59%). However, working in the presence of added water and a large excess of CO2 (40 atm), in addition to CuCl2 and TsOH, caused a significant improvement of the yields of 3-acylpyrroles (68-87%), thus making the method of general synthetic applicability.

A General and Expedient Synthesis of 5‐ and 6‐Membered Cyclic Carbonates by Palladium‐Catalyzed Oxidative Carbonylation of 1,2‐ and 1,3‐Diols

We present a general, practical, and efficient approach to 5- and 6-membered organic carbonates by palladium-catalyzed direct oxidative carbonylation of 1,2- and 1,3-diols, respectively. Reactions were carried out at 100 °C in N,N-dimethylacetamide as the solvent under 20 atm (at 25 °C; 1 atm=101.3 kPa) of a 4:1 v/v CO/air mixture in the presence of 0.5-2 mol % of PdI(2) and KI (KI/PdI(2) molar ratio=10). Excess dehydrating agent, such as trimethyl orthoacetate, was necessary in several cases to obtain appreciable results. The method could also be applied to the synthesis of a high-value-added glycerol carbonate from glycerol, a readily available raw material. When applied to α-D-glucose, a double carbonylation process took place, with direct formation of α-D-glucofuranose 1,2:5,6-dicarbonate.

Synthesis of furan-3-carboxylic and 4-methylene-4,5-dihydrofuran-3-carboxylic esters by direct palladium iodide catalyzed oxidative carbonylation of 3-yne-1,2-diol derivatives.

A variety of 3-yne-1,2-diol derivatives 1, bearing a primary or secondary alcoholic group at C-1, have been efficiently converted into high value added furan-3-carboxylic esters 2 in one step by PdI(2)/KI-catalyzed direct oxidative carbonylation, carried out in alcoholic media under relatively mild conditions (100 °C under 40 atm of a 4/1 mixture of CO and air). Carbonylated furans 2 were obtained in fair to excellent isolated yields (56-93%) through a sequential 5-endo-dig heterocyclization-alkoxycarbonylation-dehydration process, using only oxygen as the external oxidant. Under similar conditions, 2-methyl-3-yne-1,2-diols 3, bearing a tertiary alcoholic group, afforded 4-methylene-4,5-dihydrofuran-3-carboxylates 4 in satisfactory yields (58-70%).