Search

A chiral sodium glycerophosphate is successfully exploited as a catalyst in the Michael addition of methyl malonate to a number of chalcones. The reactions supplied the target adducts in satisfactory yields and good enantiomeric excesses. A tentative computational study is presented, aiming to understand the reaction mechanism.

A chiral glycerol derivative, namely 3-amino-1,2-propanediol, was employed for as the hydrogen bond donor (HBD) in the design of a new deep eutectic solvent (DES) with choline chloride acting as the hydrogen bond acceptor (HBA). The novel mixture was characterized and unambiguously classified as a DES. Furthermore, its synthetic usefulness was demonstrated in the room-temperature n -butyllithium-addition under air to carbonyl compounds and benzyl chloride. In some cases, pure products (100% conversion) were obtained by a simple extractive work-up in up to 72% isolated yield, thus suggesting the potential practical usefulness of this procedure as a green alternative to the classical Schenk procedure in volatile organic solvents for the synthesis of tertiary alcohols. The chirality of the HBD, bearing an interesting basic primary amino group, is an intriguing feature currently under investigation for further exploitation.

A deep eutectic solvent (DES) based on glycerol and KF is successfully exploited as a solvent medium in Ullmann homocoupling of arenediazonium salts. The reactions were carried out in mild conditions and target products were obtained in fairly good yields. A computational study is presented aiming to understand the reaction mechanism and Raman spectroscopy is employed as an experimental tool to support it., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Deep Eutectic Solvent (DES)-like mixtures, based on glycerol and different halide organic and inorganic salts, are successfully exploited as new media in copper-free halodediazoniation of arenediazonium salts. The reactions are carried out in absence of metal-based catalysts, at room temperature and in a short time. Pure target products are obtained without the need for chromatographic separation. The solvents are fully characterized, and a computational study is presented aiming to understand the reaction mechanism.

A chiral heterogeneous catalyst derivative of (-)-4,5-dimethyl-3,6-bis(1-naphthyl)-1,2-benzenedisulfonimide is proven here to be efficient in a three-component asymmetric Passerini protocol, carried out in a deep eutectic solvent. Reaction conditions are mild and green, while enantioselectivity is excellent. The catalyst was easily recovered and reused with no decrease in its catalytic activity., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Can green chemistry be the right reading key to let organocatalyst design take a step forward towards sustainable catalysis? What if the intriguing chemistry promoted by more engineered organocatalysts was carried on by using renewable and naturally occurring molecular scaffolds, or at least synthetic catalysts more respectful towards the principles of green chemistry? Within the frame of these questions, this Review will tackle the most commonly occurring organic chiral catalysts from the perspective of their synthesis rather than their employment in chemical methodologies or processes. A classification of the catalyst scaffolds based on their E factor will be provided, and the global E factor (E G factor) will be proposed as a new green chemistry metric to consider, also, the synthetic route to the catalyst within a given organocatalytic process., (© 2021 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

The generation of an iminium from amines is a way to functionalize the α carbon by coupling reactions. The reaction mechanism of the conversion of tertiary amines to iminium with CuCl 2 (H 2 O) 2 as catalyst in aerobic conditions has been computationally and experimentally studied in this work. This process is initiated by the oxidation of the amine to a radical cation dichlorocuprate through the reduction of Cu II to Cu I . Then, the iminium dichlorocuprate is generated from the radical-ion through a hydrogen-transfer. The H atom can be accepted by molecular oxygen or by a second molecule of catalyst (in anaerobic conditions). Therefore, O 2 also assumes the important role of acceptor along with that of regenerator of the catalyst. The experimental study confirmed the computational study and lead to the synthesis of four new molecules from the cross-coupling of N, N-diethyl- and N, N-diisoproylaniline with nitromethane and dimethylmalonate.

Diazonium salts, and precisely arenediazonium o-benzenedisulfonimides, have been used for the first time as efficient electrophilic partners in gold catalyzed Heck-coupling reactions. The synthetic protocol was general, easy and gave the target products in satisfactory yields. Mechanistic insights revealed the fundamental roles of the o-benzenedisulfonimide anion as an electron transfer agent thath promotes a radical pathway that does not require the presence of photocatalysts or external oxidants.

Arene and heteroarenediazonium o-benzenedisulfonimides can be used as efficient reagents in Sandmeyer cyanation. This work reports such reactions carried out by us under very mild conditions using tetrabutyl ammonium cyanide as a safe cyanide source and, interestingly, without the need for a Cu catalyst. The reactions have given rise to aryl nitriles in good yields (25 examples, average yield 75%). A good amount of o-benzenedisulfonimide was recovered from each reaction and then reused to prepare other salts. Mechanistic insights have allowed us to highlight the fundamental role of the o-benzenedisulfonimide anion as an electron transfer agent.

A representative number of bench-stable nonsymmetric diarylcarbenium tetrafluoroborates have been isolated via the direct coupling of aryl (or heteroaryl) aldehydes and N-heteroarenes and fully characterized. They have proven to be highly stable in the presence of both EDG and EWG substituents. An (E)-iminium vinylogous substructure has been shown as the common cation scaffold by X-ray analysis and by NOE determination.

Two chiral derivatives of 1,2-benzenedisulfonimide, namely 4-methyl-3,6-bis(o-tolyl)-1,2-benzenedisulfonimide and 4,5-dimethyl-3,6-bis(o-tolyl)-1,2-benzenedisulfonimide, have been easily synthesized in good overall yields (respectively 34% and 41%) by means of an eleven-step synthetic protocol from commercially available 2-methyl-6-nitroaniline or 2,3-dimethyl-6-nitroaniline. 4,5-Dimethyl-3,6-bis(1-naphthyl)-1,2-benzenedisulfonimide was also synthesized, but the overall yield from 2,3-dimethyl-6-nitroaniline was lower (9%). The atropisomers of these compounds have been resolved and (-)atropisomers have been demonstrated to be efficient chiral catalysts in the Strecker reaction.

o-Benzenedisulfonimide (OBS) has efficiently catalysed the one-pot three-component reaction of ketones and aromatic amines with trimethylsilyl cyanide (TMSCN) giving the corresponding α-amino nitriles in excellent yields (23 examples; average yield 85%). Reaction conditions were very simple, green and efficient. Theoretical calculations have allowed us to explain the mechanism of this reaction which has been found to take place in two phases; the first consists of the nucleophilic addition of the aniline to the ketone and the subsequent dehydration to an imine; the second one consists of the formal addition of cyanide anion to the protonated imine. OBS acts in all steps of this mechanism. Without an acid catalyst, the reaction mechanism is more simple but barriers are sensibly higher. A chiral derivative of OBS was also used and gave fairly good results.

An initial study has been accomplished into the synthetic feasibility of the preparation of diarylcarbenium salt via the direct coupling of aryl (or heteroaryl) aldehydes and arenes (or heteroaryl analogues) in the presence of a strong organic Brønsted acid. A number of stabilized aryl or heteroaryl(3-indolyl)carbenium ions, never previously prepared in the solid state, have been isolated in excellent yields as highly stable o-benzenedisulfonimide salts and have been fully characterized. Their purity has been proven by spectroscopic methods and chemical reduction with NaBH(4). An X-ray crystal structure analysis has been performed on one of the products: an azafulvenium species was shown to be the exclusive structure in the solid state.

An efficient and practical synthesis of triaryl and trisindolylmethanes is reported via the bisarylation of aryl aldehydes with activated arenes. The new method features mild solvent-free reaction conditions, in most cases nearly stoichiometric reagent ratios, catalytic amount of the readily available, easily-handled, recoverable and reusable Brønsted acid catalyst o-benzenedisulfonimide.

o-Benzenedisulfonimide, a new strong bench-stable Brønsted acid, has been shown to efficiently catalyze the Mukaiyama aldol reaction of aldehydes or dimethyl acetals with silyl enol ethers under mild solvent-free reaction conditions.

The reaction between dry arenediazonium o-benzenedisulfonimides 1 and sodium thiolates in anhydrous methanol represents an efficient and safe procedure, of general validity, for the preparation of unfunctionalized or variously functionalized alkyl aryl and diaryl sulfides. As a rule, the reaction temperature was maintained at 0-5 degrees C for the alkylthiodediazoniations and at room temperature (20-25 degrees C) for the arylthiodediazoniations. The sulfide yields are generally high; of the 63 considered examples, 43 gave yields greater than 80% and 13 were between 70% and 80%. Lower yields were obtained only when sterically hindered diazonium salts or thiols were used. A good amount of the o-benzenedisulfonimide (8) was always recovered from the reactions and could be reused to prepare salts 1. The copious experimental data collected in homogeneous conditions have offered several starting points for the study of the mechanism of these reactions.

The paper reports the results of a wide study aimed at preparing aryl chlorides 3 (19 examples), bromides 4 (19 examples), and iodides 5 (9 examples) by halodediazoniation of dry arenediazonium o-benzenedisulfonimides 1 with tetraalkylammonium halides 2. The reactions were carried out in anhydrous acetonitrile at room temperature ( approximately 20 degrees C) in the presence of copper powder and at 60 degrees C or room temperature without the catalyst. In optimal conditions the yields were from good to excellent (60 reactions, 61-94% yield), with only a few exceptions (8 reactions, 51-55% yield). A good amount of the o-benzenedisulfonimide (7) was always recovered from the reactions and could then be reused to prepare salts 1. An interesting aspect of this research is the surprising role of the anion of o-benzenedisulfonimide (9) as an electron transfer agent.

A study was made of the isomerization reaction of a great variety of trimethyl alpha-keto trithioorthocarboxylates to alpha,alpha-bis(methylthio) thiolcarboxylates, intermediates of high synthetic value for the synthesis of alpha-arylpropionic acids. The reaction was carried out in methylene chloride in the presence of catalytic amounts of trityl perchlorate or methanesulfonic acid and was complete in 2 h at rt. In most of the investigated cases the result was positive, the yields usually being greater than 90%. Also the reaction mechanism was subjected to an experimental study.