N‐Alkylation of imides using phase transfer catalysts under solvent‐free conditions (original) (raw)
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Mechanochemical N-alkylation of imides
Beilstein Journal of Organic Chemistry
The mechanochemical N-alkylation of imide derivatives was studied. Reactions under solvent-free conditions in a ball mill gave good yields and could be put in place of the classical solution conditions. The method is general and can be applied to various imides and alkyl halides. Phthalimides prepared under ball milling conditions were used in a mechanochemical Gabriel synthesis of amines by their reaction with 1,2-diaminoethane.
Alkaline carbons as base catalysts: Alkylation of imidazole with alkyl halides
Journal of Molecular Catalysis, 1993
Anionic alkylation of imidazole with alkyl halides to produce intermediates in the synthesis of pharmaceutically important antiviral products, such as famciclovir and acyclovir, have been carried out using alkaline carbons as base catalysts. Previously to the alkylation of imidazole, the condensation of benzaldehyde with malonic esters has been used as test reaction of basicity on a series of lithium, sodium, potassium and cesium exchanged Norit RX 1 Extra activated carbon. The importance of active sites and the measurement of surface basicity have been emphasized. Under reaction conditions, it has been found that most of the basic sites in alkaline carbons have 10.7d~K~g13.3, but there is a considerable number of sites able to abstract protons of 13.3<pK,< 16.5. Norit RX 1 Extra which was not subject to alkaline exchange retains most of its basic sites capable of abstracting protons of 9 d pK, < 10.7. Taking into account that the pK,, of the NH group of imidazole is 14.5, the alkaline carbons present the required basic strength to catalyze the alkylation of this N-heterocycle with alkyl halides.
Microwave-Assisted Synthesis of Acyclic Imides
Iğdır Üniversitesi Fen Bilimleri Enstitüsü Dergisi, 2022
Imides are an important class of compounds found in the structure of many biologically active and natural compounds. Imides are also important starting materials used in the synthesis of many heterocyclic compounds. Therefore, the synthesis of these compounds has attracted considerable attention and several innovative methods have been developed. Herein, the synthesis of acyclic imides has been reported from nitriles and carboxylic anhydrides in the presence of catalytic amounts of ptoluenesulfonic acid (PTSA) or H2SO4 under microwave irradiation. The reaction has proceeded in better yields with PTSA. When sulfuric acid was used, the product was obtained in lower yields since the degradation was increased. This new microwave-assisted method is compared with conventional heating, and the other methods, reported in the literature. The main advantages of this procedure are shorter reaction times, easier work-up, and good yields.
2012
The development of novel synthetic methods for the rapid and stereoselective preparation of complex molecular scaffolds constitutes the driving force behind organic synthesis. [1] In the past decade, organocatalytic [2] methods have emerged as complementary to organometallic-based techniques for catalysed transformations. In particular, enamine, [3] iminium, [4] and SOMO catalysis, [5] as well as photocatalysis [6] have contributed to the enhanced synthetic utility and versatility of carbonyl compounds. The stereoselective alkylation of carbonyl groups (aldehydes and ketones) has been achieved through conceptually different activation modes. [7] Recently, we introduced the concept of enantioselective S N 1-type alkylations to organocatalysis, [8, 9] and also established the compatibility of indiumA C H T U N G T R E N N U N G (III) Lewis acids with organocatalytic processes mediated by the MacMillan catalyst. [10, 11] The compatibility of indiumA C H T U N G T R E N N U N G (III) salts in these processes creates the possibility of using carbocations that cannot be generated in the presence of Brønsted acids. [12] The stability of the carbocation involved in the process is the primary driving force for these S N 1-type reactions, and their use can be easily rationalized by the work of Mayr et al. [13] In the presence of InBr 3 , allylic alcohols can provide straightforward access to alkylated aldehydes without the use of palladium or iridium salts. [14] Herein, we report an extension to the scope of our methods to include benzylic and benzhydrylic alcohols, substrates which give access to useful intermediates for the synthesis of biologically active enantioenriched diarylethane products. [15] This structural motif has a diverse range of biological properties that include anticancer, antidepressant, and antiviral activity. [16] We envisioned the direct synthesis of enantioenriched diarylethanes from readily available racemic diarylmethanols (Table 1). We have established a correlation between the electrophilicity (E) of the carbenium ion employed in our S N 1-type reaction and the possibility of generating such an ion. Alcohols that form carbenium ions located at À1 or above on the Mayr scale are not reactive with the enamine that is formed in situ with the MacMillan catalyst. [17] Even in the presence of strong acids, the carbenium ions are not formed or are intercepted by water. Alternatively, by using indiumA C H T U N G T R E N N U N G (III) salts (triflate or bromide), the corresponding carbenium ion can be generated from the alcohols and intercepted by the enamine formed in situ with the MacMillan catalyst. [10-11] The compatibility of indiumA C H T U N G T R E N N U N G (III) salts with water, the amine, and an excess of aldehyde is the motivation for investigating this chemistry. The reactions of model substrates 2 a-c were investigated in the presence of different Lewis acids and under various conditions. The 4-MeO derivative 2 a was rather unreactive and afforded the desired product in 75 % yield as a 1:1 diastereomeric mixture in 76 and 59 % ee after 24 h, with InBr 3 as the Lewis acid in CH 2 Cl 2 (Table 1, entry 1). Many other benzhydrylic derivatives bearing the methoxy substituent were tested, but the reactions gave poor results. In our preceding publications we have established that steric hindrance of the incoming carbenium ion controls the stereoselectivity of the reaction. [11] Therefore, to increase the stereoselectivity and reactivity, derivatives 2 b and 2 c were tested. The reaction conditions were carefully optimized by varying the solvent, Lewis acid, and MacMillan catalyst used in the reaction. Substrate 2 c is more sterically demanding because of the diphenyl substituent. The introduction of an ortho substituent results in more steric hindrance in the carbenium ion, which in turn introduces a steric bias for the enamine that is formed in situ with the MacMillan catalyst. In general, different Brønsted or Lewis acids are able to promote the formation of the corresponding carbenium ion and are compatible with secondary amines and excess aldehydes. However, only InA C H T U N G T R E N N U N G (OTf) 3 ensured high stereoselectivity in this reaction. By varying the solvent excellent stereoselectivity was obtained with catalyst 3 b. Different benzhydrylic substituents were then tested and the data obtained are shown in Table 2. The diastereoselectivity is
Asian Journal of Organic Chemistry, 2015
ABSTRACT Stable diarylcarbenium salts, obtained by the direct coupling of indole or indole derivatives with aryl (or heteroaryl) aldehydes in the presence of a strong organic Brønsted acid, have been employed in the direct alkylation of aldehydes. Excellent enantiomeric excesses and good diastereomeric ratios were obtained with a number of aryl or heteroaryl(3-indolyl)carbenium ions as the highly stable o-benzenedisulfonimide (OBS) salts and with the reaction promoted by the Hayashi-Jørgensen catalyst. A one-pot, three-component, stereoselective alkylation of aldehydes affording the same compounds was also investigated with various aldehydes, indole derivatives, and organocatalysts. The results obtained with the isolated carbenium ions were superior in terms of yields and stereoselectivity.
Molecular Diversity, 2019
Aldehydes and ketones are parts of millions of compounds and are important classes of chemicals which serve as important precursors for the synthesis of library of compounds. For the synthesis of aldehydes and ketones, one impressive approach to date, because of its excellent selectivity, high yield and stability toward over-reduction and over-oxidation, is the oxidation of organic halides (viz. aliphatic and benzyl halides). The current review covers the conventional and eco-friendly transformational approaches, from 2000 to date, toward synthesis of aldehydes and ketones from organic halides, including mechanistic studies, comparison of different transformational strategies and discussion on scope and cons and pros of each transformational approach. The review would be beneficial to get knowledge about recent synthesis techniques, select finest synthetic approach, develop further new transformational methodologies and improve current transformational approaches.
Transition metal imido catalysts for ethylene polymerisation
Journal of Organometallic Chemistry, 1999
The imido complexes CpV(N-2-MeC 6 H 4)Cl 2 (1), Cr(N-t Bu) 2 Cl 2 (2), CpNb(N-2-t BuC 6 H 4)Cl 2 (3) and Mo(N-t Bu) 2 Cl 2 (4) have been tested as procatalysts for the polymerisation of ethylene in combination with diethylaluminium chloride or methylaluminoxane (MAO) co-catalysts. The vanadium precursors give the highest activities but are short-lived, while the chromium system gives a long-lived catalyst of moderate activity. The niobium and molybdenum derivatives gave relatively low activities under all test conditions. The polyethylene generated by the vanadium and chromium catalysts is of high molecular weight with little branching. The dialkyl complexes Cr(N-t Bu) 2 (CH 2 Ph) 2 (5), Cr(N-2,6-Pr i 2 C 6 H 3) 2 (CH 2 Ph) 2 (6), Cr(N-2,6-Pr i 2 C 6 H 3) 2 Me 2 (7), Mo(Nt Bu) 2 (CH 2 Ph) 2 (8), Mo(N-2,6-Pr i 2 C 6 H 3) 2 (CH 2 Ph) 2 (9), (C 5 Me 5)Nb(N-2,6-Pr i 2 C 6 H 3)Me 2 (10) and (C 5 Me 5)Ta(N-t Bu)(CH 2 Ph) 2 (11) have been prepared by treatment of the dihalide precursors with appropriate alkylating reagents and investigated as precursors to well-defined cationic alkyl catalysts. Treatment of (5) with [Ph 3 C][B(C 6 F 5) 4 ] affords the cationic h 2-benzyl species [Cr(N-t Bu) 2 (h 2-CH 2 Ph)][B(C 6 F 5) 4 ] (12) while its reaction with [PhNMe 2 H][B(C 6 F 5) 4 ] liberates toluene to give a mixture of the mono and bis(dimethylaniline) adducts [Cr(N-t Bu) 2 (h 2-CH 2 Ph)(NMe 2 Ph)][B(C 6 F 5) 4 ] (14) and [Cr(N-t Bu) 2 (h 2-CH 2 Ph)(NMe 2 Ph) 2 ][B(C 6 F 5) 4 ] (15). Complex 12 reacts with trimethylphosphine to give the mono-phosphine adduct [Cr(N-t Bu) 2 (h 2-CH 2 Ph)(PMe 3)][B(C 6 F 5) 4 ] (13). Solutions containing cationic species (12, 14, 15) are active for ethylene polymerisation in the absence of co-catalyst, affording high-molecular-weight polyethylene with relatively broad molecular-weight distributions.