China
Africa
Explore chapters and articles related to this topic
Catalytic Asymmetric Michael Addition of 1,3-Dicarbonyls to Nitroalkenes
Published in Irishi N. N. Namboothiri, Meeta Bhati, Madhu Ganesh, Basavaprabhu Hosamani, Thekke V. Baiju, Shimi Manchery, Kalisankar Bera, Catalytic Asymmetric Reactions of Conjugated Nitroalkenes, 2020
Irishi N. N. Namboothiri, Meeta Bhati, Madhu Ganesh, Basavaprabhu Hosamani, Thekke V. Baiju, Shimi Manchery, Kalisankar Bera
Tanyeli and co-workers designed and synthesized a novel bifunctional acid/base-type organocatalyst, i.e., 2-amino-DMAP-squaramide C11 for the enantioselective Michael addition of dibenzoylmethane 2 (R2 = R3 = Ph) to nitroalkenes 1a (Scheme 1.6).12 The corresponding Michael adducts 3 were formed with high yields and enantioselectivities. The reaction involves a synergistic cooperation of 2-amino-DMAP and squaramide. In this reaction, the carbanion generated after the deprotonation of dibenzoylmethane 2 is stabilized by hydrogen bonding with 2-aminopyridine. Meanwhile, nitroalkene 1a is activated by the squaramide catalyst C11 by H-bonding interactions, thus bringing both the substrates in close proximity in the chiral pocket to afford the products 3 with excellent enantioselectivity. The Pericas group, for the first time, employed a chiral squaramide catalyst C12, which is covalently immobilized onto a polystyrene resin, for the asymmetric Michael addition of 1,3-dicarbonyl compounds 2 to nitroalkenes 1a in yielding products 3 with high enantioselectivities (Scheme 1.6).13 The advantage of the catalyst C12 is that the 1,2,3-triazole which serves as a linker provides the immobilized squaramide excellent catalytic stability and facilitates its easy recovery for further reuse.
Aldehydes and Ketones. Acyl Addition Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
Acetylide is formally the carbanion form of acetylene (ethyne) formed by removal of a hydrogen atom by base. The term acetylide is sometimes used generically for an alkyne anion R–C≡C:–. How are alkyne anions formed?
Chemicals from Olefin Hydrocarbons
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene and any equivalent of these groups. An alkyl group is a piece of a molecule with the general formula CnH2n+1, wherenis the integer depicting the number of carbons linked together. For example, a methyl group(n=1,CH3) is a fragment of a methane (CH4) molecule. Alkylating agents utilize selective alkylation by adding the desired aliphatic carbon chain to the previously chosen starting molecule. Alkyl groups can also be removed (dealkylation). Alkylating agents are often classified according to their nucleophilic or electrophilic character. In the context of refining operations, alkylation refers to, for example, the alkylation of isobutane with an olefin such as the alkylation of isobutane with propylene to produce 2,4-dimethyl pentane which is used as a blend stock to increase the octane number of gasoline:
Electrochemical synthesis of hydroxy-thioxo-imidazole carboxylates: an experimental and theoretical study
Published in Journal of Sulfur Chemistry, 2020
Najoua Sbei, Ridha Ben Said, Seyfeddine Rahali, Haouas Beya, Abdullah S. Al-Ayed, Muneerah Mogren Al Mogren, Mohamed Lamin Benkhoud, Mahamadou Seydou
Nowadays, green processes to prepare biologically active materials are among the ultimate goals and challenges in eco-friendly synthetic methodologies. In this process, the electrogenerated radical-anions and anions are basic reagents, called Electro-Generated Bases (EGBs), and are key factors which can be used to deprotonate and to initiate many base-catalyzed reactions [1]. The use of EGBs in organic synthesis is well documented [2]. In particular, radical-anions such as EGBs have great potential in synthesis. In the last years we reported the advantages of acetonitrile in electrochemistry. Carbanions, easily obtained at the cathode, are typical strong bases that can provide useful nucleophiles from acidic components of the reaction mixture. The deprotonation of benzylamine by an EGB gave 5-imino-4-thioxo-2-imidazolidinones [3] in good yields from commercially available starting compounds. It was shown that the use of disubstituted thioureas in the presence of EGBs produced different families of products depending on the electrophiles which were used. For example, the reaction with isocyanate as electrophile allowed the formation of six-membered heterocycles [4]. When the reaction was carried out in the presence of 1,2-dielectrophiles, highly biologically valuable 2-imino-1,3-thiazolines and thiazolidin-4-ones were obtained [5–7]. The preparative scale reaction to 3,4-disubstituted quinazoline-2-ones was successfully promoted by cyanomethyl anions as the EGB, starting from anilines [8]. In addition, the electroreduction of acetonitrile promoted reactions between arylacetonitrile, carbon disulfide and 1-bromo-3-chloropropane to give a family of 2-(1,3-dithian-2-ylidene)-2-arylacetonitriles [9]. Moreover, radical-anions as EGBs show high efficiency in the stereoselective conversion of cyclopropanation to homoquinones from phenacyl carbenes [10].