213772-31-7Relevant academic research and scientific papers
[Co(TPP)]-Catalyzed Formation of Substituted Piperidines
Lankelma, Marianne,Olivares, Astrid M.,de Bruin, Bas
, p. 5658 - 5663 (2019)
Radical cyclization via cobalt(III)-carbene radical intermediates is a powerful method for the synthesis of (hetero)cyclic structures. Building on the recently reported synthesis of five-membered N-heterocyclic pyrrolidines catalyzed by CoII porphyrins, the [Co(TPP)]-catalyzed formation of useful six-membered N-heterocyclic piperidines directly from linear aldehydes is presented herein. The piperidines were obtained in overall high yields, with linear alkenes being formed as side products in small amounts. A DFT study was performed to gain a deeper mechanistic understanding of the cobalt(II)-porphyrin-catalyzed formation of pyrrolidines, piperidines, and linear alkenes. The calculations showed that the alkenes are unlikely to be formed through an expected 1,2-hydrogen-atom transfer to the carbene carbon. Instead, the calculations were consistent with a pathway involving benzyl-radical formation followed by radical-rebound ring closure to form the piperidines. Competitive 1,5-hydrogen-atom transfer from the β-position to the benzyl radical explained the formation of linear alkenes as side products.
A TEMPO-free copper-catalyzed aerobic oxidation of alcohols
Xu, Boran,Lumb, Jean-Philip,Arndtsen, Bruce A.
supporting information, p. 4208 - 4211 (2015/04/14)
The copper-catalyzed aerobic oxidation of primary and secondary alcohols without an external N-oxide co-oxidant is described. The catalyst system is composed of a Cu/diamine complex inspired by the enzyme tyrosinase, along with dimethylaminopyridine (DMAP) or N-methylimidazole (NMI). The Cu catalyst system works without 2,2,6,6-tetramethyl-l-piperidinoxyl (TEMPO) at ambient pressure and temperature, and displays activity for un-activated secondary alcohols, which remain a challenging substrate for catalytic aerobic systems. Our work underscores the importance of finding alternative mechanistic pathways for alcohol oxidation, which complement Cu/TEMPO systems, and demonstrate, in this case, a preference for the oxidation of activated secondary over primary alcohols.
Metal-free, mild, nonepimerizing, chemo- and enantio- or diastereoselective N-alkylation of amines by alcohols via oxidation/imine-iminium formation/reductive amination: A pragmatic synthesis of octahydropyrazinopyridoindoles and higher ring analogues
Khan, Imran A.,Saxena, Anil K.
, p. 11656 - 11669 (2014/01/06)
A mild step and atom-economical nonepimerizing chemo- and enantioselective N-alkylating procedure has been developed via oxidation/imine-iminium formation/reduction cascade using TEMPO-BAIB-HEH-Bronsted acid catalysis in DMPU as solvent and a stoichiometric amount of amine. The optimized conditions were further extended for the nonenzymatic kinetic resolution of the chiral amine thus formed under nonenzymatic in situ hydrogen-transfer conditions using VAPOL-derived phosphoric acid (VAPOL-PA) as the Bronsted acid catalyst. The enantioselective cascade of the presented reaction was successfully utilized in the synthesis of octahydropyrazinopyridoindole and its higher ring analogues.
Stereochemical memory effects in alkene radical cation/anion contact ion pairs: Effect of substituents, and models for diastereoselectivity
Crich, David,Ranganathan, Krishnakumar
, p. 9924 - 9929 (2007/10/03)
A series of 12 stereochemically defined 2,m-dimethyl- and 2,m,n-trimethyl-6-benzylamino-2-nitro-3-(diphenylphosphatoxy)hexanes have been synthesized and their cyclization reactions leading to di- and trisubstituted N-benzyl pyrrolidines examined in the presence of tributyltin hydride and azoisobutyronitrile in benzene at reflux. The cyclizations are interpreted in terms of generation of an alkyl radical by abstraction of the nitro group with a stannyl radical. The phosphate leaving group is then expelled in a heterolytic cleavage to give a contact alkene radical cation/phosphate anion pair. For the majority of the examples studied, the cyclizations are best understood in terms of nucleophilic attack by the amine on the opposite face of the alkene radical cation to the one shielded by the leaving group, within the confines of the initial contact ion pair, resulting in overall cyclization with inversion of configuration. Dependent on the relative stereochemistry of the substituents, the cyclization is envisaged as taking place through either chair-like or twist-boat-like transition states with the maximum number of substituents pseudo-equatorial. The model breaks down when cyclization on the initial contact ion pair would engender significant destabilizing steric interactions, especially 1,3A strain in the alkene radical cation. In these cases a fully equilibrated Beckwith-Houk-type transition state provides a satisfactory model. Interesting examples of matching and mismatching in the Corey-type oxazaborolidine-mediated reduction of alkyl (methyl-1-nitroethyl) ketones by a β-methyl group in the alkyl chain are reported, and the mismatching is attributed to a developing syn-pentane interaction in the transition state.
Somatostatin analogue compounds
-
Page 19, (2010/11/30)
Compounds having somatostatin activity of the following Formula I, 1wherein, R1 is aryl, substituted-aryl, and aryl-(lower-alkyl)-; R2 is lower alkyl, amino substituted lower alkyl, -carboxy-(lower-alkyl), -carbamic acid-(lower-alkyl) and -carboxy-(lower-alkyl)-aryl; and R3 and R4 are independently, lower-alkyl, aryl, substituted-aryl, (substituted-aryl)-(lower-alkyl)-, heteroaryl, (heteroaryl)-(lower-alkyl)-, substituted-heteroaryl, (substituted heteroaryl)-(lower-alkyl)-, heterocyclic, heterocyclic-(lower-alkyl)-, substituted-heterocyclic, (substituted-heterocylic)-(lower alkyl)-, -carboxy-(lower-alkyl), and -carboxy-(lower-alkyl)-aryl; or a pharmaceutically acceptable, ester, ether, or salt thereof; methods for their use; and preparation.
Diastereoselectivity in the cyclization of alkene radical cations generated under non-oxidizing conditions: Contact ion pairs and memory effects
Crich, David,Ranganathan, Krishnakumar
, p. 12422 - 12423 (2007/10/03)
A series of highly diastereomerically enriched 1,5-dimethyl-, 2,5-dimethyl-, and 3,5-dimethyl-N-benzyl-5-nitro-4-(diphenylphosphatoxy)hexylamines were exposed to tributyltin hydride and AIBN in benzene at reflux. The ensuing reactions, interpreted in term
Pyrimidinone-1,3-oxathiolane derivatives with antiviral activity
-
, (2008/06/13)
Compounds of formula (I) wherein Ra and Rb the same or different, are hydrogen atoms, acyl groups deriving from a lower carboxylic acid or chains of formula (a) useful as reverse transcriptase inhibitors antiviral activity are described.
