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N-Heterocycles
Published in Navjeet Kaur, Metals and Non-Metals, 2020
Spiro-pyrrolidine ring has been investigated broadly for its role in constituting the core structure of many biologically important 2-oxindoles and its presence in various natural products. It has been reported that a p53-MDM2 interaction inhibitor MI-219 bearing spiropyrrolidine-oxindole backbone is about to enter phase I clinical trials as an anti-cancer agent [202]. Other studies show that MgI2 -catalyzed ring-expansion of a cyclopropane ring in N-benzylspiro[2-oxindole-3,1′-cyclopropane] synthesizes spiro-pyrrolidine-oxindoles in the presence of aldimines (Scheme 75) [203–204].
Reactions of thiocarbonyl compounds with electrophilic and nucleophilic carbenes as well as with their metal complexes
Published in Journal of Sulfur Chemistry, 2020
Grzegorz Mlostoń, Heinz Heimgartner
Under analogous conditions, reaction of the sterically crowded monothione 24 (3-thioxo-2,2,4,4-tetramethylcyclobutanone) occurred with initial ring expansion of the sterically congested cyclobutanone ring. Remarkably, this step of the reaction occurred regioselectively via addition of carbene 115a on the C = O group and led to the formation of the five-membered monothione 118a as the major product. The latter could be isolated from the reaction mixture side by side with the isomeric monothione 118b, formed via carbene addition on the C = S group, as the minor component (Scheme 29) [53]. The expected spiro-thiirane derived from 24 was not observed and only traces of the ring-expanded spiro-thiirane 119 were separated chromatographically from the crude mixture.
Structure and thermal reactivity of some 2-substituted 1,3-oxathiolane S-oxides
Published in Journal of Sulfur Chemistry, 2018
R. Alan Aitken, Sarah Henderson, Alexandra M. Z. Slawin
The previously reported thermal isomerization of 2-benzylidene-1,3-dioxolane to 3-phenylbutyrolactone proceeds well under FVP conditions. An analogous process was not observed for S-oxidized sulfur analogues, which instead underwent SOn extrusion and fragmentation to give acyclic carbonyl products. A minor process observed for the cyclic sulfoxide 7 was the formation of bis(2-hydroxyethyl) disulfide, apparently via thermal ring-expansion of thiirane S-oxide. Conformational analysis of 7 by 1H NMR showed it to be remarkably similar to the 2-p-nitrophenyl analogue, while X-ray structure determination of 8 showed a similar envelope conformation to that observed in previous bicyclic examples.
Copper-assisted synthesis of five-membered O-heterocycles
Published in Inorganic and Nano-Metal Chemistry, 2020
Navjeet Kaur, Yamini Verma, Neha Ahlawat, Pooja Grewal, Pranshu Bhardwaj, Nirmala Kumari Jangid
Chiral metal complexes were utilized for investigating an asymmetric induction in ylide formation/[1, 2]-shift. Katsuki et al.[47,48] reported the reaction of (−)-2-phenyloxetane with tert-butyl diazoacetate (0.5 equiv.) and copper(I) catalyst. Cis- and trans-tetrahydrofurans were formed in 81% and 75% ee, respectively with chiral bipyridine ligand. The trans-Whisky lactone was prepared enantioselectively on extending this asymmetric ring expansion[1b],[49,50] (Scheme 13).