1228457-89-3Relevant academic research and scientific papers
Origins of the Stereoselectivity in a Thiourea-Primary Amine-Catalyzed Nazarov Cyclization
Asari, Austin H.,Lam, Yu-Hong,Tius, Marcus A.,Houk
, p. 13191 - 13199 (2015)
The origins of stereoselectivity of the Nazarov reactions of α-hydroxydivinylketones catalyzed by a vicinal thiourea-primary amine first reported by Tius have been explored with density functional theory. The electrocyclization transition structures in which the thiourea group of the catalyst donates two hydrogen bonds to the keto carbonyl group of the Nazarov reactant and the primary amine accepts a hydrogen bond from the hydroxyl group of the reactant have been modeled. The enantiomeric Nazarov transition structures, which are conventionally described by the absolute sense of conrotation of the dienone termini ("clockwise" or "counterclockwise") in the literature, are nonplanar and adopt helically chiral conformations. The interactions of these helical electrocyclization transition structures with the chiral catalyst are studied in detail. The organocatalyst is found to employ a combination of hydrogen bonding and steric effects to achieve helical recognition of the Nazarov transition state.
Enantioselective palladium(0)-catalyzed nazarov-type cyclization
Kitamura, Kei,Shimada, Naoyuki,Stewart, Craig,Atesin, Abdurrahman C.,Atein, Tülay A.,Tius, Marcus A.
, p. 6288 - 6291 (2015/05/20)
A Pd0-catalyzed asymmetric Nazarov-type cyclization is described. The optimized ligand for the reaction incorporates a weakly coordinating pyridine ring into a TADDOL-derived phosphoramidite (TADDOL=α,α,α,α-tetraaryl-1,3-dioxolane-4,5-dimethanol). The reaction leads to the formation of cyclopentenones as single diastereoisomers that incorporate two contiguous asymmetric centers, one tertiary and one an all-carbon-atom quaternary stereocenter, in high yield and optical purity. It is noteworthy that the reaction does not require that substrates should be activated by aryl substituents.
An organocatalytic asymmetric nazarov cyclization
Basak, Ashok K.,Shimada, Naoyuki,Bow, William F.,Vicic, David A.,Tius, Marcus A.
supporting information; experimental part, p. 8266 - 8267 (2010/08/04)
An organocatalytic asymmetric Nazarov cyclization of diketoesters that proceeds by means of a dual activation mechanism has been developed. Screening of a number of catalysts led to a new thiourea that incorporates a primary amino group. The method gives rise to cyclic products with two adjacent quaternary asymmetric carbon atoms, one of which is an all-carbon stereocenter, with complete or nearly complete diastereoselectivity and in high or very high enantiomeric excess. A brief and very convenient synthesis of the acyclic diketoester starting materials through nucleophilic addition to a ketene is also described.
