Asymmetric “Acetylenic” [3+2] Cycloaddition of Nitrones Catalyzed by Cationic Chiral Pd<sup>II</sup>
Lewis Acid
作者:Kazuya Honda、Koichi Mikami
DOI:10.1002/asia.201801016
日期:2018.10.4
Highly enantioselective [3+2] cycloaddition of ynones and nitrones has been developed. Very bulky ligand, DTBM‐SEGPHOS, was used for an effective asymmetric induction over distal reaction centers on the linear ynone dipolarophile and for prevention of PdII catalyst deactivation by coordination of the nitrones. The reaction has wide scope of substrates in both ynones and nitrones.
作者:Alemayehu Gashaw Woldegiorgis、Zhao Han、Xufeng Lin
DOI:10.1002/adsc.202101011
日期:2022.1.18
An enantioselective synthesis of unnatural pyrazole-based α-chiral amino acidderivatives from the asymmetric reaction of N-aryl-5-aminopyrazoles with β,γ-alkynyl-α-imino esters using a chiral spirocyclic phosphoric acid catalyst was developed. Using the established methodology, various pyrazole-based α-aminoacidderivatives with tetrasubstituted carbon stereocenters were obtained in 67–98% yields
affording various tetrasubstituted thiophenes with aryl, alkenyl, alkyl, or silylgroup at the special position. The structural modification of alkyne substrates enabled the synthesis of diverse thiophenes to be achieved using the pyridinium 1,4-zwitterionic thiolates as the sulfur-containing building blocks. This approach is metal-free and catalyst-free.
A new synthesis of alpha-quaternary alkynyl amino esters and allenoates was developed utilizing umpolung N-addition to beta,gamma-alkynyl alpha-imino esters followed by regioselective acylation. The reaction exhibits broad substrate generality and unique regioselectivity. Moreover, synthesis of alpha-quaternary alkynyl amino esters was also carried out via oxidation of the intermediary enolate followed by alkylation.
Organocatalytic Enantioselective Synthesis of Tetrasubstituted α‐Amino Allenoates by Dearomative γ‐Addition of 2,3‐Disubstituted Indoles to β,γ‐Alkynyl‐α‐imino Esters
作者:Junxian Yang、Zheng Wang、Zeyuan He、Guofeng Li、Liang Hong、Wangsheng Sun、Rui Wang
DOI:10.1002/anie.201911420
日期:2020.1.7
phosphoric acid catalyzed dearomative γ-addition reaction of 2,3-disubstituted indoles to β,γ-alkynyl-α-imino esters is reported. This method provides access to a series of highly functionalized tetrasubstituted allenes featuring quaternary stereocenters in high yields, and with excellent regio-, diastereo-, and enantioselectivities under mild conditions without by-product formation. Representative large-scale