Synthetic studies on optically active .BETA.-lactams. II. Asymmetric synthesis of .BETA.-lactams by (2+2)cyclocondensation using heterocyclic compounds derived from L-(+)-tartaric acid, (S)- or (R)-glutamic acid, and (S)-serine as chiral auxiliaries.
作者:Nobuo IKOTA
DOI:10.1248/cpb.38.1601
日期:——
Asymmetric synthesis of β-lactams by the [2+2]cyclocondensation of an imine (7) to chiral ketene species (2b, 4b, and 6c) bearing heterocycles derived from L-(+)-tartaric acid, (S)-glutamic acid, and (S)-serine was carried out. The reaction of 2b with 7 gave the trans-β-lactams with 74% diastereomeric excess, and cis-β-lactams were predominantly formed with high diastereomeric purity (up to 96%) when 4b and 6c were employed. Asymmetric synthesis of (3S, 4S)- and (3R, 4R)-1-benzyl-3[(benzyloxycarbonyl)amino]-4-hydroxymethyl-2-azetidinones (26 and 30g) using (R)-4b as a ketene species and the chiral imine (21) prepared from L-(+)-tartaric acid was also achieved.
Preparation of Auxiliaries for Asymmetric Syntheses from Tartaric Acid. Additions of Butyllithium to Aldehydes in Chiral Media.
由酒石酸制备不对称合成助剂。在手性介质中将丁基锂添加到醛中。
Synthesis of α,ω‐Bis‐Enones by the Double Addition of Alkenyl Grignard Reagents to Diacid Weinreb Amides
作者:Stefan Wiesler、Michael A. Bau、Thomas Niepel、Sara L. Younas、Hieu‐Trinh Luu、Jan Streuff
DOI:10.1002/ejoc.201901043
日期:2019.9.30
The synthesis of bis‐enones from alkenyl bromides and α,ω‐bis‐Weinreb amides via a double Grignard reaction is reported. The work contains reliable protocols for the double addition and the efficient generation of the required substituted alkenyl Grignard reagents from alkenyl bromide precursors.
Readily available phosphoramidites incorporating TADDOL-related diols with an acyclic backbone turned out to be excellent ligands for asymmetric gold catalysis, allowing a number of mechanistically different transformations to be performed with good to outstanding enantioselectivities. This includes [2 + 2] and [4 + 2] cycloadditions of ene-allenes, cycloisomerizations of enynes, hydroarylation reactions
isopropylidene acetal unit from well‐known TADDOLligands improved the performance of the derived phosphoramiditeligands in asymmetric goldcatalysis (see scheme; Ts=4‐toluenesulfonyl). X‐ray crystallography showed that the binding pocket has an effective threefold symmetry, with through‐space interactions between the arene rings of the ligand and the gold center.