Modular Chiral Bisoxalamide–Copper-Catalyzed Asymmetric Oxo-Diels–Alder Reaction: Carbonyl Coordination for High Enantio- and Diastereocontrols

The
chiral bis-oxalamides (CBOA), readily derived from optically
pure 1,2-diphenylethylenediamine (DPEN), were proven to be a class
of efficient C2-symmetric chiral ligands
for copper­(II)-catalyzed asymmetric inverse-electron demand oxo-Diels–Alder
reactions between β,γ-unsaturated α-ketoesters and
2,3-dihydrofuran or 3,4-dihydro-2H-pyran. The reactions
proceeded smoothly under mild conditions to afford the corresponding
[4 + 2] cycloadducts in high yields with good enantioselectivities
(up to 94% ee) and diastereoselectivities (up to 99:1 dr). DFT calculations
demonstrated that carbonyl coordination of the chiral ligand to Cu­(II)
was crucial for the high stereoinduction. These CBOA ligands exhibited
high catalytic efficiency in this reaction, which combined with some
other salient features of structural fine tunability, chemical stability,
and ready accessibility might endow more practical applications in
asymmetric catalytic reactions.

手性双草酰胺类配体 (chiral bis-oxalamides，CBOA) 可由光学纯1,2-二苯乙二胺 (1,2-diphenylethylenediamine，DPEN) 简便衍生得到，被证实为一类高效的C2对称手性配体，可应用于铜(II)催化的β,γ-不饱和α-酮酸酯与2,3-二氢呋喃或3,4-二氢-2H-吡喃之间的不对称反电子需求氧杂Diels–Alder反应。该类反应可在温和条件下平稳进行，以高收率得到相应的[4+2]环加成产物，同时具备优异的对映选择性（最高可达94% ee）与非对映选择性（最高可达99:1 dr）。密度泛函理论 (DFT) 计算表明，手性配体与Cu(II)的羰基配位过程，对实现高立体诱导效应至关重要。此类CBOA配体在该反应中展现出优异的催化效能，加之其结构可精细调控、化学稳定性佳、易于制备等突出优势，有望在不对称催化反应中获得更具实用性的应用场景。