Enantioselective Cycloadditions of 2‐Alkenoylpyridine‐N‐oxides Catalysed by a Bis(oxazoline)/Cu^II Complex: Structure of the Reactive Intermediate

Abstract

Diels-Alder and 1,3-dipolar cycloadditions involving (E)-3-aryl-1-(pyridin-2-yl-N-oxide)prop-2-en-1-ones as the 2π components are efficiently catalysed by bis(oxazoline)-Cu(II) complexes. The cycloadducts are obtained in quantitative yields with up to 98 % ee; absolute configurations were determined by X-ray analysis. The structure of the reactive complex, determined by X-ray analysis, is fully consistent with the stereochemical outcome of the catalysed process (approach of the diene or nitrone to the less hindered face of the coordinated pyridine-N-oxide derivative).

Ligand spheres in asymmetric hetero Diels–Alder reactions catalyzed by Cu(ii) box complexes: experiment and modeling

“…pentacoordination) 7 show higher conversion and stereoselectivity even in the strongly coordinating solvent MeNO 2 . 74 Efficient penta-coordinate arrangements were shown for Cu(II)-containing tripodal bis(oxazoline) ("trisox") derivatives 75 and enzymes, 51,72,73 and recent NMR investigations show that solvents and counterions substantially influence the geometry of the transition-metal complexes in solution. 76 Establishing the transition state responsible for the formation of the Diels-Alder adduct in the presence of solvent and counterion molecules will be the next step of our investigations.…”

Enantioselectively-Catalyzed Reactions with (E)-2-Alkenoyl-pyridines, TheirN-Oxides, and the Corresponding Chalcones

“…reaction between 2 and 77 was tested with this catalyst (Scheme 29) and the excellent results with 2a, 2h, and 2v, in terms of yields (quantitative), diastereo-(80:81 about 99:1) and enantioselectivity (ee of 80 in the range 96−97%) are reported Table 14. 34 Luckily, the crystal structure of the endo (−)-80 adduct from 2v (R = 4−Br-C 6 H 4 ) was determined to have the (1S,2R,3R,4R) absolute configuration (Table 14, 10 The results with different (E)-2-alkenoyl-pyridines 2 are listed in Table 15, the majority of which refers to catalyst [(S)-XXII/Ti(OiPr) 4 ]. 41 Certainly, some results in terms of yield (entries 4−6), or concerning yield and enantioselectivity (entries 7−9) are not easily explainable.…”

Enantioselective Catalytic Reactions with N-Acyliden Penta-atomic Aza-heterocycles. Heterocycles as Masked Bricks To Build Chiral Scaffolds

“…The reaction yields were always good as well as the obtained enantioselectivities (Table 1, entries 9−12, 19, and 25−29). 6,14,15 Taking constant the phenyl group as the substituent R in position 3, the best results in terms of yields and enantioselectivities were obtained with imidazole derivatives 5a,d,e as reagents (Table 1, entries 1, 4,5), which may only give mono-coordination with La(III). The (1H-1,2,4-triazol-1-yl)-and (oxazolidin-2-one)-derivatives 7 and A1 (Table 1, entry 7 and footnote b), which could both give bicoordination with the Lewis acid of the catalyst, give either a worse enantioselectivity or no reaction at all.…”

“…The examples in entries 15 and 16 are a radical and a Diels−Alder reaction performed with similar catalysts on 1-(1H-pyrazol-1-yl)prop-2-en-1-one (3) and 1-(1H-indazol-1-yl)prop-2-en-1-one (4). Both of the substrates may behave as bidentate ligands, but the results are always poor.…”