Chiral ruthenium Lewis acid-catalyzed nitrile oxide cycloadditions

Asymmetric Lewis acid-catalyzed 1,3-dipolar cycloadditions

“…Electron-withdrawing aryl groups at the nitrile oxide gave products with higher ee (up to 93 %) than those with electron-releasing groups. As in the case of nitrones, the absolute configuration is in perfect agreement with an approach of the nitrile oxide on the accessible C α -Si face of the methacrolein bound at the Ru in an anti s-trans conformation [5,24,25].…”

“…Slow addition of the nitrile oxide by means of a syringe pump to a stirred mixture of methacrolein and 5 mol % of (R,R)-2 in CH 2 Cl 2 , at -15 °C, followed by reduction, led to the exclusive formation of 2-isoxazoline 9a in 71 % yield and 62 % ee (Table 2, entry 1). In the following, the study was extended to other aryl nitrile as shown below [25]. In all cases, reactions afforded the 3,5-substituted isoxazolines as single regioisomers.…”

“…In this short article, we review our recent results in asymmetric Lewis acid-catalyzed 1,3-dipolar cycloaddition reactions of enals with acyclic nitrones [24] and the extension of these reactions to nitrile oxides [25].…”

4.22 Intermolecular 1,3-Dipolar Cycloadditions of Alkenes, Alkynes, and Allenes

“…89 Recently, Suga and coworkers have disclosed a novel synthetic protocol featuring BINIM-Ni(II) complexes as chiral Lewis acid catalysts for the asymmetric cycloadditions of nitrile oxide (Scheme 87). 90 The nitrile oxides were generated from the corresponding hydroximoyl chloride 166 in the presence of MS 4 Å.…”

Metal complexes versus organocatalysts in asymmetric 1,3-dipolar cycloadditions

“…The 3,5-disubstituted isoxazolines 126 were obtained in moderate-good yields (43-71%), as single diastereoisomers (3,5-cycloadducts), with moderate to good enantioselections (63-93% ee) (Scheme 28). 60,68 The chiral complexes formed by ligands 121 and 122 with Yb(OTf) 3 ( Figure 9) were independently tested in the 1,3-DC of nitrile oxides 125 and the (Z)-allylic alcohol 127. In both reaction a and b of the Scheme 29, almost equimolar amounts of isoxazolines 3,5-128 and 3,4-128 were isolated.…”