Magnesium triflate/ligand

Desimoni et al. have shown that the use of magnesium perchlorate or magnesium triflate, and three chiral to(oxazolines) and two equivalents of achiral auxiliary ligands such as water or tetramethylurea, induces a strong change of the enantiofacial selectivity with >94% ee in the... 

Recently, very effective asymmetric conjugate addition of 1,3-dicarbonyl compounds to nitroalkenes has been reported, as shown in Scheme 4.10. The reaction of ethyl acetoacetate with nitrostyrene is carried out in the presence of 5 mol% of the preformed complex of magnesium triflate and chiral bis(oxazoline) ligands and a small amount ofW-methylmorpholine (NMM) to give the adduct with selectivity of 91%. The selectivity depends on ligands. The effect of ligands is presented in Scheme 4.10.63... 

In 1993, Evans and co-workers examined phe-box 6, /-pr-box 45, and bu-box 3 ligands in the Diels-Alder reaction of cyclopentadiene 68 and 3-acryloyl-l,3-oxazolidin-2-one 69 using a weak Lewis acid such as copper(II) triflate." The results are summarized in Table 9.9. The reaction was carried out between —50 and —78 °C for 3-18 h and achieved selectivities of up to 98 2 (endo/exo) with an endo ee of >98% (using bu-box 3). Interestingly, the enantiomer produced in these reactions was the (25) configuration, compared to the (2K) isomer obtained with iron(III) and magnesium(II) as reported by Corey. This observed stereochemistry was explained by the chelation model of the copper(II) complex 74 (Fig. 9.23)... 

While the q -bonding mode in the iron complex 3 has earlier been established crystallographically [11, 12], it is remarkable that this coordination mode is observed in a 17 electron iron(III) complex as well. Dixneuf et al. treated iron(III) chloride with magnesium and dichloride 2 in the presence of phosphane ligands and obtained the respective trimethylenemethane iron(II) complexes, which were then oxidized with silver triflate resulting in the formation of cationic trimethylenemethane complexes with the ligand still being q -coordinated [30]. Bazan et al. reported a distorted coordination to zirconium [31], and... 

---