Structural and stereochemical aspects of the enantioselective halogenation of 1,3-dicarbonyl compounds catalyzed by Ti(TADDOLato) complexes

Substrate Range of the Titanium TADDOLate Catalyzed Asymmetric Fluorination of Activated Carbonyl Compounds

“…1), the enantioselectivity in the fluorination of the strongly enolized substrates 35 and 36 was increased ( Table 4, Entries 2, 3, and 5), whereas no corresponding change of ee value in dependence of the fluorinating reagent had earlier been observed for substrate 1, for which enolization was negligible [3]. This steric model is in agreement with structural information from the X-ray structure of the complex [Ti((Nap-1)-TADDOLato) 2 (b-ketonato) 2 ] [16], incorporating the deprotonated substrate 29 twice as chelating O,O-ligand at Ti-atom. The catalytic fluorination of b-keto esters incorporating a stereogenic center in the ester alkyl group should be diastereoselective with either achiral or chiral catalysts.…”

“…This may, in part, be a consequence of the high degree of enolization of the substrates, which favors a noncatalyzed background reaction. A steric model of a substrate/catalyst complex has been developed in the preceding study [3], based on calculated structures of Ti-enolate intermediates [18] and the molecular structure of a dienolate complex determined by X-ray analysis [16]. 1), the enantioselectivity in the fluorination of the strongly enolized substrates 35 and 36 was increased ( Table 4, Entries 2, 3, and 5), whereas no corresponding change of ee value in dependence of the fluorinating reagent had earlier been observed for substrate 1, for which enolization was negligible [3].…”

“…Introduction. In parallel, the substrate range of asymmetric fluorination has been extended to cyclic b-keto esters [8 -10], achloro-b-keto esters [11 -13], b-keto phosphonates [5] [9] [10] [14] [15], a-acyl-glactames [16]. Asymmetric halogenations of b-keto esters, particularly fluorinations, have since then been studied with a range of other chiral metal catalysts, including palladium(II), nickel(II), copper(II), and zinc(II) (for reviews, see [5 -7]).…”

“…Asymmetric halogenations of b-keto esters, particularly fluorinations, have since then been studied with a range of other chiral metal catalysts, including palladium(II), nickel(II), copper(II), and zinc(II) (for reviews, see [5 -7]). [2] [3] [17]) and its use in specific applications [4] [11] [16] [18], no detailed study of the substrate range of the original titanium TADDOLate-catalyzed fluorination has been reported. Besides the examples presented in our communication [1a] (cf.…”

Carbanions and Electrophilic Aliphatic Substitution

“…157 The structural and stereochemical aspects of the enantioselective halogenation of 1,3-dicarbonyl compounds catalysed by Ti(TADDOLato) complexes have been reportee ed. 158 The observed absolute configuration at the fluorinated stereogenic centre has been found to match the one inferred from the structural analysis of the Ti(TADDO-Lato) complexes.…”