Salicylaldehyde Schiff bases derived from 2-ferrocenyl-2-amino alcohols. Part 1: New chiral ligands for the titanium-catalyzed enantioselective cyanation of aldehydes

En Route to New Chiral Ferrocene Derivatives: Dead Ends, Detours, and Avenues

“…The replacement of tert-butyl by adamantyl in our ligands resulted in the generation of slightly less efficient catalysts (entries 6 and 7). It is interesting to observe that a molecular mechanics modeling of the intermediate aldehyde-bound complexes 27 reproduced the observed experimental trends reasonably well, and gave support to the transition state model proposed by Somanathan and Cole 46b rather than that suggested initially by Oguni. 49b…”

“…12c In a similar way, several 2-amino-2-ferrocenyl alcohols 10b,c,e,g ( Figure 2) of type II were prepared from the corresponding diols in good overall yields and without loss of enantiomeric purity. 23,24,26,27 The case of amino alcohol 10g ( Figure 2) deserves some comment. The diacetylation of the corresponding diol (S)-8g proved to be very troublesome, and we decided to explore the possibility of direct azide substitution of the tertiary hydroxy group.…”

“…44 However, a relatively small number of b-amino alcohols, most of them derived from a-amino acids, have been used for their preparation, so that structure/enantioselectivity studies had been focused mainly on the substituents of the salicylaldehyde moiety. 27,45,46 In light of these precedents, we decided to prepare a collection of salicylaldehyde Schiff base ligands derived from 2-amino-2-ferrocenylalkanols with different degrees of substitution both at the C1 and the C2 positions, to investigate the relative catalytic efficiency of their titanium alkoxides in enantioselective additions to aldehydes. The condensation of amino alcohols (S)-10b, (1S,2R)-10c, (S)-10e, and (S)-10g (see Figure 2) with a Catalyst A: preformed (p-allyl)palladium complex of (S)-19b (5 mol%); B: preformed (p-allyl)palladium complex of (S)-19e (5 mol%).…”

Synthesis, Crystal Structure and Electrochemical Studies of a Hydrazone Schiff Base Complex of Titanium(IV)

“…Titanium Schiff base complexes are used in catalytic asymmetric pinacol coupling of aromatic aldehydes [4], polymerization of ethene and propene [5], as precatalysts for aldehyde allylation [6], for asymmetric additions to aldehydes and the ring opening of cyclohexene oxide [7], for titanium-catalyzed enantioselective cyanation of aldehydes [8], and asymmetric oxidation of sulfides with H 2 O 2 [9]. Titanium complexes also catalyze the 3-component coupling of an isonitrile, a 1,1-disubstituted hydrazine, and an alkyne [10].…”

Ultrasound‐mediated synthesis of camphoric acid‐based chiral salens for the enantioselective trimethylsilylcyanation of aldehydes

“…The studies of Belokon and North support the existence of a dimeric titanium species, with the two titanium atoms connected through two oxygen bridges. 5,15,[30][31][32] The involvement of a monomeric titanium species is suggested by others 10,[33][34][35][36] and is said to be favored when there are large substituents, such as t-butyl, on the aldehyde moiety. It has been referred that the catalyst structure (monomeric, dimeric, or a mixture of both) is probably related to some reaction conditions such as molar ratios, solvents, and ligand structures.…”