New chiral Schiff bases derived from (+)- and (−)-α-pinenes in the metal complex catalyzed asymmetric oxidation of sulfides

Abstract

New chiral Schiff bases were derived from (+) and (-) α pinenes for the first time. Coordi nated to vanadium ions, they can be used as ligands in catalytic oxidation of sulfides into chiral sulfoxides. Conditions for the asymmetric oxidation of thioanisole to methyl phenyl sulfoxide in optical purity up to 32% were found. Variation of substituents in the ligand has a significant effect not only on enantioselectivity of the reaction, but also on absolute configuration of the sulfoxide formed.Chiral sulfoxides belong to important class of organic compounds, widely used in asymmetric synthesis. 1-3 In addition, compounds, containing asymmetric sulfoxide group, were isolated from a number of natural sourses, as well as biologically active sulfoxides of a certain configu ration were found. 4-7 All the enumerated facts stimulate elaboration of efficient methods for the synthesis of chiral sulfoxides, among which an asymmetric oxidation of prochiral sulfides, in particular, in the presence of vana dium containing metal complex systems, 8 seems to be the most reasonable.Vanadium complexes with chiral Schiff bases, obtained from cyclohexane 1,2 diamine, were first used for asym metric oxidation of aryl methyl sulfides with cumene hy droperoxide. 9 The yields of sulfoxides were good, and their enantiomeric excess (ее) reached 40%. Later, 10 it was found that application of vanadium complexes with ligands 1a,b, synthesized from the corresponding salicyl aldehydes and optically active β aminoalcohol, in combi nation with aqueous hydrogen peroxide as the oxidant allows one to obtain sulfoxides from alkyl aryl sulfides in good yields (up to 94%) and acceptable enantioselectivity (usually ее was 50-70%). It is necessary to note the simplicity in conducting the experiment with participation of these systems as compared with the trials carried out in the presence of homogeneous catalytic complexes on the * Dedicated to Academician G. A. Tolstikov in honor of his 75th anniversary.

Complex of CuII with a chiral Schiff base (H2L) derived from the natural monoterpene (+)-6h-pinene. Synthesis and the properties of the complex and its solvate with acetonitrile. Crystal structure of [Cu(HL)Cl]•H2O

“…Ligand H 2 L was obtained according to the pro cedure described earlier, 7 [α] 580 23 +2.8 (c 2.8, CHCl 3 ). Mi croanalyses were performed on a Hewlett Packard 185 and Carlo Erba 1106 analyzers.…”

α-Pinene-type chiral Schiff bases as tridentate ligands in asymmetric addition reactions

“…Two different syntheses were applied. 10 To assess the configuration of the stereogenic centers, the conformation of the molecules and the intramolecular interactions, the crystal structure was determined for b-lactam 1 and Schiff base 4d. Some details of the diffraction experiments and structural refinement are summarized in Table 1.…”

“…Moreover, salicylidene Schiff bases containing a cis-c-aminoalcohol pinane frame-work were used with limited success as precatalysts in the catalytic oxidation of sulfides into chiral sulfoxides. 10 However, other tridentate Schiff base catalysts have also been applied in asymmetric nucleophilic addition reactions, although only a few reports with high enantioselectivities are known. 11 The main aim of our work was the preparation of chiral Schiff bases derived from (1S,2S,3R,5S)-2-amino-3-hydroxymethylpinane 3 and their application as tridentate ligands for asymmetric synthesis.…”

Stereoselective Synthesis and Antiproliferative Activity of Monoterpene-Fused 2- Imino-1,3-oxazines

“…The transformation of enantiomerically purepinene to -amino acid derivatives such as 1,3-aminoalcohols was recently reported [3,10,15,16], and these synthons have proved to be useful chiral auxiliaries in the enantioselective synthesis of secondary alcohols or pharmacons, e.g. esomeprasol [17][18][19][20][21].…”