Effective Oxidation of Secondary Amines to Nitrones with Alkyl Hydroperoxides Catalysed by (Trialkanolaminato)titanium(IV) Complexes

Abstract

The effective catalytic oxidation of secondary amines to nitrones with alkyl hydroperoxides as the primary oxidants is described. The titanium alkoxide catalysts are protected from the water co-product by the combined use of a tightly binding trialkanolamine ligand and molecular sieves. Nitrones can be obtained in high yields (up to 98%) under homogeneous, anhydrous conditions and even in the absence of solvent. The reactions are fast (2-7 h) and good selectivity and complete conversion can be achieved with as little as 1% catalys

Synthesis and Transformations of Nitrones for Organic Synthesis

“…Alkyl hydroperoxides such as cumyl hydroperoxide (CHP) and t-butyl hydroperoxide can be used as terminal oxidants in combination with (triphenolatoamino)titanium(IV) complexes (method H). 48 For comparison of the various methods for the oxidations of 1,2,3,4-tetrahydroisoquinoline are summarized in Table 2.…”

“…Various catalysts such as SeO 2 (method C), MTO (methods D and E; eq 8), − (trialkanolamino)­titanium­(IV) complexes (method F), and platinum­(II) complex (method G) have been used for the oxidation with hydrogen peroxide. Alkyl hydroperoxides such as cumyl hydroperoxide (CHP) and t -butyl hydroperoxide can be used as terminal oxidants in combination with (triphenolatoamino)­titanium­(IV) complexes (method H) . For comparison of the various methods for the oxidations of 1,2,3,4-tetrahydroisoquinoline are summarized in Table .…”

Symmetrical Tertiary Amines: Applications and Synthetic Approaches

“…[ 110 ] Later in 2010 this protocol was used by the same group to prepare chiral and achiral trialkanolamines and their titanium complexes to use them in catalytic amines to nitrones oxidation. [ 111 ]…”

“…[110] Later in 2010 this protocol was used by the same group to prepare chiral and achiral trialkanolamines and their titanium complexes to use them in catalytic amines to nitrones oxidation. [111] Such trialkanolamines were used not only as ligands but also as a precursor to the chiral phase-transfer catalysts. In 2003 Takabe and co-authors reported the preparation of a series of such chiral aminotriols with R=PhOCH 2 , Ph, Cy, iPr via reaction of the corresponding epoxides with NH 3 .…”

Metal-Free Solvent Promoted Oxidation of Benzylic Secondary Amines to Nitrones with H2O2

“…In addition, several heterogeneous catalysts have also been used. 21 Alternatively, the reaction can be also carried out in the presence of alkyl hydroperoxides, 22 oxone, 23 dimethyldioxirane, 24 m -CPBA, 25 Davis oxaziridine, 26 or molecular oxygen 27 as oxidant.…”