Imine oxidation reaction temperature

Further studies of asymmetric induction in the synthesis of optically active oxaziridines via oxidation of imines with chiral acids and the degree of stereoselectivity of these reactions have been reported. It was found that the degree of stereoselectivity in the conversion of aldimines and ketimines to oxaziridines by (+)-monopercamphoric acid (MPCA) is dependent on the solvent and the reaction temperature (Tables 4 and 5). The stereoselectivity of the reaction does not seem to depend on the nature of the alkyl group attached to nitrogen. ... 

The influ nee of reaction conditions on the stereochemistry of the oxidation of optically act ve or racemic Af-diphenylmethylene a-methylbenzylamines 40 with chiral or achiral peroxy acids to oxaziridines was investigated. It was found that asymmetric induction at the ring nitrogen in the resulting oxaziridine from optically active imine 40 does not depend on the nature of the peroxy acid or the solvent. However, the diastereoselectivity seems to be dependent only on the reaction temperature. The ratio of the resulting oxaziridine diastereomers changed by 10% when the reaction temperature was raised from — 30°C to -t-40°C. On the other hand, the enantioselectivity was found to depend on the chirality of the peroxy acid, the temperature, and the solvent. For example, the optical yield of the major oxaziridine diastereomer decreased from 3.4 to 1.3 when the solvent was changed from chloroform to methanol in the oxidation of racemic 40. 

An interesting oxidation reaction yielding an imine that violates Bredt s rule was discovered in these studies. Methyl homosecodaphniphyllate on oxidation with lead tetra-acetate in dry benzene at room temperature afforded a product, C23H35NO2, which was assigned structure (56) on the basis of chemical... 

Reduction of N-cyano-N-demethylconanine (28a) with lithium aluminium hydride, under nitrogen, afforded the methylenic ge/n-diamine (29) when the reaction was carried out at room temperature, and the secondary amine (28b) was formed when this reaction was carried out in a refluxing solvent (THF). However, in presence of air, the hydroxylamine (28c) and the imines (30) and (31) were formed in small amounts as a result of oxidation reactions. The organo-metallic intermediate (32) can explain the formation of these products. The reduction of (28a) with LiAlH4-AlCl3 led only to the secondary amine (28b). 

Che and coworkers reported the synthesis of new Au(iii) complexes and studied their ability to promote oxidative reactions. Complex XXII efficiently promoted the oxidation of secondary amines to afford the corresponding imines (Scheme 16.38). The protocol requires very mild conditions, with only 0.15 mol% of the catalyst, at room temperature, and using light k >385 nm with a 300-W xenon lamp) and ojygen as oxidants. ... 

The oxidation of /(-amino-substituted iron acyl complexes which are prepared via condensation reactions of iron-acyl enolates and imines or iminium ions26,5 -47-54 generates /(-lactams 32,33,61. Brief treatment with bromine in dichloromethane at low temperature is the usual procedure. 

Titanium silicate molecular sieves not only catalyze the oxidation of C=C double bonds but can be successfully employed for the oxidative cleavage of carbon-nitrogen double bonds as well. Tosylhydrazones and imines are oxidized to their corresponding carbonyl compounds (243) (Scheme 19). Similarly, oximes can be cleaved to their corresponding carbonyl compounds (165). The conversion of cyclic dienes into hydroxyl ketones or lactones is a novel reaction reported by Kumar et al. (165) (Scheme 20). Thus, when cyclopentadienes, 1,3-cyclohexadiene, or furan is treated with aqueous H202 in acetone at reflux temperatures for 6 h in the presence of TS-1, the corresponding hydroxyl ketone or lactone is obtained in moderate to good yields (208). 

The reaction of alkynyllithium compounds with alkoxycarbene tungsten complexes leads to anionic propargyl tungsten complexes (Figure 2.33 see also Figure 3.9). These intermediates are stable at low temperatures and react upon Lewis acid catalysis with aldehydes or A -sulfonyl imines to yield five-membered heterocycles [280]. Oxidative methoxycarbonylation [375] of the intermediate vinyl tungsten complex, followed by elimination of methanol leads to pyrroles or furanes (Figure 2.33 Entry 6, Table 2.22). 

Oxidation is generally complete after addition of the oxone solution. The oxidation is monitored by TLC as follows remove approximately 0.5 mL of the toluene solution from the nonstirring solution, spot a 250-micron TLC silica gel plate, elute with methylene chloride and develop with 10% molybdophosphoric acid in ethanol and heating (camphorsulfonyl)imine R = 0.28 and (camphorylsulfonyl)oxaziridine R = 0.62. If (camphorsulfonyl)imine is detected, stirring is continued at room temperature until the reaction is complete (See Note 8). 

Malonaldehyde (MA) is a major end product of oxidizing or rancid lipids and it accumulates in moist foodstuffs (6). Several MA-protein systems have been studied. Chio and Tappel combined RNAase and MA to demonstrate fluorescence attributed to a conjugated imine formed by crosslinking two e-amino groups with the dialdehyde (7). Shin studied the same reaction and found it to be dependent on pH and reactant concentrations (8). Crawford reported the reaction between MA and bovine plasma albumin (BPA) also to be pH dependent, and of first order kinetics with a maximum rate near pH 4.30. At room temperature 50-60% of the e-amino groups were modified—40% in the first eight hours, the remainder over a period of days (9). 

Carbonyl O-oxides 144, generated in situ by the ozonolysis of vinyl ethers at low temperature (—70 °C), readily undergo [3+2] cycloaddition with imines 145 added to the reaction mixture to afford the corresponding 1,2,4-dioxazolidines 15-18 in 14-97% isolated yields (Scheme 41) <1994J(P1)2449, 1995J(P1)41>. The repetition of these reactions in MeOH results in the quantitative recovery of the initial imines 145. The steric bulk of the a-substituents did not appear to diminish the imines 145 reactivity, because the isolated yields of 1,2,4-dioxazolidines... 

---