Imines metal catalysis

Peracid oxidation of imines is the most general synthesis of oxaziranes (Section 5.08.4.1.1). Other peroxides and metal catalysis have also been employed. 

Exposure of imidazole to normal Mannich conditions leads to A-(dimethylaminomethyl)imidazole, presumably via attack at the imine nitrogen, followed by loss of proton from the other nitrogen. A-Arylation or A-vinylation of imidazoles or benzimidazole can be achieved efficiently with metal catalysis (see 4.2). 

The addition of a diazocarbonyl compound to an alkene with metal catalysis is an effective method for the formation of cyclopropanes, as discussed above. However, direct addition to aldehydes, ketones or imines is normally poor. Epoxide or aziridine formation can be promoted by trapping the carbene with a sulfide to give an intermediate sulfur ylide, which then adds to the aldehyde or imine. For example, addition of tetrahydrothiophene to the rhodium carbenoid generated from phenyldiazomethane gave the ylide 131, which adds to benzaldehyde to give the trans epoxide 132 in high yield (4.104). On formation of the epoxide, the sulfide is released and hence the sulfide (and the rhodium complex) can be used in substoichiometric amounts. 

Formation of pyrazines and quinoxalines has been a focal point of many years of study. The most common method to make these rings relies on the condensation of 1,2-diamines with 1,2-dicarbonyls in ethanol or acetic acid in 35-85% yields. The mechanism proceeds through a double imine formation. Recently improved methods have been reported, employing transition-metal catalysis and microwaves. ... 

It worth to mention that despite the importance of the Kabachnik-Fields reaction, stereoselective versions for the synthesis of enantioenriched a-aminophosphonates are scarce [212, 213], and only few enantioselective examples have been published to date (for reviews on enantioselective catalytic direct hydrophosphonylations of imines, see Refs. [162a-c]). Organocatalytic examples use well-known chiral binol-derived phosphoric acid organocatalysts (Fig. 12.6,80 and 81) [214], and regarding metal catalysis, chiral scandium(III)-A,A -dioxide and... 

The reduction of imines is potentially useful for the synthesis of enantiomerically pure amines, since chiral amines appear in numerous interesting compounds in nature, and they have also a remarkable use as ligands in metal catalysis or as chiral organocatalysts. However, until 2001, this approach had been mainly explored using metal catalysts [2-10]. 

Chiral alcohols, respectively hydroxy groups, are a common motive in natural products and bioactive compounds. Therefore, the asymmetric reduction of ketones is a frequently used procedure. In contrast to the asymmetric reduction of imines vide infra), only few organocatalytic methods to reduce ketones are known, and mostly transition metal catalysis or enzymatic methods are used. The... 

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