Amino aldehydes, preparations listed

The reaction between a suitable imidatc and an a-aminoaldehyde or a-aminoacetal to form an amidine, which cyclizes to an imidazole, rests largely on the availability of the aminoaldehydes from a-amino acids, which are readily reduced using the Akabori method [2], Dimethyl or diethyl acetals frequently replace the aldehydes in these reactions 13,4]. Table 2.2.1 lists some 2,5-disub.stituted imidazoles prepared (ultimately) from amino acids. It is not possible to introduce a range of substituents at both the 4- and 5-positions by this method unless the amino acid is converted into a ketone rather than an aldehyde (see Section 2.1.1) (Scheme 2.2.2). 

Chan et al. have utilized hybrid binaphthyl amino alcohol for this transformation. The various ligauds prepared by them are listed in Scheme 21.14. AU these ligands were effective only in the case of aryl aldehydes in the presence of dimethyl zinc. The e.e. values varyied from 60 to 90%, and the chemical yields were found to be in the 90% range. 

Certain nucleophilic species add to carbonyl groups to give tetrahedral intermediates that are unstable and break down to form a new double bond. An important group of such reactions is that between compounds containing primary amino groups and ketones or aldehydes. Scheme 8.2 lists some of the more familiar classes of such reactions. At one time, a principal interest in these reactions was for the preparation of crystalline derivatives of ketones and aldehydes for characterization, but more recently, these types of reactions have been studied in detail because they are models of processes that are of importance in biological reactions. In... 

Globally following the method described in [17], the reduced SBs 1-7 depicted in Scheme 17.2 were prepared in alcoholic medium by the condensation of 1 equiv of the appropriate aldehyde with 1 equiv of amino acid in the presence of an equivalent of KOH. Treatment of these condensation products with NaBH4 resulted in the reduction of the imine bonds, yielding the reduced SBs. Five neat V O-complexes 8-12 (Scheme 17.2) were also prepared. The IR spectra of the solid V O-complexes present the characteristic v(V=0) bands at 950-1000 cm . The electron paramagnetic resonance (EPR) parameters for the five V O-compounds are listed in Table 17.1. For 9, 10,11, and 12, the parameters are consistent with either a (COO , 0 phenoiato- C>ROH)eq or a (COO-, 0"phe , ato, OoMF)eq donor set in methanol and dimethyl... 

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