Bond Variant

A convenient method of synthesis of pharmacologically attractive imidazoquinoxaline derivatives 75a-g has been described (DeMoliner and Hulme 2012b). The method involves the three-component reaction of A-Boc-o-phenylenediamines 76a-d with glyoxylic acid derivatives, namely, with ethyl glyoxylate (see Sect. 4.4) and benzylglyoxylamide 77, with the participation of tosylmethyl isocyanides. The reaction is carried out under microwave irradiation [the Van Leusen and Van Leusen modification (2012)]. It is likely that, first, the condensation of aldehyde at the free amino group of compounds 76a-d leads to imines 78a-d, which are 

The strategy of Van Leusen and Van Leusen (2012) served as a basis for the development of a one-pot process, which made it possible to synthesize imidazo [l,5-a]quinoxalines with the use of phenylglyoxaldehyde instead of benzylgly-oxylamide (see Sect. 4.4) (DeMoliner and Hulme 2012a). 

At the same time, aldehydes with electron-donating substituents and halogen atoms ensure the highest yield of imidazo[l,5-a]quinoxahnes 95 (Verma et al. 2013). 

Closure of bonds in synthesis of imidazoquinoxalines 108, according to the fragmental approach used by us, is shown in Fig. 4.5. 

5 Synthesis of lmidazo[l -o]quinoxalines Based on Quinoxaline Derivatives 

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Fig. 14. Conformational map for helices with i to i-4 hydrogen bonding (variants of the a-helix). The shaded areas represent those conformations which allow acceptable hydrogen bonding. Conformations inside the area (marked by 1) enclosed by the line (as shown more distinctly in Fig. 13) are sterioally allowed for single-stranded helical polyglyoine. Only conformations lying inside both areas satisfy simultaneously all criteria. The positions of the right- and left-handed standard a-helices are shown by circles, those of the cu-helioes are shown by triangles (Leach et al., 1966b).

We thus have the families cycloalkanes, cycloalkenes, and cycloalkynes, as well as the multi-double and triple-bond variants such as cycloalkadienes and -atrienes, and cycloalkadiynes, -atriynes, etc. Naming the cyclo compounds corresponds to the naming of the straight-chain forms except that carbon atoms are numbered such that substituents are on the lowest numbered carbon atoms. This... 

The term insertion reactions (see Section 11) designates a rather broad collection of processes in which the overall reaction corresponds to insertion of an unsaturated molecule (X) into a metal-ligand (M-Y) bond. Variants of processes encompassed by this designation are depicted schematically by... 

In a fashion similar to the above, one may like to consider the following localized cr orbitals for their possible combinations. Their respective anti-bonding variants are also shown. 

Design of the imidazo[l,5-a]quinoxaline system on the basis of imidazole derivatives has been much less studied than the synthesis based on quinoxaline derivatives. Three variants of assembly of such a tricyclic system are mainly used intramolecular cycUzation of imidazole derivatives with formation of the C(4)-N(5) and C(9a)-N(10) bonds (variants A2i and A4i, respectively) and intermolecular condensation with equivalents of monoatomic carbon synthons with the simultaneous formation of the C(3a)-C(4) and C(4)-N(5) bonds (variant Bli) (Fig. 4.4). Other routes are represented by single examples. 

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