Secondary Products of 4-Deoxyosones

Formula 4.59 shows examples of products obtained on the decomposition of 3-deoxy-osones. The best known compounds are 5-hydroxymethylfurfural from hexoses (HMF, II in Formula 4.59) and furfural from pentoses (I in Formula 4.59). Taking the furanoid structures of 3-deoxyosone as a basis (Formula 4.55), 3,4-dideoxyosone is obtained after ring opening, enolization, and water elimination (Formula 4.60). Water elimination from the hemiacetal form of 3,4-dideoxyosone directly yields HMF. Taking into account the water elimination required to form 3-deoxyosone (cf. Formula 4.55), 5-hydroxymethylfurfural is formed from hexose by the stoichiometric elimination of 3 mols of water. 

In the presence of higher concentrations of ammonia, primary amines or amino acids, 3-deoxyosone preferentially gives rise to 2-formyl-5-hydroxymethylpyrrole (III in Formula 4.59) or the corresponding N-alkylated derivatives rather than to HMF. The most important reaction intermediate is 3,4-dideoxyosone (cf. Formula 4.60), which can react with amino compounds with the elimination of water to give the corresponding pyrrole (Formula 4.61) or pyridine derivatives (Formula 4.62). The reaction 

If pyrrole formation occurs with an amino acid, this product can react further (Formula 4.63) to yield a bicychc lactone (V in Formula 4.59). Other secondary products of 3-deoxyosone are compounds with a pyranone structure. In fact, P-pyranone (VI in Formula 4.59) is under discussion as the most important intermediate. It can be formed from the pyranose hemiacetal form of 3-deoxyosone (Formula 4.64). This compound has been identified only in the full acetal form (e. g., with carbohydrates on drying) because only this structure makes a relatively stable end product possible. The compounds mentioned have acidic hydrogen atoms in position 4, easily allowing condensation reactions with aldehydes and polymerization or the formation of brown dyes. 

Another compound obtained from 3-deoxyosone via a relatively complex reaction is maltoxazine (VII in Formula 4.59), which has been identified in malt and beer. This compound could be formed from 3,4-dideoxyosone, which first undergoes a Streaker reaction with the secondary amino acid proline with decarboxylation to give the 1-pyrroline derivative (Formula 4.65). Enolization, formation of a five-membered carbocyclic compound and nucleophilic addition of the hydroxymethyl group to the pyrroline cation yields the tricyclic maltoxazine. In general, the formation of such carbocyclic compounds is favored in the presence of secondary amino acids like proline. 

3-Deoxyosones predominantly form pyrazines and imidazoles with ammonia. The following compounds were isolated from sugar coloring (cf. Formula 4.66). 

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