Abstract
The mechanism of osazone formation has been subject of many studies during a vast period of time. However, the regiochemistry related to osazones remained an unsolved problem until recently that we presented our theoretical findings that explain the factors that direct the regiochemistry of osazone formation. Now, we wish present to the teaching community this subject, as well as a discussion of an example of mixed osazone formation. This new topic includes the factors that conduce to the main product. This communication will fill a gap existing in the Organic Chemistry textbooks.
Highlights
An aldose reacts with three equivalents of phenylhydrazine, forming a vicinal bis-phenylhydrazone, the osazone
We have found that the regiochemistry in fructosazone is established in the oxido-reduction that occurs at C-1, C2, after the phenylhydrazone is formed
The oxido-reduction step has been explained as a 1,4-hydrogen transfer via a cyclic, concerted five-member reaction mechanism
Summary
An aldose reacts with three equivalents of phenylhydrazine, forming a vicinal bis-phenylhydrazone, the osazone. The paper is centered in the regioselective rearrangement of fructose phenylhydrazone to 2-deoxy-2-phenylhydrazinoD-glucose. This key intermediate forms glucosazone after several steps. This rearrangement was observed for the first time by Heyns [6,7], and is known as the Heyns rearrangement and as the retro-Amadori rearrangement. He employed fructose and 10% NH4OH, as well as liquid ammonia
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