Semicarbazones, acyclic

An oxidized stage of isohexide nitrates, wherein the remaining hydroxyl group is transformed into the ketone, gives rise to a number of derivatives 161, such as oximes, semicarbazones, acyclic and cyclic acetals, and hydra-zones.154 Among them, 3-amino-2-hydroxypropyl-substituted oxime ethers... 

Significant effort has been focused on bicyclic scaffolds, such as chromanes and indanes, but only recently published research has attempted to establish the role of conformational rigidity in these series, utilizing bicyclic substitutions, or substitution with acyclic derivatives. On the one hand, results from this type of chemistry on an indane scaffold suggested that conformational constraint is not required for Kvl.5 activity [55]. On the other hand, during the study of tetrahydroindolone-derived semicarbazones (see 8i in Table 1), it was observed that replacement of the tetrahydroindolone core with other heteroaromatic cores provided inactive compounds [53]. 

A reduction route similar to that of phenylhydrazones [229] seems to be rather general for azomethine derivatives of hydrazine [229] as it s followed by cyclic and acylic phenylhydrazones, semicarbazones, azines, cyclic hydrazones, and acylated cyclic and acyclic hydrazones [231] under pro tic conditions in DMF, acylated hydrazones of aromatic aldehydes are reduced with saturation of the C=N bond and cleavage of the N-N bond at a more negative potential [232]. The suggestion that the cleavage of the N-N bond precedes the saturation of the azomethine bond is also an essential part of the interpretation of many of the ring contractions of heterocyclic compounds (Chapter 18). 

Mass spectral papers include another compilation of monoterpenoid alcohol spectra, a comparison of fragmentation patterns for camphor and menthone with their oxime, semicarbazone, and nitrophenylhydrazone derivatives, and a comparison of collisional activation mass spectra of ten related acyclic, monocyclic, and bicyclic monoterpenoid hydrocarbons together with derived 7119 ions. ... 

There are some special synthetic approaches as, for example, the reaction between morpholinoenamines of aldehydes and the semicarbazone of oj-bromoacetophenone to give 31. On the other hand, enamines of acyclic ketones gave 32 or 31. In solution 31 is in fast equilibrium with the open-chain compound 33. If traces of acid are added the equilibrium disappears and 34 is formed (88G187).The tetrahydro compound 36 was prepared from 35 after hydrogenolysis and treatment with TFA (98SL1279). Glyoxylate adduct... 

In contrast to the formation of oximes, semicarbazones, and hydrazones of simple carbonyl compounds (the rate of which is governed by attack of the nitrogen nucleophile on the carbonyl group and subsequent dehydration to the product), the carbohydrates differ in that the rates of formation of their acyclic forms (which can condense) also play a role. The rates of all three types of reaction depend on the pH of the medium this is also the decisive factor affecting anomeric interconversion of the sugar and, thus, the rate of these condensation reactions. 

Acyclic semicarbazones usually exhibit a band at 1675-1645 cm for C=N. Acyclic thiosemicarbazones display a weak band at 1650-1630 cm the thiosemi-carbazones of seven aldoses did not have this band, and were therefore considered to have a cyclic structure (Holker, 1964). 

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