. Can. J. Chem. 69,706 (1991). Using microwaves to carry out organic reactions does not significantly alter the product composition. The small changes in product composition that are observed when microwaves are used arise because the microwave reactions occur at higher temperatures than reflux reactions. The results demonstrate that ions in the reaction mixture alter the heating rate of the microwave reactions. Although scaling-up the reaction leads to a slightly lower rate of reaction (lower percentage yield), one still retains large rate enhancements.
The geminal diazides ethyl α,α-diazidoacetoacetate and α,α-diazidobenzoylacetate were prepared from the corresponding dibromo precursors by nucleophilic azide displacement. Thermolysis of the diazido compounds led to the formation of 2,5-disubstituted 1,3,4-oxadiazoles in high yield.
The Synthesis of the Labdane Diterpenoid Erigerol and of Analogous CompoundsThe synthesis of Erigerol (1) and of analogous compounds in a 23-step sequence is described. The various difficulties of the synthesis and several blind alleys that have been followed are discussed.Einleitung. -Erigerol (l), ein Vertreter der Labdanditerpene, wurde neben vielen
The extent of nitronate formation in seven methyl 4,6-O-benzylidene-3-deoxy-3-nitrohexopyranosides and four methyl 4,6-O-benzylidene-2,3-dideoxy-3-nitrohexopyranosides in dilute potassium hydroxide solution was compared by means of u.v. spectroscopy. Considerable differences were found to exist in the nitromethylene acidities, and these were correlated with stereochemical features of the molecules. A facile manno → gluco epimerization occurring in this series was investigated. It was shown that, in alkaline alcoholic solution, the epimerization proceeds by an elimination–addition via an intermediate nitroalkene if the hydroxyl group at C-2 is acetylated. However, if the hydroxyl is free, the nitroalkene is not an intermediate and, in accord with the low nitromethylene acidity in this particular case, the mechanism is suggested to involve a reverse Henry reaction.
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