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Borsche–Drechsel Cyclization
The Borsche–Drechsel cyclization is a chemical reaction used to synthesize tetrahydrocarbazoles by the acid-catalyzed cyclization of cyclohexanone arylhydrazones. The reaction was first described by in 1888 and by in 1908. Borsche–Drechsel cyclization is the central step in Borsche–Drechsel carbazole synthesis, where in the first step phenylhydrazine is condensation reaction, condensed with cyclohexanone to form the cyclohexanone phenylhydrazone, and in the final step the resulting tetrahydrocarbazole is oxidized to carbazole itself. Mechanism The reaction has been described in the literature as proceeding in a manner similar to the Fischer indole synthesis. : Here, the acid-catalyzed proton transfer first converts the cyclohexanone phenylhydrazone 1 to the intermediate 2. Subsequently, a heat-induced sigmatropic reaction occurs to produce 3, which is protonated and cyclizes into 4. Elimination of ammonia then leads to the final product, the tetrahydrocarbazole 5. Se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Reaction
A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, energy change as new products are generated. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the Atomic nucleus, nuclei (no change to the elements present), and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive Chemical element, elements where both electronic and nuclear changes can occur. The substance (or substances) initially involved in a chemical reaction are called reagent, reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more Product (c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
