By R Alan Jones; Gerritt P Bean
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Extra info for Chemistry of Pyrroles
5 One-Pot Synthesis of Pyrroles from Ketones, Hydroxylamine, and Acetylene A version of the pyrrole synthesis involving one-pot transformation of ketones into NH- and N-vinylpyrroles has been worked out. Preliminary isolation of oximes is always associated with consumption of reactants, solvents, and time. , for ketoximes having high solubility in water), this procedure presents certain preparative difficulties. To exclude the stage of ketoximes isolation, a possibility of ketone oximation in situ in DMSO and the subsequent application of the oxime solutions in the reaction with acetylene has been studied .
A method for the synthesis of pyrroles and N-vinylpyrroles directly from ketones and acetylene in the system NH2OH·HCl/KOH/DMSO offers a number of essential advantages, that is, the total number of reactants decreases, the auxiliary reactor for oximation in the presence of NaHCO3 is removed from the process, degassing of the reaction mixture (CO2 elimination) is not required, and extraction of the target products from aqueous DMSO is facilitated due to desalting with potassium chloride that is formed at the oximation stage.
To assure more complete shift of equilibrium toward formation of the complex, water is removed in the form of azeotrope with toluene. In reality, the catalytic system represents suspension, a solution of sodium cyclohexanone oximate in DMSO, the phase composition and activity of which is controlled by temperature. The crucial point is that the new catalyst has been elaborated on the basis of NaOH, a cheaper and less aggressive base, which is not applied in all variation of this reaction up to the moment.