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[摘要]：Trisubstituted piperazinones, piperazines, tetrahydropyrazines, and dihydropyrazinones were prepared in a one-step procedure from easily accessible polymer-supported acyclic precursors containing either a masked aldehyde or ketone group. Acid-mediated unmasking of the aldehyde triggered cyclic iminium formation followed by reduction with triethylsilane present in the cleavage cocktail. The effect of the substituent at the iminium-forming nitrogen was evaluated: whereas complete conversion to the target compounds was observed with N-alkyl, aryl, and phenylsulfonamido derivatives, the N-acyl compound suffered from a partial reduction of the aldehyde to an alcohol. Similarly, ketones readily provided cyclic iminiums with N-alkyl compounds, whereas their cyclization with N-acyl precursors proceeded unwillingly. Interestingly, cleavage of the resin-bound acyclic precursor at 60 degrees C in the presence of triethylsilane resulted in the decomposition of the amide bond and formation of a lactone. An analogous synthetic route was also successfully used for the preparation of piperazines and tested as an alternative route for the synthesis of diazepanones. |
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