Amidination of Amines under Microwave Conditions Using Recyclable Polymer-Bound 1H-Pyrazole-1-carboxamidine

Abstract

A convenient one-step transformation of primary and secondary amines into the corresponding unprotected guanidines using 4-benzyl-3,5-dimethyl-1H-pyrazole-1-carboxamidine and its polymer-bound variant is described. The scopes and limitations of the method, the microwave-assistance of amidination as well as a recycling protocol are examined.

Key words

amines - guanidines - polymer-bound reagent - microwave-assisted synthesis - reagent regeneration

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11

We first tested this transformation with 3-benzylpentane-2,4-dione which was treated with H₂NNH₂·H₂O (CH₂Cl₂, r.t., 24 h) to yield 2a. Then the resulting pyrazole was transformed into 1a (91%) with cyanamide (anhyd dioxane, 120 °C, 4 h).