Preparation of tetraalkylformamidinium salts and related species as precursors to stable carbenes

Abstract

Methods are described for the preparation of a range of N,N,N′,N′-tetraalkylformamidinium and N,N-dialkyliminium ions 4–20 as anhydrous salts for use as precursors to diamino- and amino-carbenes. These methods include a novel method involving nucleophilic addition to formamides followed by trapping with electrophiles such as triflic anhydride, various methods of formamide activation, exchange reactions involving orthoesters and the transamination of amidinium salts, and alkylation methods.