Amidinium salts amidine synthesis

Similarly, Gupton et al. have shown that acyclic amidinium salts (63) and vinylogous amidines (65) are reactive and can be utilized for the synthesis of structurally diverse aldehydes (Scheme 11). 

Since alkoxymethyleneiminium salts with nearly any substitution pattern are easy to prepare, this amidine synthesis has attained widespread application. Thus N-unsubstituted, IV-monosub-stituted and lV,A(-disubstituted alkoxymethyleneiminium salts (138) have been transformed to amidinium salts (137) by treatment with ammonia,primary and secondary amines and amine deri-vatives. ... 

The action of ammonia, primary and secondary amines on alkoxymethyleneiminium salts or alkylmercaptomethyleneiminium salts affords amidinium salts. Provided the educts are chosen in such a manner that the substitution pattern of the resulting amidinium salts does not exceed that of A/jV.AT -trisubstituted salts, the amidines can be released from the salts by addition of bases (see also Section 2.7.2.5.3). Very often the alkoxymethyleneiminium salts were prepared in situ and reacted without further purification with the amino compound to give the desired amidine. This amidine synthesis is of special synthetic interest, since it was stated that formamidines, derived from alicyclic amines, e.g. (306 equation 164), which are simple to obtain by this method, are readily transformed to reactive carbanions. Heterocycles, e.g. (307 equation 165), containing amidine structures, are accessible by reaction of appropriate difunctional compounds with iminium salts. ... 

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