Salts amidinium

It is obvious that N,0-bis(trimethylsilylated)acetamides or N,0-bis(trimethyl-silylated)formamides 22 or N,0-bis(trimethylsilyl)benzamide 296 should react likewise with the hydrochlorides or hydriodides of primary or secondary amines or with the free amines in the presence of equivalent amounts of e.g., NH4CI or NH4I to give the corresponding amidinium salts. 

Amidinium salt 199 <2000IC105> has been prepared from 40 by reaction with 1,2-dibromoethane in acetonitrile at room temperature which was then reduced with NaBH4 to the ligand, dimethylated derivative 200 (Scheme 29)... 

In an approach toward a synthesis of tetraponerine 37, Gevorgyan first synthesized the fully aromatic tricyclic system 49 and then reduced it over two steps, first via hydrogenation under pressure (50 psi) to give 36 followed by a second reduction by lithium aluminium hydride of the amidinium salt (Scheme 1) <2002OL4697, 2004JOC5638>. 

In the examples above the sulfur dichloride links together two carbon atoms. It is equally possible to link two nitrogen atoms, as illustrated by the formation of a 1,4,2,3,5,6-dithiatetrazine (25) from a hydrazodicarboxyl-ate ester.30 Amidinium salts afford 1,2,3,5-dithiazolium salts (26).31... 

Another supporting piece of evidence was obtained in a study of the reaction of 5-nitropyrimidine with benzamidine hydrochloride in the absence of triethyl amine (which usually was added to liberate the free benzamidine). In amidinium salts the C-N bonds are about equal in length [1.314 A... 

A somewhat similar isomerization was observed with the sultam 5-methylimino-4-phenyl-l,3,4-dithiazolidine 1-dioxide (17 i = H). On heating at 60°C in the presence of benzoyl chloride, rearrangement into the isomeric 5-phenylimino-4-methyl-l,3,4-dithiazolidine 1-dioxide (19, 1 = H) was found (Scheme IV.ll). As intermediate can be proposed the amidinium salt 18 (78JOC4951). Furthermore, NMR-controlled test tube experiments revealed that this rearrangement also occurs under influence of aluminum trichloride and methanesulfonyl chloride. Also, the 2-phenyl derivative 17 (R = CeHs) could be isomerized it required heating in acetone with m-dichlorobenzoic acid as catalyst (Scheme IV.ll). 

Page, M. I., and Webster, P. (1990), The hydrolysis of azetidinyl amidinium salts. Part 1. The unimportance of strain release in the four-membered ring, J. Chem. Soc. Perkin Trans., 2, 805-811. 

Palladium on charcoal (Pd/C) is commonly used in the catalytic hydrogenation of pyrimidines in acidic media to form 1,2,4,5-tetrahydro derivatives which are stabilized as amidinium salts (62JOC2170, 65JCS1406). Platinum effects hydrogenation of the 5,6-double bond of uracils, for example, in the addition of deuterium to produce [5,6-2H2]5,6-dihydrouracil. The use of rhodium-on-charcoal and Raney nickel also gives good results. The addition of hydrogen to the 5,6-bond of thymidine and other 5-substituted uridines is stereospecific with rhodium-on-alumina as catalyst. 

Treatment of the amidinium salt (96) with LDA was found to produce the alkene (97) and the stable carbene (98).98 The dimerization of the carbene was found to be very slow and so the initial formation of alkene (97) was explained by reaction of the carbene... 

Cationic dyes with delocalized charge are classified with the methine dyes (see Section 2.6). They may be viewed as vinylogous amidinium salts 3 [1] ... 

The selectivity of acylations or alkylations of polyamines can also be modulated by protonation [78] or by conversion to cyclic aminals [71, 79, 80]. The latter strategy has, for instance, been used successfully for the preparation of monofunctionalized 1,4,7-triazacyclononanes (Scheme 10.18). In this reaction the first alkylation leads to the formation of an amidinium salt, which is more difficult to alkylate than a tertiary amine. Thus, the use of only one equivalent of alkylating agent leads to a clean monoalkylation. 

The absolute stereochemistry of the trinem 15 has been established and its debenzylated derivative shown to have interesting biological activity in contrast to its 5/3-methoxy epimer <1995BML2535>. The absolute stereochemistry of the amidinium salt 16 was established by X-ray crystallography. This technique of salt formation has been used by several workers to obtain suitable crystalline derivatives from carboxylic acids <1999T3427>. 

The Gobel group later reported the development of a new C2-symmetric chiral bis-amidinium salt 126c, which was applied to the same diene-dienophile system [114]. Compound 126c (1 equiv.) increased the rate of the cycloaddition reactions by more than 3000-fold compared to the non-promoted reactions. Also of interest is the dramatic increase - and reversal - in the regioselectivities of the reactions (Table 6.40). 

Comparison of 34E4 with a less proficient catalyst shows that merely positioning a carboxylate in a hydrophobic binding pocket does not result in efficient general base catalysis. Antibody 4B2, generated against cationic amidinium salt 14 (Scheme 4.5),... 

---