Amidines from thioamides

RCN From amide % yield from thioamide From amidine... 

Tetrakis(dimethylamino)titanium is a useful reagent for preparing amidines from secondary amides. From A X-thionyldiimidazole and secondary amides of boA aromatic and aliphatic carboxylic acids amidines (313 Scheme 50) are formed under mild conditions in moderate to good yields. N-Tosyl-amidines (314) can be obtained by reacting secondary thioamides (aliphatic and aromatic) with tosyl azide. Thiobenzamides have been condensed with anilines to afford amidines (315). Thioamides can be converted to amidines, e.g. (316), by treatment with ammonia in the presence of mercury acetate. ... 

A general route to N-protonated azomethine ylides from Af-(trimethylsilyl-methyl)amidines and thioamides and their cycloadditions to olefins was reported. This is illustrated in a general way in equation 125124. 

Activation of thioamides to thioimidates with alkylation is also applied to the synthesis of amidines. Dijkink et al. [28] applied this method to the synthesis of chiral bicyclic amidines from (5)-malic acid as a key step. However, the amidine was found to be unstable due to isomerization of the imine double bond followed by ehmination of the silyloxy group (Scheme 3.15). 

The reaction of dichlorocarbene with primary amides, amidines, thioamides, and aldoximes all yield the corresponding nitriles. N,N-Disubstituted ureas likewise yield the corresponding N,N-disubstituted amine nitrile. This reaction amounts to a dehydration in the case of primary amides, aldoximes, and N,N-disubstituted ureas the elements of hydrogen sulfide are lost from thioamides, and HCN from amidines. 

Via intermediates Amidines from nitriles via carboxylic acid thioamides and thioiminoester salts... 

Glycoamidines have been readily prepared by a mercury-promoted reaction of the corresponding thioamides with amines.69 TV-Boc protected amidines have been prepared from /V-(Boc) thioamides by treatment with base and mercury(II) chloride (Scheme 34).70... 

Amidines have been prepared from other amidines on insoluble supports by nucleophilic displacement of one amine by another (Entry 1, Table 13.18). Polystyrene-bound thioamides can be converted into amidines by treatment with an aliphatic or aromatic amine in the presence of EDC (Entry 2, Table 13.18). Alternatively, resin-... 

The resulting triazoles can be N-alkylated by treatment with alkyl halides (0.25 mol/L, 30 equiv., DMF, NaOH), but mixtures of the 1-alkylated and 2-alkylated triazoles are obtained [255]. 1,2,4-Triazoles have also been prepared from N-amino-amidines (amidohydrazones Entry 4, Table 15.20), which were prepared from resin-bound thioamides by S-alkylation with methyl triflate followed by treatment with hydrazine [256]. 1,2,4-Tri azoles undergo Michael addition to polystyrene-bound a-acetamido acrylates to yield triazole-derived a-amino acids (Entry 7, Table 15.20). Benzotriazoles have been N-arylated on insoluble supports by treatment with aryl-boronic acids in the presence of catalytic amounts of copper salts (Entry 8, Table... 

Other derivatives of minor importance, such as thioamides, amidoximes, iminoethers, and amidines have been prepared from the corresponding cyanopyridazines. ... 

It has long been known that 1,3-azoles can be assembled from a component providing the two heteroatoms, for example a thioamide or an amidine, and an a-haloketone, A more recent route employs the interaction between the anion of an isonitrile and an aldehyde, thioaldehyde or imine. 

Thiadiazoles carrying identical groups at the 3- and 5-positions are obtained by the oxidation of thioamides 5-chloro-l,2,4-thiadiazoles resnlt from the reaction of amidines with perchloromethyl... 

A solution of the A,-(ethoxycarbonyl)thioamide (10 mmol) and the amidine or the isothiourea [prepared from its HCI salt with NaOMe (NaOEt) in MeOH (ElOH)] (12 mmol) in EtOH or MeOH (10 mL), respectively, was refluxed until the evolution of H2S had ceased, and then for an additional 2 3 h. The mixture was evaporated to dryness under reduced pressure and the residue was washed with cold H,0. 

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