Thioamides, resin-bound

Support-bound C,F I-acidic compounds, such as acetoacetamides, react with isocyanates under basic conditions to yield amides through C-carbamoylation [71]. Similarly, polystyrene-bound aryllithium compounds can be converted into benzamides by treatment with isocyanates [111]. These reactions are closely related to C-thiocarbamoyla-tion, which has been used for the solid-phase synthesis of thioamides (see Section 13.9). Amides have also been prepared by C-alkylation of resin-bound N-acylaminals with allyltrimethylsilane or diethylzinc (Entry 11, Table 13.7). 

Table 13.21) or from amides by treatment with Lawesson s reagent. Thioamides can also be prepared on cross-linked polystyrene by the addition of H2S to nitriles (Entry 5, Table 13.21), by thiocarbamoylation of resin-bound organolithium compounds (Entry 6), or by the acylation of amines with reactive thio acid derivatives (Entry 7, Table 13.21). 

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... 

In a solid-phase combinatorial approach, resin-bound esters 151 underwent Tebbe-mediated methylenation, followed by bromination with Bt2 to give the corresponding dibromides 152. These were reacted in turn with a range of thioamides in a large excess to give the 2,4-disubstituted thiazoles 153 (Scheme 57). The product was easily separated from the remaining thioamide by treatment with 5-(4 -chloromethylphenyl)pentylpolystyrene resin (CMPP resin) <1998CC2019>. 

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-... 

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