The Reaction of N-Trimethylsilyl-Substituted Heteroarylamines with Esters and Thioesters: An Efficient Protocol To Access Diheteroarylamides

The S-benzyl thioester and methyl ester derivatives of a representative 4-pyridinone-based carboxylic acid were sufficiently activated to react efficiently in amide coupling reactions with the amide anion generated in situ from the N-trimethylsilyl derivative of different weakly nucleophilic heteroarylamines. In acetonitrile as solvent, the precipitated diheteroarylamide products were isolated in pure form by vacuum filtration. This simple amide bond forming protocol can be readily adapted to the parallel synthesis of compound libraries.

Some New Pyrido[2,3-d]pyridimines and their Nucleoside of Biological Importance

Chalcones (I) reacted with malanonitrile and ammonium acetate yielded 2-amino-3-cyano-4,6-disubstituted pyridines (II) in excellent yield. 4-Amino-5,7-disubstituted pyrido [2,3-d]pyrimidine-2(1H)-thiones (III), 4-amino-5,7-disubstituted pyrido[2,3-d]pyrimidines (IV) and 4-imino-3,5,7-trisubstituted pyrido[2,3-d]pyrimidin-2(1H)-ones (V) have been synthesized by the condensation of compound (II) with thiourea, formamide and arylisocynate respectively. The ribofuranosidesviz. 4-amino-5,7-disubstituted-1- [2',3',5'-tri-o-benzoyl-β,D-ribofuranosyl]pyrido[2,3-d]pyrimidine-2-(1H)-thiones (VI) and 4-imino-3,5,7- trisubstituted-1- [2',3',5'-tri-o-benzoyl-β,D-ribofuranosyl] pyrido [2,3-d] pyrimidine-2(1H)-one (VII) were synthesized by converting compounds III and V to trimethylsilyl derivative in situ by reacting them with hexamethyldisilazane to give corresponding ribofuranosides withβ-D-ribofuranose-1-acetate-2,3,5-tribenzoate. Compounds III-V and their ribofuranosides have been screened for antimicrobial and antifungal evaluations.

Syntheses of Allyl- and 3-Silylpropyl-substituted Salen-like Tetradentate Ligands via Hypercoordinate Silicon Complexes

The reaction of allylchlorosilanes (AllSiCl3, AllSiPhCl2) with the tetradentate salen-like ligand 1, o-HO-p-MeO-C6H3-C(Ph)=N-(CH2)2-N=C(Ph)-C6H3-p-OMe-o-OH, yields pentacoordinate silicon complexes of an allyl-substituted ligand system (o-O-p-MeO-C6H3-C(Ph)=N-(CH2)2- N-C(Ph,All)-C6H3-p-OMe-o-O)SiR (2a: R = Ph, 3: R = Cl). The allyl shift step involved in the formation of 2a and 3 probably occurs via an intermediate hexacoordinate silicon complex. This reaction is diastereoselective. The missing diastereomer of 2 (2b) was prepared using an alternative synthesis route, which starts from the trimethylsilyl derivative of ligand 1 o-Me3SiO-p-MeO-C6H3-C(Ph)=N- (CH2)2-N=C(Ph)-C6H3-p-OMe-o-OSiMe3. The diastereomers of 2 obtained from modified reaction pathways give rise to suggestions about the mechanism of formation of these complexes. Further functionalization of the allyl-substituted ligand system of 3 was carried out by hydrosilylation with HSiCl3 to yield complex 4 (o-O-p-MeO-C6H3-C(Ph)=N-(CH2)2-N-C(Ph)[(CH2)3-SiCl3]- C6H3-p-OMe-o-O)SiCl.