Metallation in connection with cross-coupling reactions. Coupling of hindered aryls for the synthesis of 4-phenylpyridines as part of Streptonigrin and Lavendamycin analogues
摘要:
The synthesis of the C-D ring system of Streptonigrin and Lavendamycin alkaloid analogues by cross-coupling under Suzuki's conditions has been studied. Steric hindrance is the main problem. It has been solved either by using strong bases or working in a sealed tube under pressure.
First metalation of aryl iodides: directed ortho-lithiation of iodopyridines, halogen-dance, and application to synthesis
摘要:
Metalation of iodopyridines was successfully achieved by LDA at low temperature. In many cases, lithiation is ortho directed by the iodo group which subsequently ortho-migrates very fast to give stabilized iodolithiopyridines. This procedure was applied to 2-fluoro-and 2-chloro-3-iodopyridines, 3-fluoro-4-iodopyridine, and 2-chloro-3-fluoro-4-iodopyridine. The resulting lithio intermediates were obtained in high yields before being reacted with electrophiles leading to various polysubstituted pyridines. Some of these iodopyridines were used as key molecules for the synthesis of fused polyaromatic alkaloids. Thus, perlolidine, delta-carbolines, and 2,10-diazaphenanthrenes were readily prepared in few steps taking advantage of the iodo reactivity for heteroring cross-coupling.