PAPER: Synthesis of flavones via application of nitrile oxide and the Stille reactions

Gothelf, K. V.; Torssell, K. B. G.

Acta Chem. Scand. 1994, 48, 61–67, doi: 10.3891/acta.chem.scand.48-0061

University of Aarhus, Institute of Chemistry, DK-8000 Aarhus

Abstract

Hydroxylated and methoxylated benzaldehyde oximes have been chlorinated, dehydrohalogenated and cycloadded to tributylstannylacetylene to give 3-aryl-5-tributylstannylisoxazoles in good to excellent yields. The palladium-catalyzed coupling reaction, the so-called Stille reaction, of hindered and electron-rich 2-iodophenols and a 2-iodo-1,4-benzoquinone with 3-aryl-5-tributylstannylisoxazoles gave 3-aryl-5-(2-hydroxyaryl)isoxazoles in moderate to excellent yields. The coupling reactionwas studied under various conditions and with various Pd(II) and Pd(0) complexes. Reduction of the 3,5-diarylisoxazoles with H-2/Raney-Ni, hydrolysis and acid-catalyzed cyclisation gave flavones. The synthesisof 2-iodo-3,5-dimethoxy-1,4-benzoquinone is described.

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