Nitrogen heterocycles by palladium-catalysed oxidative cyclization-alkoxycarbonylation of acetylenic ureas

Acetylenic ureas readily undergo oxidative cyclization-alkoxycarbonylation reactions in the presence of PdI2 (or Pd/C)-KI as catalyst in methanol under mild conditions (65 degrees C and 24 bar of a 3:1 mixture of CO and air). Cyclization occurs by trans-attack of oxygen or cis-attack of nitrogen functions on the triple bond, followed by stereospecific carbonylation, resulting in E or Z-stereochemistry, respectively. In the case of diacetylenic ureas condensed ring formation occurs. The triple bond can also react stereospecifically with carbon monoxide and methanol to form a maleic group by cis-attack leading to Z-stereochemistry. (C) 1998 Elsevier Science S.A. All rights reserved.