Versatile And Expeditious Synthesis Of Aurones Via IB Group Transition Metal-catalyzed Cyclization

Silver-Phosphine complexes can be utilized as highly efficient catalyst for the cyclization of 2-(1-hydroxy-3-arylprop-2-ynyl)phenols 2 to give product 3, which is the key intermediate to synthesize aurones 5, with good yields and high stereoselectivities in mixed solvent system of water and toluene. Compared with the reported method, the novel process provides a cheaper metal catlalyst and a milder reaction condition.This thesis was focused on the catalyzed cyclization reaction with silver(I)-phosphine complexes as catalysts. The influence of the reaction conditions, such as temperature, solvents, ligands, base were investigated in detail. Cy3PAgCl complex proved to be the best choice of catalysts in water-toluene mixed solvent, and i-Pr2NEt was determined to be a satisfactory base. With the optimized condition, a series of compounds 3 were synthesized, and up to 91% yield was achieved. On the other hand, with fluoride as counter anion, total stereoselectivities to E- and Z-isomer were achieved at high temperature and room temperature, respectively. Further more, by removing water from the reaction mixtures, the toluene solution containing crude products 3 can be treated by MnO2 directly without further purification, and give aurones 5 in good yields.The silver powder catalysts show good to excellent catalytic activities to annulation of 2 with highly regio- and stereoselectivities by the promotion of catalytic amount of phosphine ligands (Ph3P, Cy3P) in a mixed solvent system of water and organic solvent under the higher temperature, and up to 85% yield of 3 was achieved.