Synthesis of Polysubstituted Furans Based on a Stepwise Sonogashira Coupling of (Z)-3-Iodoalk-2-en-1-ols with Terminal Propargylic Alcohols and Subsequent Au(I)- or Pd(II)-Catalyzed Cyclization—Aromatization via Elimination of H2O.

Recently, we have developed highly regio- and stereoselective carbometalation of 2-alkynols and 2,3-allenols. The organometallacyclic intermediates may be trapped with I2 to afford 3-iodoalk-2-en-l-ols. These 3-iodoalk-2-en-l-ols may readily undergo the Sonogashira coupling with terminal propargyl alcohols to form 4-alkyn-2-ene-1,6-diols. Subsequent cycloisomerization in DMA or CH2CI2 with Au(PPh3)Cl and AgOTf as the catalyst would afford polysubstituted 2-( 1-alkenyl)furans; with PdCl2 as the catalyst and the reaction in DMA in the presence of allylic bromides, the same substrates afforded polysubstituted 2-( 1,4- alkadienyl)furans. In both types of catalyzed cyclization reactions, the elimination of H2O promoted the aromatization to form the furan ring. Different alkyl or aryl groups could be introduced into different positions of furans due to the substituent-loading capability of 3-iodoalkenols and diversity of the terminal propargyl alcohols and allylic bromides. [ABSTRACT FROM AUTHOR]