Furan-Containing Oligoaryls without Repetitive Units and Tetrasubstituted Furans

A new one-pot furan annulation from corresponding propargylic dithioacetals and aldehydes has been reported recently. The bidirectional growth approach was also employed to the one-pot furan annulation for the synthesis of higher homologues towards molecular wires. It is noticeable that propargylic dithioacetal moiety could still serve as carbon-sulfur bond umpolung even in the presence of an ester group. The iterative divergent/convergent doubling approach provide an efficient strategy for the synthesis of benzene/furan alternating oligoaryls by utilizing our one-pot furan annulation reaction. The substituents on the furan rings can be easily varied by changing the substituents in the starting propargylic dithioacetals. This route provides a useful procedure for the synthesis of alternating benzene/furan oligomers without repetitive units.
A convenient procedure for highly regioselective synthesis of tetrasubstituted furans from the corresponding propargylic dithioacetals is described. Treatment of propargylic dithioacetals with n-BuLi and an aldehyde followed by mercuric acetate-promoted annulation and desulfurization affords the corresponding mercurio-substituted furans. Subsequent replacement of the mercuric moiety with iodine and potassium iodide yield the corresponding 2,4,5-trisubstituted-3-iodofurans. It is noteworthy that although these reactions are multistage, it can be accomplished in one pot. Transition-metal catalyzed cross-coupling reactions of the iodofurans furnish a variety of fully substituted furans.