Studies On Functionalization Of YNOL Ethers

Enol ethers are an important class of structural units in natural product synthesis, materials science, and chemical biology. In particular, the functionalization of ynol ethers has stood out as one of the most efficient and straightforward methods for the assembly of these molecules. It should be noted that, however, there are only limited methods on the regio-and stereoselective functionalization of ynol ethers. Starting from ynol ethers, we have realized some regio-and stereoselective transformations such as hydroarylation and hydrocarboxylation reactions, giving new effective entries to (Z)- and (E)-enol ethers in good yields with excellent regio- and stereoselectivity. The dissertation consists of two parts:First, a Pd-catalyzed addition of boronic acids to ynol ethers has been developed, delivering trisubstituted enol ethers in good yields with perfect control of the regio-and stereoselectivity. The reaction proceeds under mild conditions and exhibits excellent atom economy and functional group compatibility. Moreover, the resultant products can be converted into pentasubstituted benzenes via the tandem Diels-Alder/aromatization reaction.Second, a silver-catalyzed trans-addition of carboxylic acids to ynol ethers is described. The reaction has a broad scope with respect to carboxylic acids and ynol ethers, delivering (Z)-α-alkoxy enol esters in good yields with excellent regio- and stereoselectivity. Meaningfully, the Ni-catalyzed selective coupling of alkenyl C-OPiv bonds of (Z)-α-alkoxy enol esters with boronic acids enables a convenient route to the access of (E)-enol ethers. In summary, the two-step procedure, being consisted of a hydrocarboxylation and a subsequent Suzuki-Miyaura coupling, offers a formal trans-hydroarylation of ynol ethers, thus providing a good complementary method to our previous work.