SYNTHESIS OF 4-ARYL-SUBSTITUTED BUTENOLIDES AND PENTENOLIDES BY COPPER-CATALYZED HYDROARYLATION

We have investigated the effect of the type of protecting group used and the tether length of 4- and 5-hydroxy-substituted 2-alkynoates on the yields and selectivity of the product of hydroarylation. The use of methyl, methoxymethyl, and tert-butyldimethylsilyl (TBS) as protecting groups increased the total yield of the products. While the protected 4-hydroxy-2-butynoates afforded products formed from two or more alkyne substrates, 5-hydroxy-2-pentynoate derivatives exclusively yielded 1:1 adducts. These facts suggest that the product selectivity depends on the distance of the alkoxy group from the alkyne moiety rather than the type of the protecting group. Among the protecting groups used in this study, the TBS group was found to produce butenolides and pentenolides in good total yields via the one-pot hydroarylation/lactonization.