No abstract

The Morita-Baylis-Hillman (MBH) reaction has been stablished as an important CÀ C bond-forming transformation between carbonyl-containing compounds and activated olefins. However, the slow reaction rate usually observed with electron-rich electrophilic partners hinders a more widespread use of this reaction. In order to overcome this drawback, the effects of several Brønsted acids on the rate of DABCO-catalyzed MBH reactions were evaluated. The protocol is operationally simple, involving neat and open-flask conditions, and is compatible with a wide range of reagents. We suggest a general acid catalysis mechanism to be responsible for the rate increase. The synthetic versatility of the MBH adducts is exemplified with a two-steps diastereoselective synthesis of the natural product (�)-sitophilure. We hope this acid-mediated protocol to have potential use as a general methodology for the MBH reaction.

We report a direct, straightforward, and regioselective hydration of 1,4-enynes designed from Morita−Baylis− Hillman adducts. Under smooth conditions and short reaction times, gold-catalyzed hydration of internal alkynes provides synthetically useful ketones as single regioisomers in yields higher than 90%. The synthetic usefulness of this protocol was demonstrated by the conversion of selected ketones into biologically valuable α-alkylidene-γ-lactones upon reduction with sodium borohydride. In the course of the scope evaluation, we discovered that this methodology could also furnish α-arylidene-β,γbutenolides.

The Cover Feature illustrates the effect of acetic acid on the rate of the Morita–Baylis–Hillman reaction. The use of acetic acid as a fuel (additive) increases the reaction rate in all tested cases, with special emphasis on electron‐rich electrophilic partners. We believe that a general acid catalysis mechanism is responsible for this increase in reaction rate. More information can be found in the Research Article by G. W. Amarante, F. Coelho et al.