No abstract

A robust, catalytic enantioselective method to construct challenging, biologically relevant, tertiary ether stereocenters has been developed. The process capitalizes on readily accessible bis(oxazoline) ligands to control the facial selectivity of the addition of copper acetylides to benzopyrylium triflates, reactive species generated in situ. Up to 99%, enantiomeric excesses are achieved with a broad substrate scope. Using density functional theory (DFT) calculations, the origin of the experimentally observed enantiocontrol was attributed to additional noncovalent interactions observed in the transition state, leading to the major enantiomer, such as π-stacking. The resultant substrates have direct applications in the synthesis of naturally occurring bioactive chromanones and tetrahydroxanthones.

The stereocontrolled construction of biologically relevantc hromanones and tetrahydroxanthones has been achieved through the additiono fa lkynes to benzopyrylium trilfates under the influence of copperb is(oxazoline) catalysis. Excellent levelso fe nantiocontrol (63-98% ee) are achieved in the addition of av ariety of alkynes to an array of chromenones with ah ydrogen in the 2-position. Promising levels of enantiocontrol (54-67 % ee)a re achieved in the alkynylation of chromenones with esters in the 2-position,g enerating tertiary ether stereocentersr esembling those frequently found in naturallyo ccurring metabolites.

Silanediol and copper catalysis are merged, for the first time, to create an enhanced Lewis acid catalyst system for enantioselective heterocycle functionalization. The promise of this silanediol and copper catalyst combination is demonstrated in the enantioselective addition of indoles to alkylidene malonates to give rise to the desirable adducts in excellent yield and high enantiomeric excess. From these studies, 1,1'-bi-2-naphthol (BINOL)-based silanediols emerge as one-of-a-kind cocatalysts. Their potential role in the reaction pathway is also discussed.

Silanediols possess unique and complementary catalytic activity in reactions that are likely to proceed through anion binding. This article directly compares silanediols, thioureas, and squaramides in three separate anion-binding processes. The catalytic abilities of select members of each family are directly correlated to association constants.