Enantioselective additions to cyclic oxocarbenium ions would provide an efficient route to alpha-substituted oxygen heterocycles, important scaffolds in a number of biologically active molecules. However, controlling facial selectivity in additions to these electrophiles remains challenging, and such enantioselective additions are rare.  Our group has recently developed enantioselective additions of terminal alkynes to racemic isochroman acetals. Here, we report an enantioselective, copper(I)-catalyzed addition of alkynes to racemic chromene acetals. For these substrates, optimal yields and selectivities were observed with use of BF3�OEt2 as Lewis acid and a bis(oxazoline) ligand. This method delivers a wide range of substituted chromenes with particularly high enantioselectivities observed in the alkynylation of 4-substituted chromene acetals.

Enantioselective copper-catalyzed alkynylation of chromene acetals

244th National Meeting (2012)

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