Enantioselective reductive coupling of alkynes and α-keto aldehydes via rhodium-catalyzed hydrogenation:: An approach to bryostatin substructures

Hydrogen-mediated reductive coupling of glyoxal 2 and 1,3-enyne 3 provides (x-hydroxy ketone 4 in 70% yield and 91% enantiomeric excess. Notably, the benzylic ether and diene side chain of 4 remain intact under the conditions of hydrogen-mediated coupling. In four steps, alpha-hydroxy ketone 4 is converted to pyrans 8 and 9, which embody key structural features of the bryostatin recognition domain.