Atom‐efficient: A selective palladium catalyst system is used for the hydroformylation of alkynes (see picture). In this syngas reaction, various alkynes were smoothly transformed to synthetically interesting α,β‐unsaturated aldehydes in good yields with high regio‐ and stereoselectivity.
A facile access to 2,3,6-trisubstituted2H-pyran-5-carboxylates is developed by employing 2-alkyl-2-enals as reactants with acetoacetates. The reaction involves Knoevenagel condensation followed by a 6π-electrocyclization, in which the presence of the C2 alkyl substituent in the enals favors the formation of (E)-Knoevenagel adducts for the ensuing electrocyclization. The resulting 2H-pyrans are hydrogenated