Combined Transition‐Metal‐ and Organocatalysis: An Atom Economic C3 Homologation of Alkenes to Carbonyl and Carboxylic Compounds

A combination of regioselective room‐temperature/ambient‐pressure hydroformylation (transition‐metal catalysis) and decarboxylative Knoevenagel reactions (organocatalysis) allowed for the development of an efficient, one‐pot C3 homologation of terminal alkenes to ( E )‐α,β‐unsaturated acids and esters, ( E )‐β,γ‐unsaturated acids, ( E )‐α‐cyano acrylic acids, and α,β‐unsaturated nitriles. All reactions proceed under mild conditions, tolerate a variety of functional groups, and furnish unsaturated carbonyl compounds in good yields and with excellent regio‐ and stereocontrol. Further, an iterative C2 homologation of ( E )‐α,β‐unsaturated carboxylic acids is possible through a combination of decarboxylative hydroformylation employing a supramolecular catalyst followed by decarboxylative Knoevenagel condensation with an organocatalyst.