A copper(I)/phosphine system that homogeneously catalyses the alkynylation of formaldehyde with acetylene or terminal alkynes is reported. Using acetylene at atmospheric pressure, the catalyst consisting of < 1 mol% copper(I) phenylacetylide and a trialkyl bisphosphine ligand shows a high selectivity towards the formation of propargyl alcohol rather than 1,4-butynediol, which is not reported for common heterogeneous copper acetylide catalysts. The biphasic water/toluene reaction mixture allows the separation of targeted products with the aqueous layer and catalyst recycling via the organic layer.

We disclose a highly regioselective, catalytic one‐step dehydrogenation of α‐substituted cyclic ketones in the presence of 2,3‐dichlorobenzo‐5,6‐dicyano‐1,4‐benzoquinone (DDQ). The high regioselectivity originates from a phosphoric acid‐catalyzed enolization, selectively affording the thermodynamically preferred enol, followed by the subsequent oxidation event. Our method provides reliable access to several α‐aryl and α‐alkyl substituted α,β‐unsaturated ketones.

Wir berichten über eine hochregioselektive, katalytische einstufige Dehydrierung von α‐substituierten cyclischen Ketonen in Gegenwart von 2,3‐Dichlorbenzo‐5,6‐dicyano‐1,4‐benzochinon (DDQ). Die exzellente Regioselektivität beruht auf einer Phosphorsäure‐katalysierten Enolisierung, die selektiv das thermodynamisch bevorzugte Enol liefert. Die anschließende Oxidation ermöglicht einen zuverlässigen Zugang zu mehreren α‐Aryl‐ und α‐Alkyl‐substituierten α,β‐ungesättigten Ketonen.