Two-Step Synthesis of (Z)-3-Aryl-5-(arylmethylidene)butenolides by an Ivanov Reaction/Silver(I)-Catalyzed Lactonization/In Situ Dehydration Sequence

A stereoselective synthesis of the title compounds was developed. Hexane- and amine-free THF solutions of α-lithiated lithium arylacetates (‘arylacetic acid dianions’) were aldol-added to 3-arylpropynals. This gave 2,5-diaryl-3-hydroxypent-4-ynoic acids with up to a 72:28 preference for the anti -diastereomer (27 examples + 1 exception). When treated with Ag 2 CO 3 (1–20 mol%) in DMF at room temperature for 2.5 days, the respective mixtures underwent regio- and stereoselective lactonizations followed by an in situ dehydration. Thereby 3-aryl-5-(arylmethylidene)butenolides were obtained with a Z -configuration of the oxygenated C=C bond. Their overall yields ranged from 46% to 83% (1 exception: 28%). Three 3-aryl-5-(arylmethyli­dene)butenolides contained a C–Br and/or a C–I bond. They allowed a subsequent Pd-catalyzed C–C coupling, which furnished follow-up butenolides.