Rhodium Carbonyl-Catalyzed Carbonylation of Acetylenes in the Presence of Ethylene Synthesis of 5-Ethyl-2(5H)-furanones

Abstract

The carbonylationo f diphenylacetylene a[4a]w ith Rh₄ (CO)₁₂ triethylamineg ave 3, 4 dipheny1-5-ethylidene-2(5H) - furanone [5] in a 5% yield, in which the ethylideneg roup was derived from the amine. Addition of ethylene to the reaction system resulted in the formation of 3, 4 -dipheny1-5-ethyl-2(5H)-furanone [6a] (16%). By usingp rotic solventss uch as alcohols and aqueousa cetone, t he yield of [6a] was increasedr emarkably( Table1 ). Amongs everal rhodiumc arbonylc omplexesa n d their precursorsu sed as the catalyst (Table2 ), the catalytic, ctivities of Rh₄ (CO)₁₂ and Rh₆ (CO)₁₆ were prominent. Similarly, the carbonylationo f 2butyne gave 3, 4 -dimethy1-5-ethy1(-52 H )-furanone [6b]in a 58% yield, and that of 1-phenyipropyneg ave 5-ethyl-3-methyl-4-phenyl-2(5H)-furanone [6c] and 5-ethy1-4-methy1-3ptieny1-2(H5) -furanone [6d] in 48% and 4% yields, respectively, i ndicatingt he reactiont o be regioselective. At higher temperatures( 150∼220°C)[6a] was mainlyo btainedby the carbonylation of [4a] in ethanol, but at lowert emperatures( 100∼125°C )3, 4 -dipheny1-5-ethoxy2 (5H)-furanone [15] and 3- ( ethoxycarbony1)-2-phenylindanone w[1e6r]e obtained as byproducts, , w hichw ere formed by the participationo f ethanol in the carbonylation. Possible mechanismsfo r the formationso f [6] and [16] are showni n Scheme1 and 2.