Cross-Dimerization of 2,5-Dihydrofuran with Conjugated Dienes Catalyzed by (Chiral Diene)ruthenium(0) Complexes and Origins of the Enantioselectivity

A new chiral diene complex of Ru(0), [Ru(6-naphthalene){ 4-(1S,4S)-1,7,7-trimethyl-2,5-diphenylbicyclo[2.2.1]hepta-2,5-diene}] (2a), catalyzes cross-dimerizations of 2,5-dihydrofuran with conjugated dienes. Treatment of 2,5-dihydrofuran (4a) with 2-phenylbutadiene (5f) catalyzed by 2a (5 mol %) at 30 °C in acetone produces the cross-dimers (E)-3-(3-phenylbut-2-en-1-yl)-2,3-dihydrofuran (6af) and (E)-3-(2-phenylbut-2-en-1-yl)-2,3-dihydrofuran (9af) in 89% yield (6af/9af = 41/48) with high enantioselectivity (91% ee for 9af). The absolute configuration of 9af is determined to be R by single-crystal X-ray spectroscopy. A series of enantioselective cross-dimerizations of 2,5-dihydrofuran with conjugated dienes are assessed for the mechanistic insight into the enantioselective cross-dimerization.