Regio- and Enantioselective Linear Cross-Dimerizations between Conjugated Dienes and Acrylates Catalyzed by New Ru(0) Complexes

New naphthalene complexes of Ru(0) with various Ru­(η⁶-naphthalene)­(cyclic diene) (<b>3</b>) ligands catalyze linear cross-dimerization between conjugated dienes and acrylates. One of the noteworthy catalysts is the dibenzocyclooctatetraene complex <b>3d</b>, which shows high catalytic activity for the cross-dimerization between 1,3-pentadiene and methyl acrylate to give the cross-dimers in 99% yield (branch/linear = 77/23) within 1 h at 50 °C with 1 mol % catalyst loading. When Ru­(η⁶-naphthalene)­[(−)-Ph-bod*] (<b>3f</b>) was used as the catalyst, treatment of 2,4-dimethylhexa-2,4-diene with <i>tert-</i>butyl acrylate produced the chiral cross-dimer in 44% yield with 49% ee. This is the first example of enantioselective cross-dimerization between conjugated dienes and substituted alkenes

Regio- and Enantioselective Linear Cross-Dimerizations between Conjugated Dienes and Acrylates Catalyzed by New Ru(0) Complexes

New naphthalene complexes of Ru(0) with various Ru­(η⁶-naphthalene)­(cyclic diene) (<b>3</b>) ligands catalyze linear cross-dimerization between conjugated dienes and acrylates. One of the noteworthy catalysts is the dibenzocyclooctatetraene complex <b>3d</b>, which shows high catalytic activity for the cross-dimerization between 1,3-pentadiene and methyl acrylate to give the cross-dimers in 99% yield (branch/linear = 77/23) within 1 h at 50 °C with 1 mol % catalyst loading. When Ru­(η⁶-naphthalene)­[(−)-Ph-bod*] (<b>3f</b>) was used as the catalyst, treatment of 2,4-dimethylhexa-2,4-diene with <i>tert-</i>butyl acrylate produced the chiral cross-dimer in 44% yield with 49% ee. This is the first example of enantioselective cross-dimerization between conjugated dienes and substituted alkenes

Ru(0)-Catalyzed C3-Selective Cross-Dimerization of 2,5-Dihydrofuran with Conjugated Dienes

Cross-dimerization of 2,5-dihydrofuran with conjugated dienes enables a straightforward and efficient synthesis of C3-substituted 2,3-dihydrofurans. The reaction has been achieved by Ru­(η⁶-naphthalene)­(η⁴-1,5-COD) (<b>1</b>) (3–10 mol %) in acetone at room temperature. This protocol is also effective for branched and linear internal conjugated dienes. The stereochemistry of the products suggests that the reaction involves the oxidative coupling step between <i>cisoid</i>-1,3-dienes and 2,5-dihydrofuran at a Ru(0) center

Ru(0)-Catalyzed C3-Selective Cross-Dimerization of 2,5-Dihydrofuran with Conjugated Dienes

Cross-dimerization of 2,5-dihydrofuran with conjugated dienes enables a straightforward and efficient synthesis of C3-substituted 2,3-dihydrofurans. The reaction has been achieved by Ru­(η⁶-naphthalene)­(η⁴-1,5-COD) (<b>1</b>) (3–10 mol %) in acetone at room temperature. This protocol is also effective for branched and linear internal conjugated dienes. The stereochemistry of the products suggests that the reaction involves the oxidative coupling step between <i>cisoid</i>-1,3-dienes and 2,5-dihydrofuran at a Ru(0) center

In Situ Routes to Catalytically Active Ru(0) Species by Reduction of Readily Available, Air-Stable Precursors

Cross-dimerization of a conjugated diene with a substituted alkene catalyzed by in situ reduction of an air-stable Ru­(II) catalyst precursor has been achieved. Reaction of 2,3-dimethylbutadiene with styrene is catalyzed by [Ru­(acac)₂(η⁴-1,5-COD)] (<b>2a</b>) (5 mol %) with BuLi (10 mol %) at 50 °C for 6 h in hexane, giving the cross-dimers in 99% yield ((<i>E</i>)-4,5-dimethyl-1-phenylhexa-1,4-diene (<b>3a</b>)/(<i>E</i>)-4,5-dimethyl-1-phenylhexa-2,4-diene (<b>3b</b>)/isomers = 84/9/7). Because neither <b>2a</b> nor BuLi separately catalyzes the cross-dimerization and reduction of <b>2a</b> with BuLi in the presence of naphthalene produces [Ru­(η⁶-naphthalene)­(η⁴-1,5-COD)] (<b>1a</b>), the active species in this catalysis is considered to be a Ru(0) compound. Interestingly, this in situ reduction method of Ru­(II) using BuLi can be applied to the cross-dimerization using an ester such as methyl acrylate. Alternatively, an air-stable Ru­(II) complex having a labile arene ligand such as [RuCl₂(η⁶-anisole)]₂ (<b>5c</b>) (5 mol %) with Na₂CO₃ (40 mol %) in the presence of 1,5-COD (20 mol %) at 100 °C for 6 h in 2-butanol also catalyzes the same cross-dimerization in 62% yield. These protocols provide facile methods for production of unsaturated linear compounds by the cross-dimerization using air-stable Ru­(II) catalyst precursors