Abstract:We report the isomerisation of α,β-unsaturated diesters to thermodynamically less favourable β,γ-unsaturated carbonyl compounds in the absence of strongly basic anhydrous or photochemical conditions.
“…Among the ligands screened, the Josiphos ligand ( L6 ) was found suitable and yielded the desired product in with high diastereo- and enantioselectivity. Use of other copper precursors was less efficient, and NaO t -Bu instead of LiO t -Bu yielded no product presumably due to reduced Lewis acidity of Na + 25 , 26 . Enantioselectivity was further improved to 93% ee by decreasing the reaction temperature to 0 °C, which was selected as the optimal condition.…”
Section: Resultsmentioning
confidence: 99%
“…4 ). However, ethylidene malonate was less efficient in the coupling with internal enynes to yield 5n possibly due to competing deconjugation of the malonate 26 and a secondary alkyl-substituted enyne failed to afford the desired product ( 5o ). Fig.…”
Asymmetric construction of C(sp3)–C(sp3) bond with good stereocontrol of the two connecting carbon centres retaining all carbon or hydrogen substituents is a challenging target in transition metal catalysis. Transition metal-catalysed reductive coupling of unsaturated π-substrates is considered as a potent tool to expediently develop the molecular complexity with high atom efficiency. However, such an asymmetric and intermolecular process has yet to be developed fully. Herein, we report an efficient strategy to reductively couple two prochiral conjugate alkenes using a copper-catalysed tandem protocol in the presence of diboron. Notably, this transformation incorporates a wide range of terminal and internal enynes as coupling partners and facilitates highly diastereo- and enantioselective synthesis of organoboron derivatives with multiple adjacent stereocentres in a single operation.
“…Among the ligands screened, the Josiphos ligand ( L6 ) was found suitable and yielded the desired product in with high diastereo- and enantioselectivity. Use of other copper precursors was less efficient, and NaO t -Bu instead of LiO t -Bu yielded no product presumably due to reduced Lewis acidity of Na + 25 , 26 . Enantioselectivity was further improved to 93% ee by decreasing the reaction temperature to 0 °C, which was selected as the optimal condition.…”
Section: Resultsmentioning
confidence: 99%
“…4 ). However, ethylidene malonate was less efficient in the coupling with internal enynes to yield 5n possibly due to competing deconjugation of the malonate 26 and a secondary alkyl-substituted enyne failed to afford the desired product ( 5o ). Fig.…”
Asymmetric construction of C(sp3)–C(sp3) bond with good stereocontrol of the two connecting carbon centres retaining all carbon or hydrogen substituents is a challenging target in transition metal catalysis. Transition metal-catalysed reductive coupling of unsaturated π-substrates is considered as a potent tool to expediently develop the molecular complexity with high atom efficiency. However, such an asymmetric and intermolecular process has yet to be developed fully. Herein, we report an efficient strategy to reductively couple two prochiral conjugate alkenes using a copper-catalysed tandem protocol in the presence of diboron. Notably, this transformation incorporates a wide range of terminal and internal enynes as coupling partners and facilitates highly diastereo- and enantioselective synthesis of organoboron derivatives with multiple adjacent stereocentres in a single operation.
“…Substrates containing a napthyl, and a heteroaryl group such as thiophene, furan, indole were also compatible under the optimal reaction conditions ( 3 i – 3 l ). Furthermore, primary alkyl substituted diesters afforded the corresponding chiral alkylboron compounds ( 3 m and 3 n ) without significantly affecting the reactivity and selectivity of the reaction [19] . However, β‐cyclohexyl substituted α,β‐unsaturated diester yielded the desired product ( 3 o ) with moderate yield and slightly decreased er value.…”
We report the diastereo‐ and enantioselective conjugate addition of chiral secondary borylalkyl copper species derived from borylalkenes in situ to α,β‐unsaturated diesters. In the presence of a chiral bisphosphine‐ligated CuH catalyst, the conjugate addition provides a direct access to enantioenriched alkylboron compounds containing two contiguous carbon stereogenic centers in good yield with high diastereo‐ and enantioselectivity (up to >98:2 dr, >99:1 er) by assembling readily available starting alkenyl reagents in a single operation without using preformed organometallic reagents or chiral auxiliaries. The resulting products were used in various organic transformations. The utility of the synthetic approach was highlighted by the synthesis of (−)‐phaseolinic acid.
“…Furthermore, primary alkyl substituted diesters afforded the corresponding chiral alkylboron compounds (3 m and 3 n) without significantly affecting the reactivity and selectivity of the reaction. [19] However, b-cyclohexyl substituted a,b-unsaturated diester yielded the desired product (3 o) with moderate yield Table 1: Optimization of reaction conditions. [a] Entry BY 2 L Yield [%] [b] er [c] (major) dr [d]…”
We report the diastereo‐ and enantioselective conjugate addition of chiral secondary borylalkyl copper species derived from borylalkenes in situ to α,β‐unsaturated diesters. In the presence of a chiral bisphosphine‐ligated CuH catalyst, the conjugate addition provides a direct access to enantioenriched alkylboron compounds containing two contiguous carbon stereogenic centers in good yield with high diastereo‐ and enantioselectivity (up to >98:2 dr, >99:1 er) by assembling readily available starting alkenyl reagents in a single operation without using preformed organometallic reagents or chiral auxiliaries. The resulting products were used in various organic transformations. The utility of the synthetic approach was highlighted by the synthesis of (−)‐phaseolinic acid.
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