- Highly enantioselective hydrogenation of β-acyloxy and β-acylamino α,β-unsaturated phosphonates catalyzed by rhodium phosphane-phosphite complexes
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The enantioselective hydrogenation of β-(acyloxy)- and β-(acylamino)vinylphosphonates with rhodium catalysts based on chiral phosphane-phosphite ligands has been studied. In the case of the β-(acyloxy)vinylphosphonates, the reaction also produces an achiral phosphonate resulting from the elimination of the benzoate group. High ligand modularity has led to a highly chemo- and enantioselective catalyst for both types of substrates, which afford a good range of β-acyloxy- and β-acylaminophosphonates with enantioselectivities between 90 and 99% ee. Most interestingly, the configuration of the hydrogenation products indicates the same stereochemical sense for the reduction of both types of substrates, which is opposite to that observed before for α-(acyloxy) vinylphosphonates. This observation has been rationalized by assuming the formation of a β-alkyl intermediate during the catalytic cycle, which also explains the formation of the elimination product in the hydrogenation of the β-(acyloxy)-vinylphosphonates. Copyright
- Chavez, M. Angeles,Vargas, Sergio,Suarez, Andres,Ulvarez, Eleuterio,Pizzano, Antonio
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experimental part
p. 2775 - 2794
(2011/12/21)
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- Highly enantioselective hydrogenation of enol ester phosphonates: A versatile procedure for the preparation of chiral β-hydroxyphosphonates
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A study was conducted to demonstrate a procedure for the preparation of chiral β-hydroxyphosphonates. The reaction sequence was investigated and the validity of the approach was demonstrated. The study also reported an olefin hydrogenation reaction, which gives access to a wide variety of chiral β-hydroxyphosphonates 2, with excellent levels of asymmetric induction, which can be converted into the corresponding alcohols. The application of phosphane-phosphite ligands 4 and 5 were investigated in diverse hydrogenation reactions. Unsaturated phosphonates 1 were chosen as substrates, in an effort to broaden the scope of these catalysts. Investigations were also initiated by the development of a convenient procedure for the synthesis of a set of olefins 1.
- Vargas, Sergio,Suarez, Andres,Alvarez, Eleuterio,Pizzano, Antonio
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supporting information; experimental part
p. 9856 - 9859
(2009/10/02)
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