Hydrophosphinations stereoselectivity

Regiospeciflc, uncatalysed hydrophosphination of typical Michael acceptors, such as methyl acrylate, has been reported to proceed readily with alkenyl- an alkynyl-phosphine oxides, e.g. R(l )P(H)0. Good stereoselectivity was observed when a chiral electrophile was used. The reaction is believed to proceed owing to the strong... 

Metal complex chemistry, homogeneous catalysis and phosphane chemistry have always been strongly connected, since phosphanes constitute one of the most important families of ligands. The catalytic addition of P(III)-H or P(IV)-H to unsaturated compounds (alkene, alkyne) offers an access to new phosphines with a good control of the regio- and stereoselectivity [98]. Hydrophosphination of terminal nonfunctional alkynes has already been reported with lanthanides [99, 100], or palladium and nickel catalysts [101]. Ruthenium catalysts have made possible the hydrophosphination of functional alkynes, thereby opening the way to the direct synthesis of bidentate ligands (Scheme 8.35) [102]. 

Hydrosilylation, hydroboration, and hydrophosphination of conjugated enynes have been recently employed to access silylated, borylated, or phosphonylated 1,3-dienes with high stereoselectivities. 

The ability of the chiral auxiliary for simultaneous control of P and C chirality was also seen in the asymmetric hydrophosphination of phenyldi[(Z)-prop-l-enyl]phos-phine with high regio- and stereoselectivity under mild conditions (Scheme 6) [47]. 

The asymmetric hydrophosphination of the cyano-functionalized phosphine has also been undertaken in view of the potential for further manipulation of the cyano moiety to formyl and hydroxyl functionalities [58]. This will serve as an elegant method for accessing these functionalized diphosphines. The diastereoselective hydrophosphination reactions of the c -cyano-functionalized phosphine complex ( = 1) gave the chiral l,2-bis(diphosphino)ethane products in high yield (90%) and stereoselectivity S isomer formed exclusively). For the trans analogue, the absolute stereoselectivity was 10 1 with the S isomer being the major product. 

The presence of ester or keto functional group is a critical factor, and nonconju-gated aUenes tested did not undergo this hydrophosphination reaction under the same conditions. The amount of triethylamine in this instance was also found to have an impact on selectivity with 10% of amine (based on diphenylphosphine) being the optimum for achieving the desired regio- and stereoselectivity. 

Apart from being air sensitive, the generally stable M-P coordination renders technical difficulties in the elimination of the tertiary phosphine product in catalytic process involving transition metal ions as catalysts. However, the asymmetric hydrophosphination of aromatic enones could be catalyzed by the same organo-palladium (II) complex with high yields and stereoselectivity (Table 1). 

Ytterbium/imine complex [Yb( / -Ph2CNPh)(HMPA)6] was reported as a catalyst for hydrophosphination of alkynes (Scheme 8.55) [137]. From 52% to quantitative product yields were found in the reaction. Regio- and stereoselective transformation was observed in case of internal alkynes, but the reaction with terminal alkynes gave a mixture of a- and -adducts with the former being... 

Mimeau D, Gaumont A-C (2003) Regio- and Stereoselective hydrophosphination reactions of alkynes with phosphine-boranes access to stereodefined vinylphosphine derivatives. J Org Chem 68 7016-7022... 

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