Phosphine Phosphinic esters, silylation, activation

Dialkyl(trimethylsilyl)phosphines undergo 1,4-addition to a,/3-unsaturated ketones and esters to give phosphine-substituted silyl enol ethers and silyl ketene acetals, respectively. A three-component coupling reaction of a silylphosphine, activated alkenes, and aldehydes in the presence of a catalytic amount of GsF affords an aldol product (Scheme 76).290 291... 

In related chemistry, the borane/silane catalytic system can cleanly dealkylate phosphonic and phosphinic esters RPO(OR,)2 or R2PO(OR/) to give silyl esters with trialkyl silanes.259 If more active silane reagents like Ph2SiH2 or PhSiH3 are employed, catalytic reduction to primary or secondary phosphines is observed. Mechanistic experiments strongly support a silane activation pathway for this chemistry. 

The role of silylated reagents in the formation of oligopeptides has been explored . Here, the bis(trimethylsilyl) ester of the [l-(trimethylsilylamino)alkyl]phosphonic acid is coupled with an activated A -cbz-amino acid and the silyl groups are subsequently removed under aqueous conditions the process can then be repeated. Oligopeptides have also been obtained as the result of enzyme catalysis when the condensations between amino carboxylic esters and (a) A -protected (aminoalkyl)phosphonic esters or (b) A -protected [(aminoalkyl)methyl]phosphinic esters is brought about in the presence of (a) alkaline phosphatase (Ej) and phosphodiesterase (E2) and (b) alkaline phosphatase and total bee venom (E3) (the latter aiding in the removal of both carboxylate ester and A -acetyl groups) ... 

On the synthetic side, single diastereomers of P-keto phosphine oxides have been generated from intermolecular acylation of phosphine oxides using either chiral esters or chiral phosphine oxides. In most cases, reduction of the ketone products was not affected by the presence of extra chiral centres. Addition of metallated phosphine oxides to proline-derived ketoaminals provides a new route to optically active P-hydroxy phosphine oxides. The P-hydroxy phosphine oxide 97 has been prepared by the caesium fluoride mediated reaction of silyl-substituted phosphine oxide 98 and benzaldehyde." The synthesis of two (E)-(6-hydroxy-2-hexen-l-yl)diphenylphosphine oxides (99) has been reported. The Horner-Wittig reactions of these compounds with various carbonyl compounds... 

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