Enol phosphonoamides

The reduction of a ketone to an alkene is feasible not only for unsaturated ketones (Figures 17.68 and 17.71) but for saturated ketones as well. To this end, the latter can be converted into enol phosphonoamidates or enol dialkylphosphonates via suitable lithium eno-lates. One substrate of each type is shown in Figure 17.73 (A and B). Lithium dissolved in EtNH2/iert-BuOH mixtures is a suitable reducing agent for both these compounds. Their Cvp2—O bond is cleaved by a sequence of three elementary steps with which you are famil-... 

Fig. 14.63. Ketone -> alkane reduction via enol phosphonoamidates (for one way to prepare A, see Figure 10.21) and enol dialkylphosphates (one way to prepare B is to use a combination of the methods depicted in Figures 10.17 and 10.22). The cleavage of the Cspi—O bond of the substrates occurs in analogy to the electron transfers in the formation of methylmagnesium iodide (Figure 14.37). The alkenyllithium intermediates are protonated in the terminating step to afford the target alkenes.

Protected-amino phosphonic acid monoesters 51 are usually activated by conversion to the phosphonochloridates 52, then coupled with appropriate amine components such as C-protected amino adds or peptides to give phosphonoamidates 53 (Scheme 17). This procedure is in contrast to typical peptide coupling conditions, in which carboxylic acid chlorides are avoided because of their susceptibility to epimerization at the a-carbon. Since enolate-... 

---