Methylphosphinite boranes

Although methylphosphinite boranes are usually used as electrophilic precursors to phosphine boranes (see Section 4.3.3.1), they can also be deprotected by amines, affording the corresponding optically pure methylphosphinites. The deprotection reaction is very enantioselective, with retention of configuration at the P centre. Only a few free phosphinites have been prepared with the Juge-Stephan method these are listed in Figure 4.1. 

Table 4.2 Methylphosphinite boranes 9 from aminophosphine boranes 8.

Methylphosphinite boranes react smoothly with organolithium reagents to afford the corresponding tertiary phosphine boranes, as will be discussed in the next section. However, phosphinite boranes are not electrophilic enough to react with other weaker nucleophiles such as alcohols, amines or thiols. More reactive precursors, capable of producing a wide variety of phosphorus compounds, were needed. In phosphorus chemistry halophosphines, and chlorophosphines 27 in particular, are essential synthons (Scheme 4.12) as nucleophilic (after transformation into metal phosphides 28) and electrophilic building blocks. 

The reaction of methylphosphinite boranes with organolithiums at low temperature affords the corresponding P-stereogenic tertiary phosphine boranes by substitution of the methoxy group and inversion of configuration at the phosphorus atom (Scheme 4.17). 

Table 4.4 Phosphine boranes 10 prepared from methylphosphinite boranes 9. ...

Martens and co-workers used several oxazaphospholidine boranes to prepare methylphosphinite boranes (Scheme 4.54). 

Deboronation of 22 in refluxing diethylamine affords 23 in quantitative yield whereas methylphosphinites 24-26 have been reported by Muller and co-workers after borane decomplexation with morpholine at room temperature. The absolute configuration of 24 was confirmed by the X-ray structure of a derived palladium complex. 

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