Science of Synthesis

Mathey, F., Science of Synthesis Knowledge Updates, (2012) 4, 359.

A number of transformations have been carried out with functionalized phosphametallocenes. In most cases, the aim was the synthesis of chelating ligands incorporating a phosphaferrocene or a phospharuthenocene unit with potentially useful catalytic applications. Along this line, several phosphaferrocene and phospharuthenocene phosphines have been made.[‌95‌–‌98‌] Their use in the rhodium-catalyzed enantioselective isomerization of unprotected allyl alcohols has been highlighted.[‌95‌,‌96‌] In the same vein, chiral phosphaferrocene–dihydrooxazoles have been made and tested in the copper-catalyzed enantioselective conjugate addition of diethylzinc to acyclic enones.[‌99‌,‌100‌] Other works deal with the synthesis of phosphaferrocene–pyrazole,[‌101‌] phosphaferrocene–imidazole,[‌101‌] phosphaferrocene–N-heterocyclic carbene,[‌102‌] and phosphaferrocene–azacymantrene[‌103‌] ligands. The reductive coupling of chiral 2-formylphosphaferrocenes by titanium has been investigated.[‌104‌] The diastereospecificity of the reactions of a 2-formyl-1,1′-diphosphaferrocene with Grignard reagents[‌105‌] and dimethyl phosphite[‌106‌] has been demonstrated. A highly electrophilic phosphacymantrenylcarbenium ion has been used for the alkylation of electron-rich arenes.[‌107‌] The synthetic potential of these phosphametallo­cenecarbenium ions is well illustrated by the synthesis of a spectacular phosphaferrocene analogue of a calixpyrrole from bis(hydroxymethyl)phosphaferrocene ‌26‌ (‌Scheme 35‌).[‌108‌]

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References