Dibenzophosphole oxides

P-chiral dibenzophosphole oxide (52a) (Scheme 14) shows liquid crystalline behaviour [52], a property that is of interest in the area of electro-optical displays [53]. Chiral resolution of (52a) was achieved by column chromatographic separation of the diastereoisomers obtained following coordination of the o -benzophosphole (52b) to chiral cyclometallated palladium(II) complexes [52]. Notably, the presence of a stereogenic P-centre is sufficient to generate a chiral cholesteric phase. 

Warren has also studied dibenzophosphole oxides. The ketophosphine oxide (230) substrate can be formed and selective reduction to either the erythro (233) or the threo (231) adducts carried out. The normal NaBH4 conditions were used for reduction to the threo isomer and CeCb was added to obtain the erythro adduct. This methodology was applied to the synthesis of ( )- and (Z)-isosafroles (232) and... 

Fig. 1 Structural illustrations of fluorene 1, carbazole 2, dibenzophosphole oxide 3, diben-zothiophene dioxide 4 and dibenzosilole 5 with ring numbering...

Poly(dibenzosilole)s are a relatively new class of compounds for the area of organic electronic materials. Poly(dibenzosilole)s are not easily oxidised and have advantages of solubility and processibility over other polyfluorene analogues, such as carbazoles, dibenzophosphole oxides and dibenzothiophene dioxides. Several groups have already incorporated poly(dibenzosilole)s in the latest organic electronic devices such as OLEDs, OFETs and OSCs and have found improved performance over similar polyfluorene-based devices. With continual advancement in their synthesis, dibenzosilole-based polymers are set to match the popularity of polyfluorenes in organic electronic materials. 

While sodium borohydride is the best-established reagent for this conversion, there are indications that it may not be the most selective. Using a dibenzophosphole oxide derivative as substrate, it was shown that L-Selectride and lithium trielhylborohydride were both capable of giving significantly better stereoselectivity without any drop in overall yield841. 

Dibenzophosphole oxides are prepared by the direct oxidation (H2O2) of the phospholes <69JOCl777> a diarylphosphinic acid can also be used for generating the phosphole ring <56JOC238, 59JOC638) (Equation (28)). 

Dibenzophosphole oxides were synthesized via Pd-catalyzed intramolecular arylation of ort/jo-halodiatylphosphine oxides (Scheme 48). ... 

Scheme 4.23 Proposed mechanism for the formation of dibenzophosphole oxides.

Dibenzophosphole oxides were obtained by the intramolecular cycliza-tion of secondary phosphine oxides having a biphenyl group. The dehydrogenation was accomplished in the presence of palladium(II) acetate (Scheme 44-1)." Modification of the biphenyl moiety of the starting... 

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