Dibenzophospholes reactions

Phenyl-dibenzophosphole (164) results from the reaction of tetraphenyl-phosphonium chloride with certain lithium dialkylamides a free-radical mechanism... 

Improved variations were described in a later patent [39], Instead of diphenylphosphino groups dibenzophosphole groups were used, which often leads to an increase in rate and selectivity. The rate of reaction was accelerated by high propene pressures, hinting at the common rate equation for hydroformylation under standard conditions. Under optimised conditions (i.e. low CO pressure) l b ratios as high as 288 were obtained for propene. 

Application of the Wittig reaction of a nonstabilized ylide to the synthesis of an ( )-alkene is practically and effectively carried out by the Schlosser modification. Alternatively, the use of a trialkylphos-phonium ylide can produce high ratios of ( )-alkene." Recently, Vedejs has developed a reagent using dibenzophosphole ylides (110) to synthesize ( )-disubstituted alkenes (111) fixnn rddehydes (equation 24). The initial addition of ylide occurs at -78 C, but the intermediate oxaphosphetane must be heated to induce alkene formation. The stereoselectivity in the process is excellent, particularly for aldehydes with branched substitution a to the reacting center. Both the ethyl and butyl yli s have b n utilized. 

Further reports on the preparation of phospholes, e.g. (113), by the addition of phosphines to diacetylenes have appeared. Braye and coworkers found that the reaction was best catalysed by concentrated potassium hydroxide or by means of cuprous or mercury salts. Contrary to previous reports the free radical reaction, catalysed by AIBN, also gave good yields. A full account has now been produced of the low inversion barrier of phospholes (114). The energy barriers to inversion of phos-phindoles (115) and dibenzophospholes (116) are significantly higher, results interpreted in terms of disruption of stabilization due to phosphole aromaticity in the planar transition state. The site of protonation of... 

A sterically hindered arylithium may react with POCI3 to give the diarylphosphinic chloride a specific example of one such synthesis is that of bis(2,4,6-triisopropylphenyl)phos-phinic chloride". Reactions 36" and 37" exemplify the use of monolithiated species. The use of 2,2 -dilithiobiphenyls leads to dibenzophospholes (239/ and the procedure has been extended to include the use of appropriately lithiated quaterphenyls". ... 

A new synthesis giving good yields of highly substituted phosphole oxides (24) is the reaction of aluminium halide complexes of cyclobutadienes (23) with phosphonous dichlorides (Scheme 2). The synthesis of several substituted dibenzophospholes, e.g., (25), has been reported. ... 

A series of papers describes the synthesis (and some reactions) of highly sterically hindered phosphinic acids based on the dibenzophosphole system, e.g., (36) and (37). These papers describe an improved synthesis of 5-phenyldibenzo-phosphole from tetraphenylphosphonium bromide, as well as that of 5-hydroxy-... 

The use of asymmetric catalysts in chiral syntheses is taking on increasing importance. Asymmetric ligands or asymmetric metal complexes used in these transformations are quite expensive and need to be efficiently separated from reaction mixtures and recycled. Scheme 16 shows the preparation of a polymer-anchored dibenzophosphole-DIOP platinum-tin catalysts system. The asymmetric ligand places the Pt-SnClj system in a chiral environment. This catalyst has given the highest enantiometric excesses ever observed in catalytic hydroformylation. The initially achieved 70-83% e.e. values were improved to >95% by the use of triethylorthoformate (TEOF) as the solvent. ... 

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