Dibenzophospholes, 5-substituted

Internal alkenes. Dibenzophosphole- and phenoxaphosphino substituted xantphos ligands 31 and 32 [62] (Figure 8.14) show a high activity and selectivity in the rhodium catalysed linear hydroformylation of 1-octene (l b = > 60). More importantly, ligands 31 and 32 exhibit an unprecedented high activity and selectivity in the hydroformylation of trans 2- and 4-octene to linear nonanal. 

Changing the ligand structure by substituting two dibenzophosphole groups for two diphenylphosphinyl groups results in a variation of the prevailing chirality in butenes but not in styrene 48). 

Here again a note on nomenclature is needed. If compounds of type 25 are considered as substituted phosphoranes, names such as the one given above are appropriate. If, on the other hand, their heterocyclic nature stays in the foreground, the correct names (as used by Chemical Abstracts) are such as 5-phenyl-5,5 -spirobi[5H-dibenzophosphole]. Both naming procedures are consistent with IUPAC rules and are applicable to similar arsenic, antimony- and bismuth-heterocycles as well (see later chapters). 

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. 

Substituted dibenzophospholes (3) on treatment with benzoyl chloride in the presence of trimethylamine, followed by hydrolysis undergo ring expansion to yield 5,6-dihydro-dibenzo[b,d]phosphorin 5-oxides (4) in high yield (D.W. Allen and A.C. Oades, J. chem. Soc., Perkin I, 1976, 2050). 

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. ... 

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