Gem-diphenyl substitution

Prakash, Olah, and co-workers256 have prepared Mosher s acid analogs by the hydroxyalkylation of substituted benzenes with ethyl trifluoropyruvate [Eq. (5.95)]. Deactivated aromatics (fluorobenzene, chlorobenzene) required the use of excess triflic acid indicative of superelectrophilic activation.3 5 In contrast to these observations, Shudo and co-workers257 reported the formation gem-diphenyl-substituted ketones in the alkylation of benzene with 1,2-dicarbonyl compounds [Eq. (5.96)]. In weak acidic medium (6% trifluoroacetic acid-94% triflic acid), practically no reaction takes place. With increasing acidity the reaction accelerates and complete conversion is achieved in pure triflic acid, indicating the involvement of diprotonated intermediates. 

Addition of bromine to the gem-diphenyl substituted d, -un aturated amines 28 was shownto afford mixtures of the pyrrolidinium and piperidinium salts, 29 and 30, which were converted into the 1-azabicyclo-hexanes 31 by treatment with sodium hydride in dimethylformamide. 

The diamidobinaphthyl dilithium salt (R)-67 was generated in situ from the free diaminobinaphthyl ligand and 2.5 equiv. of LiCH2SiMe3 [135]. This system lacks a chelating sidearm and gave predominantly low enantioselectivities except for the gem-diphenyl-substituted aminopentene. Unfortunately, the cyclization of aminoalkenes seems to be limited to activated gem-dialkyl substituted [69] aminopentene... 

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