Asymmetric hydroarsination reactions toward synthesis of alcohol functionalised C-chiral As–P ligands promoted by chiral cyclometallated complexes

The asymmetric hydroarsination reactions between diphenylarsine and 3-diphenylphosphanyl-but-3-en-1-ol and 2-diphenylphosphanyl-prop-2-en-1-ol have been achieved using the organopalladium complex containing ortho-metallated (R)-[1-(dimethylamino)ethylnaphthalene as the chiral reaction template in high stereoselectivities under mild conditions. Hydroarsination of 3-diphenylphosphanyl-but-3-en-1-ol with diphenylarsine generated only one stereoisomer as five-membered As–P bidentate chelate on chiral naphthylamine palladium template. Using the same chiral metal template, similar hydroarsination reaction was carried out on 2-diphenylphosphanyl-prop-2-en-1-ol which gave two different products in the ratio of 2.6 to 1. The major isomer was identified as the expected five-membered As–P bidentate ligand and the minor isomer was identified as the elimination product. The naphthylamine auxiliary could be removed chemoselectively by treatment with concentrated hydrochloric acid. Optically pure As–P ligands containing the hydroxy groups at the chiral carbon centres were prepared by ligand displacement. The absolute configuration and coordination properties of the complexes have been established by single crystal X-ray analysis.

Asymmetric hydroarsination of the coordinated alcohol functionalised vinyllic phosphines gave the addition products in high yields. The major isomer were subsequently isolated in fair yields in its configurationally pure form and characterised by means of single crystal- X-ray crystallography. The enantiomerically pure P–As bidentate ligands were subsequently liberated in high yield.Figure optionsDownload as PowerPoint slideHighlights
► Reactivity and stereoselectivity in asymmetric hydroarsination reactions.
► Reaction proceed with appreciable yield and good stereoselectivity.
► Provides access to optically pure As–P ligands.
► Absolute configuration established by single crystal X-ray analysis.
► Part of our efforts to understand the differences in P and As reactivity.