The regio- and stereospecific synthesis of diarylpropenyllithium compounds from dimethylamino- and dimethylaminomethyl-substituted diarylacetylenes viatransmetallation reactions involving diarylpropenylmagnesium and tin compounds

Abstract

Dimethylamino- and dimethylaminomethyl-substituted diarylacetylenes were prepared by the Pd(PPh{3}){4}-catalyzed coupling reaction of dimethylamino- and dimethylaminomethyl-substituted aryl halides with arylacetylenes.Reaction of the asymmetric diarylacetylenes with methylmagnesium bromide in the presence of NiCl{2}(PPh{3}){2} gave stereo- and regio-selectively cis addition products in which the aryl group bearing the built-in ligand (Me{2}N or Me{2}NCH{2}) and the magnesium atom are bonded to the same unsaturated carbon atom. The E-diarylpropenylmagnesium bromides were converted in two successive transmetallation steps into the corresponding E-triphenyltin and Z-lithium compounds with retention of configuration. Depending on the type of solvent, complete inversion of configuration was observed for the Z-diarylpropenyllithium compounds. From the E-lithium compounds the corresponding Z-diarylpropenyltriphenyltin compounds were prepared (Scheme 1).Retention of configuration in the series of transmetallation reactions has unambiguously been established by comparison of the }1{}1{}9{Sn@?}1{H, }1{}3{C@?}1{H and }1{}1{}9{Sn@?}1{}3{C coupling constants observed in the }1{H and }1{}3{C NMR spectra of the configurationally pure stereoisomeric pairs.