The regio- and stereospecific synthesis of diarylpropenyllithium compounds from dimethylamino- and dimethylaminomethyl-substituted diarylacetylenes via transmetallation 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 119 Sn 1 H, 13 C 1 H and 119 Sn 13 C coupling constants observed in the 1 H and 13 C NMR spectra of the configurationally pure stereoisomeric pairs.