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 2N or Me 2NCH 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 119Sn 1H, 13C 1H and 119Sn 13C coupling constants observed in the 1H and 13C NMR spectra of the configurationally pure stereoisomeric pairs.