Transmetalation of Tetraalkynyltin Compounds with Grignard Reagents: Access to Mono‐ and Dialkyltin Products

Monoalkyltrialkynyl‐ and dialkyldialkynyltin compounds can be selectively synthesized by transmetalation of tetraalkynyltin compounds with Grignard reagents; an example is given in Equation (1). This reaction provides a route to mono‐ and dialkyltin compounds that avoids the use of strongly electrophilic reagents. The labile tin–alkynyl bonds allow the transmetalation products to be converted into alkyltin oxides, chlorides, and alkoxides.     

Metallierung von Triisopropylsilylarsan durch Bis(tetrahydrofuran)calcium‐bis[tris(trimethylsilylmethyl)zinkat]

Metalation of Triisopropylsilylarsane with Bis(tetrahydrofuran)calcium‐bis[tris(trimethylsilylmethyl)zincate] The transmetalation of bis(trimethylsilylmethyl)zinc with distilled calcium in THF yields bis(tetrahydrofuran)calcium bis[tris‐(trimethylsilylmethyl)zincate] ( 1 ). The trialkylzincate anion appears as a bidentate ligand with Ca‐C‐Zn three‐center‐bonds. The CaC bond lengths show values of 265.5(2) and 271.7(2) pm. The metalation of triisopropylsilylarsane gives tetrakis(tetrahydrofuran)calcium [1, 3‐bis(triisopropylsilylarsanyl)‐2, 4‐bis(triisopropylsilyl)‐1, 3‐dizinca‐2, 4‐diarsacyclobutane‐2, 4‐diide] ( 2 ). The central moiety is a sligthly distorted trigonal As₂CaZn₂ bipyramid with the arsenic atoms in apical positions. The mean Ca‐As bond lengths lie with a mean value of 291.4 pm in the charakteristic region for calcium bis‐(arsanides).     

A convenient and efficient one pot synthesis of unsymmetrically substituted p-terphenyls via a phosphine-free double Suzuki cross-coupling protocol using 1,4-dibromo-2-nitrobenzene as the substrate

A synthetic procedure has been developed to enable the sequential regio-selective Suzuki-Miyaura cross-coupling of 1,4-dibromo-2-nitrobenzene with a variety of arylboronic acids. The first Suzuki coupling step, using a phosphine-free palladium catalyst at room temperature, gave selective coupling at the position ortho to the nitro group, opening a convenient synthetic route to unsymmetrical para-terphenyls. The bromobiaryl product was then subjected directly to the second coupling step, in situ, using preferred aryl-boronic acids to give by this one-pot batch procedure unsymmetrically substituted para-terphenyls in excellent overall isolated yields. This methodology should be particularly suited for the generation of targeted chemical libraries, as well as for the synthesis of precursors of biologically active compounds or natural products which are derived from the unsymmetrical para-terphenyl core.