Abstract
Hydrophobically shielded alkynes HCC–aryl, carrying 2,6-di- and 2,4,6-tri-tert-butylphenyl as the aryl group, can add aqueous HBr on heating in moist chloroform solutions to produce pure H2CC(–Br)–aryl (isolated yields 96%, no hydrolysis). Employment of DCC–aryl furnished initially only the E stereoisomer of DHCC(–Br)–aryl (stereospecific syn addition), which was slowly both dedeuteriated and partially transformed to the Z stereoisomer by HBr. The strongly retarded HBr addition to H3C–CC–aryl in moist chloroform produced again more E than Z product, whereas a thermodynamic E/Z ratio of 10:87 was found in moist acetic acid. Substitution of Br by LiSnMe3 produced H2CC(–SnMe3)–aryl with well resolved long range 119Sn NMR coupling constants.
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