23532-74-3Relevant articles and documents
New direct 11B NMR-based analysis of organoboranes through their potassium borohydrides
Medina, Jesus R.,Cruz, Gabriel,Cabrera, Carlos R.,Soderquist, John A.
, p. 4631 - 4642 (2003)
Representative organoborane mixtures were quantitatively converted to their borohydrides through their reaction with activated KH (KH*), permitting their detailed analysis by 11B NMR. Through the treatment of commercial KH with a THF solution of lithium aluminum hydride (LAH), a dramatic change in the surface morphology results as revealed by scanning electron microscopy (SEM). Energy dispersed spectroscopy (EDS) was employed to reveal that the LAH treatment deposits a significant amount of an unknown aluminum-containing species on the surface of the KH, which imparts a unique reactivity to the KH*. Even highly hindered organoboranes are quantitatively converted to their borohydrides by replacing electronegative groups (e.g., OR, halogen) with hydrogen, retaining only the carbon ligation. Through this simple KH* treatment, complex organoborane reaction mixtures are converted to the corresponding borohydrides whose 11B NMR spectra normally exhibit resolved signals for the individual species present. The integration of these signals provides quantitative information on the relative amounts of each component of the mixture. New generalities for the effect of α-, β-, and γ-substituents have also been determined that provide a new, simple technique for the determination of the isomeric distribution in organoborane mixtures resulting from common organoborane processes (e.g., hydroboration). Moreover, the 1H-coupled 11B NMR spectra of these mixtures reveal the extent of alkylation for each species present. Representative organoboranes were examined by this new technique permitting a simple and convenient quantitative analysis of the regio- and diastereomeric composition of a variety of asymmetric organoborane processes. Previously unknown details of pinene-based hydroborations and reductions are revealed for the first time employing the KH* 11B NMR technique.
Gold-Catalyzed Asymmetric Thioallylation of Propiolates via Charge-Induced Thio-Claisen Rearrangement
Kim, Hanbyul,Jang, Jiwon,Shin, Seunghoon
supporting information, p. 20788 - 20795 (2020/11/27)
A gold(I)-catalyzed enantioselective thioallylation of propiolates with allyl sulfides is described. The key mechanistic element is a sulfonium-induced Claisen rearrangement which helps minimize the allyl dissociation and render higher enantioselectivity. This protocol features remarkable scope of the allyl moiety, allowing enantiocontrolled synthesis of all-carbon quaternary centers, and exhibits exceptional functional group compatibility with many Lewis bases and π-bonds. This intermolecular variant of Claisen rearrangement forges both C-S and C-C bonds concomitantly, providing efficient access to interesting optically active organosulfur compounds which can be transformed further through the vinyl sulfide as a functional handle. The rate of the reaction was zeroth order with respect to allyl sulfides, which suggested a reversible inhibition, providing a resting state for the catalyst. The Hammett plot displayed a correlation with σp values, suggesting a turnover-limiting sigmatropic rearrangement where decreased electron-density on sulfur accelerated the rearrangement.
A versatile synthesis of 9-BBN derivatives from organometallic reagents and 9-(triisopropylsilyl)thio-9-borabicyclo[3.3.1]nonane
Soderquist, John A.,Justo De Pomar, Jorge C.
, p. 3537 - 3539 (2007/10/03)
Representative B-substituted-9-BBNs (3) are efficiently prepared from either organolithium or Grignard reagents through their addition to (TIPS)S- 9-BBN (1) which is readily available from TIPSSH and 9-BBN-H. The thermally induced collapse of the intermediate 'ate' complexes (2) produces 3 which is easily isolated in good yield and high purity. (C) 2000 Elsevier Science Ltd.
