Novel boron and silicon-based reagents for organic synthesis and determination of enantiomeric purity

Alkynyllithium reagents add to B-methoxy-9-borabicyclo[3.3.1]nonane to form stable lithium alkynyl(methoxy)borate complexes. These complexes undergo efficient Suzuki-Miyaura coupling to produce a variety of arylacetylenes and enynes.; The addition of B-methoxy-9-oxa-10-borabicyclo[3.3.2]decane to alkynyllithium reagents also produces stable alkynylmethoxyborates. These complexes were demethoxylated with boron trifluoride-etherate to afford B-alkynyl-9-oxa-10-borabicyclo[3.3.2]decanes. These relatively air stable alkynylborinates undergo hydroboration with dicyclohexylborane followed by selective protonolysis with acetic acid to furnish stable Z-vinylborinates. These alkynylmethoxyborate complexes also undergo Suzuki-Miyaura coupling yielding results similar or superior to those obtained with 9-BBN derivatives.; The B-alkyl-9-oxa-10-borabicyclo[3.3.2]decanes react with alpha-methoxyvinyllithium to produce stable lithium alkyl(alpha-methoxyvinyl)borinate complexes. These complexes undergo BCl3-induced alkyl group migration providing new air-stable Markovnikov vinylborinates. These intermediates are readily converted to 1,1-disubstituted alkenes via the Suzuki-Miyaura coupling. These vinylborinates were oxidatively converted to methyl ketones, one of which was converted to the antihistaminic drug, metron S, in racemic form.; Chiral 2-azido alcohols react with boracycles such as 9-BBN-H and borinane to produce air stable oxazaborolidines, namely 3-oxa-6-aza-2-boratricyclo[5.3.3.0 2,6]tridecanes and 10-oxa-7-aza-1-borabicyclo[5.3.0]decanes, respectively. Nopyl azide reacts with 9-BBN-H forming a novel N-substituted-9-aza-10-borabicyclo[3.3.2]decane through a B-C nitrene insertion. This intermediate undergoes intramolecular hydroboration at 200°C to produce a pinene-derived azaborapentacycle. These compounds were examined in the asymmetric reduction of acetophenone under the conditions employed for CBS-type catalytic processes. The enantioselectivities obtained were very low. The low selectivity is due to the lack of formation of the oxazaborolidine-borane complex, which is essential in orchestrating this process.; A new optically active chlorosilane, (1R)-(+)-methoxyethyl(diisopropyl)silyl chloride, was prepared through the asymmetric reduction of 1-acetyl-1,1-diisopropyl-3,3,3-trimethyl-1,3-disiloxane in >96% ee. Several silyl ethers were prepared from this chiral chlorosilane and chiral alcohols both in racemic and optically pure form. The resulting 1H and 13C NMR signals of the resulting diastereomeric silyl ethers are resolved providing quantitative information on the optical purities of the alcohols. These derivatives can be cleaved under mild conditions and the resulting silanol can be converted back by the reaction with thionyl chloride, regenerating the reagent. The reaction of the chiral silyl chloride reagent with chiral, aryl-substituted carboxylic acids also provides resolved NMR signals for the resultant diastereomeric esters.