5-Silylisoxazoles bearing other silyl groups different to the more usual trimethylsilyl have been prepared by condensation of silylalkynones with hydroxylamine hydrochloride. The reaction with hydrazines is more complex and leads to 5-silylpyrazoles or the corresponding hydrazones, which can be cyclized by reaction with electrophiles. This has allowed us to synthesize 5-silylpyrazoles functionalized at C-4 by groups impossible to introduce by electrophilic substitution of the pyrazole nucleus. (C) 2002 Elsevier Science Ltd. All rights reserved.
Asymmetric cyanosilylation of alkynyl ketones with the catalyst systems consisting of amino acid/2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (BINAP)/ruthenium(II) complex and lithium phenoxide (Ru⋅Li cat.) was studied. The reaction was conducted in tert‐butyl methyl ether (TBME) at −78 °C with a substrate‐to‐catalyst molar ratio (S/C) as high as 2000. A series of simple and functionalized ketones was converted
Improved Method for the Synthesis of β-Carbonyl Silyl-1,3-Dithianes by the Double Conjugate Addition of 1,3-Dithiol to Propargylic Carbonyl Compounds
作者:Sumit Mukherjee、Dimitra Kontokosta、Aditi Patil、Sivakumar Rallapalli、Daesung Lee
DOI:10.1021/jo901950e
日期:2009.12.4
Base-mediated double Conjugate addition of 1,3-propane dithiol to various silylated propargylic aldehydes and ketones allows for an efficient and scalable synthesis of beta-carbonyl silyl-1,3-dithianes.
Asymmetric Hydrogenation of Alkynyl Ketones with the η<sup>6</sup>-Arene/TsDPEN–Ruthenium(II) Catalyst
Enantioselective hydrogenation of alkynyl ketones catalyzed by Ru(OTf)(TsDPEN)(eta(6)-p-cymene) (TsDPEN = N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine) affords the propargylic alcohols in up to 97% ee. The alkynyl moieties are left intact In most cases. The reaction can be conducted with a substrate-to-catalyst molar ratio as high as 5000 under 10 atm of H-2. The mode of enantioselection is elucidated with the transition state models directed by the CH/pi attractive interaction between the substrate and the catalytic species.