borane-mediated reduction of a series of symmetrical alk-2-yne-1,4-diones (5) in the presence of the oxazaborolidine (R)-6 to afford (R,R)-alk-2-yne-1,4-diols ((R,R)-1) in good yields and high stereoselectivities (up to 99.9% ee). In some cases, the stereochemical purity of 1 was improved by a two-step process: (i) temporary transformation of 1 into its vic-dibromo derivatives 9, which allowed us to remove
synthetic route to C2-symmetric chiral 1,4-diols based on the borane-mediated oxazaborolidine-catalysed reduction of 2-ene-1,4-diones (2), of 2-yne-1,4-diones (3), and/or of Co-complexed diketones 4 is described. Good to excellent enantio- and diastereoselectivities have been obtained in the reduction of diketones 3 and 4, catalysed by oxazaborolidines 6 and 5, respectively.
Photochemistry of 3H-furo[3,4-c]pyrazoles and 3H-thieno[3,4-c]pyrazoles
作者:Alan D. Payne
DOI:10.1016/j.tet.2013.08.022
日期:2013.11
The first examples of 3H-furo[3,4-c]pyrazoles and 3H-thieno[3,4-c]pyrazoles were prepared in an attempt to isolate examples of cyclopropane-fused thiophenes and furans. Adducts of acetylenic ketones and 2-diazopropane were reacted with 10-camphorsulfonic acid or phosphorus pentasulfide to produce the title compounds. Photolysis of these compounds did not give the cyclopropane-fused products rather
3的第一实施例ħ -呋喃并[3,4- c ^ ]吡唑和3 ħ -噻吩并[3,4- c ^ ]吡唑,企图环丙烷稠合噻吩和呋喃的分离物实施例制备。炔酮和2-重氮丙烷的加成物与10-樟脑磺酸或五硫化二磷反应以产生标题化合物。这些化合物的光解没有给出环丙烷稠合的产品中观察到,而未报告的光化学碎片。