A highly efficient protocol for the large-scale oxidative cyclization of 1,5-dienes is described. This convenient ruthenium(VIII)-catalyzed (0.2 mol%) cyclization reaction allows the preparation of cis-2,5-disubstituted tetrahydrofurans in high yields (up to 92%) and excellent diastereomeric ratio (>95:5 dr). This simple and reliable method is insensitive to moisture and air and can, therefore, be carried out in an open reaction vessel.
Selective Monocarbamoylation of Symmetrical Diols with Alkyl Halides and Potassium Cyanate Using Phase-Transfer Catalysis
作者:Mahavir Prashad、John C. Tomesch、William J. Houlihan
DOI:10.1055/s-1990-26910
日期:——
A convenient method for the selective monocarbamoylation of diols by reaction with alkyl isocyanates, generated in situ from alkyl halides and potassium cyanate under phase-transfer catalysis, is described. Under these conditions the ease of reaction shows the following order cis-diols > trans-diols and diols > monoalcohols. An increase in the number of methylene groups between two hydroxyl groups lead to a decrease in product yields. A plausible mechanism to explain these results is proposed.
stereoselectively by syn oxygen addition to both double bonds. The formation of tetrahydrofuran derivatives is presumed to involve initial addition of RuO4 to one double bond of the 1,5-diene to give a ruthenium(VI) diester, which subsequently undergoes conversion into the cyclic ether with participation of the second double bond.
使用0.05当量的四氧化钌催化氧化1,5-二烯的改进方法。催化剂RuO 2 ·2H 2 O的当量,2.5当量。介绍了作为化学计量氧化剂的NaIO 4和AcOEt /(CH 3)2 CO / H 2 O(2:1:1,v / v / v)的双相溶剂体系。的1,5-二烯反应1,3,及5提供的新顺式-四氢呋喃产品2,4,6,和7具有完全的立体定向性。产品的结构是根据NMR和MS数据以及化学证据确定的。此过程以香叶基乙酸酯(中的应用8)和乙酸橙花酯(12得到)的顺式-四氢呋喃衍生物9,10,和13以高收率,并伴有少量的反式-tetrahydrofurandiols 11和14。这些产品与Sharpless等人获得的产品相同。RuO 4催化双相溶剂体系CCl 4中8和12的氧化/ CH 3 CN / H 2 O(2:2:3,v / v / v),但我们的方法具有立体特异性更高,材料回收率更高(约90%)和后处理更简单的优点。的1
Process for the preparation of monoalkylcarbamate group-containing
申请人:Sandoz Pharm. Corp.
公开号:US04868319A1
公开(公告)日:1989-09-19
An improved process for preparing monoalkylcarbamate group-containing compounds comprising reacting a hydroxy group-containing compound with an organic halide and an alkali metal cyanate in the conjoint presence of a phase transfer catalyst and a solvent.