A Five-Membered Enantiopure Cyclic Nitrone from Malic Acid by Regioselective Oxidation of Cyclic Hydroxylamine. Synthesis of (1S,7S,8aR)-Octahydro-1,7-dihydroxyindolizine
摘要:
The chiral optically pure five-membered 3-tert-butoxy-1-pyrroline N-oxide (1) was synthesized by a convenient five-step procedure from diethyl L-malate. The key step is the regioselective HgO dehydrogenation of the N-hydroxypyrrolidine 6 obtained by double-nucleophilic displacement of a (bis)mesylate with hydroxylamine. A rationalization of the observed regioselectivity of the oxidation by studying the oxidation of a deuterated N-hydroxypyrrolidine 20 is reported. Nitrone 1 has been applied to the synthesis of a new (1S,7S,8aR)-1,7-dihydroxyindolizidine (28) via 1,3-dipolar cycloaddition strategies.
Kinugasareactions between chiral acetylenes and five-membered nitrones, achiral and bearing a stereogenic center in both enantiomeric forms, proceed in moderate to good yield with high diastereoselectivity affording mostly one dominant product. The first step of the reaction is controlled by the configuration of the nitrone, whereas the protonation of intermediate enolate in the second step depends
A facile approach to carbapenams via Kinugasa reaction between terminal copperacetylides and nonracemic cyclic nitrones derived from malic and tartaric acid is reported. The stereochemical preferences observed in these reactions are explained. The reaction provides an entry to the carbapenams basic skeleton.
Hypervalentiodine compounds are viable reagents for the oxidation of N,N-disubstitutedhydroxylamines to the corresponding nitrones, with IBX performing best. The procedure is very simple and user-friendly and affords the target compounds with high efficiency and regioselectivity, highlighting IBX as the reagent of choice for preparation of aldonitrones from nonsymmetric hydroxylamines. Evidence for
Poly(4-vinylpyridine)/methylrhenium trioxide (MTO) compounds IIII and microencapsulated polystyrene/MTO systems IVV are efficient catalysts for the oxidation of secondary hydroxylamines to the corresponding nitrones with H2O2. Complete conversions of substrates and quantitative yields of products are obtained under environmentally friendly experimental conditions and with the use of simple work-up
聚(4-乙烯基吡啶)/三氧化二甲基methyl(MTO)化合物IIII和微囊化的聚苯乙烯/ MTO系统IVV是将仲羟胺氧化为相应的H 2 O 2硝酮的有效催化剂。在环境友好的实验条件下并使用简单的后处理程序即可获得底物的完全转化和定量的产品收率。对称取代的羟胺,以及非对称的3-取代和2-取代的羟基吡咯烷酮,用于生物碱和生物活性同类物合成的硝酮的前体,被认为是底物。该非均相催化剂在反应条件下是稳定的,并且可以被回收和再循环至少五次而没有任何明显的效率损失。
Inexpensive and Environmentally Friendly Oxidation of Hydroxylamines to Nitrones with Bleach