Synthesis and Reactions of 1,2-Cyclopropanated Sugars
摘要:
Diastereospecific cyclopropanation of glycals 1, 2, 3, 4, and 41 was carried out using either dihalocarbene addition or zinc-carbenoid addition to yield 1,2-cyclopropanated sugars. Dichloro- and dibromocarbenes added stereoselectively anti to the C-3 benzyloxy group, whereas (under Simmons-Smith conditions) the cyclopropanes were formed syn to the same substituent. The reactions of these 1,2-cyclopropanated sugars to provide either ring expanded glycosides or C-2-branched chain glycosides were explored. Solvolytic ring expansion of 1,2-dibromocyclopropanated sugars with K2CO3 in refluxing methanol yielded the corresponding chiral oxepins 20-22. Electrophilic ring openings of parent cyclopropanes (14 and 17 derived from glucal 1) were carried out with different electrophiles to give functionalized 2-deoxy-2-C-branched chain glycosides. The ring openings of 14 in different solvents resulted in both alpha- and beta-anomers, whereas 17 gave exclusively the alpha-anomer.
Mechanistic Studies on the Base-Promoted Ring Opening of Glycal-Derived <i>gem</i>-Dibromocyclopropanes
作者:Romain J. Lepage、Peter W. Moore、Russell J. Hewitt、Paul H. Teesdale-Spittle、Elizabeth H. Krenske、Joanne E. Harvey
DOI:10.1021/acs.joc.1c02366
日期:2022.1.7
deprotonation step. The roles of the formed alcohol molecule and the bulk (co)solvent are demonstrated by isotope-labeling studies performed with deuterated solvents. The acid-promoted isomerization of the E-bromoalkene product into the corresponding Z-bromoalkene is also described. The mechanistic knowledge gained in this investigation sheds light on the unusual chemistry of this system and facilitates its future
在存在亲核碱的情况下,衍生自d -glycals的稠环偕二溴环丙烷进行开环以产生 2-deoxy-2-( E - bromethylene)glycosides。环外环丙烷键的这种断裂与发生环内键断裂的更常见的银促进的扩环反应形成对比。报告了实验和理论研究,这些研究提供了对反应机理及其对E的动力学选择性的起源的见解-配置溴烯烃产品。密度泛函理论计算 (M06-2X) 预测该反应开始于醇盐诱导的 HBr 从二溴环丙烷中消除以形成溴环丙烯。然后开环得到构型稳定的两性离子(氧代碳鎓阳离子/乙烯基碳负离子)中间体,该中间体经过亲核加成和质子化得到溴烯烃。在最后一步中,质子有两种相互竞争的来源:一种是醇(共)溶剂,另一种是在初始去质子化步骤中产生的醇分子。用氘代溶剂进行的同位素标记研究证明了形成的醇分子和本体(共)溶剂的作用。E的酸促进异构化还描述了将-溴代烯烃产物转化为相应的Z-溴代烯烃。在这项研
Synthesis of C-furanosides from a<scp>d</scp>-glucal-derived cyclopropane through a ring-expansion/ring-contraction sequence
作者:Russell J. Hewitt、Joanne E. Harvey
DOI:10.1039/c0cc02244f
日期:——
gem-Dibromocyclopropane
1, prepared from tri-O-benzyl-D-glucal, undergoes thermal and silver-promoted ring expansion in the presence of alcohols to give substituted oxepines. With further heating, ring contraction to highly substituted tetrahydrofurans follows. These represent C-furanosides, potentially useful as precursors to C-nucleosides and other carbohydrate mimics.
Synthesis of Oxepines and 2-Branched Pyranosides from a <scp>d</scp>-Glucal-Derived <i>gem</i>-Dibromo-1,2-cyclopropanated Sugar
作者:Russell J. Hewitt、Joanne E. Harvey
DOI:10.1021/jo902306a
日期:2010.2.5
The conversion of cyclopropane-fused carbohydrates into oxepines is an attractive method for accessing diverse members of the septanoside family of carbohydrate mimetics. 2-Bromooxepines are obtained through silver(I)-promoted thermal ring expansion of a D-glucal-derived gem-dihalocyclopropanated sugar. In contrast, cyclopropane ring cleavage under basic conditions leads to 2-C-branched pyranosides, not the 2-bromooxepine structures assigned in an earlier report.
Synthesis and Reactions of 1,2-Cyclopropanated Sugars
作者:C. V. Ramana、R. Murali、M. Nagarajan
DOI:10.1021/jo970948k
日期:1997.10.1
Diastereospecific cyclopropanation of glycals 1, 2, 3, 4, and 41 was carried out using either dihalocarbene addition or zinc-carbenoid addition to yield 1,2-cyclopropanated sugars. Dichloro- and dibromocarbenes added stereoselectively anti to the C-3 benzyloxy group, whereas (under Simmons-Smith conditions) the cyclopropanes were formed syn to the same substituent. The reactions of these 1,2-cyclopropanated sugars to provide either ring expanded glycosides or C-2-branched chain glycosides were explored. Solvolytic ring expansion of 1,2-dibromocyclopropanated sugars with K2CO3 in refluxing methanol yielded the corresponding chiral oxepins 20-22. Electrophilic ring openings of parent cyclopropanes (14 and 17 derived from glucal 1) were carried out with different electrophiles to give functionalized 2-deoxy-2-C-branched chain glycosides. The ring openings of 14 in different solvents resulted in both alpha- and beta-anomers, whereas 17 gave exclusively the alpha-anomer.
Divergent synthesis of 2-C-branched pyranosides and oxepines from 1,2-gem-dibromocyclopropyl carbohydrates
作者:Peter W. Moore、Julia K. Schuster、Russell J. Hewitt、M. Rhia L. Stone、Paul H. Teesdale-Spittle、Joanne E. Harvey
DOI:10.1016/j.tet.2014.06.069
日期:2014.9
The ring opening of 1,2-(gem-dibromo)cyclopropyl carbohydrates by two different modes leads to either 2-C-(bromomethylene)pyranosides (using base) or 2-bromooxepines (using silver salts), as shown previously by us for a d-glucal-derived cyclopropane. The base-promoted ring opening is extended to encompass additional alcohol, thiol and amine nucleophiles, and diastereoisomeric cyclopropane precursors