Thermally Responsive Dendrons and Dendrimers Based on Reversible Furan-Maleimide Diels−Alder Adducts
摘要:
[GRAPHICS]Benzyl aryl ether dendrons and dendrimers containing thermally reversible furan-malelmide Diels-Alder adducts were prepared up to the third generation. The covalent cleavage and reassembly of the dendrons and dendrimers were evaluated by H-1 NMR.
We report the first asymmetric Diels–Alderreactionbetween furan and propiolates. Propiolate, a dienophile, was equipped with an Evans’ auxiliary and a sulfonyl group to control and facilitate diastereoselective cycloaddition. Treatment with furan as a diene and aluminium Lewis acid afforded a 7-oxabicyclo[2.2.1]heptadiene skeleton diastereoselectively. The origin of diastereoselectivity can be explained
An Exploratory Study of Type II [3 + 4] Cycloadditions between Vinylcarbenoids and Dienes
作者:Huw M. L. Davies、Rebecca L. Calvo、Robert J. Townsend、Pingda Ren、R. Melvyn Churchill
DOI:10.1021/jo991959b
日期:2000.7.1
dirhodium tetracarboxylate catalyzed decomposition of vinyldiazoacetates. The [3 + 4] cycloaddition is generally considered to occur by a tandem cyclopropanation/Cope rearrangement, although evidence is presented that with these substrates the [3 + 4] cycloaddition may occur in a concerted manner.
Synthesis and solid state structure of an unsymmetrical triurea
作者:Xavier Garcías、Leticia M. Toledo、Julius Rebek
DOI:10.1016/0040-4039(95)01829-7
日期:1995.11
The synthesis and single crystal X-ray diffraction analysis of 1 is reported. Hydrogen bonding and solvation play an important role in the solidstatestructure of 1.
报道了1的合成和单晶X射线衍射分析。氢键和溶剂化发挥的固态结构的重要作用,1。
Structural effects on intramolecular furan cycloadditions
作者:Larry L. Klein
DOI:10.1021/jo00210a046
日期:1985.5
Synthesis and Self-Assembly of Pseudo-Spherical Homo- and Heterodimeric Capsules
作者:Carlos Valdes、Urs P. Spitz、Leticia M. Toledo、Stefan W. Kubik、Julius Rebek
DOI:10.1021/ja00156a010
日期:1995.12
Experimental details are given for the synthesis and characterization of several new molecules capable of self-assembly. The new molecules feature glycoluril subunits held apart by various rigid spacers, ethylene (2), naphthalene (3), and ethenoanthracene (4), and assemble through hydrogen bonds into pseudo-spherical dimeric capsules. The nature of their assembly is demonstrated by the X-ray crystal structure of capsules 1.1. The capsules are shown to enclose smaller guest molecules in a reversible manner. Direct evidence of the guest molecules inside the capsules from NMR is presented. In addition to self-assembling dimerically, these new molecules are shown to disproportionate into hybrid species or heterodimers. The resulting new capsules feature internal cavities of varying sizes and shapes. Formation of hybrid dimers 1.2, 1.4, and 3.4 is observed in solutions containing mixtures of two homodimers. The dispropoaionation equilibria could be manipulated by the addition of appropriately sized solvents as guests. Even the energetically unlikely hybrids 1.4 and 3.4 are found to be the dominant species when suitable guests such as CDBr3 are present. Evidence of the existence of the heterodimers is presented from NOE measurements. Factors controlling the heterodimerization are discussed.