Synthesis of O6‐Corona[3]arene[3]pyridazines and Their Molecular Recognition Property in Organic and Aqueous Media

O₆‐Corona[3]arene[3]pyridazines were synthesized from the one‐pot macrocyclic condensation reaction of 3,6‐dichlorotetrazine with 1,4‐dihydroquinone derivatives followed by the inverse electron demand Diels‐Alder reaction of the tetrazine rings with a cyclopentanone‐derived enamine. Conversion of six ester groups within macrocycle into all sodium acetate moieties afforded a water soluble O₆‐corona[3]arene[3]pyridazine. The coronary macrocycle host formed complexes selectively with organic ammoniums and dinitrile guests in a 1: 1 stoichiometric ratio in organic solvents with association constants ranging from (2.96 ± 0.10) × 10¹ to (2.53 ± 0.33) × 10⁵ L·mol⁻¹. Water soluble O₆‐corona[3]arene[3]pyridazine was also able to complex strongly with organic ammoniums in water to give an association constant up to (2.67 ± 0.21) × 10⁴ L·mol⁻¹. The pseudo‐rotaxane and inclusion structures of the host‐guest complexes were revealed by the X‐ray crystallography.     

A novel entry to xanthones by an intramolecular Diels-Alder reaction involving 2-(1,2-dichlorovinyloxy) aryl dienones

A wide array of synthetic methods are described in the literature for the preparation of xanthones—a prominent class of tricyclic molecules that occur widely in nature. Majority of these reported methods involve linking the two aromatic rings and forming the central pyrone ring using a variety of classical and non-classical cyclization strategies. In a conceptually different approach, we describe here a new xanthone synthesis wherein both the pyrone and the second aromatic rings were forged in a single step by an intramolecular cycloaddition reaction involving 2-(1,2-dichlorovinyloxy) aryldienones.     

Stereoselectivity in the Diels‐Alder Cycloadditions of a Facially Dissymmetric Bicyclo[2.2.2]octadiene‐Grafted Maleic Anhydride with Exocyclic Butadienes. Unexpected Facial Selectivity in the Cycloaddition with 2,3,5,6‐tetramethylidenebicyclo[2.2.2]octene

The Diels‐Alder cycloadditions of facially dissymmetric maleic anhydride 1 with facially nonequivalent exocyclic 1,3‐butadienes(dimethylidenebicyclo[2.2.2]octene 3 and 2,3,5,6‐tetramethylidenebicyclo[2.2.2]‐octene ( 4 )) were investigated. In each cycloaddition, the reaction occurred via the course in which 1 added exclusively by its syn‐face (same face as the etheno‐bridge) onto either π‐face of the exocyclic 1,3‐butadiene systems to produce only two of the four possible stereoisomeric monocycloadducts ( 8a / 8b and 9a / 9b ). In the Diels‐Alder cycloaddition of 1 with bis‐exocyclic butadiene 4 , however, both monocycloadducts 9a and 9b underwent subsequent cycloaddition with distinctive facial selectivity to produce the C_s‐symmetric bis‐cyclohexanobarrelene 10a as only bis‐cycloadduct.     

A New Stigmasterol and a New Eremophilenolide from Ligularia dolichobotrys

A new stigmasterol 3β, 7α, 22-trihydoxystigmast-5-ene (1) and a new eremophilenolide 8α-methoxy-6β-angeloyloxyeremophil-7(1 l)-en-8β, 12-olide-14-oic acid (2) were isolated from Ligularia dolichobotrys Diels. Their structures were deduced on the basis of spectral data.     

两类协同非同步热周环反应

两类协同非同步热周环反应何国正（暨南大学化学系广州５１０６３２）关键词非同步Ｄｉｅｌｓ－Ａｌｄｅｒ反应σ迁移键生成键破裂协同非同步有机热周环反应可分为两类，一类以Ｄｉｅｌｓ－Ａｌｄｅｒ反应为代表，另一类以丙烯氢原子σ异面迁移为代表。前者两个σ键形成是...     

A model approach towards the polycyclic framework present in cembranoid natural products dissectolide A,plumarellide and mandapamate

A macrocyclic furanobutenolide was crafted from readily available furan building-blocks to set-up a transannular Diels–Alder reaction which delivered the carbocyclic core present in a class of cembranoid diterpene natural products.     

Oxidative oxo Diels–Alder Reactions of Baylis–Hillman Adducts with Electron-Rich Alkenes in the Presence of IBX

Baylis–Hillman adducts were oxidized by iodoxybenzoic acid (IBX) to 2-methylene-1,3-dicarbonyl compounds, which can act as oxodiene to react with electron-rich alkenes to generate a variety of oxo Diels–Alder adducts in good yields.     

Effect of spacer chemistry on the formation and properties of linear reversible polymers

A series of four pairs of bismaleimide and bisfuran monomers were combined to make thermally reversible linear polymers. The monomers were prepared using diamines having different spacer chemistries, n‐octyl, cyclohexyl, phenyl, and ethylenedioxy, such that a relatively constant spacer dimension among the four monomers was achieved. Heating of the bismaleimide/bisfuran couples resulted in low‐viscosity, easily processable liquids. Subsequent cooling to room temperature resulted in the formation of hard films, with the rate of hardening varying significantly within the series of compounds. The rate and degree of polymerization were determined using ¹H NMR spectroscopy and were both found to be dependent on the chemistry of the spacer group, as was the film rheology, which was measured using nanoindentation. Adhesion of the polymers was quantified by measurement of their tensile adhesive strength, and this was also found to be spacer dependent. Polymerization reversibility was verified using ¹H NMR spectroscopy. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5056–5066