Unsymmetrical Dienes Research Articles

Regiospecificity in the Diels-Alder reactions of an enedione

The regiochemistry of cycloaddition of 1 with unsymmetrical dienes is explained by a preference for early rehybridization of the junction carbon.

Nickel-catalysed reactions of olefins with =C=N- double bond systems

The reactions of Schiffs' bases, hydrazones, 2,3diazabutadienes and 2-azabutadienes with butadiene or activated monoenes in the presence of nickel catalysts lead to new classes of compounds, which are isolated as mixtures of isomers. The ratio of the isomer distribution can be controlled inside wide limits by variation of the nickel ligands and the reaction parameters. A comparison with the nickel-catalysed oligomerisation of butadiene or the cooligomerisation of butadiene with mono-olef ins shows that the reaction products in the two cases are not analogous. INTRODUCTION In the last twenty years the chemistry of nickel-catalysed reactions of olefins and alkynes has undergone a vigorous upsurge. This interest is connected above all with the discovery of bis(cycloocta-l,5-diene) nickel(O) in the year 1960 (1). In the following years the Mulheirn group particularly occupied itself with possible new syntheses of cyclic and linear compounds from simple olefins and acetylenes. 2 ' L) + L) + LJ — _ ___ , — Ii + Fig. 1 Characteristic nickel-catalysed reactions In spite of the multiplicity of reactions catalysed homogeneously by nickel and their simplicity and selectivity only very few have awakened the interest of the chemical industry. In addition to the trimerisation of butadiene to 1,5,9-cyclododecatriene (2), the starting material for 'Nylon 12 and dodecandicarboxylic acid, they are: a) The addition of HCN to butadiene giving adiponitrile, the starting material for hexamethylenediamine (3). b) The cooligomerisation of ethylene and butadiene to 1,4hexadiene, an important comonomer for the polymerisation of ethylene arxpropylene with an unsymmetrical diene (4).

Cyclopolymerization of conformationally controlled unsymmetrical dienes: 2‐(o‐vinylphenoxy)ethyl methacrylate and acrylate

Cyclopolymerization of conformationally controlled unsymmetrical dienes: 2‐(o‐vinylphenoxy)ethyl methacrylate and acrylate

Near Cancellation of Through Space and Through Bond Interaction in bicyclo[3.2.2]nona‐6,8‐diene

AbstractThe photoelectron spectra of bicyclo[3.2.2]nonane and its five dehydrogenated analogues are reported. Analysis of the π‐bands reveals that the unsymmetrical diene 5 retains the ‘natural order’ of the π‐orbitals present in the lower homologues, i. e. the in‐phase below the out‐of‐phase combination of the basis π‐orbitals πa and πc. The isomeric diene 4 is the first member of the symmetrical homologous series (I), which inverts this order, so that a1(π) (in phase!) lies above b2(π) (out‐of‐phase!).

Diels–Alder reaction of unsymmetrical dienes with methyl acrylate

The Diels–Alder reactions of 1-(p-substituted phenyl)buta-1,3-dienes with methyl acrylate are shown to give 2-arylcyclohex-3-enecarboxylates, irrespective of the nature of the aryl-substituent, but the steric course of the reaction is affected by the substituent. Similar results were obtained with 1-aryl-2,3-dimethylbuta-1,3-dienes.

A perturbational MO method applied to diels-alder reactions with unsymmetrical dienes and dienophiles : Prediction of the major product

A perturbational MO method applied to diels-alder reactions with unsymmetrical dienes and dienophiles : Prediction of the major product

Recent developments in polymerization by an alternating intra‐intermolecular mechanism

AbstractRecent developments in polymerization by an alternating intra‐intermolecular mechanism are summarized and discussed briefly. The methods used to prove the structure of typical polymers, which in turn established the mechanism of polymerization, are reviewed. A study of larger ring formation by Marvel and Garrison is also summarized. Ring of sizes from 7 to 21 members were formed from α‐diolefins in yields of from 4 to 25%. A study of certain unsymmetrical dienes has shown that cyclization occurs in yields up to 60%, but that gelation eventually occurs because of the difference in relative reactivities of the two olefinic double bonds. Copolymerization of certain 1,4‐dienes with certain olefins to produce linear copolymers containing six‐membered rings is discussed. In an effort to explain the strong driving force to close a six‐membered ring during polymerization of 1,6‐diolefins, a pronounced interaction between the double bonds, which can be represented by several resonance forms of the molecule, is proposed.

THE STRUCTURE OF SOME DIELS–ALDER ADDITION PRODUCTS

Six addition products have been prepared by the combination of various unsymmetrical dienes with unsymmetrical dienophiles (aldehydes and nitriles). Only one of the two possible adducts was isolated from each reactant pair. The structures of these adducts were established by their dehydrogenation to various known substituted benzaldehydes and benzoic acids. The results of this work are in complete agreement with the conclusion of Hudson and Robinson that the reaction of a diene with a dienophile involves the union of the anionoid end of the diene with the cationoid carbon of the dienophile.

Chain structure of vinyl and diene polymers in relation to polymerization mechanism

AbstractThe usual occurrence of structural units of vinyl polymers in head‐to‐tail sequence is attributed to the stabilization of the free radical of the growing polymer chain by the monomer substituent(s). Addition at the unsubstituted carbon of the vinyl group reproduces a free radical of lower energy than does addition at the substituted carbon. In at least one instance (vinyl acetate polymerization) a very small percentage of head‐to‐head addition takes place in spite of this energy difference. These ideas can be extended to polymers of dienes. Here the problem is complicated by the simultaneous occurrence of 1,2 (or 3,4) as well as 1,4 addition. In the case of an unsymmetrical diene monomer such as isoprene it is possible, from detailed examination of the structure of the polymer, to distinguish between preferred addition at carbon atoms 1 and 4 of the monomer.