Diene syntheses anthracenes

In going from benzene to pentacene the largest sum of the free valence of a pair of atoms in a para position increases as does the ease of the diene synthesis in this series. It is well known that maleic anhydride hardly reacts with benzene or naphthalene. A reaction takes place with anthracene and even more readily with naphthacene and pentacene.12... 

Anthracene homologs can also be prepared in this way, by using derivatives of cyclohexadiene. Further, 1,4-naphthoquinone can be used as starting material (for a single diene synthesis) and the ethylene bridge may be substituted without destroying the ability of the product to split off the ethylene derivative. 

A Diels-Alder diene synthesis, using maleic anhydride and anthracene, was carried out using DTA by Hartnelin et al. (26). This technique permits the determination of the temperature at which reaction occurs, the melting point of the adduct formed, and the decomposition of the adduct. 

Bridged Peroxides.—Routine procedures have been extended to the synthesis and characterization of photo-adducts of singlet oxygen with cyclo-octa-1,3,5-triene, cycloheptatrienes, 3,5-cycloheptadienone, cyclohepta-1,3-dienes, ° naphthalenes, anthracenes, a-pyrones, pyrazines and pyrimidines,imidazoles, and indenes. Transformation of some of these... 

A soln. of benz[a]anthracene in 10 moles vinylene carbonate refluxed 18 hrs. under Ng at ca. 175-180° 7,12-dihydro-7,12-ethanobenz[a]anthracene-13,14-diol cyclic carbonate. Y 80%.-This is the first step of a high-yield multi-step synthesis of 7,12-dimethylbenz[a]anthracenes from benz[a]anthracenes. F. e. s. M. S. Newman and Zia Ud Din, J. Org. Chem. 36, 966 (1971) diene synthesis with anthracenes s. a. D. M. McKinnon and J. Y. Wong, Can. J. Chem. 49, 3178 (1971) synthesis of dibenzobarrelenes s. H. P. Figeys and A. Dralantis, Tetrahedron 28, 3031 (1972). 

Generally, benzene and naphthalene derivatives show only little reactivity as dienes in Diels-Alder synthesis, contrary to anthracene and the higher acene derivatives which are frequently used as dienes. Exceptions are the reactions of benzene and naphthalene derivatives with highly reactive dienophiles such as dicyanoacetylene (DCA), which... 

Diels-Alder reactions are, of course, reversible, and the pathway followed for the reverse reaction (2,3 arrows) can sometimes be as telling as the pathway for the forward reaction. The direction in which any pericyclic reaction takes place is determined by thermodynamics, with cycloadditions, like the Diels-Alder reaction, usually taking place to form a ring because two n-bonds on the left are replaced by two Diels-Alder reaction can be made to take place in reverse when the products do not react with each other rapidly, as in the pyrolysis of cyclohexene 2.3 at 600°. It helps if either the diene or the dienophile has some special stabilization not present in the starting material, as in the formation of the aromatic ring in anthracene 2.15 in the synthesis of diimide 2.16 from the adduct 2,14, and in... 

Ferrocenyl ligands, via zinc reagents, 9, 120 Ferrocenylmethyl phosphonium salts, with gold(I), 2, 274 Ferrocenylmonophosphine, in styrene asymmetric hydrosilylation, 10, 817 Ferrocenyl oxazolines, synthesis, 6, 202 Ferrocenylphosphines with chromium carbonyls, 5, 219 in 1,3-diene asymmetric hydrosilylation, 10, 824-826 preparation, 6, 197 various complexes, 6, 201 Ferrocenylselenolates, preparation, 6, 188 Ferrocenyl-substituted anthracenes, preparation, 6, 189 Ferrocenyl terpyridyl compounds, phenyl-spaced, preparation 6, 188 Ferrocifens... 

Acylnitroso alkenes produced via rDA reactions are key intermediates in the synthesis of alkal-oids. The acylnitroso alkene intermediate (167) that is generated from anthracene adduct (166) can react by an intramolecular ene reaction, resulting in the formation of hydroxamic acid (168). If the acylnitroso alkene is produced in the presence of a diene, an intramolecular Diels-Alder reaction can occur to give a 1,2-oxazine derivative such as (170) as shown in equation (76). ... 

An RNA Diels-Alderase ribozyme recently developed that catalyses the formation of carbon-carbon bonds between a tethered anthracene diene and a biotinylated maleimide dienophile. The ribozyme active site has been further characterised by chemical substitution of the diene and dienophile. It was shown that the diene must be an anthracene, and substitution only at specific sites is permitted. The dienophile must be a maleimide with an unsubstituted double bond. The RNA-diene interaction was found to be governed preferentially by stacking interactions. A ribozyme has been selected that catalyses the synthesis of dipeptides using an aminoacyl-adenylate substrate. The ribozyme catalysed the formation of 30 different dipeptides, many with rates similar to that of the Met-Phe dipeptide used in the selection process. 

Vinyl sulfoxides are useful Diels-Alder dienophiles. Thermolysis of the adducts gives rise to alkenes via sulfoxide elimination and so over the two steps the vinyl sulfoxides are the synthetic equivalents of alkynes, e.g. phenyl vinyl sulfoxide reacts with anthracene and 1,4-diphenylbuta-1,3-diene with concomitant sulfoxide elimination under the Diels-Alder conditions to give adducts (70) and (71 Scheme 15). 3-Phenylsulfinyl-a,3-unsaturated-carbonyl compounds have also been used as Diels-Alder dienophiles in chemistry developed for a synthesis of disodium prephenate and epiprephenate. With the electron rich diene (72), vinyl sulfoxides (73) and (75) gave rise to products (74 equation 33) and (76 equation 34) after hydrolysis. For the prephenate synthesis the phenylsulfinylmethylenelactone (77) was used, giving cyclohexadienone (78 Scheme 16) after sulfoxide elimination and hydrolysis. ... 

In 2004, Porco described the application of a polymer-supported anthracene for the scavenging of excess dienophile from Diels-Alder reactions [48]. This scavenger was not only demonstrated with a range of dienophiles, but also its application was related in the synthesis of flavonoid dienes and other classes of cyclic molecules (Scheme 8.35). 

A particularly attractive application of hydrotropy in organic synthesis arises when the product is bulkier than the reactant, with the result that it has lower solubility than the reactant in the hydrotrope solution. Consequently, it selectively precipitates out of the reaction mixture and can be easily filtered out. Then the hydrotropic solution can be recycled, thus minimizing the environmental hazards associated with waste disposal. An important example is the synthesis of Diels-Alder adducts that act as flame retardants for polymer blends and formulations. One of these is also used in the manufacture of the pesticide Endosulfan. The reaction involves a diene such as hexachloro-pentadiene or anthracene and a dienophile such as p-benzoquinone or maleic anhydride. The following typical reaction carried out by Sadvilkar (1995) gave excellent results ... 

In the mid-1980s, Hoffman and co-workers described a simple synthesis of racemic mikanecic acid via in situ Diels-Alder dimerization of the diene generated from t-butyl 2-bromomethylbut-2-enoate. " The first example of a Diels-Alder reaction of a MBH adduct was the dimerization of 2-hydroxy-alkyle-nones" and the previously mentioned addition to anthracene. The appKcation of the MBH adducts as hetero dienes or precursors of dienes, and dienophiles for the Diels-Alder cycloaddition reactions was then initiated and expanded by the group of Hoffman. In a series of reports, Hofftnan and co-workers have described the in situ Diels-Alder dimerization of various dienes (157), generated via stereoselective dehydration with MsCl-DABCO-DMAP of the corresponding MBH adducts The elimination of water from MBH adducts always resulted... 

The high reactivity of benzynes as dienophiles in Diels-Alder reactions has also been observed in reactions with aromatic hydrocarbons, a class of compounds usually considered as inert as dienes. In a two-step synthesis of triptycene di- and tetracarboxylic acids, arynes generated in situ from anthranUic adds 158 cydized with anthracenes 159 affording di- or tetramethyltriptycenes 160 in 41-69% yields (Scheme 12.47) [85], Acids 161 were obtained after subsequent oxidation of the cycloadducts 160 with potassium permanganate. 

The iV-phenylmaleimide derivative (518), prepared in two steps from a-pyrone and nitrosobenzene, is a dienophile and yields the cycloaddition product (519) on reaction with cyclohexa-l,3-diene." ° The sealed-tube reaction of anthracene with excess l,2-dibromo-3,3-difluorocyclopropene at 120°C gave the crystalline adduct (520), presumably by way of intermediate (521) the mechanism is not known. A synthesis of the tricyclo[5,2,2,0 ]undecane skeleton related to isoeremolactone has been reported. The Diels-Alder adduct (522) was a key intermediate in this synthesis, being converted in two standard steps into an epimeric mixture of compounds... 

Since anthracene and maleimide form high yielding stable addncts (with cycloreversion tem-peratnre over 200°C), this combination of diene and dienophile was ntilized for the synthesis of dendronized polymers via DA reaction (Tonga et al., 2010). Thns, as shown schematically in Fig. 12.28, polymer appended with anthracene gronps was reacted with dendrons containing fnran... 

Cycloadditions. The dienophilic properties of ( )-phenyl-sulfonyl-2-trimethylsilylethylene allow the preparation of adducts with reactive dienes such as cyclopentadiene and anthracene. The adducts are smoothly converted to alkenes upon treatment with fluoride ion, establishing the equivalence of the title reagent to acetylene. Alkylation of the a-sulfonyl carbanion can precede the elimination such that synthetic equivalents to HC CH, HC CD, and RC CH are available. The use of this reagent is highlighted by the synthesis of several functionalized dibenzobarrelenes (eq 1). The equivalency to DC CD and RC=CD is illustrated by the preparation of deuterated derivatives. 

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