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Benzynes compounds

Hydroxy-THISs react with electron-deficient alkynes to give nonisol-able adducts that extrude carbonyl sulfide, affording pyrroles (23). Compound 16 (X = 0) seems particularly reactive (Scheme 16) (25). The cycloaddition to benzyne yields isoindoles in low- yield. Further cyclo-addition between isoindole and benzyne leads to an iminoanthracene as the main product (Scheme 17). The cycloadducts derived from electron-deficient alkenes are stable (23, 25) unless highly strained. Thus the two adducts, 18a (R = H, R = COOMe) and 18b (R = COOMe, R = H), formed from 7, both extrude furan and COS under the reaction conditions producing the pyrroles (19. R = H or COOMe) (Scheme 18). Similarly, the cycloadduct formed between 16 (X = 0) and dimethylfumarate... [Pg.9]

A method for the generation of benzyne involves heating the diazonium salt from o aminobenzoic acid (benzenediazonium 2 carboxylate) Using curved arrows show how this sub stance forms benzyne What two inorganic compounds are formed in this reaction" ... [Pg.990]

Benzylic carbon (Section 11 10) A carbon directly attached to a benzene nng A hydrogen attached to a benzylic carbon is a benzylic hydrogen A carbocation in which the benzylic carbon is positively charged is a benzylic carbocation A free radical in which the benzylic carbon bears the unpaired electron is a benzylic radical Benzyne (Section 23 8) The compound... [Pg.1277]

N-Arylation of azoles is achieved either by using arynes, activated halobenzenes (e.g. dinitro) or under Ullmann conditions. Thus benzyne reacts with imidazoles to give N-arylimidazoles (70AHC(12)103), and these compounds have also been prepared under modified Ullmann conditions. [Pg.54]

There is some evidence for the formation of unstable benzazetidines from [2 + 2] cycloaddition of benzyne to imines (75BCJ1063). A novel formation of a benzazetidine is reported in the solvolysis of the exo iV-chloro compound (297). Neighbouring group participation by the benzene ring leads to the cation (298), which is intercepted by methanol to give the benzazetidine (299) (81CC1028). [Pg.277]

There are several methods for generation of benzyne in addition to base-catalyzed elimination of hydrogen halide from a halobenzene, and some of these are more generally applicable for preparative work. Probably the most convenient method is diazotization of o-aminobenzoic acid. Concerted loss of nitrogen and carbon dioxide follows diazotization and generates benzyne. Benzyne can be formed in this manner in the presence of a variety of compounds with which it reacts rapidly. [Pg.595]

Benzyne can also be generated from o-dihaloaromatics. Reaction of lithium amalgam or magnesium results in formation of a transient organometallic compound that decomposes with elimination of lithium halide. l-Bromo-2-fluorobenzene is the usual starting material in this procedure. [Pg.596]

Benzyne is capable of dimerizing, so that in the absence of either a nucleophile or a reactive unsaturated compound, biphenylene is formed. The lifetime of benzyne is estimated to be on the order of a few seconds in solution near room temperature. ... [Pg.596]

When benzyne is generated in the presence of potential dienes, additions at the highly strained triple bond occur. Among the types of compounds that give Diels-Alder addition products are furans, cyclopentadienones, and anthracene. [Pg.596]

Further mechanistic evidence comes from trapping experiments. When bromobenzene is treated with KNH2 in the presence of a diene such as furan, a Diels-Alder reaction (Section 14.5) occurs, implying that the symmetrical intermediate is a benzyne, formed by elimination of HBr from bromobenzene. Ben-zyne is too reactive to be isolated as a pure compound but, in the presence of water, addition occurs to give the phenol, in the presence of a diene, Diels-Alder cycloaddition takes place. [Pg.575]

Benzyne (Section 16.8) An unstable compound having a triple bond in a benzene ring. [Pg.1236]

Compounds of special interest whose preparation is described include 1,2,3-benzothiadiazole 1,1-dioxide (a benzyne precursor under exceptionally mild conditions), bis(l,3-diphenylimida-zolidinylidene-2) (whose chemistry is quite remarkable), 6- di-melhylamino)julvene (a useful intermediate for fused-ring non-benzenoid aromatic compounds), dipkenylcyclopropenone (the synthesis of which is a milestone in theoretical organic chemistry), ketene di(2-melhoxyethyl) acetal (the easiest ketene acetal to prepare), 2-methylcyclopenlane-l,3-dione (a useful intermediate in steroid synthesis), and 2-phenyl-5-oxazolone (an important intermediate in amino acid chemistry). [Pg.145]

Acid chloride 5 is readily available from the known benzylic alcohol 6,4e but intermediate 4 is still rather complex. It was recognized that compound 4 could conceivably be formed in one step from 2-methoxyfuran (9)10 and iodotriflate 10. The latter compound was designed with the expectation that it could be converted to benzyne 8," a highly reactive species that could be intercepted in an intermolecular Diels-Alder reaction with 2-methoxyfuran (9) to give 7. The intermediacy of 7 is expected to be brief, for it should undergo facile conversion to the aromatized isomer 4 either in situ or during workup. [Pg.510]


See other pages where Benzynes compounds is mentioned: [Pg.29]    [Pg.194]    [Pg.29]    [Pg.55]    [Pg.724]    [Pg.725]    [Pg.725]    [Pg.53]    [Pg.349]    [Pg.352]    [Pg.354]    [Pg.354]    [Pg.291]    [Pg.29]    [Pg.194]    [Pg.29]    [Pg.55]    [Pg.724]    [Pg.725]    [Pg.725]    [Pg.53]    [Pg.349]    [Pg.352]    [Pg.354]    [Pg.354]    [Pg.291]    [Pg.43]    [Pg.57]    [Pg.92]    [Pg.982]    [Pg.81]    [Pg.171]    [Pg.4]    [Pg.982]    [Pg.1277]    [Pg.1069]    [Pg.60]    [Pg.512]    [Pg.72]    [Pg.188]    [Pg.221]    [Pg.289]    [Pg.869]    [Pg.1063]   
See also in sourсe #XX -- [ Pg.163 ]




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Benzyne mechanism compounds

Benzyne with heterocyclic compounds

Benzyne, reactions with heterocyclic compounds

Intermediate compounds benzynes

Reactions of benzyne with heterocyclic compounds

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