Franz Sondheimer

Synthesis and reactions of 5,6,11,12-tetradehydrodibenzo[a,e]cyclooctene and 5,6-didehydrodibenzo[a,e]cyclooctene

Abstract Syntheses of 5,6,11,12-tetradehydrodibenzo[a,e]-cyclooctene (5) and 5,6-didehydrodibenzo[a,e]cyclooctene (6) by dehydrobromination with potassum t-butoxide of 5,6,11,12-tetrabromo-5,6,11,12-tetrahydrodibenzo[a,e]cyclooctene (9) and 5,6-dibromo-5,6-dihydrodibenzo[a,e]cyclooctene (8), respectively, are described. Compounds 5 and 6 are unusual, essentially planar, conjugated anti-aromatic 8-membered ring systems, the reactions of which have been studied. The diacetylene 5 readily underwent Diels-Alder reaction with 1,3-diphenylisobenzofuran and furan to give the bis-adducts 13 and 14, respectively. [2+2]Cycloaddition between 5 and dichloroketene and subsequent hydrolysis of the gemdichloride yielded 2,3,6,7-dibenzobicyclo [6.2.0]deca-2,6,8-trien-4-yne-9,10-dione (21). The monoacetylene 6 readily underwent Diels-Alder reaction with 1,3-diphenylisobenzofuran and furan to give the mono-adducts 24 (endo and exo isomers) and 25, respectively. 1,3-Dipolar cycloaddition of phenylazide to 6 led to the 1-phenyl-1H-triazole derivative 27, whereas [2+2]cycloaddition between 6 and dichloroketene and hydrolysis yielded 2,3,6,7-dibenzobicyclo[6.2.0]deca-2,4,6,8-tetraene-9,10-dione (30). Spectral, as well as chemical and electrochemical reductions, of 5 and 6 have been studied. For instance, treatment of the monoacetylene 6 with a potassium mirror gave the aromatic 10π-electron dianion 34.

5,12-dihydro-6,11-didehydronaphthacene, A derivative of 1,4-didehydronaphthalene

Treatment of the di-lithium derivative of 1,2-diethynyl-benzene (1) with o-xylene-α,α′-diol di-p-toluenesulphonate (2) in tetrahydrofuran led to 5,12-dihydronapthacene (5) as the only identifiable product. This reaction presumably involves 5,12-dihydro-6,11-didehydronaphthacene (4) as an intermediate, and this was confirmed by the formation of 5,12-dihydro-6,11-dideuterio-naphthacene when the reaction was carried out in tetrahydrofuran-d8.

The synthesis of mono-substituted [18]annulenes☆

Abstract Syntheses of bromo[18]annulene (4), methyl[18]annulene (5), [18]annulenecarboxaldehyde (6), and methyl[18]annulenecarboxylate (7) are described. The electronic and NMR spectra of these substances are discussed. It is shown that the nitration of nitro[18]annulene (2) gives rise to a complex mixture of dinitro[18]annulenes.

The 1,5-bisdehydro[12]annulenyl and 1,5,9-tridehydro[12]annulenyl radical anions and dianions

Abstract The reduction of 1,5-bisdehydro[12]annulene ( 1 ) and 1,5,9-tridehydro[12]annulene ( 4 ) with potassium proceeds by a one electron addition to give the corresponding 1,5-bisdehydro[12]annulenyl and 1,5,9-tridehydro[12]annulenyl radical anions ( 2,5 ), Further reduction converts the radical anions into the 1,5-bisdehydro[12]annulenyl and 1,5,9-tridehydro[12]annulenyl dianions ( 3, 6 ). The properties of these ions are described.

5,6-didehydro-10-methylbenzocyclooctene

Abstract Treatment of 5-bromo-10-methylbenzocyclooctene (11) with potassium tert-butoxide gave 5-methyl-9-tert-butoxybenzocyclooctene (14), presumably via 5,6-didehydro-10-methylbenzocyclooctene (13). The cyclic acetylene (13) could be trapped by reaction with 1,3-diphenylisobenzofuran to give the adduct (15).

The synthesis of methylene-substituted macrocyclic polyacetylenes☆

Abstract Chlorination of 2-methallyl chloride (9) and subsequent treatment with sodium iodide leads to 3-iodo-2-iodomethyl-1-propene (6), which is converted to 4-methylene-1,6-heptadiyne (10) on reaction with ethynylmagnesium bromide in the presence of cuprous chloride. The bis-Grignard derivative of 10 on treatment with the diiodide 6 in the presence of cuprous chloride gives 4,9,14,19-tetramethylene- 1,6,11,16-cycloeicosatetrayne (16), a 20-membered ring cyclic tetraacetylene. Oxidative coupling of the diacetylene 10 with oxygen, cuprous chloride and ammonium chloride leads to 6,13-dimethylene-1,3,8,10- cyclotetradecatetrayne, a 14-membered ring cyclic tetraacetylene.

The synthesis of presumably planar conjugated 8-membered ring compounds

Abstract Using mainly base dehydrobromination reactions of carbocyclic 8-membered bromides, a variety of acetylenic and cumulenic compounds were isolated or postulated as transient intermediates. The physical and chemical properties of the isolable presumably planar 8-membered ring compounds were investigated. Trapping experiments were used to confirm the transitory existence of the unstable intermediates.

The structures of the two isomers of monodehydro[14]annulene

Abstract Variable temperature 1H nmr spectrometry has shown that the “unstable” isomer of monodehydro[14]annulene possesses the symmetrical di- trans configuration 1 or 2 , and the “stable” isomer (the precursor of [14]annulene) possesses the tri- trans configuration 4 .