John H. Hollinshead

The synthesis and assay of radiolabelled benzene derivatives

Abstract Several new syntheses of 1and 4-[14C]anisole have been investigated and routes from [14C]cyanide and from 2-[14C]acetone are described which are better than those previously reported. The key step in one of the syntheses was catalytic dehydrogenation of 1-[14C]cyclohexanone to 1-[14C]phenol. Degradation of 5,6,7,8-tetrachloro-3,4-dihydro-1,4-etheno-[14C]naphthalen-2(1H)-one (10) prepared from [14C]anisole and tetrachlorobenzyne has shown that the key step had proceeded without scrambling of the label.

The dechlorination of some highly chlorinated naphthalene derivatives

Abstract The [4+2]cycloadducts formed between tetrachlorobenzyne and a variety of arenes and cyclic 1,3-dienes have been reductively dechlorinated. The products are formally benzyne cycloadducts, many of which are difficult to make by other routes. High yields are obtained when sodium and t-butanol in boiling THF are used for the reduction. THF serves as a solvent but t-butanol not only acts as a proton donor but also appears to initiate the reduction. Tetrachlorobenzyne should be considered as an alternative reagent whenever benzyne itself appears to be required.

Rearrangement reactions of bicyclic systems. Part V. 1 Acid-catalysed rearrangements of 1,4-dihydro-1,5,8-trimethoxy-1,4-ethenonaphthalene and the remarkable effect of aromatic methoxy-groups on the course of the reaction

3.6-Dimethoxyanthranilic acid (2) has been prepared by a procedure that is more reliable than our earlier one and used as a 3,6-dimethoxybenzyne precursor in a reaction with anisole to give 1,4-dihydro-1,5,8-trimethoxy-1,4-ethenonaphthalene (1,5,8-trimethoxybenzobarrelene) (1). Trifluoroacetic acid-catalysed rearrangement of this benzobarrelene (1) gave as precedented products of bicyclo-rearrangement 3,4-dihydro-5,8-dimethoxy-1,4-ethenonaphthalen-2(1H)-one (5,8-dimethoxybenzobarrelenone) (3) and 5,9-dihydro-1,4-dimethoxy-5,9-methanobenzocyclohepten-6-one (7) along with 2,4′,5-trimethoxybiphenyl (6), the product of a remarkable retro-Friedel-Crafts protodealkoxyalkylative fragmentation of the bicyclic system. Similar reactions were observed with perchloric acid. The structure of this unexpected blphenyl was confirmed by its preparation by Gomberg-Bachman-Hey arylanon of 1,4-dimethoxybenzene.

Regiospecific fragmentation of benzene derivatives: synthetic and analytical applications

Abstract The cycloadducts farmed from arenes and tetrachloroand tetrafluorobenzyne have been shown to undergo specific addition-fragmentation reactions. These sequences are both simple syntheses of arenes with unusual substitution patterns and a convenient alternative to the other methods currently available for assaying the isotopic distribution in [14C]-labelled benzene derivatives.

Rearrangement reactions of bicyclic systems: Part VI. 1 A [14C]-tracer study of the acid-catalysed skeletal rearrangement of 1,4-dihydro-1-methoxy-1,4-etheno- naphthalene (1-methoxybenzobarrelene) and its 5,6,7,8-tetrahalogeno-derivatives

Abstract A degenerate skeletal rearrangement occurs during the acid catalysed conversion of 1-methoxybenzobarrelene and its tetrachloro- and tetrafluoro-derivatives into the corresponding 3,4-dihydro-1,4-ethenonaphthalen-2(1H)-ones (benzobarrelenones). A [ 14 C]-tracer study has confirmed that two pathways operate. In both pathways the methoxylated bridgehead C-1 of the benzobarrelene becomes the carbonyl C-2 of the benzobarrelenone. The pathways are distinguished by the fate of the benzobarrelene bridgehead C-4: in one pathway aryl migration leaves this formerly bridgehead C-4 as the olefinic C-5 of the newly formed benzobarrelenone; in the other pathway the bridgehead C-4 remains bonded to the aryl ring while a double migration of other skeletal bonds leaves it as the bridgehead C-4 of the benzobarrelenone. The pathway involving aryl migration is favoured in each case examined. The preference for aryl migration is greater in concentrated (> 98%) sulphuric acid than in aqueous (80%) sulphuric acid and in both cases the preference increases as the aryl substitution varies from F 4 to Cl 4 to H 4 .

Rearrangement reactions of bicyclic systems. Part I. Synthesis of a model compound related to flavothebaone trimethyl ether. The abnormal ultraviolet absorption spectrum of flavothebaone and its trimethyl ether

3,6-Dimethoxybenzenediazonium-2-carboxylate decomposed to 3,6-dimethoxybenzyne (8), which reacted with veratrole to form 1,5,8-trimethoxy-1.4-etheno-2-tetralone (9) in 40% yield. Reduction, and acid-catalysed rearrangement of the resulting exo-alcohol (10). afforded 5,9-dihydro-1,4-dimethoxy-5,9-methanobenzocyclo-hepten-6-one (7). The u.v. spectrum of compound (7) is entirely analogous to that of flavothebaone trimethyl ether (3).