Kiyoichi Hirakawa

Heterocycles by cycloaddition. Part II. Cycloaddition–extrusion reactions of five-membered mesoionic compounds with benzyne: prepartion of benz[c]azole and benzo[c]thiophen derivatives

Several five-membered mesoionic compounds react with benzyne to give benzo-fused five-membered heterocycles [(2) and (5)] with a formal quinonoid structure. A bridged intermediate adduct (4c) was isolated from the reaction of benzyne with a mesoionic thiazol-4-one (3c). Pyrolysis of the adduct gave an isobenzothiophen (5a), whereas its photolysis led to an isoquinolone (7). The corresponding adduct S-oxide (4e) gave the isoquinolone (7) by both pyrolysis and photolysis.

Reactions of spiro-indazoles containing keto-groups. Part 2. Evidence for a spiro-benzocyclopropene intermediate in the thermolysis of anthrone-10-spiro-3′-3′H-indazoles to benz[a]aceanthrylenes

The reaction of 10-diazoanthrone (4) with 4-methylbenzyne gave the spiro-indazole regioisomers (1b) and (1c), both of which thermolyzed to give the hydroxybenz[a]aceanthrylenes (8b) and (8c). Thermolysis is interpretable on the basis of formation of the corresponding biradicals (2b) and (2c) which isomerize to one another, followed by the cyclization to the benzaceanthrylenes. The intramolecular radical isomerization provides strong evidence for a spiro-benzocyclopropene intermediate (3b) in this reaction.

Syntheses and reactions of spirocyclopropaneanthrones. Part 1. Reactions of p-diazo-ketones with p-quinone methides

The carbenic reaction of 10-diazoanthrone (1) with 10-methyleneanthrone (2) gave dispiro[anthrone-10, 1′-cyclopropane-2′, 10″-anthrone](3), which thermally rearranged with synchronous ring expansion, yielding spiro[2H-aceanthrone-2, 10′-anthrone](7). Similar reactions of diazonaphthalen-1 (4H)-one (11) with the quinone methide (2) and of the diazo-ketone (1) with 2, 6′-di-t-butyl-4-methylenecyclohexa-2, 5-dien-1-one (16) afforded directly the rearrangement product, 10-hydroxytribenz[a, de, j]anthracen-5-one (12), and the cyclopropyl ring-opening product, 10-(4-hydroxy-3, 5-di-t-butylbenzyl)anthrone (17), respectively, instead of the dispiro-compounds.

Selectivity in the thermal and photochemical fragmentation of the cycloadduct from benzyne and a mesoionic thiazol-4-one

During the preparation of benzo-condensed five-membered heterocycles by cycloaddition–extrusion reaction of benzyne with mesoionic compounds, a cycloadduct with a thiazol-4-one was isolated, which behaved differently on pyrolysis and photolysis.

Syntheses and reactions of spirocyclopropaneanthrones. Part 2. Rearrangements and cyclopropyl ring-opening reactions of phenyl-substituted spirocyclopropaneanthrones and related compounds

Diphenylspirocyclopropaneanthrones [(1c) and (1d)] thermally rearranged with ring expansion to 1,10b-dihydro-2H-aceanthrones (2), whereas the phenyl analogue (1b) did not rearrange under comparable conditions. Phenyl-spirocyclopropeneanthrone (3a), prepared by the carbenic reaction of 10-diazoanthrone (6) with phenylacetylene, thermally rearranged to 10bH-aceanthrone (11). By contrast, the diphenyl analogue (3b), from the reaction with diphenylacetylene, was thermally stable. The diazoketone (6) reacted with 9-methylenefluorene to give directly the rearrangement product (2g), instead of the dispirocyclopropaneanthrone (1g). Spirocyclopropane- and spirocyclopropene-anthrones [(1) and (3)] reacted under acidic conditions to yield cyclopropyl or cyclopropenyl ring-opened products. In these reactions, the ring was shown to open from the more substituted side. These reactions are discussed in mechanistic terms.