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JournaloftheChineseChemicalSociety, 2001, 48, 81-82
81
Generationof9(10H)-Acridone from Anthranilic Acid
何子樂
周德貴
)
Tse-Lok Ho* (
) and Der-Guey Jou (
DepartmentofAppliedChemistry,NationalChiaoTungUniversity,Hsinchu,Taiwan,R.O.C.
Diazotization of anthranilic acid with butyl ni trite in refluxing THF gave rise to acridone.
The pioneering research of Wittig, Roberts, and
Huisgen have es tab lished benzyne (1,2-dehydrobenzene) as
theintermediateinnucleophilicsubstitutionofhalobenzenes
with a strong base such as sodamide.1 Sub se quently, many
methodshavebeendevelopedforthegenerationofbenzyne,
as well as polycyclic and heterocyclic analogs, while en gag-
ing them in re ac tions with nucleophiles and cycloaddends.
addend in the pre vi ous run.
The ma jor prod uct from the diazotization ex hib its pro-
ton-NMR ab sorp tion peaks at 7.24 (2H), 7.52 (2H), 7.71
(2H), 8.22 (2H) and 11.74 (1H), and car bon-13 ab sorp tions at
117.4 (d), 120.5 (s), 121.1 (d), 126.1 (d), 133.5 (d), 140.9
(s), and 176.8 (s). The cou pling pat tern of the pro ton NMR
spectrumischaracteristicofan o-disubstituted ben zene de-
Preparatively,theprotocolforbenzynegenerationbythermal rivative. This product was unequivocally identified as
orphotolyticdecompositionofbenzenediazoium-2-carbox-
ylate2 which is ob tain able from diazotization of anthranilic
acid with an alkyl ni trite is ad van ta geous. This method
and that con sist ing of thermolysis (10 C) of 1,2,3- benzo-
thiadiazole3 avoid strongly ba sic con di tions or organo metal-
licreagents.
acridone4 and a proposed mech a nism for its for ma tion is
shown in Scheme I. The rea son it eluded ob ser va tion may be
that pre vi ous work ers al ways iso lated benzenediazonium-2-
carboxylateinthesolidstate, andthedifferentconditionswe
used may also have con trib uted to the trap ping of benzyne by
anthranilic acid. Since the acridone for ma tion re quires 3
equiv a lents of anthranilic acid, the yield amounted to 47.3%.
Among pre vi ous ac cess to acridone some what re lated
to our ob ser va tion is the thermolysis of phenyl o- azido-
benzoate via an arylnitrene.5 Oth ers in clude the isomer iza-
tion of 3-phenylanthranil,6 the de com po si tion of 3-phenyl-
1,2,3-benzotriazin-4-one7 and the cyclization of 2 -alkoxy-
2-acetaminobenzophenones.8 How ever, in all these routes
quite dif fer ent mech a nisms or only one type of chem i cal
bondwerefeatured.
In a syn thetic pro ject in volv ing benzyne as a cyclo-
addendwe carriedout a pre lim i naryexperi ment usinganin
situ pro ce dure. In other words, the diazotization of anthra-
nilic acid was per formed in the pres ence of our cycloaddend.
Thedesiredreactionwasnotaccomplished,butapreviously
unreportedpathwayofdecompositionwasdiscovered.Real-
izing the cycloaddend did not par tic i pate in the trans for ma-
tion the diazotization was re peated in its ab sence. The same
result is obtained if one discounts the unchanged cyclo-
Scheme I