- Excited-state intramolecular proton transfer in o-hydroxybiaryls: A new route to dihydroaromatic compounds
-
An excited-state intramolecular proton transfer (ESIPT) from the phenol OH to the 7′-carbon on the naphthyl ring in o-(1-naphthyl)phenol (3) and 1-(1′-naphthyl)-2-naphthol (4) leads to efficient (Φ = 0.1-0.2) formation of the corresponding dihydrobenzoxanthenes (5 and 7) via quinone methide intermediates. This new reaction represents a clean, efficient, and high-yielding route to benzoxanthenes and dihydrobenzoxanthenes. A related ESIPT of similar efficiency has been detected at the 2′-aromatic position in these systems, by deuterium labeling studies. Copyright
- Lukeman, Matthew,Wan, Peter
-
-
Read Online
- Catalyst-Free Synthesis of O-Heteroacenes by Ladderization of Fluorinated Oligophenylenes
-
A novel catalyst-free approach to benzoannulated oxygen-containing heterocycles from fluorinated oligophenylenes is reported. Unlike existing methods, the presented reaction does not require an oxygen-containing precursor and relies on an external oxygen source, potassium tert-butoxide, which serves as an O2? synthon. The radical nature of the reaction facilitates nucleophilic substitution even in the presence of strong electron-donating groups and enables de-tert-butylation required for the complete annulation. Also demonstrated is the applicability of the method to introduce five-, six-, and seven-membered rings containing oxygen, whereas multiple annulations also open up a short synthetic path to ladder-type O-heteroacenes and oligodibenzofurans.
- Feofanov, Mikhail,Akhmetov, Vladimir,Takayama, Ryo,Amsharov, Konstantin
-
p. 5199 - 5203
(2021/02/21)
-
- NMR and DFT studies on persistent carbocations derived from benzo[kl]xanthene, dibenzo[d,d′]benzo[1,2-b:4,3-b′]difuran, and dibenzo[d,d′]benzo[1,2-b:4,5-b′]difuran in superacidic media
-
Persistent carbocations generated by the protonation of hetero-polycyclic aromatic compounds with oxygen atom(s) were studied by experimental NMR and density function theory calculations. Benzo[kl]xanthene (1), dibenzo[d,d′]benzo[1,2-b:4,3-b′]difuran (2), and dibenzo[d,d′]benzo[1,2-b:4,5-b′]difuran (3) were synthesized by the annulation of arenediazonium salts. Compound 1 in FSO3H-SbF5 (4:1)/SO2ClF and 3 in FSO3H-SbF5 (1:1)/SO2ClF ionized to 1aH+ with protonation at C(4) and to 3aH+ with protonation at C(6), and these cations were successfully observed by NMR at low temperatures. The density function theory calculations indicated that 1aH+ and 3aH+ were the most stable protonated carbocations and that 2 should ionize to 2aH+ with protonation at C(6). According to the changes in 13C chemical shifts (Δδ13C), the positive charge was delocalized into the naphthalene unit for 1aH+, into one benzo[b,d]furan unit for 2aH+, and into one benzo[b,d]furan unit for 3aH+. The most stable persistent cations derived from the title compounds, 1-3, were found to be 1aH+ with protonation at C(4), 2aH+ with protonation at C(6), and 3aH+ with protonation at C(6) by experimental and theoretical methods.
- Okazaki, Takao,Nakagawa, Madoka,Futemma, Takeshi,Kitagawa, Toshikazu
-
p. 107 - 111
(2016/02/03)
-
- Photocyclization and Photoaddition Reactions of Arylphenols via Intermediate Quinone Methides
-
A series of five benzannelated derivatives of 2-phenylphenol were prepared, and their photochemistry was investigated. Two of these (3-phenyl-2-naphthol, 10, and 1-phenyl-2-naphthol, 11) were photoinert. For 2-(1-naphthyl)phenol (12) and 1-(1-naphthyl)-2-naphthol (13), ESPT took place to either the 2′-position or the 7′-position of the naphthalene ring to give quinone methides (QMs) that underwent either reverse proton transfer (RPT) or electrocyclic ring closure to give dihydrobenzoxanthenes. The intermediate QMs for 12 and 13 were detected and characterized by laser flash photolysis. For 2-(9-phenanthryl)phenol (14), ESPT took place either to the 5′-position to give a QM that underwent quantitative electrocyclic ring closure to give the corresponding benzoxanthene or to the 10′-position to give a QM that underwent RPT. If the solution contained methanol, the QM produced on ESPT to the 10′-position in 14 could be trapped as the photoaddition product. The compounds studied in this work demonstrate three possible reactions of QMs produced following ESPT to aromatic carbon atoms: (1) reverse proton transfer (RPT) to regenerate starting material; (2) addition of hydroxylic solvents to give the photoaddition product; and (3) electrocyclic ring closure to give benzoxanthene derivatives.
- Lukeman, Matthew,Simon, Hilary,Wan, Peter,Wang, Yu-Hsuan
-
p. 11281 - 11293
(2015/12/01)
-
- Formation of dibenzofurans by flash vacuum pyrolysis of aryl 2-(allyloxy)benzoates and related reactions
-
Flash vacuum pyrolysis (FVP) of aryl 2-(allyloxy)benzoates 5 and of the corresponding aryl 2-(allylthio)benzoates 6 at 650°C, gives dibenzofurans 19 and dibenzothiophenes 20, respectively. The mechanism involves generation of phenoxyl (or thiophenoxyl) radicals by homolysis of the O-allyl (or S-allyl) bond, followed by ipso attack at the ester group, loss of CO2 and cyclisation of the resulting aryl radical. Synthetically, the procedure works well for p-substituted substrates, which lead to 2-substituted dibenzofurans 19b-f (73-90%) and dibenzothiophenes 20b-c (90-94%). Little selectivity is shown in the cyclisation of m-substituted substrates and competing interactions of the radical with the substituent - and ipso-attack - complicate the pyrolyses of o-substituted substrates. FVP of related radical precursors including 2-(allyloxy)phenyl benzoates 43 gave no dibenzofurans, whereas 2-(allyloxy-5-methyl)azobenzene 44 gave a much reduced yield. No carbazoles were obtained by FVP of 4-methylphenyl 2-(allylamino)benzoate 42.
- Black, Michael,Cadogan,McNab, Hamish
-
experimental part
p. 2961 - 2967
(2010/09/06)
-
- Palladium-catalyzed cross-coupling of benzyl ketones and α,β- unsaturated carbonyl and phenolic compounds with o-dibromobenzenes to produce cyclic products
-
A number of carbonyl and phenolic compounds efficiently couple with o- dibromobenzenes in the presence of a palladium catalyst and a base to give the corresponding oxygen-containing heterocycles or carbocyclic compounds. Thus, from the reactions of benzyl phenyl ketones, 1-naphthols, and α,β- unsaturated aldehydes and ketones, benzofuran, benzopyran, benzocyclobutane, and indene derivatives, respectively, are produced selectively via the successive formation of C-C and C-O bonds or of two C-C bonds.
- Terao, Yoshito,Satoh, Tetsuya,Miura, Masahiro,Nomura, Masakatsu
-
p. 2345 - 2350
(2007/10/03)
-