I found a research paper[1] which specifically talks about the reaction you mention. The paper also mentions the same mechanism as you do:
TETRAHYDROFURAN (THF) (1) is known 1 to react with strong bases like
butyl-lithium, and the product (2) is known to decompose by a
retro-cycloaddition to give ethylene (3), and the enolate ion (4) of
acetaldehyde.
Enolate ions (6) are
known 2 to react with benzyne (5) to give dihydrobenzocyclobutenes (7),
and the dihydrobenzocyclobutenes are known to decompose by an
electrocyclic opening to give o-xylylenes (9), which are
trapped by the
benzyne to give dihydroanthracenols (11). By putting these known
reactions together we have found a very simple ' one-pot ' synthesis
of symmetrical 9,lO-unsubstituted anthracenes.
The paper uses warm THF to conduct the reaction which shows that cycloreversion of the side ring actually takes place even at a temperature lower than 180°C.
When bromobenzene (13) is added to a solution of a four-fold excess of
N-lithio-2,2,6,6-tetramethylpiperidine (15) in warm THF, the major
neutral product is anthracene (16) (63% based on bromobenzene).
The paper also talks about what happens when the reaction temperature is changed:
Variations in the Reaction Conditions.-The reaction was carried out as described above, but with the following modifications. (i) When the
butyl-lithium and the tetramethylpiperidine were mixed slowly at 0°
and the reaction carried out at 20°, there was no anthracene formed,
and Nphenyl-2,2,6,6-tetramethylpiperidine was the major product (75%
by n.m.r.). (ii) When the butyl-lithium and the tetramethylpiperidine
were mixed at reflux temperature and then cooled to 0° before adding
the bromobenzene, anthracene was formed (40%, pure). We were not able
to isolate dihydrobenzocyclobutanol. ... (iv) When butyllithium (5
mmol) and tetramethylpiperidine (6 mmol) were mixed at -78° and then
the mixture was brought to reflux temperature before adding the
bromobenzene (1 mmol), the yield of anthracene was the same as in the
original reaction.
Reference:
(1) Fleming, I.; Mah, T. A Simple Synthesis of Anthracenes. J. Chem. Soc., Perkin Trans. 11975, No. 10, 964.
I found a research paper[1] which specifically talks about the reaction you mention. The paper also mentions the same mechanism as you do:
TETRAHYDROFURAN (THF) (1) is known 1 to react with strong bases likebutyl-lithium, and the product (2) is known to decompose by aretro-cycloaddition to give ethylene (3), and the enolate ion (4) ofacetaldehyde. Enolate ions (6) areknown 2 to react with benzyne (5) to give dihydrobenzocyclobutenes (7),and the dihydrobenzocyclobutenes are known to decompose by anelectrocyclic opening to give o-xylylenes (9), which are trapped by thebenzyne to give dihydroanthracenols (11). By putting these knownreactions together we have found a very simple ' one-pot ' synthesisof symmetrical 9,lO-unsubstituted anthracenes.
The paper uses warm THF to conduct the reaction which shows that cycloreversion of the side ring actually takes place even at a temperature lower than 180°C.
When bromobenzene (13) is added to a solution of a four-fold excess ofN-lithio-2,2,6,6-tetramethylpiperidine (15) in warm THF, the majorneutral product is anthracene (16) (63% based on bromobenzene).
The paper also talks about what happens when the reaction temperature is changed:
Variations in the Reaction Conditions.-The reaction was carried out as described above, but with the following modifications. (i) When thebutyl-lithium and the tetramethylpiperidine were mixed slowly at 0°and the reaction carried out at 20°, there was no anthracene formed,and Nphenyl-2,2,6,6-tetramethylpiperidine was the major product (75%by n.m.r.). (ii) When the butyl-lithium and the tetramethylpiperidinewere mixed at reflux temperature and then cooled to 0° before addingthe bromobenzene, anthracene was formed (40%, pure). We were not ableto isolate dihydrobenzocyclobutanol. ... (iv) When butyllithium (5mmol) and tetramethylpiperidine (6 mmol) were mixed at -78° and thenthe mixture was brought to reflux temperature before adding thebromobenzene (1 mmol), the yield of anthracene was the same as in theoriginal reaction.
Reference:
(1) Fleming, I.; Mah, T. A Simple Synthesis of Anthracenes. J. Chem. Soc., Perkin Trans. 11975, No. 10, 964.
I found a research paper[1] which specifically talks about the reaction you mention. The paper also mentions the same mechanism as you do:
The paper uses warm THF to conduct the reaction which shows that cycloreversion of the side ring actually takes place even at a temperature lower than 180°C.
The paper also talks about what happens when the reaction temperature is changed:
Reference:
(1) Fleming, I.; Mah, T. A Simple Synthesis of Anthracenes. J. Chem. Soc., Perkin Trans. 1 1975, No. 10, 964.
I found a research paper[1] which specifically talks about the reaction you mention. The paper also mentions the same mechanism as you do:
The paper uses warm THF to conduct the reaction which shows that cycloreversion of the side ring actually takes place even at a temperature lower than 180°C.
The paper also talks about what happens when the reaction temperature is changed:
Reference:
(1) Fleming, I.; Mah, T. A Simple Synthesis of Anthracenes. J. Chem. Soc., Perkin Trans. 1 1975, No. 10, 964.
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