SUPPORTING INFORMATION
Gas-phase synthesis of hydrodiphenylcyclopropenylium via
nonclassical Favorskii rearrangement from alkali-cationized
α,α'-dibromodibenzyl ketone
Zhi-Xiong Zhao, Hao-Yang Wang*, Chu Xu and Yin-Long Guo*
Shanghai Mass Spectrometry Center, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 345 Lingling Lu, Shanghai 200032, P.R. China
*Correspondence to: Y.-L. Guo or H.-Y. Wang, Shanghai Mass Spectrometry Center,
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling
Lu, Shanghai 200032, P.R. China.
E-mail: ylguo@mail.sioc.ac.cn, haoyangwang@mail.sioc.ac.cn
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1. Synthesis of α,α’-dibromodibenzyl ketone 1 and diphenylcyclopropenone 2
A. Synthesis of α,α’-dibromodibenzyl ketone 1 from dibenzyl ketone
To a solution of 7 g (33 mmol) of commercial dibenzyl ketone in 25 mL of glacial
acetic acid, a solution of 11 g (67 mmol) of bromine in 50 mL of acetic acid was
added with stirring over 15 min at ambient temperature. After the addition was
complete, the mixture was stirred until the color of the solution turned to
orange-yellow (heat when necessary). The solution was then poured into 100 mL of
water. Solid Na2SO3 was added in small portions until the initial yellow color of the
solution was discharged, and the mixture was allowed to stand for 1 h. The slightly
yellow mixture of meso- and dl-α,α'-dibromodibenzyl ketone was collected and air
dried. Recrystallization from hexane (ca. 100 mL) afforded 9.3 g (25mmol, 79%) of
white needles. Found: 1H-NMR (300MHz, δ, CDCl3): 7.4 (10H), 5.7 (2H). EI-MS:
m/z 368.
B. Synthesis of diphenylcyclopropenone 2 from α,α’-dibromodibenzyl ketone 1
This mixture of isomers (7.2 g, 19.6mmol) was dissolved in 33 mL of methylene
chloride and the solution was added with stirring over 1 h to 7.2 mL of triethylamine
in 16.5 mL of methylene chloride at room temperature. The mixture was stirred for an
additional 30 min, extracted with 12 mL 3 N HC1 three times (discarded), and the
organic phase was transferred to a flask and cooled in an ice bath. A cooled solution
of 6 mL of concentrated H2SO4 in 2 mL of water was slowly added into the organic
phase. A slightly pink precipitate of diphenylcyclopropenone bisulfate separated and
this was collected on a sintered glass funnel. The solid was then returned to the flask
along with 18 mL of methylene chloride and 36 mL of water, and 0.35 g of solid
Na2CO3 was added in small portions. The organic layer was collected and the aqueous
solution was extracted with three 18 mL portions of methylene chloride. The
combined organic layers were dried over MgSO4 and evaporated to dryness. The
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impure diphenylcyclopropenone was recrystallized by repeated extractions with
boiling cyclohexane (total 100 mL), the solution being decanted from a reddish, oily
impurity. On cooling, the solution deposited white crystals 1.8 g (9.7 mmol, 45%) of
diphenylcyclopropenone. Found: 1H-NMR (300MHz, δ, CDCl3): 8.0 (4H), 7.6 (6H).
EI-MS: m/z 178 (as the standard mass spectrum).
Figure S1. 1H-NMR spectrum for α,α’-dibromodibenzyl ketone.
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Figure S2. 1H-NMR spectrum for diphenylcyclopropenone.
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2. Characterization of α,α’-dibromodibenzyl ketone 1
ESI mass spectra of α,α’-dibromodibenzyl ketone 1
Figure S3. ESI-MS spectrum of α,α’-dibromodibenzyl ketone 1 in methanol.
Figure S4. ESI-MS spectra of α,α'-dibromodibenzyl ketone 1 in methanol with
alkali-metal salt: (a) LiCl and (b) NaCl.
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ESI-MS/MS of 1·Li+
Figure S5. ESI-MS/MS spectra for CID of 1·Li+: (a) at m/z 373; (b) at m/z 375; and (c)
at m/z 377 (CID energy at 20 eV by TSQ).
The product ion for 2·H+ at m/z 207 could also be observed in the ESI-MS/MS
spectra of 1·Li+ and the ESI-MS/MS spectra of 1·Na+. However, a 'byproduct' ion at
m/z 214 could also be observed clearly. The reason for the formation of this ion was
attributed to the behavior of the Li atom. As a stronger Lewis acid than Na, Li shows
stronger affinity to oxygen. Furthermore, the atomic radius of Li+ is smaller than that
of Na+. For these reasons, the interaction between the Li+ and the bromide atom in the
five-membered ring mentioned in the full text might be weaker than that of Na+ and
the catalytic debromination effect was also weaker for Li+. Thus, we proposed the
'side reaction' fragmentation pathway shown in Scheme S1. The proposed structure
for the ion at m/z 214 formed by loss of [H+2Br] from 1·Li+ seem to more stable for
the aromatic effect.
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Scheme S1. The proposed dissociation pathway of the 1·Li+ ion at m/z 373.
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3. Characterization of diphenylcyclopropenone 2
Standard EI-MS (70 eV) of diphenylcyclopropenone 2
Figure S6. Standard EI-MS spectrum of diphenylcyclopropenone 1 (data from NIST
08 Mass Spectral Library).
ESI mass spectra of diphenylcyclopropenone 2
Figure S7. ESI-MS spectrum of diphenylcyclopropenone 1 in methanol.
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Figure S8. ESI-MS/MS spectrum of the fragment ion at m/z 179 (CID energy at 10
eV by TSQ).
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