V.A. Shcherbinin, V.V. Konshin / Tetrahedron Letters xxx (2018) xxx–xxx
5
1:4. A plausible explanation is that the intermediate oxocarbenium
References
cation formed has a planar structure which preferentially under-
goes nucleophilic attack from one of the two possible sides.
Additionally, we found that the starting dioxolanones 1 isomer-
ize under the reaction conditions into a mixture of cis- and
trans-isomers. For example, dioxolanone 1b isomerizes into a 1.5:1
mixture of trans- and cis-isomers, respectively (GC analysis, Fig. 3).
During further studies, bis-addition products 4 were found to
form when the nucleophiles were electron-rich aromatic com-
pounds. The reaction time and the product yields in this case
strongly depend on the nucleophilicity of the aromatic compounds
used. For example, in the case of less nucleophilic tert-butylben-
zene (Entry 3) or ethyl furoate (Entry 6), the corresponding
methanes 4 were either not produced (4f) or were produced in
trace amounts (4c) (Table 3).
Alkoxy benzenes and 2-methylfuran were found to be the most
reactive (Entries 1, 2, 4, 5). The presence of an electron-withdraw-
ing substituent in the starting dioxolanone 1b increases the reac-
tion time and decreases the product yield (Entry 5).
The GC/MS and TLC studies of a competitive addition reaction
showed that, when using a mixture of aryl and silicon-containing
nucleophiles, both mono- and bis-addition products can form
depending on the nucleophilicity of the substrates used. In both
cases the alternative product is produced only in trace amounts
(Fig. 4).
Based on the data obtained, we assume that two possible path-
ways for addition are realized depending on the ability of the
nucleophile to stabilize the intermediate cation. For example, in
the case of nucleophiles, after addition of which a CH2 unit or car-
bon-carbon triple bond is present next to the cationic site, the reac-
tion terminates at the mono-addition step. In contrast, when the
first addition step leads to the formation of an aromatic ring vicinal
to the cationic site, addition of the second nucleophile molecule
takes place (Fig. 5).
[15] General procedure for the synthesis of acids 3a–d: To
a
solution of
L, 0.9
Conclusion
dioxolanone 1a (144 mg, 0.6 mmol) and allyltrimethylsilane (144
l
mmol) in dry CH2Cl2 (5.5 mL) under an argon atmosphere, FeCl3 (9.7 mg, 0.06
mmol) was added at room temperature. The reaction mixture was stirred for
30 min, poured into water, and extracted with EtOAc. The organic phase was
dried with anhydrous Na2SO4 and evaporated. The residue was purified by
column chromatography using EtOAc: Hex (1: 9) as eluent to give compound
3a (142 mg, 84%) as a colorless solid (dr = 1: 1.5).
The reaction between 1,3-dioxolan-4-ones and C-nucleophiles
was studied. The reaction proceeds either as mono-addition
to form O-substituted mandelic acids or bis-addition to form
tri-(hetero)arylmethanes.
[16] General procedure for the synthesis of acids 3e-l: To
a solution of
phenylacetylene (66 mL, 0.6 mmol) in dry toluene (4 mL) under an argon
atmosphere, DIPEA (87 mL, 0.5 mmol) and ZnBr 2(11.3 mg, 0.5 mmol) were
added at room temperature. The reaction mixture was stirred for 30 min at
Acknowledgments
room temperature and cooled to À10C.
A
cooled to À10C solution of
dioxolanone 1a (120.1 mg, 0.5 mmol) and TMSOTf (90 mL, 0.5 mmol) in
toluene (1 mL) was added. The resulting mixture was stirred for 2 h, poured
into water acidified with 2N HCl (1 mL), and extracted with EtOAc. The organic
phase was dried with anhydrous Na2SO4 and evaporated. The residue was
purified by column chromatography using gradient elution with EtOAc: Hex
(1:10 ? 1:6) to give compound 3e (128.4 mg, 75%) as a pale oil (dr = 1:1.5).
[17] General procedure for the synthesis of arylmethanes 4a–e: To a solution of
dioxolanone 1a (96 mg, 0.4 mmol) and 1,3,5-trimethoxybenzene (148 mg,
0.88 mmol) in dry CH2Cl2 (4 mL) under an argon atmosphere, FeCl3 (6.5 mg,
0.04 mmol) was added at room temperature. The reaction mixture was stirred
for 2 h, poured into water, and extracted with EtOAc. The organic phase was
dried with anhydrous Na2SO4 and evaporated. The residue was purified by
column chromatography using CH2Cl2: Hex (1:1) as eluent to give compound
4a (91 mg, 54%) as colorless crystals.
This work was financially supported by the Russian Science
Foundation (project No. 17-73-10251) and accomplished with
the use of scientific equipment of the Collective Employment
Centre «Ecoanalytical Centre», Kuban State University
(RFMEFI59317X0008).
A. Supplementary data
Supplementary data associated with this article can be found, in