Thermolysis and acid-catalyzed decomposition of 4-Diazotetrahydrofuran-3- ones. A new efficient synthesis of tetrasubstituted dihydrofuran-3-ones

Full text of DOI:10.1134/S1070428012040252

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2012, Vol. 48, No. 4, pp. 602–604. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © L.L. Rodina, Yu.Yu. Medvedev, P.N. Moroz, V.A. Nikolaev, 2012, published in Zhurnal Organicheskoi Khimii, 2012, Vol. 48, No. 4,
pp. 604–606.
SHORT
COMMUNICATIONS
Thermolysis and Acid-Catalyzed Decomposition
of 4-Diazotetrahydrofuran-3-ones. A New Efficient Synthesis
of Tetrasubstituted Dihydrofuran-3-ones
L. L. Rodina, Yu. Yu. Medvedev, P. N. Moroz, and V. A. Nikolaev
St. Petersburg State University, Universitetskii pr. 26, St. Petersburg, 198504 Russia
e-mail: LRodina@VN6646.spb.edu
Received November 18, 2011
DOI: 10.1134/S1070428012040252
The Wolff rearrangement is one of the most charac-
teristic transformations of diazo ketones [1]. Diazo
ketones of the tetrahydrofuran series are thus con-
verted into oxetane derivatives. Using tetramethyl-
substituted diazotetrahydrofuranone as an example, we
previously showed [2] that its photolytic Wolff rear-
rangement was the most efficient [2]. Photoinduced
reactions of aryl-substituted diazotetrahydrofuranones
are characterized by lower selectivity, and they give
rise to a number of products [3, 4].
in the absence of solvent (in melt), and the progress of
reactions was monitored by TLC and 1H NMR.
Diazofuranone IIa completely decomposed in 7 h,
whereas thermolysis of its di-para-fluoro-substituted
analog IIb required more than 48 h, other conditions
1
being equal. According to the H NMR data, dihydro-
furanones IVa and IVb were formed as almost the only
products. Thermal decomposition of regioisomeric
diazo ketones IIIa and IIIb occurred at a much higher
rate (in 3 h); like thermolysis of IIa and IIb, the only
observed path of decomposition of IIIa and IIIb was
elimination of nitrogen molecule and 1,2-migration of
one methyl group with formation of dihydrofuranones
Va and Vb.
The goal of the present work was to study thermal
and acid-catalyzed decomposition of 2,2,5,5-tetrasub-
stituted 4-diazotetrahydrofuran-3-ones, compare the
results with those obtained by photolysis, and estimate
synthetic potential of these processes. As substrates we
selected 4-diazo-2,2,5,5-tetramethyltetrahydrofuran-3-
one (I), 4-diazo-2,2-dimethyl-5,5-diphenyltetrahydro-
furan-3-one (IIa), 4-diazo-5,5-bis(4-fluorophenyl)-2,2-
dimethyltetrahydrofuran-3-one (IIb), 4-diazo-5,5-di-
methyl-2,2-diphenyltetrahydrofuran-3-one (IIIa), and
4-diazo-2,2-bis(4-fluorophenyl)-5,5-dimethyltetra-
hydrofuran-3-one (IIIb).
O
Ar
Δ, ~Ar
Me
Me
IVa, IVb; 72–88%
Me
IIa, IIb
–N2
Ar
O
O
Δ, ~Me
Ar
Ar
Va, Vb; 76–90%
IIIa, IIIb
–N2
Me
O
N2
O
N2
O
N2
O
Me
Me
Me
Me
Me
Me
Ar
Ar
Ar
Ar
Me
Me
O
O
O
Acid-catalyzed decomposition of diazofuranones I–
III in trifluoroacetic acid was complete in 5–6 min.
The reaction was exothermic, and diazo ketone I was
converted almost quantitatively into 2,2,4,5-tetrameth-
yl-2,3-dihydrofuran-3-one (VI), whereas diazo ketones
I and III gave rise to the same 1,2-alkyl or 1,2-aryl
migration products (IV, V) as in the thermolysis. The
structure of newly synthesized compounds IVb and
I
IIa, IIb
IIIa, IIIb
Ar = Ph (a), 4-FC6H4 (b).
Preliminary experiments showed that diazo ketones
I–III are very resistant to heat. Taking into account
unexpected thermal stability [5, 6], thermolysis of
diazo ketones II and III was performed at 150–160°C
602

THERMOLYSIS AND ACID-CATALYZED DECOMPOSITION
603
3JCF = 9.0 Hz), 131.9 d (Co, 3JCF1 = 9.0 Hz), 161.3 d (Cp,
1JCF = 248.3 Hz), 163.8 d (Cp, JCF = 248.3 Hz), 179.5
(C5), 207.9 (C=O). Found, %: C 72.06; H 4.68.
C18H14F2O2. Calculated, %: C 72.03; H 4.66.
4,5-Dimethyl-2,2-diphenyl-2,3-dihydrofuran-
3-one (Va). Yield 34 mg (76%; from 50 mg of IIIa;
150°C, 4 h), mp 108–109°C (from petroleum ether),
Rf 0.18 (petroleum ether–t-BuOMe, 5:1) [4].
1
Vb was determined on the basis of their H and
13C NMR spectra and elemental analyses.
Presumably, thermolysis of diazo ketones I–III
with formation of dihydrofuran-3-ones IV–VI follows
concerted nitrogen elimination–alkyl (aryl) group
migration mechanism without intermediate generation
of oxocarbenes. The latter are believed to be the most
probable intermediate species in the photolysis of such
diazo ketones [3, 4], and they tend to undergo Wolff
rearrangement and concomitant transformations which
were not observed in the thermolysis of diazo ketones
I–III. Acid-catalyzed decomposition of aliphatic diazo
compounds is known to follow two main paths [5, 7].
However, taking into account appreciably higher sta-
bility of diazo ketones I–III with respect to organic
acids, as compared to diazo alkanes, we presume that
the initial step is reversible protonation of the carbonyl
group in I–III, which is followed by elimination of ni-
trogen to produce finally dihydrofuran-3-ones IV–VI.
2,2-Bis(4-fluorophenyl)-4,5-dimethyl-2,3-dihy-
drofuran-3-one (Vb). Yield 52 mg (90%; from 65 mg
of IIIb; 160°C, 8 h), mp 70–71°C (from petroleum
ether), Rf 0.32 (petroleum ether–t-BuOMe, 2:1).
1H NMR spectrum, δ, ppm: 1.75 s (3H, CH3), 2.35 s
(3H, CH3), 7.01–7.07 m (4H, Harom), 7.42–7.46 m (4H,
Harom). 13C NMR spectrum, δC, ppm: 6.2 (4-CH3), 15.4
2
(5-CH3), 107.8 (C4), 111.2 (C2), 115.7 d (Cm, JCF
=
21.9 Hz), 128.7 d (Co, JCF = 8.0 Hz), 134.6 (Ci),
3
162.5 d (Cp, JCF = 247.4 Hz), 184.3 (C5), 205.5
1
(C=O). Found, %: C 72.16; H 4.71. C18H14F2O2. Cal-
culated, %: C 72.03; H 4.66.
Thus, unlike photolysis, thermal and acid-catalyzed
decomposition of 4-diazotetrahydrofuran-3-ones hav-
ing alkyl or aryl substituents leads to the formation of
unsaturated ketones IV–VI, and these reactions may be
regarded as an efficient method for the preparation of
tetrasubstituted dihydrofuran-3-ones.
Reaction of diazo ketones I–III with trifluoro-
acetic acid (general procedure). Trifluoroacetic acid,
0.4–0.8 mmol, was added dropwise to 0.3–0.6 mmol of
diazo ketone I, IIa, IIb, IIIa, or IIIb. When the exo-
thermic reaction ceased and evolution of nitrogen
terminated, the mixture was cooled, volatile com-
ponents were removed under reduced pressure (10–
15 mm), and the residue was purified by chromatog-
raphy on silica gel or by recrystallization from petro-
leum ether. From 97 mg (0.6 mmol) of I and 96 mg
(0.8 mmol) of CF3COOH we obtained 80 mg (95%) of
VI; from 100 mg (0.34 mmol) of IIa and 58 mg
(0.42 mmol) of CF3COOH, 83 mg (92%) of IVa; from
100 mg (0.3 mmol) of IIb and 60 mg (0.5 mmol) of
CF3COOH, 88 mg (98%) of IVb; from 100 mg
(0.3 mmol) of IIIa and 70 mg (0.61 mmol) of
CF3COOH, 81 mg (90%) of Va; from 100 mg
(0.3 mmol) of IIIb and 60 mg (0.5 mmol) of
CF3COOH, 86 mg (95%) of Vb.
Diazo ketone I was synthesized from commercial
2,5-dimethylhex-3-yne-2,5-diol according to [8]; diazo
ketones II and III were obtained from 2-methylbut-
3-yn-2-ol and benzophenone or 4,4′-difluorobenzo-
phenone according to the procedures described in [9].
Thermolysis of diazo ketones I, IIa, IIb, IIIa,
and IIIb (general procedure). The reactions were
carried out in a 10–15-ml flask equipped with an air
condenser. The progress of the process was monitored
1
by TLC and H NMR. Dihydrofuranones IV and V
were isolated by chromatography on silica gel (gradi-
ent elution with petroleum ether–tert-butyl methyl
ether) or recrystallization from petroleum ether.
1
The H and 13C NMR spectra were recorded on
2,2-Dimethyl-4,5-diphenyl-2,3-dihydrofuran-
3-one (IVa). Yield 44 mg (88%; from 55 mg of IIa;
150°C, 7 h), mp 79–80°C (from petroleum ether),
Rf 0.24 (petroleum ether–t-BuOMe, 5:1) [4].
a Bruker DPX-300 spectrometer at 300 and 75.5 MHz,
respectively (CDCl3, TMS). Reaction mixtures were
separated by chromatography on Silicagel L (40–
100 μm, activity grade I). The progress of reactions
was monitored, and Rf values were determined, by
TLC on Silufol UV-254 plates (Kavalier, ČSSR).
4,5-Bis(4-fluorophenyl)-2,2-dimethyl-2,3-dihy-
drofuran-3-one (IVb). Yield 60 mg (72%; from
88 mg of IIb; 160°C, 9.5 h), mp 109–110°C (from
petroleum ether), Rf 0.21 (petroleum ether–t-BuOMe,
1
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