Novel photochemical reactions of carbocyclic diazodiketones without elimination of nitrogen – a suitable way to N-hydrazonation of C–H-bonds

Article abstract of DOI:10.3762/bjoc.14.200

The sensitized photoexcitation of 2-diazocyclopentane-1,3-diones in the presence of THF leads to the insertion of the terminal N-atom of the diazo group into the α-С–Н bond of THF, producing the associated N-alkylhydrazones in yields of up to 63–71%. Further irradiation of hydrazones derived from furan-fused tricyclic diazocyclopentanediones culminates in the cycloelimination of furans to yield 2-N-(alkyl)hydrazone of cyclopentene-1,2,3-trione. By contrast, the direct photolysis of carbocyclic diazodiketones gives only Wolff rearrangement products with up to 90–97% yield.

Full text of DOI:10.3762/bjoc.14.200

Novel photochemical reactions of carbocyclic diazodiketones
without elimination of nitrogen – a suitable way to
N-hydrazonation of C–H-bonds
Liudmila L. Rodina1, Xenia V. Azarova1, Jury J. Medvedev1, Dmitrij V. Semenok2
and Valerij A. Nikolaev*1
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2018, 14, 2250–2258.
1Department of Organic Chemistry, St-Petersburg State University, 26
University pr., 198504, Saint-Petersburg, Russia and 2Skolkovo
Institute of Science and Technology, 143026, Moscow, Skolkovo
Innovation Center, 3 Nobel st., Russia
doi:10.3762/bjoc.14.200
Received: 24 April 2018
Accepted: 09 August 2018
Published: 28 August 2018
Email:
Valerij A. Nikolaev* - valerij.nikolaev@gmail.com
Associate Editor: J. A. Murphy
* Corresponding author
© 2018 Rodina et al.; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
C–H insertion; diazo compounds; excited state; photochemistry; Wolff
rearrangement
Abstract
The sensitized photoexcitation of 2-diazocyclopentane-1,3-diones in the presence of THF leads to the insertion of the terminal
N-atom of the diazo group into the α-С–Н bond of THF, producing the associated N-alkylhydrazones in yields of up to 63–71%.
Further irradiation of hydrazones derived from furan-fused tricyclic diazocyclopentanediones culminates in the cycloelimination of
furans to yield 2-N-(alkyl)hydrazone of cyclopentene-1,2,3-trione. By contrast, the direct photolysis of carbocyclic diazodiketones
gives only Wolff rearrangement products with up to 90–97% yield.
Introduction
Photochemical reactions of diazocarbonyl compounds are well- served upon irradiation of diazo compounds with longer wave-
known transformations in the synthesis of the diversified length UV light.
acyclic, carbo- and heterocyclic structures [1-5]. A direct irradi-
ation of diazo compounds by UV light usually gives rise to Recently a new light-induced reaction of diazo compounds with
nitrogen elimination and generation of carbenes [6-10] or retention of the diazo group nitrogen atoms in the structure of
ketenes [11-18] and their ensuing transformations. On the other the reaction products was discovered by our group. The sensi-
hand, photochemical reactions of diazocarbonyl compounds tized photoexcitation of heterocyclic diazoketones – diazote-
without elimination of dinitrogen are essentially limited to their trahydrofuranones resulted in the formation of N-alkyl-substi-
isomerization into α-ketodiazirines [19-26] which is usually ob- tuted hydrazones and other nitrogen-containing compounds [27-
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30]. This photochemical process is assumed to proceed through porting Information File 1, Table S1) and in the case of the
the triplet excited states of diazoketones via ‘insertion’ of the tricyclic diazodiketone 1с the structure was also confirmed by
terminal nitrogen atom of the diazo group into the С–Н bond of means of X-ray analysis (Supporting Information File 1, Figure
the organic substrates [27,30].
S1). As it is evident from these data, the tricyclic diazodike-
tones 1b–e all have endo-configuration of the molecular struc-
Hence it was principally demonstrated that by carefully varying ture.
the irradiation conditions one can direct the photochemical reac-
tion of diazo compounds at the alternative way, which provides Analysis of the UV spectra of diazodiketones 1 shows that they
the retention of ‘dinitrogen’ in the structure of molecule formed. have four absorption bands: two intense ones at 216–222 and
It is reasonable that a question arises on the scope and limita- 248–250 nm, and two bands with very week intensities at
tions of this new light-induced reaction of diazo compounds.
311–316 nm (215 < ε < 290) and 363–367 nm (30 < ε < 49)
(see Supporting Information File 1, Table S1). By analogy with
The main objective of our current research was to elucidate the the literature data [40], the absorption bands in the short wave-
possibility of using carbocyclic diazodiketones in this photo- length region (216–250 nm) are attributed to π–π* electronic
chemical process. For this purpose, diazocyclopentanediones transitions, whereas the long wavelength bands are most likely
1a–g were tested in the study including unsubstituted diazocy- caused by n–π* transitions. Based on the position of the long
clopentanedione 1a, tricyclic diazodiketones 1b–e with CH2- wavelength bands (363–367 nm) the energy of the singlet
and O-bridges in their structure, diazoindandione 1f, diazocy- excited state 1S1 of diazodiketones 1 can be estimated at about
clopentenedione 1g, and as a С–Н donor tetrahydrofuran was 78–79 kcal/mol [41].
employed in the study (Figure 1).
The characteristics of the absorption bands of the sensitizers
To determine the most efficient conditions for this reaction with used in this study (acetophenone, benzophenone and Michler’s
diazodiketones 1, three sensitizers, acetophenone, benzo- ketone) demonstrate that they show appropriate absorption of
phenone, and Michler’s ketone, with different levels of triplet the actinic light at the irradiation conditions of diazodiketones 1
state energy were tested. Furthermore, to clearly demonstrate (Supporting Information File 1, Table S2).
the difference of light-induced reactions of diazo compounds 1
in the triplet and singlet excited states, the direct photolysis of The sensitized photoreactions of diazodiketones 1a–g were
diazodiketones 1a-c without sensitizers was also examined.
carried out in THF solutions with added sensitizers (Table 1). In
the case of diazodiketone 1а the only isolated product was
hydrazone 2а with 33–49% yields (Table 1, entries 1–3). In-
Results and Discussion
The starting diazocyclopentanediones (DDK, 1a–f) were syn- creasing the amount of sensitizer (up to 10:1) enhanced the
thesized from the corresponding 1,3-dicarbonyl compounds yield of hydrazone 2а by 1/2 while reducing the irradiation time
[31-33] employing a diazotransfer reaction [34-39]. Diazocy- by 50% (Table 1, entries 1 and 3).
clopentenedione 1g was prepared by thermal cycloelimination
from diazodiketones 1d,e [38,39]. The structures of diazodike- The irradiation of tricyclic diazodiketone 1b in the presence of
tones 1a–g were established using a standard set of spectroscop- 1 equiv of benzophenone in THF solution led to the formation
ic methods (1Н and 13С NMR, IR and UV; for details, see Sup- of hydrazone 2b in a yield of 32% (Table 1, entry 4), whose
Figure 1: The structures of carbocyclic diazodiketones 1a–g and C–H-donating tetrahydrofuran used in the project.
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Table 1: Sensitized light-induced reactions of diazodiketones 1а–f.a
Entry
DDKb
Sensitizer
Ph2CO
Ratio sensitizer/DDK
Time, h
Yields of 2a–d,f and 3 [%]
1
2
3
2:1
1.5
2a; 33
2a; 42
2a; 49
1a
4:1
0.75
0.75
10:1
4
Ph2CO
Ph2CO
Ph2CO
Ph2CO
MePhCO
M Kd
1:1
1:1
4:1
10:1
4:1
2:1
1.3
6.5
2
2b; 32
2b; 34
2b; 52
2b; 71
2b; 40
n.d.e
5c
6
1b
7
1.5
1.5
3.5
8
9
10
11
12
13
1c
1d
1e
1f
Ph2CO
Ph2CO
Ph2CO
Ph2CO
10:1
4:1
0.8
0.5
1.0
0.8
2c; 63
2d; 35 + 3; 47 (total yield 82%)
4:1
3; 34
4:1
2f; 52
aIrradiation at λ > 210 nm. bDiazodiketone. cIrradiation at λ > 310 nm. dMichler’s ketone. eInseparable complex reaction mixture was obtained with
Michler’s ketone.
structure was unambiguously established by X-ray analysis As can be seen from the data in Table 1 the most effective
(Figure 2).
sensitizer for the light-induced reaction studied in the series of
acetophenone, benzophenone, and Michler’s ketone was found
to be benzophenone. The application of acetophenone reduced
the yield of hydrazone 2b by about 1/4 as compared to benzo-
phenone (from 52 to 40%; Table 1, entries 6 and 8). With
Michler’s ketone, a complex product mixture was obtained,
from which it was impossible to isolate pure compounds.
When varying the ratio of sensitizer/diazodiketone 1b, the best
result was obtained with a 10-fold excess of benzophenone
(Table 1, entry 7; 71% yield). Application of a 4-fold excess of
this sensitizer diminished the yield of hydrazone 2b to 52%
(Table 1, entry 6). In going from short wavelength (λ > 210 nm)
to longer wavelength (λ > 310 nm) irradiation, the yield of
hydrazone 2b remained practically unchanged, however the
reaction time considerably increased from 1.3 to 6.5 h; Table 1,
entries 4 and 5).
Figure 2: Molecular structure of hydrazone 2b as determined by X-ray
analysis data (Olex2 plot with 50% probability level of ellipsoids).
To increase the yields of hydrazones 2, an effort was under-
taken to optimize the photochemical reaction conditions by The reactions of tricyclic diazodiketone 1c and diazoindan-
varying the wavelength of irradiation, sensitizer, as well as the dione 1f in the presence of benzophenone as sensitizer
ratio of sensitizer/diazodiketone 1b (Table 1, entries 4–9).
proceeded in a similar way to diazo compound 1b under the
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optimal conditions affording hydrazones 2c,f in yields of 63 and hydrazones 2a–d,f and the most effective sensitizer for this
52%, respectively (Table 1, entries 10 and 13).
reaction was found to be benzophenone.
An unexpected side reaction was observed during irradiation of The direct photolysis of diazodiketones 1a–c was carried out by
furan-fused tricyclic diazodiketones 1d,e (Scheme 1). In the UV light (λ > 210 nm) in THF solution containing a small
case of diazodiketone 1d, hydrazone 3 (47%) was isolated from amount of H2O or MeOH to trap the proposed intermediate
reaction mixture in addition to the expected hydrazone 2d α-oxoketene. These light-induced processes with diazodike-
(35%; total yield 82%, Table 1, entry 11), whereas the same tones 1a–c resulted in formation of 2-oxocyclobutanecar-
reaction with diazodiketone 1e afforded hydrazone 3 exclusive- boxylic acid 4a or methyl esters 5a–c in high isolated yields of
ly (Table 1, entry 12).
up to 90% (Table 2). At the same time no insertion products of
the possible intermediate dioxocarbenes into O–H-bonds
Additional experiments showed that hydrazone 3 was not of the nucleophilic reagents (H2O, MeOH) or C–H-bonds at С5
formed on sensitized photoexcitation of diazocyclopentene- or С6 atoms in 1 [26,42-45] were detected in the reaction
dione 1g in the presence of the C–H-donor THF (Scheme 1). mixtures. Thus, it was experimentally shown that the direct
Thus one can conclude that product 3 is generated by a light-in- photolysis of diazodiketones 1а–c employing UV light with
duced cycloelimination of furan from the initially generated λ > 210 nm produces only Wolff rearrangement products in
tricyclic hydrazones 2d,e.
high yields.
Hence it was established that the sensitized photoexcitation of The structure of 2-oxocyclobutanecarboxylic acid 4a and the
diazodiketones 1a–d,f in THF solution proceeds through the methyl esters 5a–c was established by spectroscopic data
insertion of the terminal N-atom of the diazo group in the (1Н, 13С NMR, and HRMS), and in case of 4a and 5a, also con-
α-С–Н-bond of THF with the formation of the appropriate firmed by comparison with the known literature data [46-48].
Scheme 1: Photochemical cycloelimination of furans from hydrazones 2d,e.
Table 2: Direct photolysis of diazodiketones 1a–с by UV light with λ > 210 nm.
Entry
DDK 1a–c
Solvent/NuH (ratio)
Time, min
Yields of 4,5 [%]a
1
2
1a
1a
THF/Н2О (45:1)
50
55
4a; 90
5a; 86
THF/МеОН (20:1)
3
4
1b
1c
THF/МеОН (200:1)
THF/МеОН (50:1)
55
45
5b; 79 (97)
5с; 82
aYield determined by 1H NMR spectroscopy is given in parenthesis.
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It was found that 2-oxocyclobutanecarboxylic acid 4a and ester photochemical process of C–H-insertion followed by cycloelim-
5a were easily hydrolyzed in the presence of H2O or during ination of furan from the initially generated hydrazones 2d,f
chromatography on silica gel to produce glutaric acid and the apparently occurs, giving rise to the formation of hydrazone 3
corresponding methyl ester (Table 2). By contrast, esters 5b,c as the final reaction product (Scheme 1).
proved to be much more stable to hydrolysis on SiO2 and in the
presence of nucleophilic reagents. For example, when heating in On direct irradiation of tricyclic diazodiketones 1 possessing
boiling MeOH for 2 h no hydrolysis of ketoester 5с occurs ac- endo-configuration (Figure 2), one would expect in addition to
cording to 1H NMR spectra.
the Wolff rearrangement also the occurrence of an intramolecu-
lar cyclopropanation (with 1b,d,e) [53-55] or an insertion of the
The assumed ways for light-induced reactions of diazodike- assumed intermediate dioxocarbenes in C–H-bonds at С5 or
tones 1 can be represented as follows. The direct irradiation С6-atoms (with 1c) [26,42-45]. However, the performed experi-
(λ > 210 nm) of diazodiketones 1 gives rise to accumulation of ments did not confirm the formation of corresponding reaction
one of their upper singlet excited states 1(1)* [13,15,18,20,49- products in the photochemical reactions studied. This can be
51] which turn into usual Wolff rearrangement products, i.e., considered as an argument in favor of the concerted Wolff rear-
highly reactive oxoketenes 6 (Scheme 2, reaction I). The inter- rangement [11-18] in the case of these diazodiketones.
mediate ketenes 6 react with H2O or MeOH present in the reac-
tion mixture to give 2-oxocarboxylic acid 4a or esters 5a–c.
Conclusion
The sensitized photoexcitation of carbocyclic diazodiketones
On the other hand, the sensitized photoexcitation of diazodike- proceeds without elimination of dinitrogen. Instead, the reac-
tones 1 gives rise to generation of triplet excited states of diazo tion leads to the insertion of the terminal N-atom of the diazo
compounds 3(1)1 which interact with the H-donor (tetrahydro- group into the C–H bond of THF giving rise to the appropriate
furan) producing N-alkyl-substituted hydrazones 2 (Scheme 2, N-alkyl-substituted hydrazones in yields of up to 63–71%. The
reaction II). Based on the comparison study of the sensitizers’ most powerful sensitizer for this light-induced process in the
efficiency in this reaction (Table 2) one can conclude [41,52], series of acetophenone, benzophenone and Michler’s ketone
that the energy of the triplet excited states 3T1 of diazodike- was found to be benzophenone. Hence, the diazodicarbonyl
tones 1 are about 68 kcal/mol. This provides a possible explana- compounds can be successfully used for a photochemical
tion why the use of Michler’s ketone was found to be ineffec- N-functionalization of C–H-bonds of organic compounds. In
tive as a photosensitizer in the process. The energy of the triplet contrast to this, the direct photolysis of carbocyclic diazoke-
excited state 3T1 of this sensitizer (64 kcal/mol) is somewhat tones produces exclusively Wolff rearrangement products in
lower than the corresponding energy of the diazodiketones 1 yields of 90–97%.
making it inadequate to initiate the C–H insertion reaction.
Experimental
On the other hand, the triplet excited state energy of benzo-
phenone (69 kcal/mol) renders it a suitable sensitizer for this General methods
reaction.
All reactions were carried out under argon atmosphere in sol-
vents that were purified and dried before use by common
In the case of tricyclic diazodiketones 1d,f (with annulated methods. Monitoring of the reaction course was accomplished
furan and 2-methylfuran-motifs in their structures), a tandem by thin layer chromatography (TLC) on silica gel SIL G/UV254
Scheme 2: Different pathways of diazodiketones 1 light-induced reactions in the singlet (reaction I) and triplet (reaction II) excited states.
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Beilstein J. Org. Chem. 2018, 14, 2250–2258.
plates (Marcherey, Nagel & Co.). Chromatography was per- 198.7, 130.9, 92.5, 69.2, 33.3, 31.8, 31.2, 24.4 ppm;
formed using Merck silica gel 60, 230–400 mesh. 1H and HRMS–ESI (m/z): [M + Na]+ calcd for C9H12N2O3, 219.0746;
13C NMR spectra were recorded using a Bruker-400 Avance found, 219.0746.
NMR spectrometer. All HRMS spectra were recorded on a
«MaXis» (Bruker Daltonik GmbH), the HPLC system B. Sensitized photoexcitation of 2-diazo-3a,4,7,7a-tetra-
(UHPLC) with the combined high-resolution quadrupole-time- hydro-1H-4,7-methanoindene-1,3(2H)-dione (1b). The reac-
of-flight mass spectrometer with electrospray ionization (ESI- tion was performed according to the general procedure with
QTOF). Chemical shifts are reported in ppm, and coupling con- 380 mg (2 mmol, 1 equiv) of diazodiketone 1b and 3.64 g
stants are given in hertz (Hz). All signals in NMR spectra were (20 mmol, 10 equiv) of benzophenone in 20 ml of THF with an
normalized relative to signals of CНCl3 (δ = 7.26 ppm in irradiation time of 90 min. After the standard workup proce-
1H NMR) and CDCl3 (δ = 77.0 in 13C NMR spectra).
dure hydrazone 2b was isolated.
For single crystal X-ray diffraction experiments of 1c (CCDC 2-(2-(Tetrahydrofuran-2-yl)hydrazono)-3a,4,7,7a-tetra-
1584937) and 2b (CCDC 1584938) an Agilent Technologies hydro-1H-4,7-methanoindene-1,3(2H)-dione (2b). Yield
«Xcalibur» diffractometer with monochromated MoKα radia- 374 mg (71%); bright-yellow solid; mp 127–129 °С; 1H NMR
tion was used. All samples were measured at 100 K. The unit (400 MHz, CDCl3, δ) 12.78 (s, 1H), 6.11–5.98 (m, 1H),
cell parameters were refined by least square techniques in 6.00–5.87 (m, 1H), 5.54–5.41 (m, 1H), 4.05–3.94 (m, 1H),
CrysAlisPro (Agilent Technologies, 2012) program complex. 3.92–3.82 (m, 1H), 3.38 (d, J = 20.3 Hz, 2H), 3.20–3.07 (m,
Empirical absorption correction was applied using spherical 2H), 2.32–2.10 (m, 2H), 2.03–1.92 (m, 2H), 1.63 (dt, J = 8.6,
harmonics, implemented in SCALE3 ABSPACK scaling algo- 1.5 Hz, 1H), 1.48 (d, J = 8.6 Hz, 1H) ppm; 13C NMR
rithm. The structures were solved by the Superflip [56-58] and (101 MHz, CDCl3, δ) 201.3, 199.51, 199.49, 134.9, 134.8,
ShelXS [59] structure solution programs using Charge Flipping 133.7, 133.63, 133.55, 133.53, 92.44, 92.39, 69.0, 68.9, 52.39,
and Direct Methods, respectively, then refined by means of the 52.37, 49.8, 48.2, 48.14, 46.14, 46.11, 46.04, 46.00, 31.2, 31.1,
ShelXL [60] program, incorporated in the Olex2 program 24.4, 24.3 ppm; 1H NMR (400 MHz, acetone-d6, δ) 6.36–5.71
package [61].
(m, 2H), 5.48 (dd, J = 6.6, 3.6 Hz, 1H), 4.14–3.75 (m, 2H),
3.46–3.01 (m, 5H), 2.46–2.12 (m, 2H), 2.10–1.73 (m, 2H),
1.62–1.52 (m, 2H) ppm; 13C NMR (101 MHz, acetone-d6, δ)
Sensitized reactions of diazodiketones 1a–g
General procedure. The solution of diazodiketone 1a–g 199.8, 134.1, 133.7, 92.1, 68.5, 52.0, 48.8, 45.9, 30.3,
(1 equiv) and benzophenone (up to 10 equiv) in THF 24.4 ppm; HRMS–ESI (m/z): [M + Na]+ calcd for C14H16N2O3,
(10–30 ml) was irradiated in a quartz reactor (λ > 210 nm) 283.1059; found, 283.1065.
under an argon atmosphere for up to 6.5 h (control of the
reacted diazodiketone 1 by TLC). Thereupon the reaction mix- C. Sensitized photoexcitation of 2-diazohexahydro-1H-4,7-
ture was dried over magnesium sulfate, the solvent completely methanoindene-1,3(2H)-dione (1c). The reaction was per-
distilled off in vacuum and the residue separated by column formed according to the general procedure with 376 mg
chromatography (SiO2, eluent: petroleum ether → petroleum (2 mmol, 1 equiv) of diazodiketone 1c and 3.64 g (20 mmol,
ether/acetone 8:1) to give the hydrazones 2 and 3.
10 equiv) of benzophenone in 20 ml of THF with an irradiation
time of 1 h. After the standard workup procedure hydrazone 2c
A. Sensitized photoexcitation of 2-diazocyclopentane-1,3- was isolated.
dione (1a). The reaction was performed according to the
general procedure with 496 mg (4 mmol, 1 equiv) of diazodike- 2-(2-(Tetrahydrofuran-2-yl)hydrazono)hexahydro-1H-4,7-
tone 1a and 2.912 g (16 mmol, 4 equiv) of benzophenone in methanoindene-1,3(2H)-dione (2c). Yield 328 mg (63%);
30 ml of THF with an irradiation time of 45 min. After the bright-yellow oil; 1H NMR (400 MHz, CDCl3, δ) 13.10 (broad,
workup procedure hydrazone 2a and unreacted diazoketone 1a 1H, NH), 5.66–5.51 (m, 1H), 4.11–4.01 (m, 1H), 3.98–3.89 (m,
were isolated.
1H), 3.02–2.90 (m, 2H), 2.75–2.86 (m, 2H), 2.37–2.19 (m, 2H),
2.11–1.99 (m, 2H), 1.65–1.54 (m, 2H), 1.53–1.44 (m, 2H),
2-(2-(Tetrahydrofuran-2-yl)hydrazono)cyclopentane-1,3- 1.39–1.31 (m, 1H), 1.27–1.15 (m, 1H) ppm; 13C NMR
dione (2a). Yield 168 mg (42%, calculated on the reacted (101 MHz, CDCl3, δ) 202.96, 202.95, 202.0, 201.0, 133.2,
diazodiketone 1a), bright-yellow oil; 1H NMR (400 MHz, 133.0, 92.7, 92.6, 69.2, 69.1, 52.68, 52.65, 50.99, 50.98, 42.49,
CDCl3, δ) 12.93 (s, 1H), 5.61–5.53 (m, 1H), 4.08–3.99 (m, 1H), 42.47, 40.62, 40.59, 40.55, 40.52, 31.34, 31.26, 24.7, 24.59,
3.95–3.88 (m, 1H), 2.69–2.60 (m, 4H), 2.33–2.19 (m, 2H), 24.56, 24.5, 24.4 ppm; HRMS–ESI (m/z): [M + Na]+ calcd for
2.08–1.96 (m, 2H) ppm; 13C NMR (101 MHz, CDCl3, δ) 200.3, C14H18N2O3, 285.1215; found, 285.1210.
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Beilstein J. Org. Chem. 2018, 14, 2250–2258.
D. Sensitized photoexcitation of 2-diazo-3a,4,7,7a-tetra- 13C NMR (101 MHz, CDCl3, δ) 188.3, 186.4, 140.2, 138.6,
hydro-1H-4,7-epoxyindene-1,3(2H)-dione (1d). The reaction 135.1, 134.8, 130.1, 123.1, 122.7, 91.9, 68.6, 31.0, 24.7 ppm;
was performed according to the general procedure with 380 mg HRMS–ESI (m/z): [M + H]+ calcd for C13H12N2O3, 245.0926;
(2 mmol, 1 equiv) of diazodiketone 1d and 1.46 g (8 mmol, found, 245.0926.
4 equiv) of benzophenone in 20 ml of THF with an irradiation
time of 0.5 h. After the standard workup procedure hydrazones Direct photolysis of diazodiketones 1a–c
2d, 3 and unreacted diazoketone 1d were isolated.
Photolysis of diazodiketone 1a (with H2O). A solution of
sublimated diazodiketone 1а (1.24 g, 0.01 mol) in 90 ml of pure
2-(2-(Tetrahydrofuran-2-yl)hydrazono)-3a,4,7,7a-tetra- anhydrous THF and distilled H2O (1.8 ml, 0.1 mol) was irradi-
hydro-1H-4,7-epoxyindene-1,3(2H)-dione (2d). Yield 134 mg ated in a quartz reactor (λ > 210 nm) for 50 min until complete
(35% based on reacted diazodiketone 1d); yellow oil; 1H NMR disappearance of diazodiketone 1a (control by TLC). Then the
(400 MHz, CDCl3, δ) 12.83 (broad, 1H), 6.67–6.31 (m, 2H), reaction mixture was dried with magnesium sulfate and the
5.60–5.49 (m, 1H), 5.29 (s, 1H), 5.23 (s, 1H), 4.10–3.95 (m, solvent distilled off in vacuum. The obtained residue was
1H), 3.98–3.85 (m, 1H), 2.76–2.60 (m, 2H), 2.34–2.20 (m, 2H), dissolved in 25 ml of anhydrous Et2O, cooled to −75 to
2.11–1.89 (m, 2H) ppm; 13C NMR (101 MHz, CDCl3, δ) −78 °C. The precipitated resinous matter was separated by
198.73, 198.70, 197.37, 197.36, 137.4, 136.8 133.50, 133.46, decantation and the solvent was completely removed in
92.7, 92.4, 82.5, 81.8, 69.25, 69.22, 51.01, 50.99, 49.51, 49.48, vacuum. The resulting oily residue was taken up in 2–3 ml of
31.3, 31.2, 24.3 ppm; HRMS–ESI (m/z): [M + H]+ calcd for anhydrous Et2O and separated by column chromatography (5 g
C13H14N2O4, 263.1032; found, 263.1029.
of anhydrous neutral SiO2; eluent: anhydrous diethyl ether) to
give acid 4a as a crystalline solid after usual workup and careful
2-(2-(Tetrahydrofuran-2-yl)hydrazono)cyclopent-4-ene-1,3- removal of solvent in vacuum from the proper fractions
dione (3). Yield 135 mg (47%, on the reacted diazodiketone (0.5–0.1 mm Hg).
1d); yellow oil; 1H NMR (400 MHz, CDCl3, δ) 11.07 (s, 1H),
7.09 (d, J = 6.7 Hz, 1H), 7.05 (d, J = 6.7 Hz, 1H), 5.62–5.45 (m, Cyclobutane-2-one carboxylic acid (4а) [46,47]. Yield
1H), 4.13–3.79 (m, 1H), 2.40–1.75 (m, 1H) ppm; 13C NMR 1.03 g (90%); mp 43–44.5 °C (distilled); bp 93.5–94 °C
(101 MHz, CDCl3, δ) 191.9, 189.9, 145.8, 143.5, 137.0, 91.5, (0.2–0.1 mm Hg). It is noteworthy that acid 4а is a very hygro-
68.5, 30.7, 24.7 ppm; HRMS–ESI (m/z): [M + H]+ calcd for scopic compound which is easily hydrolyzed to produce glutaric
C9H10N2O3, 195.0770; found, 195.0774.
acid.
E. Sensitized photoexcitation of 2-diazo-4-methyl-3a,4,7,7a- Photolysis of diazodiketone 1a (with MeOH). A solution of
tetrahydro-1H-4,7-epoxyindene-1,3(2H)-dione (2e). The sublimated diazodiketone 1а (2.48 g, 0.02 mol) in 80 ml of an-
reaction was performed according to the general procedure with hydrous THF and pure CH3OH (4 ml, 0.10 mol) was irradiated
204 mg (2 mmol, 1 equiv) of diazoketone 1e and 728 mg in a quartz reactor (λ > 210 nm) for 55 min and worked up simi-
(8 mmol, 4 equiv) of benzophenone in 10 ml of THF with an ir- larly as described in the previous experiment. The resulting
radiation time of 1 h. After the workup procedure hydrazone 3 reaction mixture after removal of THF and methanol in vacuum
[66 mg (34%)] was isolated exclusively.
was distilled to give methyl ester 5а.
F. Sensitized photoexcitation of 2-diazo-1H-indene-1,3(2H)- Methyl cyclobutane-2-one carboxylate (5а) [48]. Yield 2.20 g
dione (2f). The reaction was performed according to the general (86%); bp 43.5–45 °С (1 mm Hg); nD20 1.5111. During
procedure with 344 mg (2 mmol, 1 equiv) of diazodiketone 1f column chromatography with SiO2 of I or II activity, methyl
and 1.46 g (8 mmol, 4 equiv) of benzophenone in 20 ml of THF ester 5а considerably hydrolyzes to give Me ester of glutaric
with and irradiation time of 0.8 h. After standard workup proce- acid.
dure hydrazone 2f and unreacted diazodiketone 1f were isolat-
ed.
Photolysis of diazodiketone 1b (with MeOH). A solution of
diazodiketone 1b (141 mg, 0.75 mmol) in 10 ml of THF/
2-(2-(Tetrahydrofuran-2-yl)hydrazono)-1H-indene-1,3(2H)- CH3OH 200:1 was irradiated for 55 min in a quartz reactor
dione (2f). Yield 70 mg (52%, calculated on the reacted (λ > 210 nm). Then the reaction mixture was dried with magne-
diazodiketone 1f); yellow oil; 1H NMR (400 MHz, CDCl3, δ) sium sulfate and the solvent and excess of CH3OH were com-
11.79 (broad, 1H), 7.96–7.85 (m, 1H), 7.84–7.77 (m, 1H), pletely removed in vacuum. The residue containing ester 5b
7.77–7.65 (m, 2H), 5.71–5.45 (m, 1H), 4.14–3.95 (m, 1H), (140 mg; 97% by 1H NMR) was separated by preparative TLC
3.96–3.67 (m, 1H), 2.44–2.12 (m, 2H), 2.15–1.70 (m, 2H) ppm; to furnish Me ester 5b.
2256

Beilstein J. Org. Chem. 2018, 14, 2250–2258.
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Methyl 4-oxotricyclo[4.2.1.02,5]non-7-ene-3-carboxylate
(5b). Yield 114 mg (79%; 97% by 1H NMR); colorless oil; 1Н
NMR (400 MHz, CDCl3, δ) 6.23–6.19 (m, 2H), 4.02–3.80 (m,
1H), 3.71 (s, 3H), 3.32–2.99 (m, 4H), 1.82–1.75 (m, 1H),
1.53–1.47 (m, 1H) ppm; 13C NMR (101 MHz, CDCl3, δ) 201.4,
167.8, 136.2, 133.4, 67.1, 63.9, 54.3, 52.4, 46.6, 43.9, 30.8
ppm; HRMS–ESI (m/z): [M + Na]+ calcd for C11H12O3,
215.0684; found, 215.0681.
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