Photochemical reactions of regioisomeric 2,2-dimethyl-5,5-diphenyl- and 5,5-dimethyl-2,2-diphenyl-substituted diazo ketones of a tetrahydrofuran series

Article abstract of DOI:10.1002/hlca.200900079

The principal direction of conventional photolysis of the regioisomeric 2,2-dimethyl-5,5-diphenyl-and 5,5-dimethyl-2,2-diphenyl-substituted 4-diazodihydrofuran-3(2H)-ones 1a and 1b, respectively, is the Wolff rearrangement, while other photochemical proce

Full text of DOI:10.1002/hlca.200900079

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Helvetica Chimica Acta – Vol. 92 (2009)
Photochemical Reactions of Regioisomeric 2,2-Dimethyl-5,5-diphenyl- and
5,5-Dimethyl-2,2-diphenyl-Substituted Diazo Ketones of a Tetrahydrofuran
Series
by Ludmila L. Rodinaa), Sergey A. Malashikhina)b)1), Olesya S. Galkinaa)2), and
Valerij A. Nikolaeva)*
a) Department of Organic Chemistry, Saint-Petersburg State University, University prosp. 26,
RU-198504 Saint-Petersburg, Russia
(phone: þ 7-812-3231068; fax: þ 7-812-4286939; e-mail: vnikola@vn6646.spb.edu)
b) Organisch-chemisches Institut der Universitꢀt Zꢁrich, Winterthurerstrasse 190, CH-8057 Zꢁrich
The principal direction of conventional photolysis of the regioisomeric 2,2-dimethyl-5,5-diphenyl-
and 5,5-dimethyl-2,2-diphenyl-substituted 4-diazodihydrofuran-3(2H)-ones 1a and 1b, respectively, is the
Wolff rearrangement, while other photochemical processes, which are giving rise to the formation of
CꢀH-insertion, 1,2-alkyl- or -aryl-shifts, as well as H-atom-abstraction products occur to a much lower
degree (Schemes 2 and 3). The ratio of similar reaction products from both regioisomers 1a and 1b is
essentially independent of their structure, and a substantial effect of the relative position of the Ph and
diazo group to each other on the yield of CꢀH-insertion products does not occur. Based on
stereochemical considerations, the Wolff rearrangement of diazodihydrofuran-3(2H)-ones apparently
proceeds in a concerted manner, whereas the appearance in the reaction mixture of 1,2-shift and H-atom-
abstraction products points to the parallel generation during photolysis of singlet and triplet carbenes
(Schemes 4 and 5).
1. Introduction. – Direct photolysis of cyclic diazocarbonyl compounds usually
proceeds with elimination of N2 and formation of the Wolff rearrangement products
(for reviews, see [1 – 6]). Thus, light-induced decomposition of diazo ketones A with
2,2,5,5-tetraalkyl substituents at the heterocycle (R ¼ Me, Et, and others) by short-
wavelength UV light (l > 210 nm) in dioxane solution, as a rule, gives rise to
oxetanecarboxylic acids B or their derivatives (Scheme 1) in yields of up to 90 – 95%
[7].
On the other hand, it was recently established [8] that photolysis of tetraphenyl-
substituted diazo ketone A (R ¼ Ph) in THF solution, besides ordinary Wolff-
rearrangement products C, furnished the adduct D of diazo ketone A with THF
(Scheme 1). The latter can be considered as the product of the insertion of the terminal
N-atom of the diazo group into the HꢀC(2) bond of THF. The revealed transformation
of tetraphenyl-substituted diazo ketone A is apparently the first example of the
photolysis of diazo ketones which proceeds with the retention of both N-atoms of the
diazo group in the reaction products [9][10].
1
)
)
Part of the Diploma Thesis of S.A.M., Saint-Petersburg State University, 2005.
Part of the Bachelor research of O.S.G., Saint-Petersburg State University, 2009.
2
ꢂ 2009 Verlag Helvetica Chimica Acta AG, Zꢁrich

Helvetica Chimica Acta – Vol. 92 (2009)
1991
Scheme 1
Having in mind the difference in the structure of the above-mentioned diazo
ketones A (R ¼ Me or Ph), one could assume that the pivotal effect on the appearance
of a new direction during photolysis of diazo ketone A (R ¼ Ph) is due to the presence
of two Ph substituents in the a,a-position to the diazo group. In this connection, the
main goal of the current research was to compare the photochemistry of the
regioisomeric 2,2-dimethyl-5,5-diphenyl- and 5,5-dimethyl-2,2-diphenyl-substituted
diazo ketones 1a and 1b with alternative location of the Ph substituents relative to
the diazo group.
It was anticipated that 4-diazodihydro-2,2-dimethyl-5,5-diphenylfuran-3(2H)-one
(1a), by analogy with the tetraphenyl-substituted diazo ketone A (R ¼ Ph) will give rise
to the formation of the CꢀH-insertion products (along with the Wolff rearrangement)
[8], whereas 4-diazodihydro-5,5-dimethyl-2,2-diphenylfuran-3(2H)-one (1b), with the
diazo group adjacent to the a,a-methyl groups, should be photolyzed similarly to the
tetramethyl-substituted diazo ketone A (R ¼ Me) [7], i.e., 1b will produce solely the
Wolff rearrangement products.
2. Results and Discussion. – 2.1. Synthesis and UV Spectra of the Diazodihydrofur-
an-3(2H)-ones 1a and 1b. Diazo ketones 1a and 1b were prepared in accordance with
the previously elaborated scheme and protocols [7][11]; their structures as regioiso-
meric dimethyl-diphenyl-substituted diazodihydrofuran-3(2H)-ones were established
by spectroscopic methods and X-ray crystal-structure analysis [11]. The preliminary
tests for thermal stability have shown that both diazo ketones are quite persistent on
heating up to 1008 and above in the molten state or in toluene and dioxane solutions
[12].
The electronic spectra of diazo ketones 1a and 1b in solutions are characterized by
two major absorption bands, a strong one in the region l 252 – 257 nm, and a weaker
one at 305 – 307 nm (Table). The position of these absorbance bands is virtually
independent from the polarity of the solvents used, and thus does not allow a confident

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Helvetica Chimica Acta – Vol. 92 (2009)
assignment to the relevant transitions. However, by analogy with other diazocarbonyl
compounds [13 – 16], these absorptions can be evidently attributed to p – p* and n – p*
electronic transitions, respectively (see also [17]).
Table. UV Spectra of the Diazofuranidones 1a and 1b. lmax in nm.
lmax (log e)
hexane
THF
MeOH
1a
1b
252 (4.22), 306 (2.99)
255 (4.40), 307 (3.17)
253 (4.18), 305 (3.30)a)
256 (4.79), 305 (3.76)
255 (4.02), 306 (3.03)
257 (4.15), 306 (3.27)
a) Inflection point at the absorption curve.
2.2. Photochemical Transformations of Diazo Ketones 1a and 1b. Conventional
photolysis of diazo ketone 1a or 1b was performed in solution of freshly distilled THF,
containing a nucleophilic reagent NuH (¼ H2O, MeOH, or Me2NH) to trap the
intermediate ketene (Schemes 2 and 3). Irradiation was carried out in a quartz vessel
with UV light of a medium-pressure Hg lamp (l > 210 nm) under an O2-free
atmosphere until complete disappearance of 1a or 1b in the reaction mixture (by
TLC; normally 1.5 – 2 h). After removal of the solvent and nucleophile by distillation in
vacuo, the residue was recrystallized or/and subjected to chromatography (silica gel),
and the crude reaction mixture or the isolated compounds were analyzed by
spectroscopic methods (see Exper. Part). After photolysis of diazo ketone 1a, four
major products were isolated, namely oxetanecarboxylic acid 2a (or its methyl ester 2b
or amide 2c), hydrazone 3a (the CꢀH-insertion product), unsaturated ketone 4a, and
monoketone 5a (Scheme 2)3). The UV irradiation of the regioisomeric diazo ketone 1b
gave, under the same reaction conditions, the four similar reaction products 2a,b,c, 3b,
4b, and 5b (Scheme 3).
Scheme 2
The structures of the obtained compounds 2a,b,c, 3a,b, 4a,b, and 5a,b were
established by 1H- and 13C-NMR spectroscopy as well as by IR and MS data. In the 1H-
and 13C-NMR spectra of oxetanecarboxylic acid 2a and its derivatives 2b and 2c, the
3
)
Usually, the reaction mixtures of diazo ketones 1a and 1b also contained minor amounts of other
compounds with unknown structure.

Helvetica Chimica Acta – Vol. 92 (2009)
1993
Scheme 3
position of the 1H and 13C signals of HꢀC(3) in the quite narrow regions d(H) 4.2 – 4.4
and d(C) 56.1 – 58.2, respectively, as well as the d(C) 80.8 and 83.8 of C(2) and C(4) of
the oxetane ring, are most characteristic.
The 1H-NMR data of the CꢀH-insertion products 3a,b point to the formation of a
rather strong intramolecular H-bond C¼O ··· HꢀN, which gives rise to the displace-
ment of the NꢀH signal to d(H) 11.4 – 11.6 [18][19].
In the 13C-NMR spectra of the unsaturated ketones 4a and 4b, only one signal of a
tertiary C-atom C(2) is observed at d(C) 87.0 and 91.3, respectively, and at lower field
appear the signals of the olefinic C(4) and C(5) at d(C) 113.4 and 110.2, and 178.3 and
183.9, respectively, besides the usual aromatic C-signals. The position of the C¼C bond
in the heterocyclic vinyl ketone 4b was in addition confirmed by the COLOC
~
experiments. In the IR spectra of 4a and 4b, the absorption bands nc¼o are observed at
1680 and 1640 cmꢀ1, respectively, that is also typical for unsaturated conjugated ketones
[20].
The product analysis shows that the main direction of the photochemical reactions
of both regioisomeric diazo ketones 1a,b is the Wolff rearrangement (with yields up to
62%), whereas other photochemical processes, which give rise to the formation of the
insertion products 3a,b, vinyl ketones 4a,b, and monoketones 5a,b, proceed to a smaller
extent (up to 10 – 14%). Furthermore, it is evident that the efficiency of all
photoreactions observed is little affected by the structure of the regioisomers 1a,b
(Schemes 2 and 3).
As for the ratio of CꢀH-insertion products 3a,b, it turned out that the yields of 3a,b
under the same reaction conditions were little affected by the structure of the starting
diazo ketones 1a,b (the yields of hydrazones 3a,b were 3 – 6% (with H2O), 6 – 14%
(with MeOH), and 0.5 – 1% (with Me2NH)). Thus, it may be concluded that the
assumption of the pivotal effect of the a,a-phenyl groups on the yield of CꢀH-insertion
products (as was observed previously with tetraphenyl-substituted diazodihydrofuran-
3(2H)-one [8]) did not get essential support from these experimental data.
2.3. Pathways of Photochemical Transformations of Diazo Ketones 1a and 1b. Based
on the obtained results and known literature data [1 – 6][9][10][21 – 25], we propose
the following explanations for the observed photochemical transformations of the
regioisomeric diazo ketones 1, as exemplified by the diazodihydrofuran-3(2H)-one 1a
(Scheme 4). Irradiation of diazo ketone 1a by UV light results in the excitation of 1a to
one of the singlet excited states 11a*, which can basically undergo subsequent chemical
transformations with the elimination of N2 or retention of both diazo group N-atoms in

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1
the structure of reaction products. Elimination of the N2 molecule from 1a* leads to
either a singlet a-oxocarbene 1E or – in the case of the concerted Wolff rearrangement –
directly to the formation of ketene F (Scheme 4). The succeeding reaction of F with a
nucleophile NuH (¼ H2O, MeOH, or Me2NH) produces oxetanecarboxylic acid 2a or
its derivatives 2b,c.
Scheme 4
The migration of the Ph group (or Me with 1b) at the vacant p-orbital of the singlet
1
a-oxocarbene E furnishes the unsaturated ketone 4a (or 4b) (Scheme 5), which is a
typical product of 1,2-nucleophilic rearrangements of singlet carbenes [1][5][22][26].
Apparently, the conformation of carbene 1E with the PhꢀC(5) bond (or MeꢀC(5) for
1b) of the migrating group located essentially parallel to the vacant carbene p-orbital
strongly favors this migration, as it has been already suggested before in the case of
other cyclic diazo ketones [1][2][27]. The acyl group C(2)ꢀC¼O, on the other hand, is
aligned in the plane of the occupied s-orbital of 1E, which is orthogonal to the vacant p-
orbital. In this situation, the migration of the C(2) atom of the acyl group with its
1
electrons on the occupied s-orbital of the singlet carbene E is hardly probable [28],
and thus the Wolff rearrangement with the formation of ketene F via the oxocarbene
pathway seems unlikely (Scheme 5).
1
Partial intersystem crossing (ISC) of the singlet carbene E leads to the triplet a-
oxocarbene 3E, which is formally a biradical. The latter reacts with the solvent to give
products typical for a triplet carbene reduction (ꢃdouble H-atom abstractionꢄ)
[9][21][22], i.e., monoketones 5a (or 5b) (Scheme 4).
And lastly, unusual for diazocarbonyl compounds, the photochemical reaction with
the retention of both N-atoms in the reaction products is probably initiated by a partial
interconvertion of the singlet diazo compound 11a* into a triplet one, 31a*. The latter,

Helvetica Chimica Acta – Vol. 92 (2009)
1995
Scheme 5
being essentially a biradical species, reacts with one of the HꢀC(2) bonds of THF by,
ordinary for radicals, an ꢃabstraction – recombinationꢄ mechanism, and as the final
product of this reaction, triplet intermediate 31a* gives the CꢀH-insertion product, i.e.,
hydrazone 3a (or 3b) (Scheme 4)4).
2.4. Conclusions. Thus, the main direction of the photolysis of the regioisomeric
diazo ketones 1a and 1b is the Wolff rearrangement, while competitive photochemical
processes, which give rise to the formation of CꢀH-insertion products 3a,b, 1,2-shift
products 4a,b, as well as reduction products 5a,b occur to a much lower degree. The
ratio of similar reaction products from both regioisomers is essentially independent of
their structure. The Wolff rearrangement of the isomeric diazodihydrofuran-3(2H)-
ones 1a,b apparently proceeds as a concerted process, whereas the appearance of the
1,2-shift and reduction products in the reaction mixture indicates that during photolysis,
a parallel formation of singlet and triplet carbenes occurs.
This comparison study of the photolysis of regioisomeric diazodihydrofuran-3(2H)-
ones did not reveal a pronounced effect of the relative location of the Ph and diazo
group to each other on the efficiency of the interaction of the excited diazo ketones
with tetrahydrofuran, i.e., on the stabilization of their excited states and, consequently,
on the increasing of their lifetimes, which is necessary for accomplishing the
bimolecular interactions.
Further studies focused on the elucidation of the genuine reasons of the significant
difference in the photochemical behavior of tetramethyl- and tetraphenyl-substituted
3-diazodihydrofuran-3(2H)-ones are currently in progress.
Experimental Part
1. General. All reagents and solvents were used after recrystallization or distillation unless otherwise
specified. TLC Monitoring: Silufol-UV/VIS 254 plates (Czechia); detection by UV light and I2. Column
chromatography (CC): neutral silica gel (SiO2; Merck 70 – 230 mesh or Chemapol L 40/100); eluting
solvent optimized by TLC. M.p.: Boetius micro-melting-point apparatus; uncorrected. UV Spectra:
Specord M-40 in the range 200 – 500 nm; cell thickness 1.0 cm; concentration of solns. 3 · 10ꢀ4 – 6 ·
10ꢀ3 mol lꢀ1. IR Spectra: Perkin-Elmer-Spectrum-One (FT-IR) spectrophotometer or Specord-IR-75
instrument; in KBr; in cmꢀ1. 1H- (300 MHz) and 13C-NMR (1H-decoupled; 75.5 MHz) Spectra: Bruker-
AV-300 instrument; in CDCl3; d in ppm (Me4Si ¼ 0 ppm), coupling constants J in Hz. CI-MS (NH3):
4
)
However, one cannot rule out an alternative possibility for the appearance of the triplet diazo
compound 31* in the reaction mixture, for example, via sensitization of the initial diazo ketone 1 by
one of the reaction products in the triplet excited state, followed by an insertion reaction of the
3
formed 1* with THF.

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Finnigan-MAT-90 instrument; in m/z (rel. %). Elemental analyses were performed at the Department of
Organic Chemistry, StPSU, and at the Institute of Organic Chemistry, University of Zꢁrich.
2. Regioisomeric Diazodihydrofuran-3(2H)-ons 1a and 1b. 2.1. 4-Diazodihydro-2,2-dimethyl-5,5-
diphenylfuran-3(2H)-one (1a) was prepared by a diazo-transfer reaction [4][29] from dihydro-2,2-
dimethyl-5,5-diphenylfuran-3(2H)-one [30] and 2,4,6-tris(isopropyl)benzenesulfonyl azide [31] accord-
ing to [11]. Yield 66%. M.p. 92 – 938 [11]5).
2.2. 4-Diazodihydro-5,5-dimethyl-2,2-diphenylfuran-3(2H)-one (1b) was obtained from 5,5-dimeth-
yl-2,2-diphenylfuran-3,4(2H,5H)-dione 4-hydrazone [11]. Yield 86%. M.p. 116 – 1178 [11]5).
3. Photolysis of 4-Diazofuran-3(2H)-ons 1a and 1b: General Procedure (G. P.). Irradiation of diazo
ketone 1a or 1b was carried out in a small (25 ml) quarz device with a Hanau S-81 medium-pressure
mercury lamp (100 – 130 W) without any monocromatization of UV light (i.e., with l > 210 nm) [8]. The
soln. of 1a or 1b (1 g, 3.4 mmol) and a corresponding nucleophile (34 mmol) in freshly distilled THF
(20 ml) was irradiated by UV light at 20 – 258 until complete consumption of 1 (TLC monitoring; usually
1.5 – 2 h). The solvent and nucleophile were removed at 25 – 358 in vacuo (initially at 10 – 15, then at 1 –
0.5 Torr). The reaction products were isolated from the solid residue by recrystallization or/and CC (light
petroleum ether (40 – 658)/Et2O in different ratio).
3.1. Photochemical Reactions of 1a. 3.1.1. In the Presence of H2O. A soln. of 1a (1 g; 3.4 mmol) in
THF (20 ml) and H2O (0.6 g, 34 mmol) was irradiated for 2 h according to the G. P. To separate the main
portion of 2a, the solid mixture was recrystallized from petroleum ether. The residue from the mother
liquid was subjected to CC (SiO2, petroleum ether/Et2O 50 :1 ! 10 :1): 0.48 g (overall yield 49%,
including preliminary crystallization) of 2a, 0.078 g (6%) of 3a, 0.018 g (2%) of 4a, and 0.056 g (6%) of
5a.
3.1.2. In the Presence of MeOH. Irradiation of 1a (1 g, 3.4 mmol) in THF (20 ml) and MeOH (1.1 g,
34 mmol) according to the G. P. for 2 h, followed by CC (SiO2, petroleum ether/Et2O 100 :1 ! 5 :1)
provided 0.49 g (49%) of 2b, 0.172 g (14%) of 3a, 0.027 g (3%) of 4a, and 0.094 g (10.5%) of 5a.
3.1.3. In the Presence of Me2NH. Irradiation of 1a (1 g, 3.4 mmol) in THF (20 ml) and Me2NH (1.5 g,
34 mmol) for 2 h according to the G. P. followed by usual workup and CC (SiO2, petroleum ether/Et2O
50 :1 ! 1:1) provided 0.50 g (48%) of 2c, 0.0012 g (1%) of 3a, 0.027 g (3%) of 4a, and 0.09 g (10%) of
5a.
3.2. Photochemical Reactions of 1b. 3.2.1. In the Presence of H2O. A soln. of 1b (1 g, 3.4 mmol) in
THF (20 ml) and H2O (0.6 g, 34 mmol) was irradiated for 2 h according to the G. P. The main portion of
2a was separated by recrystallization from petroleum ether, and the residue from the mother liquid was
subjected to CC (SiO2, petroleum ether/Et2O 6 :1 ! 3 :1): 0.59 g (overall yield 62%, including
preliminary crystallization) of 2a, 0.03 g (2%) of 3b, 0.02 g (2%) of 4b, and 0.04 g (4%) of 5b.
3.2.2. In the Presence of MeOH. Irradiation of 1b (1 g, 3.4 mmol) in THF (20 ml) and MeOH (1.1 g,
34 mmol) for 2 h according to the G. P. followed by CC (SiO2, petroleum ether/Et2O 100 :1 ! 5 :1)
provided 0.46 g (46%) of 2b, 0.07 g (6%) of 3b, 0.06 g (7%) of 4b, and 0.05 g (5.5%) of 5b.
3.2.3. In the Presence of Me2NH. Irradiation of 1b (1 g, 3.4 mmol) in THF (20 ml) and Me2NH (1.5 g,
34 mmol) for 2 h according to the G. P. followed by usual workup and CC (SiO2, petroleum ether/Et2O
20 :1 ! 1:1) provided 0.54 g (51%) of 2c, 0.006 g (0.5%) of 3b, 0.07 g (8%) of 4b, and 0.18 g (14%) of
5b.
2,2-Dimethyl-4,4-diphenyloxetane-3-carboxylic Acid (2a): Colorless solid. M.p. 185.5 – 186.58. Rf
1
(petroleum ether/Et2O 5 :1) 0.15. H-NMR: 1.44 (s, Me); 1.61 (s, Me); 4.23 (s, CH); 7.09 – 7.50 (m, 10
arom. H). 13C-NMR: 25.9 (Me); 32.5 (Me); 58.2 (CH); 80.8 (Me2C); 83.9 (Ph2C); 125.2, 126.5, 127.4,
127.5, 128.1, 128.7 (6 arom. CH); 142.9, 148.2 (2 arom. C); 174.6 (C¼O). CI-MS: 282 (5.6, Mþ), 183 (69),
182 (100), 178 (5.6), 83 (12), 77 (47.5). Anal. calc. for C18H17O3 (282.33): C 76.87, H 6.05; found: C 76.47,
H 6.36.
2,2-Dimethyl-4,4-diphenyloxetane-3-carboxylic Acid Methyl Ester (2b): Colorless solid. Rf (petro-
leum ether/Et2O 10 :1) 0.27. IR: 3200w, 3000w, 2955w, 2935w, 1740vs, 1710m, 1480m, 1440s, 1430s, 1365s,
1390w, 1222s, 1180m, 1150s, 1122s, 1450m, 990s, 960m, 865m, 730s. 1H-NMR: 1.42 (s, Me); 1.66 (s, Me);
3.48 (s, MeO); 4.22 (s, CH); 7.10 – 7.51 (m, 10 arom. H). 13C-NMR: 26.1 (Me); 32.6 (Me); 51.7 (MeO);
5
)
In [11], incorrect melting points of diazo ketones 1a and 1b were given.

Helvetica Chimica Acta – Vol. 92 (2009)
1997
58.2 (CH); 80.8 (Me2C); 83.8 (Ph2C); 125.4, 126.5, 127.4, 127.5, 128.2, 128.7 (6 arom. CH); 143.4, 148.4 (2
arom. C); 169.5 (C¼O). Anal. calc. for C19H19O3 (296.36): C 77.29, H 6.44; found: C 77.24, H 6.77.
N,N,2,2-Tetramethyl-4,4-diphenyloxetane-3-carboxamide (2c): Colorless solid. M.p. 117.5 – 1198. Rf
(petroleum ether/Et2O 3 :1) 0.1. IR: 3040w, 3000w, 2940w, 2900w, 1650vs, 1480m, 1440m, 1370s, 1310w,
1250w, 990m, 720m, 690s. 1H-NMR: 1.52 (s, Me); 1.54 (s, Me); 2.86 (s, MeN); 2.94 (s, MeN); 4.37 (s, CH);
7.16 – 7.49 (m, 10 arom. H). 13C-NMR: 25.5 (Me); 31.6 (Me); 35.5, 37.4 (Me2N); 50.1 (CH); 80.9 (Me2C);
83.9 (Ph2C); 125.6, 126.1, 126.6, 127.1, 127.4, 128.2 (6 arom. CH); 143.2, 148.1 (2 arom. C); 168.1 (C¼O).
Anal. calc. for C20H22NO2 (309.40): C 77.92, H 7.14, N 4.55; found: C 77.78, H 7.23, N 4.48.
2,2-Dimethyl-5,5-diphenylfuran-3,4(2H,5H)-dione 4-[2-(Tetrahydrofuran-2-yl)hydrazone] (3a):
1
Colorless solid. M.p. 108 – 1098. Rf (petroleum ether/Et2O 10 :1) 0.16. H-NMR: 1.26 (s, Me); 1.34 (s,
Me); 1.81 – 2.25 (m, CH2CH2); 3.81 – 3.89 (m, CH2O); 5.37 – 5.43 (m, CHN); 7.19 – 7.49 (m, 10 arom. H);
11.60 (d, J ¼ 6.5, NH). 13C-NMR: 25.0 (CH2); 25.24, 25.27 (2 Me); 30.17 (CH2); 67.9 (CH2O); 80.7
(Me2C); 82.9 (Ph2C); 90.7 (CHN); 126.8, 126.9, 127.1, 127.1, 127.8, 127.9 (6 arom. CH); 135.2 (C¼N);
145.5, 145.7 (2 arom. C); 200.2 (C¼O). Anal. calc. for C22H24N2O3 (364.44): C 72.53, H 6.59, N 7.69;
found: C 72.70, H 6.68, N 7.59.
2,2-Dimethyl-4,5-diphenylfuran-3(2H)-one (4a): Colorless solid. Rf (petroleum ether/Et2O 10 :1)
0.23. IR: 3020w, 3010w, 2970w, 2910w, 1680vs, 1600s, 1440m, 1370vs, 1230s, 1040s, 900m, 690vs. 1H-NMR:
1.56 (s, 2 Me); 7.29 – 7.65 (m, 10 arom. H). 13C-NMR: 23.4 (2 Me); 87.0 (Me2C); 113.4 (C(4)); 127.6,
128.03, 128.07, 128.4, 128.6, 129.6, 130.1, 131.8, (8 arom. C); 178.5 (C(5)); 205.4 (C¼O). CI-MS: 264 (69,
Mþ), 263 (20), 178 (100), 105 (18), 77 (16). Anal. calc. for C18H16O2 (264.32): C 81.82, H 6.06; found: C
81.77, H 6.05.
Dihydro-2,2-dimethyl-5,5-diphenylfuran-3(2H)-one (5a): Colorless solid. M.p. 63 – 658. Rf (petro-
leum ether/Et2O 10 :1) 0.38. 1H-NMR: 1.21 (s, 2 Me); 3.32 (s, CH2); 7.20 – 7.42 (m, 10 arom. H).
13C-NMR: 25.3 (2 Me); 48.1 (CH2); 81.4, 82.7 (Me2C, Ph2C); 126.0, 127.4, 128.3 (6 arom. CH); 146.1 (2
arom. C); 200.2 (C¼O).
5,5-Dimethyl-2,2-diphenylfuran-3,4(2H,5H)-dione 4-[2-(Tetrahydrofuranyl)hydrazone] (3b): Color-
1
less solid. M.p. 79 – 808. Rf (petroleum ether/tBuOMe 8 :1) 0.22. H-NMR: 1.45 (s, Me); 1.46 (s, Me);
1.89 – 2.33 (m, CH2CH2); 3.80 – 3.94 (m, CH2O); 5.39 (d, J ¼ 6.5, CHN); 7.20 – 7.54 (m, 10 arom. H); 11.41
(d, J ¼ 6.8, NH). CI-MS: 364 (9, Mþ), 183 (93), 182 (74), 105 (100), 84 (76), 77 (63).
4,5-Dimethyl-2,2-diphenylfuran-3(2H)-one (4b): Colorless solid. M.p. 110 – 110.58. Rf (petroleum
ether/tBuOMe 8 :1) 0.27. IR: 3020w, 3005w, 2935w, 2900w, 2840w, 1930w, 1860w, 1700s, 1640vs, 1480m,
1440m, 1400s, 1340m, 1210s, 1080m, 980m, 690s, 660m, 610m. 1H-NMR: 1.71 (s, Me); 2.32 (s, Me); 7.22 –
7.51 (m, 10 arom. H). 13C-NMR: 6.30 (Me); 15.5 (Me); 91.3 (Ph2C); 110.2 (C(4)); 126.9, 128.6, 128.8,
139.1 (8 arom. C); 183.9 (C(5)); 203.1 (C¼O). CI-MS: 264 (82, Mþ), 235 (7.2), 221 (100), 182 (8.7), 166
(50), 115 (13), 105 (52.6), 77 (28.9), 54 (21.1). Anal. calc. for C18H16O2 (264.32): C 81.82, H 6.06; found: C
81.53, H 5.99.
Dihydro-5,5-dimethyl-2,2-diphenylfuran-3(2H)-one (5b): Colorless solid. M.p. 79 – 808. Rf (petro-
leum ether/tBuOMe 8 :1) 0.51. 1H-NMR: 1.44 (s, 2 Me); 2.61 (s, CH2); 7.20 – 7.62 (m, 10 arom. H).
13C-NMR: 29.7 (2 Me); 49.3 (CH2); 77.7, 86.8 (Me2C, Ph2C); 126.1, 127.4, 128.2, 128.3, 130.0, 132.4 (6
arom. CH); 137.6, 142.3 (2 arom. C); 196.7 (C¼O). CI-MS: 266 (4.9, Mþ), 183 (47.3), 182 (31.6), 165
(4.9), 105 (100), 77 (44.7), 56 (7.0), 51 (19.6). Anal. calc. for C18H18O2 (266.33): C 81.20, H 6.77; found: C
81.09, H 6.78.
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Received March 9, 2009