Interaction of 3,5-di-tert-butyl-o-benzoquinone with secondary amines - A pathway to new sterically hindered N,N-disubstituted o-aminophenols

Article abstract of DOI:10.1016/j.tet.2010.11.030

The interaction of 3,5-di-tert-butyl-o-benzoquinone with secondary amines has been studied. The synthetic procedure was developed in order to synthesize a series of new N,N-disubstituted o-aminophenols. The interaction of 3,5-di-tert-butyl-o-benzoquinone

Full text of DOI:10.1016/j.tet.2010.11.030

Tetrahedron 67 (2011) 80e84
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Interaction of 3,5-di-tert-butyl-o-benzoquinone with secondary aminesda
pathway to new sterically hindered N,N-disubstituted o-aminophenols
*
Vladimir Cherkasov, Nikolay Druzhkov, Tatiana Kocherova, Georgii Fukin, Andrey Shavyrin
G.A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences, 49 St. Tropinina, 603950 Nizhny Novgorod, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 June 2010
Received in revised form 20 October 2010
Accepted 8 November 2010
Available online 12 November 2010
The interaction of 3,5-di-tert-butyl-o-benzoquinone with secondary amines has been studied. The syn-
thetic procedure was developed in order to synthesize a series of new N,N-disubstituted o-aminophenols.
The interaction of 3,5-di-tert-butyl-o-benzoquinone with dimethylamine leads to 2-(N,N-dimethylamino)
-4,6-di-tert-butyl-phenol, which is oxidized in the reaction medium by the parent 3,5-di-tert-butyl-o-
benzoquinone forming spirocompound 4,50,6,70-tetra-tert-butyl-30-methyl-30H-spiro[1,3-benzodioxol-
2,20-[1,3]benzoxazole].
Keywords:
Quinones
Ó 2010 Elsevier Ltd. All rights reserved.
3,5-Di-tert-butyl-o-benzoquinone
Amines
o-Aminophenol
Spirocompound
1. Introduction
The condensation product depends on the nature of amine. Re-
action of 1 with 2,6-disubstituted anilines leads to o-iminoqui-
The chemistry of o-quinones is wide and interesting. For ex-
ample, they can form chelate semiquinone or catecholate com-
plexes with metals.1 3,5-Di-tert-butyl-o-benzoquinone (1) and its
derivatives are widely used in coordination chemistry as spin labels
or redox active ligands and their chemical properties have been
previously studied. It is known that interaction of 1 withammonia
leads to 2,4-di-tert-butyl-6-iminocyclohexa-2,4-dienone. This re-
action is reversible and the equilibrium can be shifted toward o-
iminoquinone by an excess of the ammonia (Scheme 1).2
nones.3 Interaction of 1 with aliphatic amines having
a-methylene
protons results in o-aminophenols. Benzoxazoles can be obtained by
the reaction of 1 with amines of the type RCH2NH24,5 (Scheme 2).
t-Bu
O
R
= i-Pr; Me
t-Bu
N
2
H
t-Bu
R
N
R
h
P
+
O
O
t-Bu
t-Bu
t-Bu
+
t-Bu
R
C
H
2N
O
OH
N=CHR
(O)
O
N
H
2
t-Bu
t-Bu
CR
O
O
O
t-Bu
t-Bu
NCH2R
t-Bu
NH3
H2O
+
+
t-Bu
t-Bu
NH
Scheme 2.
1
Scheme 1.
2. Results and discussion
3,5-Di-tert-butyl-o-benzoquinone
1 interacts with primary
In this paper, we report a study of the interaction of 1 with
secondary amines when primary addition products cannot be sta-
bilized by water elimination. It was found that 3,5-di-tert-butyl-o-
benzoquinone 1 interacts with the excess of secondary amines
(dimethyl- and diethyl-amines). The main products are the corre-
sponding o-aminophenols 2 and 3 (yields 65% and 50%, re-
spectively) (Scheme 3).
amines via the less hindered carbonyl group (1,2-addition) with
subsequent water elimination. Formally, this process can be consid-
ered to be a condensationprocess, as in case of reaction of 1 with NH3.
* Corresponding author. E-mail address: andrew@iomc.ras.ru (A. Shavyrin).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.11.030

V. Cherkasov et al. / Tetrahedron 67 (2011) 80e84
81
t-Bu
t-Bu
Unfortunately our efforts to strictly identify reductant and
structures of formed by-products were unsuccessful due to the
presence of a wide variety of amine-derived by-products in the
reaction mixture. This result conforms with previously published
papers.6 It seems that the most probable source of hydrogen is the
excess of amine. This is confirmed by the fact that excess of amine is
required for complete quinone disappearance. Quinone was not
consumed during several days of reaction if an equimolar ratio of
reagents was used.
The interaction of 1 with dimethylamine does not stop at the
formation of 2. Increasing the reaction temperature up to 50 ꢀC leads
to a decrease of yield of 2. We have established two products of
oxidation of 2, which accumulated in the reaction mixture: spi-
rocompound 6dproduct of oxidation of 2 by parent o-quinone 1 and
N-arylformamide 7dproduct of oxidation of 2 by air (Scheme 6,
Fig. 2).
OH
O
O
HNR2
t-Bu
NR2
t-Bu
2)
3
)
R =CH3
(
; C2H5
(
1
65%
50%
Scheme 3.
Using cyclic secondary amines (piperidine, morpholine, 1-phe-
nylpiperazine, 1-(diphenylmethyl) piperazine) allow the synthesis
of a number of new o-aminophenols 4(aed) under the same con-
ditions. Bis-o-aminophenol 5 with a piperazine bridge was syn-
thesized analogously (Scheme 4).
a
b
c
d
53%
59%
N
N
N
N
t-Bu
OH
N
O
X
52%
60%
N Ph
HN
t-Bu
t-Bu
t-Bu
X
N
CH(Ph)2
4
O
O
t-Bu
t-Bu
t-Bu
OH
HO
HN
62%
1
NH
N
N
t-Bu
5
Scheme 4.
All o-aminophenols were isolated and characterized by IR-,
NMR-spectroscopy and elemental analysis (see Experimental
section, Fig. 1).
Scheme 6.
Fig. 1. The molecular structure of bis-o-aminophenol 5. Bond lengths and angles are in
the range as expected for comparable aromatic or cyclohexane systems, respectively.
In order to explain the mechanism of transformation of the in-
termediate product of 1,2-addition into aminophenols we studied
the interaction of 1 with dimethylamine thoroughly. The process
was carried out at ambient temperature with a threefold excess of
amine in dry methanol, acetonitryl, benzene, and heptane. The
parent quinone conversion was monitored by TLC. Reaction occurs
remarkably faster in the polar solvents: 2e3 h compared to 24 h in
the case of benzene or heptane. Finally benzene or heptane reaction
mixtures were refluxed with a DeaneStark receiver. The amount of
water in reaction mixtures has been measured in both cases. The
water yield corresponds to a 60% yield of 2. Consequently 2 is
formed from the primary product of nucleophilic addition (cyclo-
hexadienone) through the water elimination (Scheme 5).
Fig. 2. The molecular structures of spirocompound 6 and N-methylformamide 7. Bond
lengths and angles are in the range as expected for comparable aromatic or spi-
rocompound systems, respectively.
The o-aminophenol 2 was oxidized by PbO2 and 1, respectively,
in order to prove the formation of 6 and 7 in the reaction mixture.
After the treatment of 2 by PbO2 followed by filtration from lead
oxides, the reaction mixture was separated by column chroma-
tography and two products were isolated: compound 7 and N-
methyl-2,3-dihydrobenzooxazole (8). The latter is the primary
product of o-aminophenol oxidation because it can be fully con-
verted into 7 during prolonged oxidation by a fivefold excess of
PbO2 (Scheme 7). Formation of compounds of benzoxazole type as
the products of interaction of 1 with primary aliphatic amines is
known from literature.5
t-Bu
t-Bu
t-Bu
O
OH
NR2
OH
O
O
HNR2
t-Bu
t-Bu
NR2
t-Bu
1
(2)
(
3)
R =CH3
; C2H5
Scheme 5.

82
V. Cherkasov et al. / Tetrahedron 67 (2011) 80e84
t-Bu
t-Bu
obtained on ‘EuroEA-3028-HT’. X-ray structure analyses were car-
t-Bu
O
N
OH
OH
N
[O]
[O]
O
H
ried out on ‘SmartApex’ diffractometer (BrukerAXS). The H atoms
were found from Fourier syntheses and refined isotropically. The
structure was solved by direct method and refined on F2 using
SHELXTL package.9 CCDC-772232 (5), 772231 (7), 772230 (6) con-
tains the supplementary crystallographic data, which can be
obtained free of charge at www.ccdc.cam.ac.uk/conts/retrie-
ving.html or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (internat.) þ44 1223 336
033; e-mail: deposit@ccdc.cam.ac.uk.
CH2
C
t-Bu
t-Bu
N
Me
t-Bu
Me
2
8
7
Scheme 7.
The quinonic colour of the solution disappears upon heating of
a benzene solution of 1 with 2 (molar ratio 3:1) in an evacuated am-
poule. Spirocompound 6 and 3,5-di-tert-butylcatechol (in 2:1 ratio)
were detected by 1H NMR as the products of the reaction (Scheme 8).
4.2. All N,N-disubstituted o-aminophenols were synthesized
using the single general procedure
t-Bu
t-Bu
t-Bu
t-Bu
O
N
A solution of 3,5-di-tert-butyl-o-benzoquinone (2.2 g; 0.01 mol) in
MeOH (50 mL) and three-fold excess of dried amine was stirred at
room temperature. When the cherry-red solution turned colorless o-
aminophenol wasformed. Upon concentration of the reaction mixture
to 15e20 mL colorless crystals was collected by filtration and dried.
OH
N
O
O
N
1
2 eq 1
CH2
C
t-Bu
t-Bu
OH
OH
OH
t-Bu
t-Bu
t-Bu
O
t-Bu
OH
t-Bu
t-Bu
Me
Me
2
8
6
Scheme 8.
4.2.1. 2-(N,N-Dimethylamino)-4,6-di-tert-butylphenol (2). Colorless
crystals, yield: 1.62 g (65%); mp¼43e44 ꢀC. Found (%): C, 77.09; H,
o-Quinone participates in both stages of the reaction: in the first
step o-quinone oxidizes forming N-methyl-2,3-dihy-
drobenzooxazole 8. The latter transforms quantitatively into 6
consuming 2 equiv of o-quinone 1. Both reactions were monitored
by 1H NMR spectroscopy.
10.95. Calculated for C16H27NO (%): C, 77.06; H, 10.91. IR (Nujol, n/
1
2
cmꢁ1): 3240br, 1610m, 1435s, 1365s, 1320s, 1275m, 1250s, 1205m,
1190s, 1160w, 1140w, 1115w, 1096w, 1045w, 970s, 875m, 855w,
815w, 785w, 770m, 740w, 700m, 650w, 630w, 535w, 455w. 1H NMR
(CDCl3,
NeCH3); 7.08 (d, 1Harom, J¼2.3); 7.11 (d, 1Harom, J¼2.3); 7.70 (br s,
1H, OH). 13C NMR (CDCl3,
/ppm): 29.6 and 31.9 (C(CH3)3); 34.7 and
35.1 (C(CH3)3); 45.6 (CH (NeCH3)); 115.0 and 120.5 (CH, C(3 and 5));
133.4 and 141.1 (C-t-Bu); 141.1 (CeNeCH3); 148.0 (CeP).
d/ppm, J/Hz): 1.30 and 1.41 (both s, 9H, t-Bu); 2.64 (s, 6H,
The oxidation of 2 by 3,6-di-tert-butyl-o-benzoquinone was
carried out under similar conditions (Scheme 9) in order to evaluate
the possibility of using the aforementioned reaction for the syn-
thesis of similar structures. The product of this reaction 9 was
isolated in 80% yield. It differs from 6 by the positions of the tert-
butyl group in catecholate part of the molecule.
d
4.2.2. 2-(N,N-Diethylamino)-4,6-di-tert-butylphenol (3). Colorless
crystals, yield: 1.38 g (50%); mp¼22 ꢀC. Found (%): C, 77.89; H, 11.25.
t-Bu
t-Bu
t-Bu
t-Bu
t-Bu
Calculated for C18H31NO (%): C, 77.92; H, 11.26. IR (Nujol, n
/cmꢁ1):
O
O
OH
N
O
O
O
N
OH
OH
C
2
3
3260 br, 1620s, 1490s, 1455s, 1425s, 1410m, 1400s, 1365m, 1345w,
1310m, 1300m, 1270m, 1255s, 1230s, 1210m, 1185w, 1150w, 1140w,
t-Bu
t-Bu
t-Bu
t-Bu
t-Bu
Me
1090w, 955w, 875w, 815w, 775m, 730w, 690w. 1H NMR (CDCl3,
d/
2
9
80%
ppm, J/Hz): 0.96 (t, 6H, CH3, J¼7.2); 1.28 and 1.40 (both s, 9H, t-Bu);
Scheme 9.
2.90 (q, 4H, NeCH2, J¼7.2); 6.99 (d, 1Harom, J¼2.3); 7.09 (d, 1Harom
,
J¼2.3); 8.05 (s, 1H, OH). 13C NMR (CDCl3,
d/ppm): 13.0 (CH (CH2-
CH3)); 29.5 and 31.8 (C(CH3)3); 34.5 and 34.7 (C(CH3)3); 49.8 (CH
(NeCH2)); 116.8 and 120.2 (CH, C(3 and 5)); 133.4 and 140.7 (C-t-
Bu); 135.9 (CeNeCH2); 150.0 (C]P).
3. Conclusion
A convenient procedure for the synthesis of sterically hindered
o-aminophenols via the interaction of 3,5-di-tert-butyl-o-benzo-
quinone with secondary amines has been developed.
It is significant that 2-(N,N-dimethylamino)-4,6-di-tert-butyl-
phenol 2 can be oxidized into various products. The product nature
depends on the oxidant used: formamide is a main product of the
oxidation of 2byoxygenorPbO2 whilespirocompoundsareformedin
the reaction of 2 with o-benzoquinones. This method can be used for
a synthesis of various substituted formamides and spirocompounds.
4.2.3. 2-(Piperidin-1-yl)-4,6-di-tert-butylphenol
(4a). Colorless
crystals, yield: 1.53 g (53%); mp¼82 ꢀC. Found (%): C, 78.95; H,10.81.
Calculated for C19H31NO (%): C, 78.84; H, 10.79. IR (Nujol, n
/cmꢁ1):
3260 br, 1610w, 1480s, 1425m, 1395m, 1365m, 1325w, 1290w,
1275w, 1250s, 1220m, 1205m, 1150w, 1120w, 1105w, 1065w, 1055w,
1030w, 970m, 865w, 810w, 770m, 735w, 675w, 650w, 630w. 1H
NMR (CDCl3,
d/ppm, J/Hz): 1.29 and 1.41 (both s, 9H, t-Bu);
1.64e1.79 (m, 6H, CH2); 2.72e2.86 (m, 4H, NeCH2); 7.04 (d, 1Harom
,
d/
J¼2.3); 7.10 (d, 1Harom, J¼2.3); 7.85 (br s, 1H, OH). 13C NMR (CDCl3,
ppm): 24.0 (CH2); 27.0 (CH2); 29.5 and 31.7 (C(CH3)3); 34.6 and 34.9
(C(CH3)3); 54.2 (CH (NeCH2)); 115.5 and 120.2 (CH, C(3 and 5));
133.8 and 140.8 (C-t-Bu); 139.7 (CeNeCH2); 147.6 (CeP).
4. Experimental section
4.1. General
4.2.4. 2-Morpholino-4,6-di-tert-butylphenol (4b). Colorless crys-
tals, yield: 1.72 g (59%); mp¼143e145 ꢀC. Found (%): C, 74.21; H,
3,5-Di-tert-butyl-o-benzoquinone (1) was prepared according
to previously described procedures.7 Solvents were purified by
standard methods.8
The NMR spectra were recorded on a ‘Bruker Avance DPX-200’
spectrometer (200 MHzd1H, 50 MHzd13C) using CDCl3 as the
solvent and tetramethylsilane as the internal standard. IR-spectra
were recorded by ‘Specord M-80. Elemental analyses were
10.01. Calculated for C19H31NO (%): C, 74.18; H, 10.03. IR (Nujol, n/
cmꢁ1): 3215 br, 1610w, 1600w, 1425s, 1320m, 1300m, 1280s, 1260s,
1225m, 1210s, 1160m, 1150m, 1120s, 1065m, 1020w, 980m, 920w,
910w, 860m, 815w, 780w, 770m, 730m, 720m, 650w, 630w, 540w.
1H NMR (CDCl3,
d/ppm, J/Hz): 1.30 and 1.41 (both s, 9H, t-Bu); 2.88
(t, 4H, NeCH2); 3.87 (t, 4H, OeCH2); 7.08 (d, 1Harom, J¼2.2); 7.15 (d,

V. Cherkasov et al. / Tetrahedron 67 (2011) 80e84
83
1Harom, J¼2.2); 7.67 (s, 1H, OH). 13C NMR (CDCl3,
d
/ppm): 29.5 and
1265m, 1240s, 1210m, 1200m, 1165s, 1130w, 1100w, 1020s, 1000s,
965m, 935w, 915w, 865m, 855w, 840w, 820w, 795w, 750w, 740w,
31.7(C(CH3)3); 34.6 and 35.0 (C(CH3)3); 53.1 (CH (NeCH2)); 67.8 (CH
(OeCH2)); 115.6 and 120.9 (CH, C(3 and 5)); 134.4 and 141.3 (C-t-
Bu); 138.0 (CeNeCH2); 147.7 (CeP).
720s, 655w. 1H NMR (CDCl3,
d/ppm, J/Hz): 1.32,1.33,1.34, and 1.35 (all
s,9H, t-Bu); 2.97 (s, 3H, CH3);6.53 and6.77 (bothd, C (40), (60)H, J¼1.9);
6.88e6.90 (AB, 2H, C (5), (7)H, J¼1.9). 13C NMR (CDCl3,
d/ppm): 27.0
4.2.5. 2-(4-Phenylpiperazin-1-yl)-4,6-di-tert-butylphenol
(4c). Colorless crystals, yield: 1.90 g (52%); mp¼112 ꢀC. Found (%):
C, 78.60; H, 9.36. Calculated for C24H34N2O (%): C, 78.64; H, 9.35. IR
(NCH3); 29.5, 29.7, 31.9, 32.0 (C(CH3)3); 34.1, 34.3, 35.0, 35.1(C(CH3)3);
101.0 (CH); 103.9 (CH); 113.4 (CH); 115.6 (CH); 130.8 (C); 131.6 (C);
134.9 (C); 136.3 (C); 140.1 (C); 140.5 (C); 144.8 (C); 145.1 (C); 145.2 (C).
The crystals of 7 (CCDC 772231) suitable for X-ray were obtained from
CH3CN. Crystal data: C30H43NO3, M¼465.65, monoclinic, space group
P2(1)/c, Z¼4 in a cell of dimensions: a¼9.9571(5ꢀ ), b¼22.3032(12),
(Nujol,
n
/cmꢁ1): 3250 br, 1610s, 1510m, 1500m, 1425s, 1400m,
1385m, 1370m, 1325m, 1295w, 1250s, 1240s, 1210m, 1160w, 1145m,
1105w, 1065w, 990m, 985s, 920m, 875w, 820w, 790w, 765s, 690m,
650w, 635w, 520w. 1H NMR (CDCl3,
d/ppm): 1.30 and 1.42 (both s,
c¼13.0620(7) A,
a
¼90ꢀ,
b
¼109.7810(10)ꢀ,
g
¼90 , V¼2729.6(2) A ,
3
ꢀ
ꢀ
9H, t-Bu); 3.03e3.07 (m, 4H, CeNeCH2); 3.36 (m, 4H, CH2eNePh);
6.89e6.99 (m, 4H, m-, p-Ph, H(5)); 7.26e7.35 (m, 2H, o-Ph); 7.69 (s,
T¼130(2) L,
m
¼0.072 mmꢁ1, dcal¼1.133 g/cm3, 23421 reflections were
measured, 5352 unique (Rint¼0.0375), which were used in all calcu-
1H, OH). 13C NMR (CDCl3,
d/ppm): 29.5 and 31.7 (C(CH3)3); 34.6 and
lations. R1[I>2
s
(I)]¼0.0502, wR2¼0.1251, GOF(F2)¼1.036.
35.0 (C(CH3)3); 50.4 and 52.8 (NeCH2); 115.6; 116.5; 120.2; 120.9;
129.2; 134.3; 138.1; 141.3; 147.7; 151.3.
4.3.2. 4,50,7,70-Tetra-tert-butyl-30-methyl-30H-spiro[1,3-benzodioxol-
2,20-[1,3]benzoxazole] (9). Colorless microcrystalline powder, yield:
3.73 g (80%); mp¼187e188 ꢀC. Found (%): C, 77.41; H, 9.30. Calculated
4.2.6. 2-(N-Diphenylmethyl-piperazin-1-yl)-4,6-di-tert-butylphenol
(4d). Colorless crystals, yield: 2.74 g (60%); mp¼155e156 ꢀC. Found
(%): C, 81.53; H, 8.83. Calculated for C31H40N2O (%): C, 81.49; H, 8.85.
for C30H43NO3 (%): C, 77.38; H, 9.31. IR (Nujol, n
/cmꢁ1): 1620m, 1510m,
1490s, 1425s, 1400m, 1370s, 1310s, 1265m, 1245s, 1210m, 1155s,
1130m, 1030s, 1000s, 970m, 890w, 845w, 810m, 795m, 740m, 655w,
IR (Nujol, n
/cmꢁ1): 3230 br, 1610w, 1430m, 1395m, 1365s, 1350m,
1340m, 1315m, 1285s, 1270m, 1255s, 1225m, 1210m, 1185w, 1170w,
1135s, 1080m, 1010m, 990s, 960m, 930m, 880w, 850m, 820w,
785w, 770m, 755s, 750m, 700s, 695s, 650m, 630w, 590w, 520w. 1H
640w. 1H NMR (CDCl3,
d/ppm, J/Hz): 1.33 and 1.34 (both s, 9H, t-Bu);
1.36 (s,18H, t-Bu); 2.99 (s, 3H, CH3); 6.56 and 6.78 (both d, C (40), (60)H,
J¼1.8); 6.83 (s, 2H, C (5), (6)H). 13C NMR (CDCl3,
d/ppm): 27.5 (NCH3);
NMR (CDCl3,
d/ppm, J/Hz): 1.31 and 1.41 (both s, 18H, t-Bu); 2.58 (br
29.3 (C (4), (7), C(CH3)3); 29.4 and 31.9 (C (50), (70), C(CH3)3); 33.7, 34.0,
34.9(C(CH3)3); 100.9(CH);113.2 (CH);118.3 (CH);130.3(C);130.6(C);
134.7 (C); 135.5 (C); 140.0 (C); 142.7 (C); 145.0 (C).
m, 4H, CH2NCH); 2.91 (m, 4H, CH2NC); 4.32 (s, 1H, NCHPh2);
7.147.48 (m, 10H (Ph) and 2Harom); 7.77 (br s, 1H, OH). 13C NMR,
DEPT (CDCl3, d/ppm): 29.5 and 31.7 (C(CH3)3); 34.6 and 34.9 (C
(CH3)3); 52.9 and 53.1 (NCH2); 115.8 and 120.7 (CH, C(3 and 5));
127.1 (CH, p-Ph); 128.0 and 128.6 (CH, o-, m-Ph); 134.0 and 141.0 (C-
t-Bu); 138.3 (CeN); 142.6 (CHPh2); 147.8 (CeP).
4.3.3. N-(3,5-Di-tert-butyl-2-hydroxyphenyl)-N-methylformamide
(7). p-Aminophenol 2 (2.5 g, 0.01 mol) was dissolved in ether
(40 mL) and PbO2 was added (4.8 g, 0.02 mol). The reaction mixture
was stirred at 20 ꢀC for 1 h and then filtered. The ether was evap-
orated and residue was separated by column chromatography
(silicagel ‘Acros’ 0.060e0.200 mm; eluent hexane/ethylacetate is
50:1). Two products were isolated.
4.2.7. 6,6’-(Piperazine-1,4-diyl)bis(2,4-di-tert-butylphenol)
(5). Colorless crystals, yield: 1.53 g (62%); mp¼287e288 ꢀC. Found
(%): C, 77.70; H, 10.21. Calculated for C32H50N2O2 (%): C, 77.68; H,
10.19. IR (Nujol,
n
/cmꢁ1): 3250 br, 1615w, 1425s, 1400m, 1365m,
From the first fraction 5,7-di-tert-butyl-3-methyl-2,3-dihy-
1325m, 1285m, 1270m, 1245s, 1220m, 1200m, 1160m, 1130m,
1120m, 1075m, 950w, 895w, 870w, 845w, 815m, 790w, 765m,
drobenzo[d]oxazole (8)was extracted. 1H NMR (CDCl3,
d/ppm, J/Hz):
1.30 and 1.35 (both s, 9H, t-Bu); 2.74 (s, 3H, CH3); 5.17 (s, 2H, CH2);
740w, 680m, 410w. 1H NMR (CDCl3,
d
/ppm, J/Hz): 1.33 and 1.43
6.51 and 6.70 (both d,1Harom, J¼1.8). 13C NMR, DEPT (CDCl3,
d/ppm):
(both s, 18H, t-Bu); 3.07 (m, 8H, CH2), 7.15 and 7.18 (both d, 1Harom
,
29.7 and 31.9 (C(CH3)3); 34.2 and 34.9 (C(CH3)3); 35.2 (NCH3); 90.8
(CH2); 104.2 (CH); 114.4 (CH); 131.1 (C); 140.6 (C); 144.2 (C); 146.5
(C). After adding excess of PbO2 to the solution of dihydrobenzox-
azole 8 in ether its quantitative gives N-methylformamide 7.
Then the second fraction was collected and the eluent was
evaporated and residue was crystallized in ether. After being fil-
tered colorless crystals of 7 washed with cold pentane and dried
(mp¼173e174 ꢀC.) Found (%): C, 73.00; H, 9.55. Calculated for
J¼2.3); 7.69 (br s, 1H, OH). 13C NMR, DEPT (CDCl3,
d/ppm): 29.5 and
31.7 (C(CH3)3); 34.6 and 35.0 (C(CH3)3); 53.6 (CH2); 115.5 and 120.9
(CH, C(3 and 5)); 134.3 and 141.2 (C-t-Bu); 138.1 (CeN); 147.7
(CeP). The crystals of 6 (CCDC-772232) suitable for X-ray structure
determination were obtained by recrystallization from MeOH.
Crystal data: C32H50N2O2, M¼494.74, monoclinic, space group C2/C,
Z¼4 in a cell of dimensions: a¼17.2309(1), b¼8.8066(7), c¼19.4719
3
(1) A,
m
a
¼90ꢀ,
b
¼94.511(2)ꢀ,
g
¼90 , V¼2945.6(4) A , T¼100(2) L,
C16H25NO2 (%): C, 72.96; H, 9.57. IR (Nujol, n
/cmꢁ1): 3320s, 1670s,
ꢀ
ꢀ
ꢀ
¼0.068 mmꢁ1, dcal¼1.116 g/cm3, 9618 reflections were measured,
1590m, 1270w, 1250s, 1210m, 1185m, 1140w, 1120w, 1035m,
1020w, 920w, 875w, 825w, 810w, 775w, 745w, 720m, 660w, 640w.
3373 unique (Rint¼0.0249), which were used in all calculations.
R1[I>2
s
(I)]¼0.0438, wR2¼0.1181, GOF(F2)¼1.030.
1H NMR (CDCl3,
d/ppm, J/Hz) isomer 1: 1.29 and 1.43 (both s, 9H, t-
Bu); 3.21 (s, 3H, CH3); 5.92 (br s, 1H, OH); 6.92 and 7.33 (both d,
1Harom, J¼1.8); 8.18 (s, 1H, HeC]O). Isomer 2: 1.29 and 1.43 (both
s, 9H, t-Bu); 3.45 (s, 3H, CH3); 6.67 (s, 1H, OH); 7.00 and 7.29 (both
d, 1Harom, J¼1.8); 8.31 (s, 1H, HeC]O). Ratio of isomers 2:1. 13C
4.3. General procedure for preparation of spirocompounds 6
and 9
A solution of p-aminophenol 2 (2.5 g; 0.01 mol) and three-fold
excess of 3,5- or 3,6-di-tert-butyl-o-benzoquinone (6.6 g; 0.03 mol)
in benzene (50 mL) was refluxed until o-quinone color disappeared.
Benzene was replaced by CH3CN. The resulting solution was filtered
off. Upon cooling colorless crystals are formed.
NMR, DEPT (CDCl3, d/ppm): 29.6 and 31.5 (C(CH3)3); 29.9 (NCH3);
34.3 and 35.3 (C(CH3)3); 122.4 (CH); 124.5 (CH); 128.4 (C); 137.6
(C); 142.8 (C); 148.8 (C); 164.6 (CH). Event of the barrier to internal
rotation about the NeCO bond was discussed.10 The crystals of 7
(CCDC 772230) suitable for X-ray structure determination were
obtained from ether. There is one independent molecule of 7 in
the unit cell. Disorders in molecule of 7 are absent. Therefore, only
one type of rotamers exists in crystal of 7. Crystal data: C16H25NO2,
4.3.1. 4,50,6,70-Tetra-tert-butyl-30-methyl-30H-spiro[1,3-benzodioxol-
2,20-[1,3]benzoxazole] (6). Colorless crystals, yield: 3.54 g (76%);
mp¼159 ꢀC. Found (%): C, 77.40; H, 9.35. Calculated for C30H43NO3 (%):
M¼263.37, triclinic, space group Pꢁ1, Z¼2 in a cell of dimensions:
/cmꢁ1):1615s,1420s,1310s,1290m,1275m,
a¼6.0017(7), b¼9.7281(11), c¼14.3535(16) A,
a
¼70.565(2)ꢀ,
ꢀ
C,77.38;H, 9.31.IR(Nujol,
n

84
V. Cherkasov et al. / Tetrahedron 67 (2011) 80e84
3
ꢀ
ꢀ
b
m
¼86.834(2)ꢀ,
g
¼75.457(2)
,
V¼764.59(15) A , T¼100(2) L,
References and notes
¼0.074 mmꢁ1, dcal¼1.144 g/cm3, 4249 reflections were measured,
1. Pierpont, C. G.; Buchanan, R. M. Coord. Chem. Rev. 1981, 38, 45.
2. Vol’eva, V. B.; Prokof’eva, T. I.; Prokof’ev, A. I.; Belostotskaya, I. S.; Komissarova,
N. L.; Ershov, V. V. Russ. Chem. Bull., Int. Ed. 1995, 44, 1720.
2687 unique (Rint¼0.0222), which were used in all calculations.
R1[I>2
s
(I)]¼0.0466, wR2¼0.1189, GOF(F2)¼1.034.
3. Abakumov, G. A.; Druzhkov, N. O.; Kurskii, Y. A.; Shavyrin, A. S. Russ. Chem. Bull.,
Int. Ed. 2003, 52, 712.
4. Corey, E. J.; Achiwa, K. J. Am. Chem. Soc. 1969, 91, 1429.
Acknowledgements
5. (a) Vinsova, J.; Horak, V.; Buchta, V.; Kaustova, J. Molecules 2005, 783; (b)
Jampilek, J.; Vinsova, J.; Dohnal, J. 10th International Electronic Conference on
Synthetic Organic Chemistry (ECSOC-10), 2006. http://www.usc.es/congresos/
ecsoc/-10/ECSOC10.htm and http://www.mdpi.org/ecsoc-10/.
6. (a) Feldman, K.; Quideau, S.; Appel, H. J. Org. Chem. 1996, 61, 6656; (b) Quideau,
S.; Feldman, K.; Appel, H. J. Org. Chem. 1995, 60, 4982; (c) Shurygina, M. P.;
Kurskii, Y. A.; Chesnokov, S. A.; Abakumov, G. A. Tetrahedron 2008, 64, 1459.
7. Shuize, H.; Flaig, W. Liebigs Ann. Chem. 1952, 575, 231.
This work was made according to FSP ‘Scientific and scientific-
pedagogical cadres of innovation Russia’ for 2009e2013 years (GK-
P839 from 25.05.2010), Russian Foundation for Basic Research
(Grant 10-03-00788-a) and Russian President Grant supporting
scientific schools (Grants NSh-7065.2010.3).
8. Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of Laboratory Chem-
icals; Pergamon: Oxford, 1980.
9. Sheldrick, G. M. Structure Determination Software Suite. SHELXTL; Bruker AXS:
Madison, Wisconsin, USA, 2000; Vol. 6.12.
10. (a) Drakenberg, T.; Dahlqvist, K. I.; Forsen, S. J. Phys. Chem. 1972, 76, 2178; (b)
Rabinovitz, M.; Pines, A. J. Am. Chem. Soc. 1969, 91, 1585.
Supplementary data
Supplementary data associated with this article can be found in
the online version at doi:10.1016/j.tet.2010.11.030.