2-Zincoethylzincation of 2-Alkynylamines and 1-Alkynylphosphines Catalyzed by Titanium(IV) Isopropoxide and Ethylmagnesium Bromide

Article abstract of DOI:10.1055/s-0037-1612009

Titanium(IV) isopropoxide and ethylmagnesium bromide catalyzed reaction of 2-alkynylamines with Et ₂ Zn, followed by deuterolysis/hydrolysis and iodinolysis, affords substituted (Z)-pent-2-en-2,5- d ₂ -1-amines, (Z)-pent-2-en-1-amine

Full text of DOI:10.1055/s-0037-1612009

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© Georg Thieme Verlag Stuttgart · New York
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R. N. Kadikova et al.
Letter
Synlett
2-Zincoethylzincation of 2-Alkynylamines and 1-Alkynylphos-
phines Catalyzed by Titanium(IV) Isopropoxide and Ethylmagne-
sium Bromide
Et2Zn (2.5 equiv, 1 M in hexanes)
Rita N. Kadikova*
Ilfir R. Ramazanov
Oleg S. Mozgovoi
Azat M. Gabdullin
Usein M. Dzhemilev
Ti(O-iPr)4 (0.1 equiv, 0.5 M in hexanes)
EtMgBr (0.2 equiv, 2.5 M in Et2O)
R
R
X
zn
Et2O, 18 h
X
zn
X = CH2NR'2 or PPh2
R = alkyl, Ph
I2
1. D2O (H2O)
2. H2O2 (S8)
D2O (H2O)
Institute of Petrochemistry and Catalysis of Russian Academy of
Sciences, 141 Prospekt Oktyabrya, Ufa 450075, Russian Federation
kadikritan@gmail.com
R
R
R
NR'2
NR'2
P(Q)Ph2
D(H)
D(H)
D(H)
I
D(H)
I
4 examples (55–63%)
11 examples (65–88%)
8 examples (62–80%)
zn = Zn1/2; ZnEt. Q = O, S.
Received: 07.11.2018
Accepted after revision: 18.12.2018
Published online: 10.01.2019
and stereoselective carbometallation of a triple bond was
demonstrated by carbozincation of phenyl-substituted
propargyl ethers with dialkyl- and diphenylzinc.12 Howev-
er, CoCl2-catalyzed allylzincation of substituted propargyl
alcohols with allylzinc bromide proceeds with a low yield
giving mixtures of regio- and stereoisomers.13 The Rh- and
Co-catalyzed carbozincation of ynamides can be used for
selective synthesis of multisubstituted enamides and di-
enamides,14 and also 3-arylenamides.15 The number of
known catalytic carbozincation reactions of alkynylamines
is modest. For example, diastereoselective carbozincation of
propargyl amine derivatives obtained from methylbenzyl-
amine has been reported.16 As regards P- and Se-containing
alkynes, no examples of carbozincation of alkynyl phos-
phines or selenides are available from the literature. Mean-
while, it is known that 1-alkynylphosphines, 1-alkynyl-
phosphonates, propargylamines, 1-alkynyl selenides, and
1-alkynyl sulfides are efficient substrates for the prepara-
tion of zirconacyclopentenes17–20 and aluminacyclo-
pentenes.21–24 Regarding 2-zincoethylzincation, only one
case of the preparation of organozinc derivative in 63% yield
only after 4 days using the Ti-Mg-catalyzed reaction of 5-
decyne with Et2Zn has been reported in the literature.25
However, this reaction is a unique example of carbozinca-
tion of the triple carbon–carbon bond with Et2Zn using oxi-
dative coupling of ethylene and 5-decyne on titanium(II) in
catalytic cycle. Evidently, the full-scale application of the
synthetic potential of this reaction is impossible without
systematic research of its scope and mechanism. Currently,
nothing is known about the behaviors of N-, P-, O-, S-, and
Se-containing alkynes and alkenes in this reaction. In this
paper, we report our results on the selective 2-zincoethyl-
zincation of heteroatom-substituted alkynes such as 2-
alkynylamines and 1-alkynylphosphines. This work demon-
DOI: 10.1055/s-0037-1612009; Art ID: st-2018-r0725-l
Abstract Titanium(IV) isopropoxide and ethylmagnesium bromide
catalyzed reaction of 2-alkynylamines with Et2Zn, followed by deuter-
olysis/hydrolysis and iodinolysis, affords substituted (Z)-pent-2-en-2,5-
d2-1-amines, (Z)-pent-2-en-1-amines (65–88%), and substituted (Z)-
2,5-diiodopent-2-en-1-amines (55–63%). It is suggested that the reac-
tion proceeds through the formation of cyclic organotitanium deriva-
tives. The reaction between 1-alkynylphosphines and Et2Zn in the pres-
ence of catalytic amounts of Ti(O-iPr)4 and EtMgBr leads to
trisubstituted 1-alkenylphosphine oxides with high regioselectivity and
stereoselectivity.
Key words 2-alkynylamines, 1-alkynylphosphines, 2-zincoethylzinca-
tion, titanium catalysis
Carbometallation is an efficient method of regio- and
stereocontrolled synthesis of olefins of various structure.
The most widely encountered synthetic methods for
alkynes carbometallation include Zr-catalyzed Negishi
methylalumination of alkynes,1–3 carbocupration,4,5 carbos-
tannylation,6 carboboration,7,8 and carbomagnesiation.9 De-
spite the attractiveness of alkenyl organozinc intermediates
due to their high functional group compatibility, carbozin-
cation of only activated alkynes proceeds generally in satis-
factory yield. Copper-catalyzed сarbozincation of alkynyl
sulfoximines and alkynyl sulfones with dialkylzinc or al-
kylzinc halides is an example of regio- and stereoselective
route to polysubstituted vinyl sulfoximines and sulfones.10
The Cu-catalyzed carbozincation of 1-alkynyl sulfoxides
with structurally different O-, N-, and Br-containing zinc
halides can be used to synthesize chiral β,β-disubstituted
vinylic sulfoxides with various functionalities with high
syn-selectivity.11 The efficiency of using Ni(acac)2 for regio-
© Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–D

B
R. N. Kadikova et al.
Letter
Synlett
strates that α- or β-heteroatom-substituted alkynes react
much more promptly than internal aliphatic alkynes, and
thus enhances significantly the synthetic scope of the
transformation by disclosing an efficient access to some he-
teroatom-functionalized alkenes with control of the dou-
ble-bond geometry. The study represents an improvement
over previous works on Zr-catalyzed cycloalumination of
propargylamines21 and alkynylphosphines22 because the
current catalytic system consisting of Et2Zn, Ti(O-iPr)4, and
EtMgBr is more practical and less costly. Moreover, the di-
zincated species offer more potential for subsequent func-
tionalization than the dialuminated species.
We found that 2-alkynylamines 1 react with 2.5 equiv of
Et2Zn (1 M in hexanes) in the presence of 10 mol% Ti(O-
iPr)4, (0.5 M in hexanes) and 20 mol% EtMgBr (2.5 M in
Et2O) in diethyl ether at room temperature for 18 hours to
give, after deuterolysis, hydrolysis, or iodinolysis substitut-
ed allylamines 3–5 (Scheme 1).26
stereoselectivity of this reaction coincide with those that
we observed earlier for the cycloalumination of 2-alkynyl-
amines.20 We carried out the iodinolysis of the organome-
tallic intermediates formed during the carbozincation of 2-
alkynylamines. Thus, the reaction of organozinc intermedi-
ates 2 obtained by 2-zincoethylzincation of 2-alkynyl-
amines 1b,c,f,g with 5.3 equiv of I2proceeds selectively to
afford Z-configured diiodo-substituted allylamines 5 b,c,f,g
(55–63%). It is also noteworthy that diethyl ether is the sol-
vent of choice for 2-zincoethylzincation of 2-alkynylamines,
whereas tetrahydrofuran, dimethoxyethane, and 1,4-diox-
ane completely inhibit the transformation of 2-alkynyl-
amines.
Previously, we have shown that Zr-catalyzed cycloalu-
mination of α,ω-bis(aminomethyl)alkadiynes with Et3Al re-
sults in the selective formation of a bis-alkylidene cyclohex-
ane derivative.21 A similar formation of bis-alkylidene-sub-
stituted cyclohexane was also observed upon the
carboalumination of trimethyl(oct-7-en-1-yn-1-yl)silane.27
Similarly, the reaction of N,N,N′,N′-tetramethyldeca-2,8-
diyne-1,10-diamine with 2.5 equiv of Et2Zn in the presence
of 10 mol% Ti(O-iPr)4and 20 mol% EtMgBr carried out in di-
ethyl ether at room temperature for 18 hours and followed
by deuterolysis or hydrolysis affords bis-alkylidene cyclo-
hexane 6 and 7 derivative (Scheme 2).
1a: R = n-Bu, NR1R2 = NMe2
1b: R = n-Pent, NR1R2 = NMe2
1c: R = n-Hex, NR1R2 = NMe2
R
1d: R = n-Oct, NR1R2 = NMe2
NR1R2
1e: R = c-Pr, NR1R2 = N(CH2)5
1f: R = n-Bu, NR1R2 = N(CH2)5
1g: R = n-Bu, NR1R2 = N-morpholyl
Et2Zn (2.5 equiv, 1 M in hexanes)
Et2O, rt, 18 h
Ti(O-iPr)4 (0.1 equiv, 0.5 M in hexanes)
1. Et2Zn (2.5 equiv, 1 M in hexanes)
(a)
EtMgBr (0.2 equiv, 2.5 M in Et2O)
Ti(O-iPr)4 (0.1 equiv, 0.5 M in hexanes)
EtMgBr (0.2 equiv, 2.5 M in Et2O)
Et2O, rt, 18 h
NMe2
NMe2
R
R
D2O
(or H2O)
NR1R2
NR1R2
2. D2O (H2O)
X
zn
zn
X
Me2N
2
3a: X = D, 88%
4a : X = H, 67%
4b: X = H, 70%
4c: X = H, 73%
4d: X = H, 79%
4e: X = H, 65%
4f: X = H, 81%
4g: X = H, 87%
5b: X = I, 60%
5c: X = I, 55%
5f: X = I, 63%
5g: X = I, 58%
X
X
6: X = D (85%)
7: X = H (72%)
zn = Zn1/2; ZnEt
Ti(O-iPr)4 + 2 EtMgBr
Et2Ti(O-iPr)2 + 2 MgBr(O-iPr)
Me2N
– C2H6
(O-iPr)2Ti
(O-iPr)2TiEt2
Scheme 1 Ti-Mg-catalyzed 2-zincoethylzincation of 2-alkynylamines
with Et2Zn
Me2N
(b)
NMe2
NMe2
(iPr-O)2Ti
(O-iPr)2Ti
The structures of the resulting substituted allylamines
were established using 1D and 2D NMR spectroscopy for
the their deuterolysis 3a and hydrolysis 4a–g products. In
the 1Н NMR spectra of compounds 4a–g, the doublet for the
methylene group of the N,N-dimethylaminomethyl moiety
unambiguously proves the formation of regioisomer 4. The
NOESY spectrum of compound 4a clearly shows two cross-
peaks of the triplet for the vinylic proton with the triplet for
the methyl proton of the ethyl group, and also with the
quadruplet for the methylene group of the ethyl substitu-
ent, indicating the Z-configuration of the formed substitut-
ed allylamine. The 2-zincoethylzincation reaction is equally
regio- and stereoselective for 1-(3-cyclopropylprop-2-yn-
1-yl)piperidine (1e), 1-(hept-2-yn-1-yl)piperidine (1f), and
4-(hept-2-yn-1-yl)morpholine (1g) as well. The regio- and
– C2H4
Me2N
+ Et2Zn
– Et2Ti(O-iPr)2
Me2N
zn
zn
zn = Zn1/2, ZnEt
Me2N
Scheme 2 Ti-Mg-catalyzed reaction of N,N,N′,N′-tetramethyldeca-2,8-
diyne-1,10-diamine with Et2Zn
According to Scheme 2 (b) , Ti(O-iPr)4 reacts with EtMgBr
with fast ligand exchange giving (O-iPr)2TiEt2, which forms
the (O-iPr)2Ti–ethylene complex. The insertion of one of the
triple bonds of tetramethyldeca-2,8-diyne-1,10-diamine
© Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–D

C
R. N. Kadikova et al.
Letter
Synlett
1
into the Ti–C bond of this complex results in ethylene dis-
placement from the titanium coordination sphere and cou-
pling of two alkyne moieties to give titanacyclopentadiene,
which is then transmetalated in the catalytic cycle to be
converted, after subsequent deuterolysis (or hydrolysis),
into the target bis-alkylidene cyclohexane derivative 6 and
7. The NOESY spectrum of compound 7 shows coupling be-
tween the methylene group of the N,N-dimethylamino-
methyl moiety and the α-methylene group of the cyclohex-
ane moiety, thus indicating E-configuration of the double
bonds. The cross-peak between the triplet for the proton at
the double bond and the doublet for the N-methylene group
in the COSY spectrum of hydrolysis product 7 attests to the
geminal positions of the hydrogen atom andN,N-dimethyl-
aminomethyl group at a double-bond carbon atom.
the Н NMR and 13C NMR signal intensities for compounds
10a and 10′a leads to the conclusion that compound 10a is
present in a 1.5-fold greater amount in the isomer mixture.
Presumably, agostic interaction between the titanium atom
and the ortho-hydrogen atom of the phenyl group may be
one of the causes for the observed lack of regioselectivity in
the transformation of aryl-substituted propargylamines 8.28
Thus, the presence of the amine function in the mole-
cule of alkyne does not preclude the reaction of Ti-Mg-cata-
lyzed 2-zincoethylzincation. Meanwhile, phosphorus is a
close electronic analogue of nitrogen. Previously, we have
shown that 1-alkynylphosphines are useful substrates for
the synthesis of 1-alkenylphosphines by Zr-catalyzed cy-
cloalumination with Et3Al.22 Tertiary phosphines and their
oxides are widely used ligands in organometallic and coor-
dination chemistry.29 In order to develop new methods for
the synthesis of various phosphorus oxides, we studied the
Ti-Mg-catalyzed reaction of 1-alkynylphosphines with
Et2Zn. Earlier, Takahashi investigated the pair-selective cou-
pling of (hex-1-yn-1-yl)diphenylphosphine with zircono-
cene–ethylene complex, which was generated in situ from
Cp2ZrEt2.30 The (Z)-(2-ethylhex-1-en-1-yl)diphenylphos-
phine was formed in 96% GC yield with perfect regio- and
stereoselectivity.17 We found that the reaction of 1-alkynyl-
phosphines 11 with 2.5 equiv of Et2Zn (1 M in hexanes) in
the presence of 10 mol% Ti(O-iPr)4, (0.5 M in hexanes) and
20 mol% EtMgBr (2.5 M in Et2O) carried out in diethyl ether
at room temperature for 18 hours, followed by deuterolysis
(or hydrolysis) and then oxidation with H2O2, as well as
then sulfonation with S8furnishes Z-configured 1-alkenyl-
phosphine oxides 12b–e, 13a,e and alkenyl sulfides 14a,b
(Scheme 4). Since 1-alkenylphosphines are readily oxidized
in air to give phosphorus oxides,21 we carried out the oxida-
tion of deuterated (or hydrogenated) alkenylphosphines
with H2O2to 1-alkenylphosphine oxides, which were readily
purified by column chromatography. The structure of the 1-
alkenylphosphine oxides was established using 1D and 2D
NMR spectroscopy for the products of deuterolysis 12b–e
and hydrolysis 13a,e. All experimental data for compounds
Similar results were obtained for 2-alkynylamines 8
prepared from phenylacetylene: N,N-dimethyl-3-phenyl-
prop-2-yn-1-amine and 1-(3-phenylprop-2-yn-1-yl)piperi-
dine (Scheme 3). However, unlike the reaction of alkyl-sub-
stituted propargylamines, in this case, the reaction was not
regioselective and gave a mixture of regioisomers 9, 10 and
9′,10′. The Overhauser effects between the methylene-
group protons Н2С-1 (δ = 2.83 ppm) and the phenyl-group
proton at С-13 (δ = 7.14 ppm) observed in the NOESY spec-
trum of regioisomer 9a are indicative of cis-arrangement of
the aromatic and dimethylaminomethyl groups relative to
the double bond (Scheme 3). Z-Configuration of the double
bond in 9′a is evidenced by the cross-peak between the
methylene-group protons Н2С-1 (δ = 3.07 ppm) and the
phenyl-group proton at С-13. Coupling between the pro-
tons at С-4 (δ = 2.38 ppm) and the С-8 carbon (δ = 141.16
ppm) in 10a points to the geminal positions of the phenyl
and ethyl groups at a double-bond carbon. Comparison of
Ph
Et2Zn (2.5 equiv, 1 M in hexanes)
NR2
Ti(O-iPr)4 (0.1 equiv, 0.5 M in hexanes)
EtMgBr (0.2 equiv, 2.5 M in Et2O)
zn
zn
Ph
NR2
+
Et2O, rt, 18 h
1
8a: NR2 = NMe2
8b: NR2 = N(CH2)5
NR2
12b–e and 13a,eare in good agreement with the H NMR,
13C NMR, and 31P NMR characteristics reported previously
for structurally identical 1-alkenylphosphine oxides.22 Note
that in the case of 1- alkynylphosphines, the presence of a
phenyl substituent at the triple bond does not change the
reaction regiochemistry, unlike the case of propargyl-
amines. The 2-zincoethylzincation of diphenyl(phenyl-
ethynyl)phosphine proceeds regioselectively to give a single
regioisomer 12e (13e) with geminal positions of the phenyl
and ethyl substituents at a double-bond carbon atom.
This study demonstrates that the presence of the amine
or phosphine functional groups in the molecule of alkyne
does not prevent but rather facilitates the 2-zincoethylzin-
cation reaction. The strategy we developed opens up the
way to the synthesis of heterofunctional alkenes of various
structure via catalytic 2-zincoethylzincation of functionally
D2O (or H2O)
Ph
zn
zn
10
8
11
zn = Zn1/2; ZnEt
9
12
1
NR2
4
3
13
+
:
13
4
3
12
11
8
5
NR2
X
2
5X
X
X
2
1
9
10
1.5
1
NR2
Regioisomers
X
Overall yield (%)
NMe2
NMe2
9a
10a
10b
9'a
D
H
H
87
73
89
10'a
10'b
N(CH2)5
Scheme 3 Ti-Mg-catalyzed 2-zincoethylzincation of phenyl-substitut-
ed propargylamines with Et2Zn
© Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–D

D
R. N. Kadikova et al.
Letter
Synlett
(10) Sklute, G.; Bolm, C.; Marek, I. Org. Lett. 2007, 9, 1259.
(11) Maezaki, N.; Sawamoto, H.; Yoshigami, R.; Suzuki, T.; Tanaka, T.
Org. Lett. 2003, 5, 1345.
(12) Stüdemann, T.; Ibrahim-Ouali, M.; Knochel, P. Tetrahedron
1998, 54, 1299.
(13) Yasui, H.; Nishikawa, T.; Yorimitsu, H.; Oshima, K. Bull. Chem.
Soc. Jpn. 2006, 79, 1271.
11a: R = n-Bu
11b: R = n-Am
11c: R = n-Hex
11d: R = n-Oct
11e: R = Ph
R
PPh2
Et2Zn (2.5 equiv, 1 M in hexanes)
Ti(O-iPr)4 (0.1 equiv, 0.5 M in hexanes)
EtMgBr (0.2 equiv, 2.5 M in Et2O)
Et2O, rt, 18 h
(14) Gourdet, B.; Lam, H. W. J. Am. Chem. Soc. 2009, 131, 3802.
(15) Sallio, R.; Corpet, M.; Habert, L.; Durandetti, M.; Gosmini, C.;
Gillaizeau, I. J. Org. Chem. 2017, 82, 1254.
(16) Rezaei, H.; Marek, I.; Normant, J. F. Tetrahedron 2001, 57, 2477.
(17) Xi, Z.; Zhang, W.; Takahashi, T. Tetrahedron Lett. 2004, 45, 2427.
(18) Ben-Valid, S.; Quntar, A. A. A.; Srebnik, M. J. Org. Chem. 2005, 70,
3554.
(19) Negishi, E. Dalton Trans. 2005, 827.
(20) Al-Aziz, Al-Quntar. A.; Srebnik, M. J. Organomet. Chem. 2005,
690, 2504.
R
Ph2
P
1. H2O or D2O
2. H2O2
R
O
PPh2
zn
zn
X
X
12b: X = D, 71% 13a: X = H, 80%
12c: X = D, 69% 13e: X = H, 66%
12d: X =D, 68%
1. H2O
R
2. S8 (5.3 equiv), rt, 24 h
Ph2
P
S
12e: X = D, 62%
(21) Ramazanov, I. R.; Kadikova, R. N.; Dzhemilev, U. M. Russ. Chem.
Bull. 2011, 60, 99.
(22) Ramazanov, I. R.; Kadikova, R. N.; Saitova, Z. R.; Dzhemilev, U. M.
Asian J. Org. Chem. 2015, 4, 1301.
X
14a: X = H, 62%
14b: X = H, 59%
X
zn = Zn1/2; ZnEt
(23) Kadikova, R. N.; Ramazanov, I. R.; Vyatkin, A. V.; Dzhemilev, U.
M. Synthesis 2017, 49, 4523.
(24) Kadikova, R. N.; Ramazanov, I. R.; Vyatkin, A. V.; Dzhemilev, U.
M. Synlett 2018, 29, 1773.
Scheme 4 Ti-Mg-catalyzed 2-zincoethylzincation of 1-alkynylphos-
phines with Et2Zn
(25) Montchamp, J.-L.; Negishi, E.-i. J. Am. Chem. Soc. 1998, 120,
5345.
substituted alkynes. In addition, the disclosed regio- and
stereoselective transformation of 1-alkynylphosphines and
2-alkynylamines opens up new prospects for the synthesis
of various polyfunctional compounds using a broad range of
transformations of the functionally substituted organozinc
intermediates formed in situ. These and other goals will be
pursued in our subsequent studies.
(26) To a solution of N,N-dimethylhept-2-yn-1-amine (278 mg, 2
mmol) and Et2Zn (1 M in hexanes, 5 mL, 5 mmol) in Et2O (6 mL)
was added Ti(O-iPr)4 (0.5 M in hexanes, 0.4 mL, 0.2 mmol). Eth-
ylmagnesium bromide (2.5 M in Et2O, 0.16 mL, 0.4 mmol) was
then added, and the reaction mixture rapidly turned black.
After 18 h at 23 °C, the reaction mixture was diluted with Et2O
(5 mL), and 25 wt% NaOH (3 mL) was added dropwise while the
reaction flask was cooled in an ice bath. The aqueous layer was
extracted with Et2O (3 × 5 mL). The combined organic layers
were washed with brine (10 mL) and dried over anhydrous
CaCl2. The reaction mixture was filtered through a filter paper
and concentrated in vacuo to give crude product as a yellow oil.
The residue was distilled through a micro column at 10 mmHg
to give (Z)-3-ethyl-N,N-dimethylhept-2-en-1-amine (226 mg,
67%) as a colorless oil; bp 86–88 °С (10 mmHg). 1H NMR (400
MHz, CDCl3): δ = 0.92 (t, J= 6.6 Hz, 3 Н, С(11)Н3), 1.02 (t, J= 7.4
Hz, 3 Н, С(5)Н3), 1.25–1.40 (m, 4 Н, С(9,10)Н2), 2.00–2.10 (m, 2
Н, С(4)Н2), 2.10–2.35 (m, 2 Н, С(8)Н2), 2.24 (s, 6 Н, С(6,7)Н3),
Funding Information
18-03-00817This work was supported by the Russian Foundation for
Basic Research (grant no. 16-33-60167, 18-03-00817) and by Grant of
the RF President (Sci. Sh.-6651.2016.3).
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Supporting Information
Supporting information for this article is available online at
2.91 (d, J= 6.7 Hz, 2 Н, С(1)Н2), 5.23 (t, J= 6.6 Hz, 1 Н, С(2)Н1).13
C
https://doi.org/10.1055/s-0037-1612009.
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NMR (100 MHz, CDCl3): δ = 12.73 (C(5)), 14.03 (C(11)), 22.85
(C(10)), 29.57 and 30.31 and 30.72 (C(4,8,9)), 45.24 (2 C(6,7)),
56.83 (C(1)), 120.47 (C(2)), 144.38 (C(3)). MS (EI): m/z,% = 169
(15) [M+], 140 (9), 124 (14), 112 (21), 95 (100), 82 (32), 58 (49),
46 (48). Anal. Calcd for C11H23N (%): C, 78.03; H, 13.69; N, 8.27.
Found: C, 78.1; H, 13.7; N, 8.1.
References and Notes
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