Novel α-silyl-α-diazoacetates containing a silicon-heteroatom bond

Article abstract of DOI:10.1055/s-1999-3534

Silylation of diazoacetic esters with (t-Bu)₂Si(Cl)OTf or Ph(t- Bu)Si(Cl)OTf (Tf = SO₂CF₃) yields α-(chlorosilyl)-α-diazoacetates 3a-d, which can be converted into azidosilyl- (7), isocyanatosilyl- (8), and isothiocyanatosilyl- (9) substituted diazoacetates. Acid-catalyzed hydrolysis of 8a or 9a generates (hydroxysilyl)diazoacetate 10. (Allylaminosilyl)diazoacetates 12a,b can be prepared from diisopropylsilyl bis(triflate) by successive treatment with diazoacetic esters and allylamine.

Full text of DOI:10.1055/s-1999-3534

PAPER
1175
Novel a-Silyl-a-diazoacetates Containing a Silicon–Heteroatom Bond
Gerhard Maas,a* Susanne Benderb
a Abteilung Organische Chemie I, Universität Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany
Fax +49(731)5022803; E-mail: gerhard.maas@chemie.uni-ulm.de
b Fachbereich Chemie, Universität Kaiserslautern, Erwin-Schrödinger-Straße, D-67663 Kaiserslautern, Germany
Received 14 December 1998; revised 13 March 1998
tention to chlorosilyl triflates 111 and 2.12 Since the triflate
anion is a much better leaving group than chloride, selec-
tive introduction of one nucleophile or stepwise introduc-
tion of two different nucleophiles is possible, as has been
Abstract: Silylation of diazoacetic esters with (t-Bu)2Si(Cl)OTf or
Ph(t-Bu)Si(Cl)OTf (Tf = SO2CF3) yields a-(chlorosilyl)-a-diazoac-
etates 3a–d, which can be converted into azidosilyl- (7), isocyana-
tosilyl- (8), and isothiocyanatosilyl- (9) substituted diazoacetates.
Acid-catalyzed hydrolysis of 8a or 9a generates (hydroxysilyl)dia- demonstrated for the successive reaction of 1 with an al-
lylic alcohol and an enolate.11
zoacetate 10. (Allylaminosilyl)diazoacetates 12a,b can be prepared
from diisopropylsilyl bis(triflate) by successive treatment with dia-
zoacetic esters and allylamine.
Reaction of 1 with ethyl or methyl diazoacetate in the
presence of ethyldiisopropylamine provided (chloro-
silyl)diazoacetates 3a,b in good yields (Scheme 1). Chlo-
rosilyl triflate 2 was transformed into 3c,d analogously.
As expected, this electrophilic diazoalkane substitution
process13 occurred exclusively with replacement of the
triflate group, while the Si–Cl bond was not affected.
Compounds 3a–d are stable enough to be purified by vac-
Key words: diazoacetates, organosilicon compounds, silyl triflates,
silyl pseudohalides, nucleophilic substitution at silicon
Silyl-substituted diazoalkanes and diazocarbonyl com-
pounds are the precursors of choice for the photochemi-
cal, thermal, or transition metal-catalyzed generation of
uum distillation. However, even short exposure to atmo-
silyl carbenes or carbenoids.1,2 The substituents attached
spheric moisture leads to partial hydrolysis followed by
to silicon can become actively involved in subsequent in-
destruction of the diazo function by the liberated acid.
tramolecular reactions of these short-lived intermediates.
Therefore, these compounds were used immediately for
Especially useful in this respect are a-silyl-a-diazoace-
further transformations.
tates, for which the traditional Wolff rearrangement3 [i.e.
1,2(C→C) migration of an alkoxy group] can often be
suppressed by a suitable choice of substituents and reac-
tion conditions in favor of carbene or carbenoid reactions
involving the silyl group. The range of possibilities1,4
comprises the carbene-to-silene rearrangement3,5,6 [i.e.
1,2(Si→C) substituent migration], and the formation of
silaheterocycles by intramolecular reactions such as C,H
insertion,7,8 cyclopropanation,7 and attack at C,C triple
bonds.9 So far, only silyl diazoacetates with alkyl, aryl,
trimethylsilyl, and RO substituents attached to silicon
have been studied. Other hetero substituents at silicon
Scheme 1
might generate carbene-derived organosilicon com-
pounds with additional functionality at silicon or even
give rise to new reactivity patterns. Under these aspects,
Efforts to prepare (chlorodimethylsilyl)diazoacetate 5
we decided to synthesize azidosilyl-, isocyanatosilyl-,
were hampered by the low stability of chloro(dimethyl)si-
isothiocyanatosilyl- and aminosilyl-substituted diazoace-
lyl triflate 4. When this compound was prepared from
tates, all of which have a silicon–nitrogen bond in com-
equimolar amounts of Me2SiCl2 or Me2Si(Ph)Cl and tri-
mon.
flic acid at 0 °C, the 1H NMR spectrum indicated the ex-
Silicon-functionalized a-silyl-a-diazoacetates are pre-
pared conveniently from silyl-bis(triflates) by successive
treatment with a diazoacetic ester and a (hetero)nucleo-
phile in the presence of a tertiary amine.10 It was reported
recently that under appropriate conditions, the twofold nu-
cleophilic substitution of dichlorosilanes can be achieved
as well.8
clusive formation of 4. However, disproportionation into
Me2SiCl2 and Me2Si(OTf)2, a reaction which seems to oc-
cur also with other chlorosilyl triflates,14 occurred on
standing and during attempted distillation. Thus, reaction
of ethyl diazoacetate with freshly prepared 4 finally gave
a mixture of diazoacetates 5 and 6 (Scheme 2). Bis(di-
azoacetate) 6 has been obtained from Me2Si(OTf)2 and
ethyl diazoacetate before,10 while chlorosilanes do not un-
dergo the electrophilic diazoalkane substitution under
standard conditions.
Preliminary experiments, in which a (trifloxysilyl)diaz-
oacetate was treated with sodium azide, surprisingly did
not lead to a clean product. Therefore, we turned our at-
Synthesis 1999, No. 7, 1175–1180 ISSN 0039-7881 © Thieme Stuttgart · New York

1176
G. Maas, S. Bender
PAPER
placement of the two triflate groups with ethyl diazoace-
tate and water.
Scheme 2
The chloro substituent in diazoacetates 3a–d can be re-
placed by a variety of pseudohalides. Thus, reaction with
sodium azide, potassium cyanate, or potassium thiocyan-
ate leads to azidosilyl-(7), isocyanatosilyl-(8), and
isothiocyanatosilyl-(9) substituted diazoacetates (Scheme
3). In all cases, the solubility of the alkali salts in acetoni-
trile is sufficiently high to allow a smooth reaction at room
temperature. All new diazoacetates are thermally quite
stable and can be vacuum distilled without decomposi-
tion.
Scheme 4
NMR data and characteristic IR absorptions of silicon-
functionalized silyldiazoacetates 3,7–10 are given in the
Table. It can be seen that the variation of the Si–X substit-
uent in general does not significantly affect the 13C chem-
ical shifts of the diazo and carbonyl carbon atoms. The
same is true for the stretching vibrations of the diazo and
carbonyl groups in the IR spectrum. As an exception, the
carbonyl absorption of 10 [n(C=O) = 1660 cm–1] is found
at unusually low wavenumbers; this and the deshielding
of the carbonyl resonance [Dd(13C=O) = 1.9-2.8 as com-
pared to the other compounds in the Table] can be taken
as an indication of a (Si)OH...O(=C) hydrogen bond. We
assume that an intramolecular hydrogen bond, forming a
six-membered ring, is present15 since the H chemical
1
shift of the OH resonance (d = 3.85) is not concentration
dependent in CDCl3 solution. In DMSO-d6 solution, the
OH resonance appears at much lower yield (d = 6.3) and
also does not vary significantly with concentration. Both
phenomena are known and have been attributed to strong
intermolecular hydrogen bonding between a silanol and
DMSO.16
The spectroscopic data also confirm that compounds 8
and 9 contain a Si-NCX rather than a Si-XCN (X = O, S)
function. Silylcyanates17 and silylthiocyanates18 have be-
come known much later than their iso-forms. With respect
comparison19
between
Scheme 3
to
a
spectroscopic
(Me3Si)3CSiMe2-OCN and (Me3Si)3CSiMe2-NCO, the
silylisocyanate constitution of 8a–c is established by the
value of the nas(NCO) vibration (2270 cm–1), the absence
of an IR absorption around 1160 cm–1, and the 13C chem-
ical shift of the isocyanate carbon atom (d ≈ 125 ppm). For
the cyanate structure, IR absorptions at 2240 and 1160
cm–1 and d(OCN) ≈ 110 ppm would be expected. Further-
more, 8a–c all show an IR absorption at 1460 cm–1 which
can be assigned to ns(NCO).20,21 For the distinction be-
tween Si-NCS and Si-SCN, the asymmetric stretching
vibration of these groups is not a useful criterion.18 How-
In contrast to the chlorosilanes 3, silyl isocyanates 8 and
isothiocyanates 9 are rather stable towards hydrolysis.
While 8a and 9a could be recovered unchanged from wet
acetonitrile after two days, they were slowly hydrolyzed
over several days in acetone-water containing a few
drops of hydrochloric acid. After workup, (hydroxysi-
lyl)diazoacetate 10 could be isolated besides minor
amounts of di(tert-butyl)silanediol (11) (Scheme 4). The
diazoacetate was prepared independently from di(tert-
butyl)silyl bis(triflate) by successive nucleophilic dis-
Synthesis 1999, No. 7, 1175–1180 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Novel o-Silyl-a-diazoacetates Containing a Silicon–Heteroatom Bond
1177
Table IR and 13C NMR Data of Diazoacetates 3, 7–10; R1(t-Bu)Si(X)-C(N2)-COOR2
Product
X
R1
R2
Et
IR (film, cm–1)
13C NMR (100.61 MHz, CDCl3, TMS, δ/ppm, J/Hz)
n(C=O)
n(C=N2) n(N3)
n(NCO)
n(NCS)
C=N2
COOR
Other Signals
3a
Cl
t-Bu
1678
2095
–
45.6
168.2
14.3 (CH2CH3), 23.5 (CMe3), 27.6 (CMe3),
60.9 (OCH2)
3b
3c
Cl
Cl
t-Bu Me
1677
1675
2095
2095
–
–
Ph
Et
46.4
46.1
43.9
44.4
44.0
43.8
43.6
44.6
167.9
168.2
168.6
168.3
168.4
168.4
168.6
168.0
14.2 (CH2CH3), 21.8 (CMe3), 26.2 (CMe3),
61.2 (OCH2), 127.9, 130.6, 130.8, 134.7
3d
7a
7c
7d
8a
8b
8c
Cl
N3
N3
N3
Ph
Me
1700
1680
1678
1700
1679
1680
1683
2100
2095
2095
2095
2090
2095
2095
–
21.8 (CMe3), 26.1 (CMe3), 51.9 (OMe),
127.9, 130.4, 130.8, 134.7
t-Bu Et
2140
2140
2140
2270
2270
2270
14.4 (CH2CH3), 23.5 (CMe3), 27.6 (CMe3),
61.1 (OCH2)
Ph
Ph
Et
20.2 (CMe3), 25.9 (CMe3), 61.4 (OCH2),
128.2, 129.5, 130.8, 134.3
Me
20.4 (CMe3), 25.9 (CMe3), 52.1 (OMe),
128.2, 129.2, 130.8, 134.3
NCO t-Bu Et
NCO t-Bu Me
14.4 (CH2CH3), 22.2 (CMe3), 27.4 (CMe3),
61.1 (OCH2), 124.8 (NCO)
22.3 (CMe3), 27.4 (CMe3), 51.8 (OMe),
125.0 (NCO)
NCO Ph
Et
14.1 (CH2CH3), 20.2 (CMe3), 25.9 (CMe3),
61.2 (OCH2), 125.3 (NCO), 128.0, 129.9,
130.8, 134.2
9a
9b
9c
NCS t-Bu Et
NCS t-Bu Me
1680
1680
1684
2095
2095
2110
2053
2055
2055
43.7
43.4
44.6
168.1
168.3
167.7
14.4 (CH2CH3), 22.7 (CMe3), 27.4 (CMe3),
61.2 (OCH2), 144.7 (NCS)
22.7 (CMe3), 27.3 (CMe3), 51.9 (OMe),
144.7 (NCS)
NCS Ph
Et
14.1 (CH2CH3), 20.7 (CMe3), 25.9 (CMe3),
61.3 (OCH2), 128.1, 128.8, 131.0, 134.2,
144.9 (NCS)
10
OH
t-Bu Et
1660
2094
3459
41.5
170.5
14.2 (CH2CH3), 22.1 (CMe3), 27.2 (CMe3),
[n(OH)]
60.9 (OCH2)
ever, the isothiocyanate structure of 9a–c is indicated treatment with equimilar amounts of a diazoacetate and
from a chemical point of view by the relative stability to- allylamine.
wards solvolysis, by the observation that silylthiocyanates
so far have been isolated only for very bulky silanes and
when the exchange reaction was performed with AgOCN
rather than alkali cyanates.18
Diazoacetates bearing an aminosilyl substituent have not
been described yet. We expected their preparation to be
analogous to the corresponding (alkoxysilyl)diazoacet-
ates.10 As an example, we describe here the synthesis of
(allylaminosilyl)diazoacetates 12 (Scheme 5). By com-
plete analogy to (allyloxysilyl)diazoacetates, they can be
obtained from diisopropylsilyl bis(triflate) by successive
Scheme 5
Synthesis 1999, No. 7, 1175–1180 ISSN 0039-7881 © Thieme Stuttgart · New York

1178
G. Maas, S. Bender
PAPER
Spectroscopic and analytical data for 5:
In summary, we have described a variety of novel a-silyl-
a-diazoacetates with heteroatom substituents (Cl, N3,
NCO, NCS, OH, NHR) attached to silicon. All of these di-
azo compounds show remarkable thermal stability, and
some of them are also rather stable against hydrolysis of
the Si–X bond. Some chemistry of these compounds will
be reported in forthcoming papers.
IR (film): n = 2104 (CN2), 1690 (C=O), 1395, 1268, 1214, 1157,
1083 cm–1.
1H NMR (CDCl3, 90 MHz): d = 0.66 (s, 6 H, SiMe2), 1.29 (t, 3 H,
CH2CH3), 4.21 (q, 2 H, OCH2).
Anal. calcd for C6H11ClN2O2Si (206.71): C 34.86; H 5.36; N 13.56.
Found: C 34.16; H 5.19; N 12.15.
a-(Azidosilyl)-a-diazoacetates 7a,c,d; General Procedure
Solid sodium azide (0.65 g, 10.0 mmol) was added to a solution of
3a,c,d (5.0 mmol) in MeCN (40 mL), and the suspension was stirred
for 15 h. The solvent was evaporated and pentane or Et2O (40 mL)
was added. The solids (NaCl and NaN3) were filtered off with suc-
tion, and the solvent was evaporated at r.t./0.001 mbar. Products 7a
and 7c were bulb-to-bulb distilled for further purification.
All reactions except the hydrolyses were carried out in rigorously
dried glassware under an Ar atmosphere. Solvents were dried by
standard procedures and stored under Ar. Column chromatography
was performed using silica gel (Macherey & Nagel, 0.063–0.2 mm).
1H NMR spectra: Varian EM 390 (90 MHz), Bruker AC 200
(200.13 MHz), TMS as internal standard. 13C NMR: Bruker AMX
400 (100.61 MHz); solvent signal as internal standard (CDCl3, δ =
77.0). IR spectra: Perkin-Elmer IR-397. Elemental analyses: Per-
kin-Elmer EA-240 and 2400 CHN instruments. Mps were deter-
mined in a copper block and are uncorrected.
Ethyl 2-[Azido(di-tert-butyl)silyl]-2-diazoacetate (7a)
Yellow oil; bp. 70 °C/0.001 mbar (Kugelrohr); yield: 0.95 g (64%).
1H NMR (CDCl3, 90 MHz): d = 1.17 (s, 18 H, CMe3), 1.31 (t, 3 H,
CH2CH3), 4.23 (q, 2 H, OCH2).
a-(Chlorosilyl)-a-diazoacetates 3a–d; General Procedure
A solution of di(tert-butyl)chlorosilyl triflate11 (1, 10 mmol) or
(tert-butyl)chlorophenylsilyl triflate12 (2, 10 mmol) in Et2O (30 mL)
was cooled at 0 °C, and a solution of ethyl diazoacetate22 (1.14 g,
10.0 mmol) or methyl diazoacetate22 (1.00 g, 10.0 mmol) and ethyl-
diisopropylamine (1.74 mL, 10 mmol) in Et2O (20 mL) was added
dropwise. The mixture was then stirred at r.t. for 15 h, the precipi-
tated ammonium salt was filtered off, and the solvent was evaporat-
ed at r.t./0.001 mbar. The crude, moisture-sensitive diazoacetates
were sufficiently pure for further transformations, but could be pu-
rified further by bulb-to-bulb distillation (IR and 13C NMR data: Ta-
ble).
Anal. calcd for C12H23N5O2Si (297.45): C 48.46; H 7.79; N 23.55.
Found: C 48.20; H 7.80; N 23.30.
Ethyl 2-[Azido(tert-butyl)phenylsilyl]-2-diazoacetate (7c)
Yellow oil, bp. 100 °C/0.01 mbar (Kugelrohr); yield: 1.43 g (90%).
1H NMR (CDCl3, 90 MHz): d = 1.08 (s, 9 H, CMe3 and t, 3 H,
CH2CH3), 4.16 (q, 2 H, OCH2), 7.31–7.75 (m, 5 H, Ph).
Anal. calcd for C14H19N5O2Si (317.44): C 52.97; H, 6.03; N 22.07.
Found: C 52.10; H 6.20; N 22.30.
Methyl 2-[Azido(tert-butyl)phenylsilyl]-2-diazoacetate (7d)
Yellow oil; yield: 1.44 g (95%).
1H NMR (CDCl3, 90 MHz): d = 1.06 (s, 9 H, CMe3), 3.70 (s, 3 H,
OCH3), 7.30–7.73 (m, 5 H, Ph).
Ethyl 2-[Di(tert-butyl)chlorosilyl]-2-diazoacetate (3a)
Yellow oil; bp. 80–85 °C/0.005 mbar (Kugelrohr); yield: 2.21 g
(76%).
1H NMR (CDCl3, 90 MHz): d = 1.18 (s, 18 H, CMe3), 1.28 (t, 3 H,
CH2CH3), 4.23 (q, 2 H, OCH2).
Anal. calcd for C13H17N5O2Si (303.41): C 51.46; H 5.65; N 23.09.
Found: C 49.20; H 5.70; N 22.70.
a-(Isocyanatosilyl)-a-diazoacetates 8a–c and a-(Isothiocyana-
tosilyl)-a-diazoacetates 9a–c; General Procedure
To a solution of 3a–c (2–7 mmol) in MeCN (40 mL) was added an
equimolar amount of solid KOCN or KSCN, and the mixture was
stirred overnight. Workup as described above for diazoacetates 7
gave the products as yellow oils, most of which were purified fur-
ther by bulb-to-bulb distillation.
Methyl 2-[Di(tert-butyl)chlorosilyl]-2-diazoacetate (3b)
Yellow oil; yield: 2.48 g (76%).
1H NMR (CDCl3, 90 MHz): d = 1.16 (s, 18 H, CMe3), 3.78 (s, 3 H,
OMe).
Ethyl 2-[tert-Butyl(chloro)phenylsilyl]-2-diazoacetate (3c)
Yellow oil, bp. 130 °C/0.01 mbar (Kugelrohr); yield: 2.80 g (90%).
Ethyl 2-[Di(tert-butyl)isocyanatosilyl]-2-diazoacetate (8a)
Bulb-to-bulb distillation at 65–90 °C/0.01 mbar; yield: 60%.
1H NMR (CDCl3, 90 MHz): d = 1.13 (s, 18 H, CMe3), 1.29 (t, 3 H,
CH2CH3), 4.22 (q, 2 H, OCH2).
1H NMR (CDCl3, 90 MHz): d = 1.16 (s, 9 H, CMe3), 1.19 (t, 3 H,
CH2CH3), 4.17 (q, 2 H, OCH2), 7.31–7.94 (m, 5 H, Ph).
Methyl 2-[tert-Butyl(chloro)phenylsilyl]-2-diazoacetate (3d)
Yellow oil; yield: 2.52 g (85%).
Anal. calcd for C13H23N3O3Si (297.44): C 52.50; H 7.79; N 14.13.
Found: C 52.30; H 8.10; N 11.30.
1H NMR (CDCl3, 90 MHz): d = 1.14 (s, 9 H, CMe3), 3.75 (s, 3 H,
OCH3), 7.32–7.92 (m, 5 H, Ph).
Methyl 2-[Di(tert-butyl)isocyanatosilyl]-2-diazoacetate (8b)
Yield: 58%.
Ethyl 2-[Chloro(dimethyl)silyl]-2-diazoacetate (5)
1H NMR (CDCl3, 90 MHz): d = 1.11 (s, 18 H, CMe3), 3.74 (s, 3 H,
Triflic acid (1.50 g, 10.0 mmol) was slowly added to a solution of
chloro(dimethyl)phenylsilane (1.71 g, 10.0 mmol) in pentane. After
1 h, the mixture was cooled at 0 °C and a solution of ethyl
diazoacetate22 (1.14 g, 10.0 mmol) and ethyldiisopropylamine (1.7
mL, 10.0 mmol) in pentane (5 mL) was added. The mixture was
kept at 0 °C for 30 min., then at r.t. for 10 h. The precipitated am-
monium salt was filtered off, the solvent was evaporated, and the
residue was fractionated by bulb-to-bulb distillation to furnish first
5 [light yellow oil, yield: 0.43 g (21%); bp. 45–50 °C/0.01 mbar],
then diethyl 2,2'-dimethylsilylbis(2-diazoacetate)10 (6) [yield: 0.11
g (8% based on ethyl diazoacetate); bp. 130–135 °C/0.1 mbar].
OMe).
Ethyl 2-[tert-Butyl(isocyanato)phenylsilyl]-2-diazoacetate (8c)
Bulb-to-bulb distillation at 150–170 °C/0.01 mbar; yield: 91%.
1H NMR (CDCl3, 200 MHz): d = 1.09 (s, 9 H, CMe3), 1.17 (t, 3 H,
CH2CH3), 4.16 (q, 2 H, OCH2), 7.36–7.71 (m, 5 H, Ph).
Anal. calcd for C15H19N3O3Si (317.43): C 56.76; H 6.03; N 13.24.
Found: C 55.70; H 6.10; N 12.30.
Ethyl 2-[Di(tert-butyl)isothiocyanatosilyl]-2-diazoacetate (9a)
Bulb-to-bulb distillation at 80–100 °C/0.015 mbar; yield: 60%.
Synthesis 1999, No. 7, 1175–1180 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Novel o-Silyl-a-diazoacetates Containing a Silicon–Heteroatom Bond
1179
1H NMR (CDCl3, 90 MHz): d = 1.17 (s, 18 H, CMe3), 1.29 (t, 3 H,
CH2CH3), 4.21 (q, 2 H, OCH2).
13C NMR (CDCl3, 100.61 MHz): d = 12.2 (CHMe2), 14.1
(CH2CH3), 17.0 (CHMe), 17.3 (CHMe), 42.6 (CN2), 44.6 (SiCH2),
60.1 (OCH2), 113.0 (=CH2), 139.5 (=CH), 169.0 (C=O).
Anal. calcd for C13H23N3O2SSi (313.51): C 49.80; H 7.39; N 13.41.
Found: C 49.40; H 7.50; N 13.10.
Anal. calcd for C13H25N3O2Si (283.46): C 55.09; H 8.89; N 14.83.
Found: C 54.80, H 8.70, N 14.30.
Methyl 2-[Di(tert-butyl)isothiocyanatosilyl]-2-diazoacetate (9b)
Yield of crude product: 43%.
Methyl 2-[Allylamino(diisopropyl)silyl]-2-diazoacetate (12b)
was prepared analogously; yield: 1.67 g (89%).
1H NMR (CDCl3, 90 MHz): d = 1.13 (s, 18 H, CMe3), 3.74 (s, 3 H,
OMe).
IR (film): n = 3360 (broad, NH), 2080 (CN2), 1680 (C=O), 1425,
1260, 1195, 1072 cm–1.
1H NMR (CDCl3, 200 MHz): d = 0.92–1.35 (m, 14 H, 2 x i-Pr), 3.44
(mc, 2 H, CH2), 3.72 (s, 3 H, OMe), 5.02/5.17 (each mc, 2 H, =CH2),
5.90 (mc, 1H, =CH).
13C NMR (CDCl3, 100.61 MHz): d = 12.4 (CHMe2), 17.2 (CHMe),
17.6 (CHMe), 42.7 (CN2), 44.8 (SiCH2), 51.5 (OCH3), 113.3
(=CH2), 139.7 (=CH), 169.7 (C=O).
Anal. calcd. for C12H21N3O2SSi (299.48): C 48.13; H 7.07; N 14.03.
Found: C 48.10; H 7.10; N 12.70.
Ethyl 2-[tert-Butyl(isothiocyanato)phenylsilyl]-2-diazoacetate
(9c)
Yield of crude product: 72%.
1H NMR (CDCl3, 200 MHz): d = 1.13 (s, 9 H, CMe3), 1.19 (t, 3 H,
CH2CH3), 4.18 (q, 2 H, OCH2), 7.35–7.73 (m, 5 H, Ph).
Anal. calcd for C12H23N3O2Si (269.43): C 53.50; H 8.60; N 15.60.
Found: C 53.20; H 8.40; N 14.70.
Anal. calcd for C15H19N3O2SSi (333.50): C 54.02; H 5.74; N 12.60.
Found: C 52.60; H 5.90; N 11.20.
Ethyl 2-[Di(tert-butyl)hydroxysilyl]-2-diazoacetate (10)
a) Isocyanatosilyl-diazoacetate 8a (1.75 g, 5.9 mmol) was dissolved
in acetone (30 mL) containing H2O (10 mL) and 10 drops of conc.
HCl. After 9 days, H2O (100 mL) was added, and the product was
extracted into CHCl3 (40 mL). The organic phase was dried
(Na2SO4), and the solvent was removed. Addition of petroleum
ether furnished crystalline di(tert-butyl)silanediol (11),23 which was
isolated by filtration; yield: 0.16 g (15%). The filtrate was subjected
to column chromatography [silica gel (50 g), Et2O-petroleum ether
(2:8), rapid elution] and gave 10 as a yellow oil which solidified on
standing, mp. 62 °C (pentane).
Acknowledgement
This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie. We thank Ms. Alexandra
Maier for help with the synthetic work.
References
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mmol), ethyldiisopropylamine (0.7 mL, 4.0 mmol), and ethyl diaz-
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1H NMR (CDCl3, 90 MHz): d = 1.08 (s, 18 H, CMe3), 1.28 (t, 3 H,
CH2CH3), 3.85 (s, 1 H, OH), 4.21 (q, 2 H, OCH2).
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Found: C 52.80; H 8.60; N 9.90.
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Ethyl 2-[Allylamino(diisopropyl)silyl]-2-diazoacetate (12a)
A solution of diisopropylsilyl bis(triflate) (2.06 g, 5.0 mmol) in pen-
tane (30 mL) was cooled at 0 °C, and a solution of ethyl
diazoacetate22 (0.57 g, 5.0 mmol) and ethyldiisopropylamine (0.87
mL, 5.0 mmol) in Et2O (10 mL) was added gradually. After 30 min
at 0 °C and 1 h at r.t., the mixture was cooled to 0 °C again, and al-
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1.32 g (93%).
IR (film): n = 3365 (broad, NH), 2095 (CN2), 1680 (C=O), 1460,
1362, 1260, 1200, 1090 cm–1.
1H NMR (CDCl3, 200 MHz): d = 0.96–1.34 (m, 14 H, 2 x i-Pr), 1.26
(t, 3 H, CH2CH3), 3.46 (mc, 2 H, CH2), 4.18 (q, 2 H, OCH2), 5.02/
5.18 (each mc, 2 H, =CH2), 5.91 (mc, 1 H, =CH).
Synthesis 1999, No. 7, 1175–1180 ISSN 0039-7881 © Thieme Stuttgart · New York

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Synthesis 1999, No. 7, 1175–1180 ISSN 0039-7881 © Thieme Stuttgart · New York