1-Organosulfonyl-2-sila-5-piperazinones: Synthesis, molecular and crystal structure, and chemical transformations into 2-aminoacid derivatives

Article abstract of DOI:10.1016/j.jorganchem.2013.05.044

The reaction of chloro(chloromethyl)dimethylsilane and hexamethyldisilazane with N-methylamides of N0-organosulfonyl-2-amino acids (1aee), the derivatives of N-mesylglycine (a), N-tosylglycine (b), Nnosylglycine (c), N-nosylalanine (d) and N-nosylleucine (e), affords new type of silacyclanes, 1-organosulfonyl-2- sila-5-piperazinones 2aee. The presence of very labile SieN bonds in compounds 2 can be utilised in a variety of synthetic applications. The hydrolysis of 2aee yields disiloxanes 3aee, which can be subsequently transformed into fluorosilanes, such as 4a, by the reaction with boron trifluoride. Ring-opening reactions of piperazinones 2b with 1-chloromethyl-2-pyrrolidone and acetyl bromide lead to previously unknown silyloxonium chloride 6b and silyloxonium bromide 8b, respectively, containing fragments of 2-amino acids as C,O-chelate ligands. Crystal structures of N-methylamide 1b, piperazinones 2a, d, e, disiloxanes 3c, e, fluorosilane 4a, silyloxonium chloride 6b and silyloxonium bromide 8b have been determined by X-ray diffraction study. The silicon atom in piperazinones and disiloxanes is tetracoordinated while compounds 4a, 6b and 8b contain pentacoordinated Si atoms. Crown Copyright.

Full text of DOI:10.1016/j.jorganchem.2013.05.044

Accepted Manuscript
1-Organosulfonyl-2-sila-5-piperazinones: synthesis, molecular and crystal structure,
and chemical transformations into 2-aminoacid derivatives
Alexandr G. Shipov, Eugenia P. Kramarova, Huntse Fang, Dmitry E. Arkhipov, Alexey
A. Nikolin, Sergey Yu. Bylikin, Vadim V. Negrebetsky, Alexandr A. Korlyukov, Natalia
A. Voronina, Alan R. Bassindale, Peter G. Taylor, Yuri I. Baukov
PII:
S0022-328X(13)00434-8
10.1016/j.jorganchem.2013.05.044
JOM 18066
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 3 April 2013
Revised Date: 22 May 2013
Accepted Date: 29 May 2013
Please cite this article as: A.G. Shipov, E.P. Kramarova, H. Fang, D.E. Arkhipov, A.A. Nikolin, S.Y.
Bylikin, V.V. Negrebetsky, A.A. Korlyukov, N.A. Voronina, A.R. Bassindale, P.G. Taylor, Y.I. Baukov,
1-Organosulfonyl-2-sila-5-piperazinones: synthesis, molecular and crystal structure, and chemical
transformations into 2-aminoacid derivatives, Journal of Organometallic Chemistry (2013), doi: 10.1016/
j.jorganchem.2013.05.044.
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ACCEPTED MANUSCRIPT
1-Organosulfonyl-2-sila-5-piperazinones: synthesis, molecular and crystal
structure, and chemical transformations into 2-aminoacid derivatives
Alexandr G. Shipov,a Eugenia P. Kramarova,a Huntse Fang,a Dmitry E. Arkhipov,b
Alexey A. Nikolin,a Sergey Yu. Bylikin,c Vadim V. Negrebetsky,a Alexandr A. Korlyukov,b
Natalia A. Voronina,b Alan R. Bassindale,c Peter G. Taylor,c,* Yuri I. Baukova
aN.I. Pirogov Russian National Research Medical University, 1 Ostrovityanova St., 117997
Moscow, Russia. Tel.: +7 (495) 434 1100. Fax: +7 (495) 434 0329. E-mail: baukov@rsmu.ru.
bA.N. Nesmeyanov Institute of Organoelement Compounds (INEOS RAS), 28 Vavilova St.,
119991 Moscow, Russia. Tel./Fax: +7 (495) 135 5085. E-mail: alex@xrlab.ineos.ac.ru.
cThe Open University, Walton Hall, Milton Keynes, MK7 6AA, UK.
Tel.: +44 (0) 1908 652512. E-mail: p.g.taylor@open.ac.uk.
Abstract
The reaction of chloro(chloromethyl)dimethylsilane and hexamethyldisilazane with
N-methylamides of N'-organosulfonyl-2-amino acids (1a–e), the derivatives of N-mesylglycine (a),
N-tosylglycine (b), N-nosylglycine (c), N-nosylalanine (d) and N-nosylleucine (e), affords new type
of silacyclanes, 1-organosulfonyl-2-sila-5-piperazinones 2a–e. The presence of very labile
Si–N bonds in compounds 2 can be utilised in a variety of synthetic applications. The hydrolysis of
2a–e yields disiloxanes 3a–e, which can be subsequently transformed into fluorosilanes, such as 4a,
by the reaction with boron trifluoride. Ring-opening reactions of piperazinones 2b with
1-chloromethyl-2-pyrrolidone and acetyl bromide lead to previously unknown silyloxonium
chloride 6b and silyloxonium bromide 8b, respectively, containing fragments of 2-amino acids as
C,O-chelate ligands.
Crystal structures of N-methylamide 1b, piperazinones 2a, d, e, disiloxanes 3c, e, fluorosilane
4a, silyloxonium chloride 6b and silyloxonium bromide 8b have been determined by X-ray
diffraction study. The silicon atom in piperazinones and disiloxanes is tetracoordinated while
compounds 4a, 6b and 8b contain pentacoordinated Si atoms.
Keywords: 2-sila-5-piperazinones, pentacoordinate silicon compounds, synthesis, X-ray
diffraction study.

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1. Introduction
Silacyclanes, a diverse group of chemically and biologically active compounds, have recently
become the focus of extensive studies [1]. Polyfunctional silicon-containing heterocycles, such as
silapiperazines and their derivatives, are particularly interesting as potential precursors in organic
synthesis due to the presence of very labile Si–N bonds in their molecules [2]. At the same time,
certain classes of such compounds, including 2-sila-5-piperazinones, are virtually unknown — the
only silacyclane of this type described in literature is a bicyclic derivative of proline [3].
Earlier, we studied the cyclosilylmethylation reaction of 2-hydroxyamides and the properties
of the reaction products, 2-sila-5-morpholinones [4][5]. Recently, we have extended the scope of
this synthetic approach towards the derivatives of 2-amino acids [3]. In the present paper, we report
the general strategy of the synthesis of 1-organosulfonyl-2-sila-5-piperazinones by the reaction of
N'-organosulfonyl-2-amino-N-methylamides with chloro(chloromethyl)dimethylsilane and the use
of the resulting silacyclanes for the preparation of N'-(organosulfonyl)-2-amino acids derivatives.
2. Results and discussion
Cyclosilylmethylation of substituted amides of glycine 1a–c, alanine (S)-1d and leucine 1e
was achieved by their reaction with a mixture of chloro(chloromethyl)dimethylsilane and
hexamethyldisilazane — a versatile system that allows a one-pot synthesis involving both
N-trimethylsilylation and subsequent N-dimethylchlorosilylmethylation [6]. For 2-sila-5-
piperazinones 2a, 2b, (S)-2d and 2e, the target products were isolated with yields of 53, 90, 65 and
68%, respectively. Piperazinone 2c was used in further transformations without purification
(Scheme 1).
Scheme 1
SO2R
Me
N
R'
O
R'
Si
ClCH2SiMe2Cl, (Me3Si)2NH
Me3SiCl, NH4Cl
Me
RSO2NHCHCONHMe
N
Me
1a–c, (S)-1d, 1e
2a–c, (S)-2d, 2e
R = Me, R' = H (a); R = 4-MeC6H4, R' = H (b); R = 4-NO2C6H4, R' = H (c);
R = 4-NO2C6H4, R' = Me (d), R = 4-NO2C6H4, R' = CH2CHMe2 (e)
The composition and structures of hydrolytically labile 2-sila-5-piperazinones 2 were
1
confirmed by elemental analysis, IR, NMR H, 13C and 29Si spectra. In addition, the crystal
structures of compounds 2a, (S)-2d and 2e were determined by X-ray diffraction study. All isolated

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piperazinones 2a, 2b, (S)-2d and 2e had a characteristic absorption at 1630–1650 cm–1 (NCO
29
fragment) in the IR spectra and the chemical shift of the central atom in their NMR Si spectra at
4–7 ppm, which is typical for a tetracoordinate silicon with similar environments [4][5][7][8]. The
1
SiMe2 and SiCH2 groups in the H NMR spectra of piperazinones (S)-2d and 2e were non-
equivalent due to the presence of chiral centres in these molecules.
According to X-ray data, the absolute configuration of the alanine derivative (S)-1d was
retained during its cyclosilylmethylation into silapiperazinone (S)-2d.
Earlier, we established a route for the formation of 2-sila-5-morpholinones from
O-trimethylsilyloxy-N-methylamides and ClCH2SiMe2Cl in the presence of Et3N. The process
involved intermediate pentacoordinated chlorosilanes, which subsequently underwent
intramolecular elimination of Me3SiCl and heterocyclisation into the final products [4][5].
Similarly, we propose that the formation of 2-sila-5-piperazinones, 2, proceeds through initial
N-dimethylchlorosilylmethylation of the amide nitrogen atom and the formation of pentacoordinate
C,O-chelate chlorosilanes A (or their N'-trimethylsilyl derivatives), with subsequent elimination of
HCl (or Me3SiCl) and cyclisation into final compounds 2 (Scheme 2). At the same time, the process
could also involve the initial trans-silylation of hexamethyldisilazane with ClCH2SiMe2Cl and
subsequent reaction of the resulting Me2SiNHSiMe2CH2Cl [9] with methylamides 1 affording the
final 2-sila-5-piperazinones 2.
Scheme 2
R'
RSO2NCH
O
Me
Me
ClCH2SiMe2Cl, (Me3Si)2NH
Me3SiCl
H
1
2
Si
N
HCl
Cl
Me
A
From the synthetic point of view, the lability of the Si–N bond in 2-sila-5-piperazinones 2
makes these compounds very useful intermediates for further chemical transformations at silicon. In
aqueous ethanol, compounds 2a–c, (S)-2d and 2e readily undergo hydrolysis even at ambient
temperature and afford disiloxanes 3a–c, (S,S)-3d and 3e, respectively (Scheme 3, reaction a).
Disiloxanes 3b and 3c have been prepared by a simplified one-pot method, where 2-sila-5-
piperazinones formed according to Scheme 1 were hydrolysed "in situ". The yields of disiloxanes,
3, in all cases varied from moderate to good (46–72%).

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Scheme 3
MeSO2NHCH2
R'
Me
O
Me
Me
b. BF3 Et2O
a. H2O
(RSO2NHCHCONCH2SiMe2)2O
3a–c, (S,S)-3d, 3e
Si
N
F
Me
4a
O
c. L5CH2Cl
e. AcBr
[TsN(CH2L5)CH2CN(Me)CH2SiMe2OH2]+Cl–
d. H2O
2
[5b]
[7b]
6b
O
f. H2O
[TsNCH2CNCH2SiMe2OH2]+Br–
Ac
Me
8b
A typical transformation of disiloxanes into fluorosilanes was achieved by the reaction of 3a
with BF3 • Et2O, which afforded pentacoordinate fluoride 4a in a 75% yield (Scheme 3, reaction b).
Chloride 5b and bromide 7b, the expected products of the reaction of 2-sila-5-piperazinone
2b with 1-chloromethyl-2-pyrrolidone (L5CH2Cl) and acetyl bromide (Scheme 3, reactions c and e)
were hydrolytically unstable and could not be isolated. Instead, the C,O-chelate silyloxonium
chloride 6b and bromide 8b were obtained (Scheme 3, reactions d and f).
The composition and structures of disiloxanes 3 and halides 4a, 6b, 8b were confirmed by
1
elemental analysis, IR, H, 13C, 19F (for 4a) and 29Si NMR spectra. The crystal structures of
compounds 3c, 3e, 4a, 6b and 8b were determined by X-ray diffraction study.
The presence of the O→Si coordination in compounds 4–8 and the absence of such
interaction in disiloxanes 3 were confirmed by IR spectroscopy. The two absorption bands at 1615–
1640 cm–1 (strong) and 1450–1520 cm–1 (weak) observed in the IR spectra of compounds 4–8 were
typical for pentacoordinate (O→Si)-chelates [10][11]. At the same time, the IR spectra of
disiloxanes 3 contained only one strong absorption at 1625–1645 cm–1.
The chemical shifts of fluorine (–136.4 ppm) and silicon (+2.3 ppm) in the NMR 19F and 29Si
spectra of fluorosilane 4a are similar to those in a previously reported derivative of N-mesylproline,
Ms-Pro-N(Me)CH2SiMe2F (–126.4 and –3.3 ppm, respectively) [12]. Therefore, the O→Si
intramolecular coordination in solutions of 4a must be relatively weak. In contrast, the 29Si signal of
silyloxonium chloride 6b in solution has a chemical shift of –30.0 ppm, which indicates the
29
presence of a much stronger O→Si coordination in this compound. A similar chemical shift of Si
(–32.8 ppm) was observed for another cyclic proline derivative, [Ms-Pro-N(Me)CH2SiMe2OH2]+Cl–
[3].

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3. Single crystal X-ray studies
3.1. N-tosylglycinemethylamide 1b
The compound crystallized in two polymorph modifications (1b and 1b'). Both modifications
are colourless crystals with approximately equal cell volumes. In the crystal packing of the triclinic
polymorph, two independent molecules are assembled into a three-dimensional network via weak
N–H…O bonds. The monoclinic polymorph contains infinite chains along the c direction of the unit
cell, with additional stacking interaction between the phenyl groups (the interplanar distance and the
distance between centroids of the Ph groups are 3.478(5) and 4.40 Å, respectively). Further details
are given in the supplementary materials.
3.2. 2-Sila-5-piperazinones 2a, (S)-2d and 2e
Compounds 2a, (S)-2d and 2e are the first structurally characterised examples of
organosilicon species with a Si–N bond in a six-membered ring. The heterocyclic fragments in all
silapiperazinones adopt distorted boat conformations with the following deviations of C3 and C6
atoms, respectively: 0.619(3) and 0.572(3) for 2a, 0.663 and 0.492(2) for (S)-2d, 0.693(2) and
0.518(2) for 2e. The Si1–N2 distances are almost the same in all compounds; the longest bond is
observed for 2e where a relatively short intermolecular contact Si…O (3.594(2) Å) is present. The
Si1N2S1O2 moieties are nearly planar in all cases, which is in line with other sulfonamides
reported in literature (CSD [13] ref. codes: DUGWEH01, FACZIS, HIJGOW, SUQBIP, SUQQUQ,
VEDDOX, VEDGEQ, VOGJUW, XINXOH, YILFOP, YILGAC, YILGEG).
Figure 1 shows the structure of 2-sila-5-piperazinone 2a; selected geometrical parameters of
structures 2a, (S)-2d and 2e are given in Table 1.
Table 1
Selected bond lengths and angles (Å and °) in structures 2a, (S)-2d and 2e.
Bond
Si1–N2
Si–C
(S)-2d
2a
2e
1.774(2)
1.863(3)
1.227(3)
1.437(2)
1.468(3)
97.46(11)
1.776(2)
1.857(2)
1.222(2)
1.439(2)
1.491(2)
97.98(8)
1.779(2)
1.859(2)
1.231(3)
1.435(2)
1.491(3)
97.28(10)
O1–C5
S–O
N2–C6
N2Si1C3

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Fig. 1. Molecular structure of 2a presented with thermal ellipsoids at 50% probability. Hydrogen
atoms are omitted for clarity.
3.3. Disiloxanes 3c and 3e
To date, the structures of four disiloxanes similar to 3c and 3e have been reported in the
literature [14][15][16]. In three published structures of this type, short Si…O intramolecular
contacts between the silicon atom and the oxygen atom of a carbonyl or hydroxyl moiety were
observed. The only exception was 1,1,3,3-tetramethyl-1,3-bis(2-oxo-1-pyrrolidinomethyl)-1,3-
disiloxane, where the Si…O interatomic distance (3.959 Å) was greater than the sum of van-der-
Waals radii of respective atoms (3.48 Å [17]). The structure of disiloxane 3c contains two carbonyl
groups, with the C2A=O2A group involved in an intermolecular N–H…O interaction with an
adjacent molecule. Intermolecular distances Si1…O2, Si1A…O2 [-x+1,-y+1,-z+1] and the
intramolecular contact Si1A…O2A (3.961(3), 3.978(3) and 4.017(3) Å, respectively) exceed the
sum of van-der-Waals radii of corresponding elements. In addition, the C6H4NO2 moieties
participate in weak stacking interactions (the distances between the planes of the six-membered
rings and their centroids are 3.468(4) and 4.916 Å, respectively). Another interesting feature of the
structure 3c is a linear SiOSi fragment. The analysis of anisotropic displacement parameters has
shown that each of the O1 and O1A atoms is disordered over two positions with equivalent
populations.
In disiloxane 3e, both carbonyl oxygen atoms participate in the N–H…O interactions but the
Si1…O2, Si1'…O2 and Si2…O7 distances are shorter than those in 3c (3.487(4), 3.822(6) and
3.674(4) Å, respectively). The NO2 moieties participate in peak-hole interactions O…N (the
distances between the planes of nitro groups are 2.887(11) and 2.951(6) Å).
Representative structures of disiloxanes 3c and 3e are shown in Figures 2 and 3.

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Fig. 2. Molecular structure of 3c presented with thermal ellipsoids at 50% probability. Hydrogen
atoms (except H2N) are omitted for clarity.
Fig. 3. Molecular structure of 3e presented with thermal ellipsoids at 50% probability. Hydrogen
atoms (except H2N and H5N) and minor positions of the disordered atoms are omitted for clarity.
3.4. Fluoride 4a, silyloxonium halides 6b and 8b
Table 2
Selected geometrical parameters (Å and °) of structures 4a, 6b and 8b.
*
Si1–X, Å
1.6699(8)
1.888(3)
Si1–O1, Å
2.1949(9)
1.943(3)
O1–Si1–X, °
171.39(4)
ΔSi , Å
0.2204(3)
4a (X = F1)
6b (X = O1W)
8b (X = O1W)
174.35(14)
173.24(6)
0.0637(12)
–0.0094(6)
1.9765(13)
1.8924(12)
* The deviation of the Si atom from the plane of equatorial substituents С1, С2, С3; a positive value means deviation
towards X fragment.

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Organosilicon compounds containing OSiC3F coordination polyhedra are often described in
the literature as snapshots of the SN2 reaction potential surface [18][19]. The Si…O interatomic
distances in such compounds are strongly affected by the inductive effects of substituents at the C
and N atoms of the five-membered ring. The shortest Si…O distance and the longest Si–F bond
(2.065(1) and 1.675(1) Å, respectively) have been found in a quinolinone complex [19], which is
probably a result of the –M effect of the vicinal C=C bond. In the derivative of 1,3-oxazin-4-one
[16], the Si…O distance exceeds that in the quinolinone complex by 0.16 Å while the Si–F bond is
only 0.01
Å
shorter. The same Si–F bond lengths were observed in
N,N-bis(dimethylfluorosilylmethyl)acetamide [20] and (N-acetyl-N-((S)-1-phenylethyl)amino-
methyl)dimethylfluorosilane [21]. The Si…O distances in these compounds were also very similar
(2.147 and 2.187 Å, respectively). Such minor variations of the Si–F and Si–O bond lengths are in
good agreement with the nature of the F atom, which is a poor leaving group in the SN2 reactions.
In 4a the Si atom has a strongly distorted trigonal bipyramidal (TBP) configuration with a deviation
from the plane of the equatorial substituents (ΔSi) of 0.2204(3) Å (see Table 2 for selected
geometrical parameters of structures 4a, 6b and 8b). The F1 and O1 atoms occupy axial positions
(Fig. 4), the angle F1-Si1-O1 is 171.39(4)°. The lengths of the Si1–F1 and Si1–O1 bonds are
1.6699(8) and 2.1949(9) Å respectively. The five-membered chelate ring Si1C3N1C4O1 is almost
planar (maximum deviation from the plane is 0.03 Å). The molecules of 4a are assembled into
chains via N–H…OSO bonds, the F1 and O1 atoms are not involved in H-bonding.
In 6b and 8b, the configurations of Si atoms correspond to slightly distorted TBP (Figs. 5, 6)
with ΔSi of 0.0637(12) and –0.0094(6) Å respectively. The O1 and O1W atoms occupy axial
positions, the O1-Si1-O1W angles are 174.35(14) and 173.24(6)° in 6b and 8b, respectively. The
chelate ring in 6b adopts an envelope conformation while in 8b it is almost planar. It should be
noted that the average ΔSi values in 6b and 8b are close to zero and the axial angles O1-Si1-O1W
are more close to 180° than the axial angle O1-Si1-F1 in fluoride 4a. The published data
[3][22][23][24] provide the ranges for the axial Si1–O1 and Si1–O1W bond lengths: 1.878–1.960
and 1.907–2.009 Å respectively; the values for 6b and 8b (Table 2) slightly expand the above
ranges. Thus the structures 6b and 8b correspond to the steps within the middle stage of an SN2
process. The chlorine and bromine atoms in 6b and 8b reside in the outer sphere with respect to Si
atoms and do not form interatomic contacts with it (the shortest Si…Cl and Si…Br distances are
4.058 and 4.320 Å respectively). In 6b, the cations and Cl– are assembled into chains via O–H…Cl
bonds, and in 8b, the cations and Br– form centrosymmetric dimers.

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Fig. 4. Molecular structure of 4a presented with thermal ellipsoids at 50% probability. Hydrogen
atoms (except H2N) are omitted for clarity.
Fig. 5. Molecular structure of 6b presented with thermal ellipsoids at 50% probability. Hydrogen
atoms (except H1W and H2W) are omitted for clarity.
Fig. 6. Molecular structure of 8b presented with thermal ellipsoids at 50% probability. Hydrogen
atoms (except H1WA and H1WB) are omitted for clarity.

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Thus, a new type of silacyclanes, 1-organosulfonyl-2-sila-5-piperazinones, were prepared
from N-methylamides of N'-organosulfonyl-2-amino acids and used in a variety of synthetic
applications, including the synthesis of disiloxanes, fluorosilanes and silyloxonium halides
containing fragments of 2-amino acids as C,O-chelate ligands. These synthetic applications
illustrate the versatility and high reactivity of the silacyclanes due to the presence of labile Si–N
bonds in their molecules. The structures of most compounds in solutions and in the solid state were
confirmed by multinuclear NMR spectra and X-ray diffraction study.
4. Experimental
IR spectra of compounds in KBr pressings were recorded on Specord M80 instrument. IR
spectra of neat solid samples were recorded on Bruker Tensor-27 instrument using attenuated
internal reflection module.
Multinuclear NMR spectra of compounds in CDCl3 and CD3CN were recorded on Bruker
13
19
29
AC-200 (1H, 200 MHz), Bruker Avance II 300 (1H, 300 MHz; C, 75 MHz; F, 282 MHz; Si,
59.63 MHz) and Bruker Avance II 600 (1H, 600 MHz; 13C, 151 MHz; 29Si 119.2 MHz) instruments
2
using a pulse sequence with Fourier transformation and H-stabilization of the resonance
conditions. Tetramethylsilane and CFCl3 were used as internal and external references, respectively.
In some cases, 29Si NMR spectra were recorded using 2D NMR techniques (pulse sequence 1H–29Si
HSQC) [25].
Optical rotations of compounds were measured in 10 cm cuvettes using a Perkin Elmer 341
instrument.
The starting materials and solvents were obtained from commercial sources (Acros and
Sigma-Aldrich).
N-Nosylglycine [26], N-Nosyl-(S)-alanine [27], N-methylamides of N'-mesylglycine (1a) [28]
and N'-tosylglycine (1b) [29], and 3-tosyl-4-methyl-5-oxazolidinone [30] were prepared by
common synthetic methods.
Synthetic details and spectroscopic data for N-methylamides 1 are given in the supplementary
materials.
Single crystals suitable for X-ray diffraction analysis were obtained by recrystallisation from:
1b (triclinic), (S)-2d, 3d and 6b – benzene; 1b' (monoclinic) and 2e – toluene; 3c – ethanol; 4a –
heptane/benzene mixture; 8b – acetonitrile; 2a – directly from the reaction mixture.
X-ray diffraction measurements were carried out using SMART 1000 CCD and Smart APEX
II diffractometers. The frames were integrated and corrected for absorption by the APEX 2 program
package [31]. The details of crystallographic data and experimental conditions are given in Tables 3
and 4 as supplementary materials. The structures were solved by direct method and refined by full-

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matrix least-squares technique against F2 in the anisotropic-isotropic approximation. Hydrogen
atoms were located from the difference Fourier maps and refined in a rigid body model. All
calculations were performed using the APEX 2 program package [31]. Crystallographic data for the
structural analysis of 1b, 1b', 2a, (S)-2d, 2e, 3c, 3d, 4a, 6b and 8b have been deposited with the
Cambridge Crystallographic Data Centre, CCDC Nos. 826708–826710, 826713–826717, 911025,
911027.
4.1. Preparation of N-methylamides of 2-amino acids
The syntheses of N-methylamides of 2-amino acids are described in the Supplementary
materials.
4.2. Preparation of 2-sila-5-piperazinones
4.2.1. 2,2,4-Trimethyl-1-mesyl-2-sila-5-piperazinone (2a)
A mixture of methylamide 1a (13.1 g, 80 mmol) [28], hexamethyldisilazane (11.4 g,
70 mmol), chloro(chloromethyl)dimethylsilane (11.3 g, 80 mmol) and benzene (100 mL) was
refluxed for 3 h, allowed to cool down, the precipitate formed filtered out, the volatiles removed
in vacuo, and the residue distilled to afford 9.9 g (53%) of piperazinone 2a, b. p. 205–
206 °C/3 mm Hg, m. p. 81–85 °C.
Found, %: C 35.26, H 6.54, N 11.64. C7H16N2O3SSi. Calculated, %: C 35.57, H 6.82, N
11.85.
IR spectrum (KBr, ν, cm–1): 1632 s (NCO), 1316 s and 1152 s (SO2).
1H NMR (CDCl3, δ, ppm): 0.30 (s, 6H, SiMe2), 2.69 (s, 2H, CH2Si), 2.81 (s, 3H, CH3S), 2.87
(s, 3H, NCH3), 3.74 (s, 2H, NCH2).
13C NMR (CDCl3, δ, ppm): –2.0 (SiMe2), 37.29 (NCH3), 39.91 (CH2Si), 40.25 (CH3S), 48.94
(NCH2), 168.35 (C=O).
29Si NMR (CDCl3, δ, ppm): 4.0.
4.2.2. 2,2,4-Trimethyl-1-tosyl-2-sila-5-piperazinone (2b)
A mixture of methylamide 1b (2.3 g, 10 mmol) [29], hexamethyldisilazane (1.4 g, 9 mmol),
chloro(chloromethyl)dimethylsilane (1.4 g, 10 mmol) and benzene (20 mL) was refluxed for 3 h,
allowed to cool down, the precipitate formed filtered out, the volatiles removed in vacuo, and the
residue dried in vacuo for 2 h at 100 °C/20 mm Hg to afford 2.8 g (90%) of crude piperazinone 2b
as a yellow oil.
Found, %: C 49.23, H 6.61, N 9.91. C13H20N2O3SSi. Calculated, %: C 49.97, H 6.45, N 8.96.

ACCEPTED MANUSCRIPT
IR spectrum (KBr, ν, cm–1): 1648 s (NCO), 1596 w, 1496 m (Ar), 1336 s and 1164 s (SO2).
4.2.3. 2,2,4,6-Tetramethyl-1-nosyl-2-sila-5-piperazinone ((S)-2d)
25
A mixture of methylamide (S)-1d (5.9 g, 20 mmol), [α]D +16.2° (c 2.00, CH3CN),
hexamethyldisilazane (3.2 g, 20 mmol), chloro(chloromethyl)dimethylsilane (2.9 g, 20 mmol) and
toluene (80 mL) was refluxed for 3 h, allowed to cool down, the precipitate formed filtered out, and
the volatiles removed in vacuo. The remaining solid was washed with dry ether and re-crystallised
25
from benzene to afford 4.5 g (65%) of piperazinone (S)-2d, m. p. 128–130 °C (benzene), [α]D
+4.4° (c 5.62, CH3CN).
Found, %: C 49.25, H 5.39, N 10.60. Calculated for C13H19N3O5SSi × 0.5C6H6, %: C 48.47,
H 5.59, N 10.60.
IR spectrum (KBr, ν, cm–1): 1648 s (NCO), 1526 s (Ar, NO2), 1333 s (NO2, SO2), 1161 s
(SO2).
1H NMR (CD3CN, δ, ppm): 0.51 (s, 3H, SiMe), 0.55 (s, 3H, SiMe), 1.34 (d, 3H, CHCH3, 3JHH
3
3
7 Hz), 2.77 and 3.09 (two d, 2H, SiCH2, JHH 16 Hz, JHH 16.5 Hz), 2.89 (s, 3H, NCH3), 3.98 (br,
1H, NCH), 8.06 (d, 2H, Ar, 3JHH 9 Hz), 8.32 (d, 2H, Ar, 3JHH 8 Hz).
13C NMR (CD3CN, δ, ppm): 1.24 (SiMe2), 19.95 (CH3CH), 37.82 (NCH3), 41.75 (NCH2),
49.75 (CHCH3), 125.19 (C(2), C(6) Ar), 129.22 (C(3), C(5) Ar), 147.17 (C(1), Ar), 151.06 (C(4),
Ar), 170.40 (C=O).
29Si NMR (CD3CN, δ, ppm): 4.8.
4.2.4. 2,2,4-Trimethyl-6-isobutyl-1-nosyl-2-sila-5-piperazinone (2e)
Piperazinone 2e was prepared in the same manner as (S)-2d from methylamide 1e (6.6 g, 20
mmol), hexamethyldisilazane (3.2 g, 20 mmol), chloro(chloromethyl)dimethylsilane (2.9 g, 20
mmol) and toluene (80 mL). Yield 5.4 g (68%), m. p. 130–135 °C (benzene).
Found, %: C 47.52, H 6.31, N 10.15. C16H25N3O5SSi. Calculated, %: C 48.10, H 6.31, N
10.51.
IR spectrum (solid, ν, cm–1): 1647 s (NCO), 1525 s (Ar, NO2), 1347 s (NO2, SO2), 1157 s
(SO2).
1H NMR (CD3CN, δ, ppm): 0.57 (s, 3H, SiMe), 0.62 (s, 3H, SiMe), 0.95 (d, 6H, CH(CH3)2,
3JHH 7 Hz), 1.54 (br, 1H, CHMe2), 1.86 (br, 2H, CH2CH), 2.82 and 3.23 (two d, 2H, SiCH2, 3JHH 16
3
3
Hz, JHH 16.5 Hz), 2.98 (s, 3H, NCH3), 4.04 (br, 1H, NCH), 8.12 (d, 2H, Ar, JHH 9 Hz), 8.42 (d,
2H, Ar, 3JHH 8 Hz).
13C NMR (CD3CN, δ, ppm): 0.45 (SiMe2), 20.97, 22.44 (Me2CH), 24.91 (CHMe2), 37.35
(NCH3), 37.8 (NCH2), 42.06 (CH2CH), 60.65 (NCH), 124.75 (C(2), C(6) Ar), 128.61 (C(3), C(5)
Ar), 146.12 (C(1) Ar), 150.45 (C(4), Ar), 168.67 (C=O).

ACCEPTED MANUSCRIPT
29Si NMR (CD3CN, δ, ppm): 7.0.
4.3. Preparation of disiloxanes
4.3.1. 1,1,3,3-Tetramethyl-1,3-bis(2-mesylamido-N-methylacetamidomethyl)-1,3-disiloxane (3a)
A solution of 2-sila-5-piperazinone 2a (1 g, 4.2 mmol) and water (2 mL, 0.11 mol) in ethanol
(20 mL) was stirred at ambient temperature for 24 h. The crystals formed were isolated by filtration
and dried in the open air to afford 0.47 g (46%) of disiloxane 3a, m. p. 139–141 °C (ethanol).
Found, %: C 33.44, H 7.09, N 11.02. C14H34N4O7S2Si2. Calculated, %: C 33.72, H 6.87, N
11.27.
IR spectrum (KBr, ν, cm–1): 2904 w (NH), 1632 s (NCO), 1316 s and 1152 s (SO2).
1H NMR (CDCl3, δ, ppm): 0.11 (s, 12H, 2SiMe2), 2.74 and 2.90 (two d, 4H, 2SiCH2, 3JHH 15
Hz), 2.91 (s, 6H, 2CH3S), 2.93 (s, 6H, 2NCH3), 3.91 (s, 4H, 2CH2CO), 5.51 (br, 2H, 2NH).
13C NMR (CDCl3, δ, ppm): 0.63 (SiMe2), 26.42 (CH3S), 39.41 (NCH3), 40.34 (NHCH2),
41.61 (SiCH2), 150.09 (C=O).
29Si NMR (CDCl3, δ, ppm): 4.0.
4.3.2. 1,1,3,3-Tetramethyl-1,3-bis(2-tosylamido-N-methylacetamidomethyl)-1,3-disiloxane (3b)
A mixture of methylamide 1b (4.8 g, 20 mmol), hexamethyldisilazane (2.2 g, 13 mmol),
chloro(chloromethyl)dimethylsilane (2.9 g, 20 mmol) and benzene (40 mL) was refluxed for 3 h,
allowed to cool down, the precipitate formed was filtered out, and the volatiles were removed
in vacuo. The remaining oil was treated with a mixture of ethanol (30 mL) and water (0.5 mL). The
crystals formed were re-dissolved in 50 mL of a mixture of ethyl acetate and acetonitrile (3 : 1) and
filtered through silica. The volatiles were removed in vacuo, the residue was washed with ethanol
and dried in the open air to afford 4.6 g (72%) of disiloxane 3b, m. p. 162–164 °C (ethanol).
Found, %: C 48.61, H 6.57, N 8.59. C26H42N4O7S2Si2. Calculated, %: C 48.57, H 6.58, N
8.71.
IR spectrum (KBr, ν, cm–1): 3192 (NH), 1640 s (NCO), 1595 m and 1495 m (Ar), 1336 s and
1164 s (SO2).
1H NMR (CDCl3, δ, ppm): 0.08 (s, 12H, 2SiMe2), 2.55 (s, 6H, 2CH3Ar), 2.66 and 2.81 (two
d, 4H, 2SiCH2, 3JHH 15 Hz), 2.85 (s, 6H, 2NCH3), 3.65 (s, 4H, 2CH2CO), 5.65 (br, 2H, 2NH), 7.23
(d, 4H, Ar, 3JHH 8 Hz), 7.69 (d, 4H, Ar, 3JHH 8 Hz).
13C NMR (CDCl3, δ, ppm): 0.43 (SiMe2), 21.47 (CH3Ar), 36.36 (CH2Si), 41.58 (NCH3),
43.44 (NHCH2), 124.92, 127.14, 143.50, 145.28 (Ar), 150.19 (C=O).
29Si NMR (CDCl3, δ, ppm): 4.0.
4.3.3. 1,1,3,3-Tetramethyl-1,3-bis(2-nosylamido-N-methylacetamidomethyl)-1,3-disiloxane (3c)

ACCEPTED MANUSCRIPT
A mixture of methylamide 1c (2.7 g, 10 mmol), hexamethyldisilazane (1.6 g, 10 mmol),
chloro(chloromethyl)dimethylsilane (1.4 g, 10 mmol) and toluene (40 mL) was refluxed for 3 h,
allowed to cool down, the precipitate formed filtered out, and the volatiles removed in vacuo. The
residue was washed with a mixture of ethanol (30 mL) and water (0.5 mL), the crystalline material
isolated by filtration and dried in the open air to afford 1.8 g (52%) of disiloxane 3c, m. p. 150–
151 °C (ethanol).
Found, %: C 40.75, H 5.07, N 11.87. C24H36N6O11S2Si2. Calculated, %: C 40.89, H 5.15, N
11.92.
IR spectrum (solid, ν, cm–1): 3202 br (NH), 1647 s (NCO), 1526 s (Ar, NO2), 1348 s (NO2,
SO2), 1168 s (SO2).
1H NMR (CDCl3, δ, ppm): –0.08 (s, 12H, 2SiMe2), 2.62 and 2.77 (two d, 4H, 2SiCH2, 3JHH 15
3
Hz), 2.87 (s, 6H, 2NCH3), 3.79 (s, 4H, 2CH2CO), 6.28 (br, 2H, 2NH), 8.08 (d, 4H, Ar, JHH 8 Hz),
8.29 (d, 4H, Ar, 3JHH 8 Hz).
13C NMR (CD3CN, δ, ppm): –0.16 and –0.02 (SiMe2), 40.25 (SiCH2), 40.74 (NHCH2), 43.65
(NCH3), 124.22 (C(2), C(6) Ar), 128.43 (C(3), C(5) Ar), 145.47 (C(1) Ar), 150.09 (C(4) Ar),
165.28 (C=O).
29Si NMR (CDCl3, δ, ppm): 3.9.
4.3.4. (S,S)-1,1,3,3-Tetramethyl-1,3-bis(2-nosylamido-N-methylpropanamidomethyl)-1,3-disiloxane
((S,S)-3d)
A solution of piperazinone (S)-2d (1.8 g, 5 mmol) and water (5 mL) in 25 mL of ethanol was
stirred for 24 h. The crystals formed were isolated by filtration and dried in the open air to afford
1.0 g (54%) of disiloxane (S,S)-3d, m. p. 146–147 °C (ethanol), [α]D25 +5.6° (c 3.36, CH3CN).
Found, %: C 42.18, H 5.55, N 11.27. C26H40N6O11S2Si2. Calculated, %: C 42.60, H 5.50, N
11.46.
IR spectrum (solid, ν, cm–1): 3111 br (NH), 1625 s (NCO), 1527 s (Ar, NO2), 1348 s (NO2,
SO2), 1166 s (SO2).
1H NMR (CDCl3, δ, ppm): –0.08 (s, 6H, 2SiMe), 0.16 (s, 6H, 2SiMe), 1.17 (d, 6H, 2CH3CH,
3
3JHH 6.9 Hz), 2.43 and 2.71 (two d, 4H, 2SiCH2, JHH 6.9 Hz), 2.88 (s, 6H, 2NCH3), 3.65 (m, 2H,
CHCO), 6.45 (br, 2H, 2NH), 8.02 (d, 4H, Ar, 3JHH 8.8 Hz), 8.3 (d, 4H, Ar, 3JHH 8.8 Hz).
13C NMR (CDCl3, δ, ppm): 0.38 and 0.41 (SiMe2), 19.77 (CH3CH), 37.34 (NCH3), 48.61
(SiCH2), 49.09 (CHCH3), 124.19 (C(2), C(6) Ar), 128.17 (C(3), C(5) Ar), 146.19 (C(1), Ar),
149.95(C(4), Ar), 169.53 (C=O).
29Si NMR (CDCl3, δ, ppm): 3.8.

ACCEPTED MANUSCRIPT
4.3.5. 1,1,3,3-Tetramethyl-1,3-bis(2-nosylamido-4-methyl-N-methylpentanamidomethyl)-1,3-
disiloxane (3e)
A solution of piperazinone 2e (1.3 g, 3.3 mmol) and water (0.5 mL) in 30 mL of ethanol was
stirred for 24 h. The crystals formed were isolated by filtration and dried in the open air to afford
0.65 g (49%) of disiloxane 3e, m. p. 153–154 °C (ethanol).
Found, %: C 47.03, H 6.37, N 10.14. C38H56N4O10S2Si2. Calculated, %: C 47.04, H 6.41, N
10.29.
IR spectrum (solid, ν, cm–1): 3177 s (NH), 1630 s (NCO), 1529 s (Ar, NO2), 1348 s (NO2,
SO2), 1163 s (SO2).
1H NMR (CDCl3, δ, ppm): –0.25 and 0.08 (two s, 12H, 2SiMe2), 0.93 and 0.96 (two d, 12H,
3
2(CH3)2CH, JHH 6.9 Hz), 1.48 (br, 2H, 2CHMe2), 1.89 (br, 4H, 2CH2CH), 2.69 (d, 4H, 2SiCH2,
3JHH 16 Hz), 2.92 (s, 6H, 2NCH3), 4.26 (br, 2H, 2CHNH), 6.12 (br, 2H, NHCH), 8.18 (d, 4H, Ar,
3JHH 9 Hz), 8.32 (d, 4H, Ar, 3JHH 9 Hz).
13C NMR (CDCl3, δ, ppm): 0.29 (SiMe2), 23.18 (Me2CH), 24.09 (CHMe2), 37.12 (NCH3),
41.48 (CH2CH), 42.24 (SiCH2), 51.56 (CHNH), 124.00 (C(2), C(6) Ar), 128.31 (C(3), C(5) Ar),
146.08 (C(1), Ar), 149.90 (C(4), Ar), 169.65 (C=O).
29Si NMR (CDCl3, δ, ppm): 3.8.
4.4. Preparation of (O→Si)-chelates: fluorosilane 4a, silyloxonium chloride 6b and silyloxonium
bromide 8b
4.4.1. N-(dimethylfluorosilylmethyl)-N-methyl-2-(mesylamido)acetamide (4a)
A solution of disiloxane 3a (0.95 g, 1.96 mmol) in acetonitrile (8 mL) was heated up to 60 °C,
and BF3–Et2O complex (0.10 g, 0.72 mmol) was added. The reaction mixture was refluxed for 1 h,
cooled down, the volatiles removed in vacuo, and the remaining mixture extracted with 15 mL of
boiling benzene. The extract was filtered, the volatiles removed in vacuo, and the remaining oil
washed with heptane to afford 0.77 g (75%) of fluoride 4a, m. p. 109–111 °C (benzene–heptane,
3 : 2).
Found, %: C 32.67, H 6.77, N 10.77. C7H17F1N2O3S1Si1. Calculated, %: C 32.79, H 6.68, N
10.92.
IR spectrum (KBr, ν, cm–1): 2960 br (NH), 1640 s (NCO), 1494 br (NCO), 1330 s and 1160 m
(SO2).
1H NMR (CDCl3, δ, ppm): 0.25 (d, 6H, SiMe2, 3JHF 5.4 Hz), 2.55 (s, 2H, CH2Si), 2.93 (s, 3H,
NCH3), 2.97 (s, 3H, CH3S), 3.95 (s, 2H, CH2CO), 5.15 (br, 1H, NH).
13C NMR (CDCl3, δ, ppm): 6.94 (SiMe2), 36.42 (SiCH2), 39.44 (NCH3), 40.7 (CH3S), 42.99
(CH2NH), 168.09 (C=O).

ACCEPTED MANUSCRIPT
19F NMR (CDCl3, δ, ppm): –136.4.
29Si NMR (CDCl3, δ, ppm): 2.3 (d, 1JSiF 256 Hz).
4.4.2. {2-[N-(2-oxopyrrolidinylmethyl)tosylamido]-(N'-methylacetamido)methyl}dimethylsilyl-
oxonium chloride (6b)
A solution of 1b (2.4 g, 10 mmol), hexamethyldisilazane (1.6 g, 10 mmol) and
chloro(chloromethyl)dimethylsilane (1.4 g, 10 mmol) in toluene (40 mL) was refluxed for 5 hrs,
cooled down, filtered and evaporated in vacuo to afford 2.5 g (8 mmol) of 2-sila-5-piperazinone 2b.
The intermediate 2b was dissolved in benzene (15 mL) and a solution of 1-chloromethyl-2-
pyrrolidone (1.1 g, 8.5 mmol) in benzene (5 mL) was added dropwise. The mixture was stirred 5
days at room temperature. The crystals formed were filtered, washed with 2 mL of benzene and
dried over phosphorus(V) oxide to afford 2.8 g (75%) of silyloxonium chloride 6b, m. p. 102–
104 °C (CH3CN).
Found, %: C 46.58, H 6.39, N 9.26. C18H30Cl1N3O5S1Si1. Calculated, %: C 46.58, H 6.51, N
9.05.
IR spectrum (KBr, ν, cm–1): 1690 s (NCO lactam), 1615 m and 1490 w (NCO→Si), 1340 s
and 1160 s (SO2).
1H NMR (CDCl3, δ, ppm): 0.44 (s, 6H, SiMe2). 2.02–2.13 (m. 2H, C4H2 lactam), 2.40 (t, 2H,
C3H2 lactam, J3 8.08 Hz), 2.45 (s, 3H, CH3), 2.78 (s, 2H, SiCH2), 3.06 (s, 3H, MeN), 3.56–3.64 (m,
2H, C5H2 lactam), 4.25 (s, 2H, NCH2 lactam), 4.77 (s, 2H, NCH2CO), 7.33 and 7.71 (two d, 4H, J3
8.08 Hz, Ar).
13C NMR (CDCl3, δ, ppm): 6.17 (SiMe2), 17.88 (C4 lactam), 21.52 (CH3Ar), 30.67 (C3
lactam), 127.17 (C2 and C6 Ar), 129.83 (C3 and C5 Ar), 136.62 (C1 Ar), 144.26 (C4 Ar), 170.56
(C=O amide), 177.2 (C=O lactam).
29Si NMR (CDCl3, δ, ppm): –30.0.
4.4.3. [2-(N-tosylacetamido)-(N'-methylacetamido)methyl]dimethylsilyloxonium bromide (8b)
A solution of 1b (2.4 g, 10 mmol), hexamethyldisilazane (1.6 g, 10 mmol) and
chloro(chloromethyl)dimethylsilane (1.4 g, 10 mmol) in toluene (40 mL) was refluxed for 5 hrs,
cooled down, filtered and evaporated in vacuo to afford 2.5 g (8 mmol) of 2-sila-5-piperazinone 2b.
The intermediate 2b was dissolved in benzene (15 mL) and a solution of acetyl bromide (4.9 g, 40
mmol) in benzene (5 mL) was added dropwise. The mixture was allowed to stand for 5 days at
room temperature. The crystals formed were filtered and re-crystallised from absolute CH3CN
(4 mL) to afford 1.3 g (37%) of silyloxonium bromide 8b, m. p. 118–120 °C (CH3CN).
Found, %: 39.99, H 5.78, N 5.93. C15H25N2O5Br1S1Si1. Calculated, %: C 39.73, H 5.56, N
6.18.

ACCEPTED MANUSCRIPT
IR spectrum (KBr, ν, cm–1): 1700 s (O=CNSO2), 1644 s and 1491 s (NCO→Si), 1598 w (Ar),
1370 s and 1168 s (SO2).
1H NMR (DMSO-d6, δ, ppm): 0.13 (s, 6H, SiMe2), 2.04 (s, 3H, MeCO), 2.39 (s, 3H, Me),
2.79 (s, 2H, SiCH2), 3.11 (s, 3H, MeN), 4.67 (s, 2H, NCH2CO), 5.98 (br, 2H, H2O), 7.36 and 7.86
(two d, 4H, Ar, J 8 Hz).

ACCEPTED MANUSCRIPT
Acknowledgments
This work was financially supported by the Russian Foundation for Basic Research (Project
Nos. 09-03-00669, 10-03-00824, 11-03-00655 and 13-03-01084) in the framework of activity of the
Scientific and Educational Center of RSMU.
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