Synthesis and structure of chiral silatranes derived from terpenes

Synthesis and Structure of Chiral Silatranes Derived from Terpenes

Gabriele Wagner3, Rudolf Herrmann3, Bj0 m Pedersenb, and Wolfgang Schererb

a Instituto de Tecnologia Quimica e Biolögica (ITQB),

Av. da Repüblica (EAN), Apt. 127, P-2781 901 Oeiras (Portugal)

b Anorganisch-chemisches Institut der Technischen Universität München,

Lichtenbergstr. 4, D-85747 Garching (Germany).

Reprint requests to Dr. G. Wagner. Fax: 00351-214411277. E-mail: gabriele@itqb.unl.pt

Dedicated to Prof. Paul J. Scheuer

Z. Naturforsch. 56 b, 25-38 (2001); received August 8, 2000

Silatranes, Terpenes, Chiral Pool

Starting with the chiral pool compounds (—)-menthone, (—)-limonene, (—)-/3-pinene, and

(—)-carvone, new homochiral triethanolamine derivatives were obtained and converted to chi-

ral silatranes. These silatranes were characterized by crystal structure analyses and NMR

techniques. Conformational analyses in the solid state and in solution show that the chiral

terpene residues determine the direction of the ring puckering of the silatrane moiety.

N-alkylation of aminoethanol derivatives with suit-

Introduction

able alkylating reagents containing a hydroxy group

(e.g., by double alkylation of /3-hydroxy-amino

acids with chloroethanol [2]). The most convenient

way to obtain chiral triethanolamines is the ring-

opening of oxiranes by amines. The chirality may

be introduced either by employing chiral oxiranes

or chiral amines, or by making both oxirane and

amine chiral [3,5]. We chose to open chiral oxiranes

by achiral diethanolamine. By this strategy, chiral-

ity is introduced only in one hydroxyethyl arm of

the triethanolamine, which leads to relatively simple

NMR spectra which still can be readily interpreted.

Terpenes with C=C and/or C =0 double bonds are

easily accessible in enantiomerically pure form and

can therefore be considered as ideal starting ma-

terials for such syntheses. We selected menthone,

limonene, carvone and the pinenes as entries, since

these are inexpensive commercial products. Fig. 1

shows the reactions performed and Fig. 2 the num-

bering of the carbon atoms in the silatranes. The

carbon atoms in the triethanolamine intermediates

2 are numbered accordingly. In the case of a- and

/3-pinene and limonene, the corresponding oxiranes

are also commercially available, but in any way, the

conversion of the starting materials into oxiranes is a

simple one step reaction. Stereochemically uniform

oxiranes are obtained by the peracid oxidation of

the pinenes [6 ], and the conversion of /3-pinene ox-

Silatranes (CAS name: 5-aza-2,8,9-trioxa-l-

silabicyclo[3.3.3]undecane) contain a hypervalent

silicon atom with a transannular (comparatively

weak) bond to nitrogen (bond length 2.0-2.4 A)

which is responsible for their chemical stability, e. g.

towards hydrolysis [1]. Only very few chiral (non-

racemic) silatranes (derived from amino acids as

source of chirality) have been reported before [2 ,3].

This is surprising since they may be of interest as

chiral materials; some silatranes have recently been

shown to possess non-linear optical properties [4].

Here we present our results on the synthe-

sis and structural investigation of some chiral

silatranes derived from the chiral pool com-

pounds (—)-menthone ( (2S,5i?)-5-methyl-2-(l-me-

thylethyl)cyclohexanone), (—)-limonene ((S')-l-

methyl-4-(l-methylethenyl)cyclohexene), (-)-/?-

pinene ( (15',55')-6,6-dimethyl-2-methylenbicyclo-

[3.1.1]heptane), and (—)-carvone ((/?)-methyl-5-

(1 -methylethenyl)-2 -cyclohexen- 1 -one ).

Results and Discussion

Syntheses

Silatranes are obtained by the reaction of tri-

ethanolamines with derivatives of silicic acids (such

as trialkoxysilanes or trichlorosilanes). Generally,

C-substituted triethanolamines can be prepared by

fiir Naturforschung, Tübingen • www.znaturforsch.com

K

Brought to you by | New York University Bobst Library Technical Services

Authenticated

Download Date | 8/6/15 3:14 PM

26

G. Wagner et al. • Chiral Silatranes Derived from Terpenes

a) : diethanolam ine,

120°C, 2d

conditions

R

starting

from

2a 2b 2c

2d 2e 2f

PhSi(0Et)3

MeSi(0Ac)3

Ph

Me

3a 3b 3c

3d 3e 3f

Fig. 1. Synthesis of the chiral sila-

tranes derived from terpenes.

4a

4b 4c

ide into the silatrane via the chiral triethanolamine not react at all and is recovered unchanged even af-

derivative is straightforward; the ring opening of ter two weeks at 160 °C. This is probably due to the

the oxirane by diethanolamine is a standard SN2 higher thermodynamic stability of the endocyclic

reaction. The ring-opening occurs by simple mix- a-pinene oxide. Similarily, commercial caryophyl-

ing of the oxiranes with diethanolamine and heating lene oxide does not react with diethanolamine even

at 200 °C. When limonene is oxidized by peracids,

a cö. 1 : 1 mixture of the cis- and trans-isomers of

to 120 °C for some days. The reactivity of the oxi-

ranes varies considerably; a striking example are the

pinenes where /3-pinene oxide leads to the expected limonene oxide is obtained (the descriptors cis and

chiral triethanolamine while a-pinene oxide does trans apply to the relative configurations of the car-

Brought to you by | New York University Bobst Library Technical Services

Authenticated

Download Date | 8/6/15 3:14 PM

27

G. Wagner et al. • Chiral Silatranes Derived from Terpenes

Fig. 2. Numbering of the com-

pounds 3 (compounds 4 analo-

gously).

bon substituents in positions 1and 4 at the cyclohex-

solution at —78 °C the strong nucleophile LiPPh2

ane ring). The separation of the isomers is possible, reacts selectively with rra«s-limonene oxide and

leads to a product of the same configuration as

but difficult due to very similar boiling points. We

therefore applied the mixture of (—)-limonene oxide with diethanolamine [8 ]. For the weaker nucle-

as supplied (ca. 1:1). Surprisingly, we obtained only ophilic amines higher temperatures are required,

a single silatrane (compound 3a) after ring open- but in contrast to the reaction with dimethylamine

ing by diethanolamine and subsequent reaction with [7] the selectivity towards preferential ring opening

of frans-limonene oxide is retained in the case of

diethanolamine. Interestingly, the same authors [8 ]

phenyltriethoxysilane. From the crystal structure of

this silatrane, we know that its precursor, the limon-

ene-derived triethanolamine, must be (li?,2i?,4S')-l- also reacted LiPPhb with a- and /3-pinene oxide and

hydroxy-2-[7V,Af-bis(2-hydroxyethyl)amino]-1-me- found, in complete analogy to our results, that ß-

thyl-4-(l-methylethenyl)cyclohexane which in turn pinene oxide undergoes the ring opening smoothly

is derived from the rrans-limonene oxide (\R,2S, while a-pinene oxide does not react at all.

45)-1 -methyl-4-( 1-methylethenyl)-7-oxabicyclo-

Another access to oxiranes consists in the

[4.1.0]heptane by a normal S^/2 type ring open- methylenation of C =0 bonds by sulfur ylides [9].

ing. This regio- and stereoselective reaction is in While the use of dimethyl sulfoxonium methylide is

complete accord with the results found for the ring a convenient and robust method, the same is not true

opening of fra/is-limonene oxide with dimethyl- for the less stable dimethyl sulfonium methylide.

amine [7], There are only very few reports on dif- Therefore, we used the sulfoxonium ylide pref-

erentially. Commercial (—)-menthone contains ca.

ferences in the reactivity of cis- and rrans-limon-

ene oxide in nucleophilic ring opening. In THF

15% of so-called isomenthone ( (2/?,5/?)-5-methyl-

Brought to you by | New York University Bobst Library Technical Services

Authenticated

Download Date | 8/6/15 3:14 PM

G. Wagner et al. • Chiral Silatranes Derived from Terpenes

28

ethyl)aminomethyl]-2-hydroxy-1-methyl-4-( 1-me-

thylethenyl)-bicyclo[4.1.0]heptane. Since the nu-

cleophilic attack of the diethanolamine occurs at

the carbon atom of the oxirane with less steri-

cal hindrance, the configuration of the other car-

2 -(l-methylethyl)cyclohexanone) in an equilib-

rium mixture. The equilibration of both isomers can

be catalyzed by acids and occurs via the enol, even

without adding acid, simply on standing for some

time. When this mixture is treated with dimethyl

sulfoxonium ylide, a single oxirane is formed which bon atom does not change. Hence the major prod-

uct of the double methylenation of (/?)-carvone

must be (2/?,4/?,5/?,7/?)-l-methyl-4-(l-methylethe-

nyl)-bicyclo[4.1,0]heptane-2-spiro-2’-oxirane, and

the minor product its (2S,4R,5RJR) isomer. Thus,

the ylide attacks the carbonyl group preferentially

from the side where already the cyclopropane ring

resides; it does not follow the general pattern in

cyclohexane derivatives that the methylene group

of the oxirane ring is introduced by the sulfoxo-

nium ylide such that it remains equatorial in the

product. In contrast, the oxygen atom is the equa-

torial substituent in the major product. We attribute

is derived from menthone and not from the corre-

sponding isomenthone. The silatrane obtained from

this oxirane (compound 3c) shows the configuration

(IS,25,5/?) in the cyclohexane ring, and the same

must be true for the oxirane. Thus, the ylide attacks

the carbonyl group such that the methylene group

of the oxirane ring is placed in the equatorial and

the oxygen atom in the axial position at the spiro

carbon atom of the cyclohexane ring. This is in ac-

cord with the preferences claimed for reactions of

the sulfoxonium ylide with cyclic ketones [9, 10].

The carvone-derived oxirane 4-methyl-7-(l-me-

thylethenyl)-l-oxaspiro[2.5]-oct-4-ene (Id) could this behaviour to the distortion of the cyclohexane

be obtained in poor yield by the reaction of carvone ring by annulation of the cyclopropane. As a conse-

with dimethyl sulfonium methylide. This product quence, the norcarane-type silatranes obtained with

has the expected configuration (2S,1R) and contains

ca. 10% of the (2R,7R) isomer [11]. Its ring open-

ing with diethanolamine and the silatrane formation

did not pose any problems, although no crystals suit-

dimethyl sulfoxonium ylide as reagent (major com-

ponent 3e) show a close analogy in stereochemistry

to the oxirane (and the silatrane 3d) obtained by the

reaction of carvone with dimethyl sulfonium ylide.

able for crystal structure analysis could be obtained. We were therefore able to calculate the structure of

Dimethyl sulfoxonium methylide reacts with a,ß-

unsaturated carbonyl compounds such as carvone

at the C=C double bond, leading to the introduction

of cyclopropane rings. When we used two equiv-

alents of ylide, the carbonyl group reacted as well

and the norcarane type oxiranes le,f (ratio ca. 2 :1 )

were formed in reasonable yields. There was no dif-

ference in the result of a one-step reaction with two

equivalents of ylide and a two-step reaction with iso-

lation of the norcarane-type ketone. The first step

in the reaction of (/?)-(—)-carvone with dimethyl

sulfoxonium methylide is the methylene addition to

the conjugated C=C double bond. The stereochem-

istry of the product (l/?,4/?,6/?)-l-methyl-4-(l-me-

thylethenyl)bicyclo[4.1.0]heptan-2-one was made

plausible by chemical correlation with chiral com-

pounds of known configuration [12]. However, the

reaction of this ketone with a second equivalent

of dimethyl sulfoxonium methylide has never been

reported. After conversion into the silatranes, the

major component gave crystals suitable for X-ray

structure analysis while the minor did not. From

the structure analysis, we can conclude that the

precursor is (ltf,2/?,4/?,6/?)-2-[/V,yV-bis(2-hydroxy-

the silatrane 3d (for which we do not have a crystal

structure) from that of the silatrane 3e by simply

replacing the methylene group of the cyclopropane

ring by a double bond and optimizing the structure

with PM3 (see below).

Characterization

All compounds were characterized by their NMR

and mass spectra, and by microanalysis. In addition,

crystal structures were obtained for 3a, 3c, 3e, and

4b. Salient bond lengths and angles are collected

in Table 1. PLATON drawings of the structures are

shown in Fig. 3. Since the terpene residues do not

contain polar groups, they influence the structure of

the silatrane moiety mainly by their different steric

requirements. As expected, it is the weak Si-N bond

whose length shows considerable variation, while

the influence on other structural features is less pro-

nounced. The Si-N bond is shortest in the norcarane-

type silatrane 3e (2.127(1) A) and longest in the

limonene-derived silatrane 3a (2.241(1) A). Bond

lengths in this range are often found in silatranes

not containing polar substituents, e. g. phenylsila-

trane (2.193(5) A in the a-modification [13]) and in

Brought to you by | New York University Bobst Library Technical Services

Authenticated

Download Date | 8/6/15 3:14 PM

29

G. Wagner et al. • Chiral Silatranes Derived from Terpenes

Table 2. Bond lengths (A) and angles (°) for compounds

3d, 3e, and 3f in their optimized geometries (PM3). The

Si-N distance was fixed to 2.128 A in all cases.

Table 1. Selected bond lengths (A) and angles (°) for

compounds 3a, 3c, 3e, and 4b, as obtained by X ray crys-

tallography.

3e

3f

3d

3a

3c

3e

4b

1.717

1.724

1.723

1.917

(77=17)

1.496

1.499

1.386

1.561

1.538

1.539

1.557

1.550

1.719

1.724

1.914

(77=17)

1.497

1.500

1.498

1.383

1.569

1.538

1.539

1.552

1.558

Si-Ol

S i-02

Si-03

Si-Cn

1.720

1.724

1.722

1.913

(n=16)

1.494

1.498

1.387

1.562

1.539

1.552

1.525

Si-N

2.241(1)

1.661(1)

1.649(1)

1.655(1)

1.890(1)

(n=15)

1.479(2)

1.475(2)

1.470(2)

1.426(2)

1.524(2)

1.500(2)

1.517(3)

1.530(2)

—

2.166(2)

1.645(1)

1.665(1)

1.662(1)

1.898(2)

(77= 16)

1.474(3)

1.482(3)

1.474(2)

1.424(2)

1.549(3)

1.503(4)

1.511(3)

1.548(3)

1.532(3)

2.127(1) 2.172(1)

1.660(1) 1.643(1)

Si-Ol

Si-02

Si-03

Si-Cn

1.664(1)

1.671(1)

1.898(2)

(n=17)

1.663(1)

1.666(1)

1.873(2)

(77= 15)

N-C2

N-C4

N-C6

N-C2

N-C4

N-C6

0 -C av

C1-C2

C3-C4

C5-C6

C1-C7

C l-C ll

1.471(2)

1.481(2)

1.477(2)

1.428(2)

1.559(2)

1.516(3)

1.510(3)

1.532(2)

1.539(2)

1.474(2)

1.475(3)

1.471(2)

1.418(3)

1.547(2)

1.497(3)

1.505(3)

1.530(2)

1.553(3)

O-Cav

C1-C2

C3-C4

C5-C6

C1-C7

C l-C ll

Si-N-C2

Si-N-C4

Si-N-C6

S i-0-C av

N-Si-Oav

O l-S i-0 2

O l-S i-0 3

0 2 -S i-0 3

01-C 1-C 2

01-C 1-C 7

N-Si-Cn

106.7

105.5

104.7

121.8

84.6

123.7

115.4

118.3

110.8

106.2

176.6

(77= 17)

107.6

105.2

104.1

121.5

84.3

125.1

114.0

117.9

110.8

106.5

175.8

(n= 17)

106.3

105.8

104.2

121.7

84.6

124.7

114.7

117.9

111.5

108.0

175.4

(77=16)

Si-N-C2

Si-N-C4

Si-N-C6

101.7(1)

103.5(1)

105.2(1)

122.9(1)

82.4(1)

117.6(1)

117.9(1)

119.3(1)

106.2(1)

109.7(1)

179.2(1)

(n=15)

106.6(1)

104.7(1)

104.5(1)

123.7(1)

83.4(1)

120.8(1)

118.6(1)

116.7(1)

108.1(1)

108.8(1)

178.3(1)

(n=16)

106.5(1) 106.0(1)

104.1(1)

105.3(1)

129.8(1)

83.7(1)

104.5(1)

124.6(1)

82.7(1)

S i-0-C av

N-Si-Oav

O l-S i-0 2

0 1 -S i-0 3

0 2 -S i-0 3

01-C 1-C 2

01-C 1-C 7

N -Si-Cn

118.0(1) 120.2(1)

119.7(1) 118.0(1)

118.8(1)

107.7(1)

106.0(1)

177.7(1)

(n=17)

117.0(1)

106.9(1)

106.0(1)

179.0(1)

(77=15)

formed calculations on the compounds 3d - f to get

some insight in their structures and conformations.

Geometry optimizations were done with the pro-

gram Gamess(US) [15] using the PM3 Hamiltonian.

Due to the well-known problems of semiempirical

methods in dealing with hypervalent compounds,

in particular with the Si-N distance [16, 17], we

decided to fix this value to 2.128 A and allowed

all other coordinates to relax. The starting geom-

etry for 3e was the crystal structure, while for 3d

the CH2 group of the cyclopropane ring was re-

moved. The input geometry for 3f was obtained

by preserving the geometry of the terpene residue

and exchanging the positions of the oxygen atom

and the CH2N group at C l. Important calculated

bond lengths and angles can be found in Table 2,

and graphical representations in Fig. 4. Comparing

the measured (Table 1) and the calculated (Table 2)

structure of the norcarane-type silatrane 3e, one can

see that PM3 leads to somewhat larger Si-0 dis-

tances (about 0.06 A), while the agreement of all

ferrocenylsilatrane (2.181(2) A [14]). The remain-

ing structural parameters in the silatrane moieties

are quite similar and are in agreement with those ob-

served in many other silatranes [1]; e. g. the O-Si-O

bond angles remain between 116andl21°,justasin

ferrocenylsilatrane. The coordination sphere of the

hypervalent silicon atom is approximately trigonal-

bipyramidal with the three oxygen atoms occupy-

ing equatorial positions. The silicon atom is shifted

slightly out of the plane formed by the three oxy-

gen atoms in the direction of the carbon substituent;

the deviation is highest for the limonene-derived

silatrane 3a (0.220(1) A) and lowest for the nor-

carane-type silatrane 3e (0.182(1) A). The nitrogen

and carbon atoms occupying the apical positions

complete the approximate trigonal-bipyramidal ge-

ometry with almost ideal N-Si-Csubst angles in the

small range of 177.7(1) and 179.2(1)°.

For some of the silatranes prepared, no crys-

tal structures could be obtained. We therefore per-

Brought to you by | New York University Bobst Library Technical Services

Authenticated

Download Date | 8/6/15 3:14 PM

30

G. Wagner et al. • Chiral Silatranes Derived from Terpenes

C17

C19

3e

Fig. 3. PLATON plots of the crystal structures of 3a, 3c, 3e, and 4b with 50% probability.

3d

3e

3f

Fig. 4. PLATON plot of the calculated (PM3) structures of the compounds 3d, 3e, and 3f.

other bond lengths is much better (maximum de- ues (maximum deviation from the crystal structure

viation ca. 0.03 A). The deviation of the calculated is for 01-Si-02, 5.7°). Similar properties can be

bond angles is always greatest in cases where the expected for the calculated structures of 3d and 3f

oxygen atoms are involved, while other angles are which show both Si-O distances of 1.718 -1.724 A

in close agreement with the crystal structure val- and bond angles very similar to those calculated for

Brought to you by | New York University Bobst Library Technical Services

Authenticated

Download Date | 8/6/15 3:14 PM

31

G. Wagner et al. • Chiral Silatranes Derived from Terpenes

Table 3. Pople and Cremer ring puckering parameters

for the silatrane moieties. Ring 1 is substituted, ring 2

is found clockwise from the substituted ring when look-

ing downward the N-Si axis. Abbreviations: E: envelope

conformation with atom deviating most from the Pople

& Cremer mean plane; T: twisted conformation around

the specified bond; C: chair conformation; HC: half-chair

conformation.

these five-membered rings are non-planar but show

envelope or twisted conformations, the atoms which

deviate most from the mean plane through the rings

are located either on the left or on the right side of

this plane. This additional element of chirality can

be quantified by the Cremer & Pople ring puckering

analysis [18]. The corresponding data are shown in

Table 3. The parameter Q (in A) is a measure for the

deviation of the atoms from the mean plane (i.e. the

amount of puckering, its amplitude), while the an-

gle <£>indicates how this puckering occurs (/. e. if the

overall geometry can be considered as an envelope

or a twisted conformation). In addition, an angle

between 0 and 180° indicates a puckering to the left

and an angle between 180 and 360° a puckering to

the right when the silatrane is viewed along the N-Si

axis, as shown in Fig. 4. The puckering amplitude

is generally lower for the substituted ring of the

silatranes when both substituents are on the same

carbon atom C l, as in most cases, but the deforma-

tion is higher in the limonene-derived silatrane 3a

where annulation of the chiral residue to Cl and C2

has occured. The different chiral residues impose

a clear preference for the direction of the puck-

ering to all silatrane rings; thus, menthyl 3c and

pinanyl 4b lead to right-handed puckering (angles

> 180°) while the other silatranes show left-han-

ded puckering. In every compound, the direction

of the puckering is the same for all three rings;

no mixed left-right conformers were found in the

crystal structure, although this has already been ob-

served in other substituted silatranes [19]. In par-

ticular, the carboxylic group as substituent seems

to have a pronounced influence on the ability of the

silatrane to invert the puckering direction of the sub-

stituted ring [2]. The stability of such conformers

increases with the degree of substitution, and their

effect on the NMR spectra of silatrane dendrimers is

considerable [20], Older structure analyses have oc-

casionally overlooked this kind of conformational

freedom, and average geometries not accounting for

disorder phenomena were calculated; thus, unreal-

istic C-C bond lengths and angles (e. g. 1.43 -1.46 A

for a C-C single bond) were published [21], Theory

has been used to predict reasonable values [22]. In

all of our cases, no indication for significant disor-

der was found, resulting in normal, expected values

for all geometrical parameters.

Comp. Param.

Ring 1

Ring 2

Ring 3

Cyclohexane

(or -ene)

_

4b

0.246

295.4

E(C2)

0.383

90.9

0.355

281.5

E(C4)

0.342

90.8

0.353

279.6

E(C6)

0.336

85.3

Q

—

<2>

—

0.588

323.7

9.7

Descr.

3a

Q

<P

0

—

Descr. T (C1-C2) T (C3-C4) T (C5-C6) C

0.352

275.8

—

3c

0.225

290.4

—

0.351

273.3

—

T (C3-C4)

0.314

108.0

—

E(C4)

0.382

104.9

—

E(C4)

0.317

103.2

—

0.573

136.0

3.6

Q

<2>

0

Descr. E(C2)

Q

T (C5-C6) C

3d

(PM3) <P

0.289

139.6

—

0.325

110.2

—

E(C6)

0.351

104.4

—

E(C6)

0.318

105.4

—

0.502

81.4

48.5

0

Descr. E(N)

HC

3e

0.510

100.1

50.2

HC

0.527

115.7

53.9

E(C8)

0.535

109.2

51.7

0.235

136.1

Q

<z>

—

0

Descr. E (N)

0.264

134.5

3e

Q

(PM3) <P

—

0

Descr. T (C2-N)

E(C4)

0.323

109.1

—

E(C6)

0.321

111.2

—

0.302

175.8

—

E (Si)

3f

Q

(PM3) <P

0

Descr.

E(C4)

E(C6)

HC

3e. The calculations also reproduce the trigonal-bi-

pyramidal structure of the hypervalent silicon, with

slightly lower deviations of the positions of the sili-

con atoms from the plane through the three oxygen

atoms (e. g. 0.182(1) A in the crystal structure and

0.163 A in the PM3 calculation for 3e). As a whole,

it seems that the calculations undertaken give a quite

realistic picture of the structures in the condensed

phase and allow to compare also those compounds

where no crystal structures are available.

Conformational study

The silatrane cage can be considered as an assem-

bly of three five-membered rings of the composition

i

Si-O-C-C-N. Looking along the N-Si axis, an ap-

A comparison of the measured and calculated

proximate C3 symmetry can be seen. However, as (PM3, with the Si-N bond length fixed to 2.128 A)

Brought to you by | New York University Bobst Library Technical Services

Authenticated

Download Date | 8/6/15 3:14 PM

32

G. Wagner et al. ■Chiral Silatranes Derived from Terpenes

conformations of 3e shows that PM3 increases the tween axial protons are larger (> 9 Hz, dihedral an-

puckering amplitude in the substituted ring and low- gle > 160°), while the coupling between one axial

and one equatorial proton (dihedral angle 70-90°)

ers it in the unsubstituted rings, while the change in

the puckering angles is not very great. Having this is almost zero and contributes to the shape of the

difference in mind, the calculated conformations of signals only by broadening. If any distortion of the

the silatrane moieties in 3d and 3f (for which no cyclohexane ring occurred, this would lead to dif-

ferent dihedral angles and to deviations of the cou-

pling constants from the rule given for the chair

conformation. The broad unresolved signal of H-9

crystal structures analyses exist) are very similar

to that of 3e in the calculation, with the exception

of the puckering angle for the substituted silatrane

ring in 3f (0 = 175.9°) which is close to the point of thus points to its equatorial position at the cyclo-

hexane ring, as in the crystal structure, ascertaining

ing at 180°. Despite this difference, the calculations that the methyl and isopropylidene substituents re-

inversion from left-handed to right-handed pucker-

main in their axial positions. The H-2 proton at the

ring junction is axial (J 13.2 Hz to H-10 axial), and

thus the silatrane moiety remains in a fixed con-

formation as well, showing the expected couplings

in the ethylene units (geminal coupling J > 12 Hz,

vicinal coupling ~ 4 Hz and ~ 7 Hz for dihedral an-

gles of ~ 4 0 and ~ 150°, respectively). The well-

resolved structure of all signals of the silatrane CH2

groups indicates that not only in the solid but also

should reflect the structure in the condensed phase

reasonably well.

All chiral silatranes contain a six-membered car-

bocyclic ring. In 3a and 3c, it is a cyclohexane which

adopts an almost perfect chair conformation. The

angle 0 (Table 3) is a measure for the deviation

from the ideal chair conformation (0=0°). In the

carvone-derived silatranes 3d - f, the six-membered

ring is distorted by the endocyclic double bond or

the annulated cyclopropane ring. The measured (for in solution the rigid structure is preserved, and no

3e) and calculated (for 3d) conformational param-

change from left- to righthanded puckering occurs

eters are close to the ideal value for a half-chair on the NMR timescale. In addition, a crosspeak be-

conformation (0= 50.8°). However, the calculated tween the methyl group H -11 and one proton of the

conformation of the six-membered ring in 3e can

be interpreted rather as an envelope with C8 as the

atom deviating most from the mean Cremer & Pople

plane. Interestingly, the calculated conformation of

the six-membered ring in the isomer 3f (with in-

verted configuration relative to 3e at the spiro car-

bon atom C l) is a distorted half chair (with a ten-

dency towards an envelope conformation with CIO

as atom deviating most from the Cremer & Pople

plane), thus resembling the measured rather than

the calculated conformation of 3e. As a whole, the

terpene moieties are well integrated in the poly-

cyclic framework of the silatranes and do not show

significant ring strain effects.

H- 6 methylene group is observed in the ROESY

spectrum. The existence of this NOE can be ex-

i

plained only if the puckering in the Si-0-C5-C6-N

ring is the same as in the solid state, i. e. lefthanded

(average distance in the crystal structure: 2.730A).

Due to the lack of observable NOE effects between

i

the Si-0-C3-C4-N ring and the other parts of the

molecule, one cannot prove directly that the left-

handed puckering is also preserved here. This is,

however, highly probable because of the complete

analogy in the chemical shifts and the coupling con-

stants in both unsubstituted rings.

Conclusion

The conformation of the silatranes in solution

can be elucidated by NMR spectroscopy, provided

that no severe overlap of the signals occurs. Al-

Chiral silatranes derived from terpenes were pre-

pared and structurally characterized. Their overall

most ideal cases are the limonene-derived silatranes geometry is similar to that of many known achiral

3a and 4a. We discuss here only the phenyl com- silatranes, and the terpene moiety does not inter-

pound 3a; analogous arguments are valid also for fere much with the silatrane unit. The Si-N bond

lengths are in the expected range for silatranes with

cyclohexane ring occurs in an almost ideal chair a phenyl substituent at silicon (2.1 -2.3A). For the-

the methyl compound 4a. As in the crystal, the

ory, this bond with the hypervalent silicon atom is

an important topic [1, 16, 17, 22]. For the pinene-

derived silatrane 4b, we showed already [23] that

conformation in chloroform solution. The axial and

equatorial protons are clearly distinguished by their

vicinal coupling constants. Coupling constants be-

Brought to you by | New York University Bobst Library Technical Services

Authenticated

Download Date | 8/6/15 3:14 PM

33

G. Wagner et al. ■Chiral Silatranes Derived from Terpenes

Table 4. Crystal structure determinations of 3a, 3c, 3e, and 4b.

4b

3a

3c

3e

F o rm u la

C ,5H 2 7 N 0 3Si

297.47

o rth o rh o m b ic

P2i2i2i (No. 19)

7.9750(2)

C 20H 29N O 3Si

359.54

o rth o rh o m b ic

P2,2,2i (No. 19)

7.3171(1)

C 22H 3iN 0 3 S i

385.58

o rth o rh o m b ic

P2,2,2! (No. 19)

11.2846(2)

C 21 H 33N O sSi

375.58

o rth o rh o m b ic

P212121 (No. 19)

11.9115(3)

F o rm u la w eig h t

C ry sta l system

S p ace gro u p

a (A)

11.4650(2)

12.3417(2)

12.1417(1)

9.2206(2)

6 (A )

23.1197(3)

14.1792(3)

14.9394(2)

21.7279(5)

c (A )

1939.52(5)

4

2084.46(8)

4

2046.91(5)

4

1597.75(6)

4

v

Z

(Ä 3)

D x ( g e m - 3 )

F (0 0 0 )

1.197

816

1.237

648

1.231

776

1.251

832

/x(M o -K ö ) (c m - 1 ) 1.4

1.3

1.4

1.5

C ry stal size (m m ) 0.33x0.48x0.51

0 .1 0 x 0 .1 0 x 0 .2 0

293

0.10x0.20x0.35

293

0.20x0.22x0.30

293

T em p eratu re (K )

293

R ad iatio n

—

M o-K q , A = 0.71073 A —

4.4, 27.1

±10; ±11; ±27

17369, 3459

0.035

4.8, 28.7

±9; ±15; ±31

15943,4790

0.036

4.6, 26.4

4.7, 26.4

6>min , ©max (°)

D ataset

±14; ±13; ±17

13547,4106

0.033

±14; ±12; ±18

28553, 3902

0.048

T ot., uniq. d ata

■ßint

O b serv ed d ata

4041

3577

3645

3089

( I > 2.0cr(I))

4790, 342

4106,235

3902, 369

3459, 289

Nref, Npar

0.034, 0.094, 1.06

R \,w R 2 ,S

0.035,0.092, 1.04

0.034, 0.091, 1.04

0.027,0.072, 1.03

W eighting funct.

w = l / [ a 2(F 2) + (a P )2 + bP], w h ere P = (F 2 + 2 F 2)/3,

a = 0.0566, 6 = 0.0277

a = 0.0526,6 = 0.1672

a = 0.0510,6 = 0.1935 a = 0.0421, 6 = 0.2312

M ax . and av.

S h ift/erro r

< 0.001

M in. and M ax.

resid u al electro n

-0.17,0.16

-0.16, 0 .1 2

-0.17,0.16

-0.16, 0.18

d en sity (e A - 3 )

there is indeed a bond between silicon and nitrogen

by analysing the bond path with the Atoms-In-Mo-

lecules (AIM) method [24]. In addition, high reso-

lution X-ray studies which allow the experimental

determination of the electron density in combina-

tion with a topological analysis of observed and

calculated electron density have been performed for

several silatranes at TU München*. Practical appli-

cations of the chiral silatranes are conceivable for

situations where crystallization in non-centrosym-

metric space groups is advantageous, such as in the

design of materials for non-linear optics. The inclu-

sion of our silatranes as chiral building blocks in

such materials is a topic of research in our labora-

tories.

Experimental Section

General methods

NMR spectra were measured with a Bruker AM 360 in-

strument, operating at 360.13 MHz fo r1H and 90.56 MHz

for 13C, in CDCI3 unless otherwise stated, and refer-

enced to TMS. J values are given in Hz. For assign-

ment of the signals and conformational analysis, H,H-

COSY with double quantum filter, ROESY, H,C-COSY,

and C,H-correlation over 2 and 3 bonds (BIRDTRAP

[25]) were used. Optical rotations were measured with a

Perkin-Elmer 241 M polarimeter. [a]Dvalues are given in

10“ 1 deg cm2 g~1. Mass spectra were obtained with a Var-

ian CH5 instrument (El mode, 70 eV), and a LCQ Finni-

gan instrument (ESI). Semiempirical calculations were

performed with the program GAMESS(US) [15] running

on a Pentium 90 PC with Linux as operating system.

Single crystal data for 3a, 3c, 3e, and 4b were collected

on a kappa-CCD system from Nonius with a rotating an-

ode generator (Nonius FR591; Mo-KQ, A= 0.71073Ä)

*For 1-phenylsilatrane, the observed bond critical point

is p(Si-N) 0.41(3) e/A3; Vj(Si-N) 1.22(6) e/Ä5; B. Pedersen,

W. Scherer, to be published.

Brought to you by | New York University Bobst Library Technical Services

Authenticated

Download Date | 8/6/15 3:14 PM

34

G. Wagner et al. ■Chiral Silatranes Derived from Terpenes

(m, 1 H, 9-H), 2.46 (d, J = 5.5 Hz, 1 H, 2-H), 2.68 (d, J

= 5.5 Hz, 1 H, 2-H), 4.67 (s,2H , 15-H).- 13C{'H} NMR

(90.56MHz, CDC13): 6 = 15.5 (C-12), 20.3 (C-16), 21.7

(C-10), 22.2 (C-2), 23.0 (C-13), 28.9 (C-7), 29.0 (C-l 1),

36.8 (C-9), 37.4 (C-8 ), 59.8 (C-l), 109.1 (C-15), 148.5

(C-14).

If: 'H NMR (360.13 MHz, CDCI3): 6 = 0.34 (m, 2 H,

12-H), 0.80 (m, 1 H, 10-H), 1.00 (s, 3 H, 13-H), 1.30 (m,

1 H, 9-H), 1.69 (s, 3 H, 16-H), 1.74 (m, 1 H, 7-H), 1.80

(m, 1 H, 7-H), 1.84 (m, 1 H, 8-H), 1.88 (m, 1H, 9-H),

2.59 (d, J = 4.8 Hz, 1 H, 2-H), 3.10 (d, J = 4.8 Hz, 1 H,

2-H), 4.65 (s, 2 H, 15-H). - 13C{'H} NMR (90.56MHz,

CDCI3): 6 = 14.7 (C-12), 20.3 (C-16), 21.2 (C-10), 22.0

(C-13), 22.2 (C-2), 28.8 (C-7), 28.8 (C-l 1), 35.7 (C-8 ),

38.0 (C-9), 61.3 (C-l), 108.9 (C-15), 148.5 (C-14). -

Ci2H]80 (178.28): calcd. C 80.9, H 10.2; found C 80.4,

H 10.8.

in rotation mode (#-scans). Details on measurement and

processing are given in Table 4. All frames were scaled

using the Denzo-SMN program suite [26]. No crystal

decay was observed and no corrections were applied for

absorption. Only in the case of 3e an extinction correction

was performed. The structures were solved by automatic

direct methods [27] (all non-H atoms) and refined [28]

by full-matrix least-squares on F2 with all non-hydro-

gen atoms assigned anisotropic displacement parameters.

Solely in the case of 3c the hydrogen atoms were placed

geometrically and constrained to ride on their parent car-

bon atoms, while for 3a, 3e, and 4b, the atomic positions

of the hydrogen atoms were freely refined with isotropic

displacement parameters. For data analysis and visualisa-

tion, the program PLATON [29] was used. Full crystal-

lographic details, excluding structure factor tables, have

been deposited at the Cambridge Crystallographic Data

Center (CCDC). Any request to the CCDC (E-mail: de-

posit@ccdc.cam.ac.uk) for this material should quote the

full literature citation and the reference numbers 151699

(3a), 151700 (3c), 151701 (3e), 151702 (4b).

General procedure fo r the preparation o f chiral

triethanolamines 2a - f

A mixture of diethanolamine (1.05 g, 10 mmol) and

the corresponding oxirane la-f (1 0 mmol) was stirred

at 120 °C for 2 d. Volatile impurities were distilled off at

120 °C at 6 mmHg. The residual yellow oil was used with-

out further purification, but could be purified by Kugel-

rohr distillation (160 °C, 6 x 10-2 mmHg). The properties

of 2b have already been described [23].

Starting materials

(—)-Menthone was prepared by Na2Cr2Ü7-oxidation

of commercial (—)-menthol (Merck). (—)-Carvone was

purchased from Roth and diethanolamine, (—)-/?-pinene

oxide and (—)-limonene oxide from Aldrich, the latter

being a ca. 1:1 mixture of the cis and trans diastereoiso-

mers. The silicon compounds were obtained from Merck.

Menthone and carvone were converted to the oxiranes lc

and Id as described [9].

(l/?,2Ä,4S)-2-[N,N-Bis(2-hydroxyethyl)amino]-l-hy-

droxy-1-methyl-4-( 1-methylethenyl)cyclohexane 2a:

Yield: 90% relative to frans-limonene oxide. 'H NMR

(360.13 MHz, CDCI3): 8 = 1.29 (s, 3 H, 11-H), 1.46 (m,

1 H, 7-H), 1.48 (m, 1 H, 8 -H ax.), 1.56 (m, 1 H, 7-H),

1.60 (m, 1 H, 10-H ax.), 1.70 (s, 3 H, 14-H), 1.91 dm, J

= 9.5 Hz, 1 H, 8 -Heq.), 1.97 (dm, J = 12.2 Hz, 1 H, 10-H

eq.), 2.38 (m, 2 H, 4-H or 6 -H), 2.40 (br s, 1 H, 9-H eq.),

2.54 (dd, J = 3.0, 12.8 Hz, 1 H, 2-H ax.), 2.74 (m, 2 H,

4-H or 6 -H), 3.48 (m, 2 H, 3-H or 5-H), 3.70 (m, 2H, 3-H

or 5-H), 4.38 (br s, 3 H, OH), 4.78 (br s, 1 H, 13-H trans

to C-14), 4.90 (br s, 1 H, 13-H cis to C-14). - n C { xH}

NMR (90.56MHz, CDC13): 6 = 21.4 (C-l 1), 22.5 (C-14),

24.9 (C-10), 25.2 (C-8 ), 36.9 (C-7), 38.8 (C-9), 53.8 (C-

4, C-6 ), 59.9 (C-3, C-5), 63.0 (C-2), 73.4 (C-l), 110.8

(C-13), 145.6 (C-12). - HPLC-ESI: mJz = 257 [M+]. -

Ci4H27N03(257.38): calcd. C 65.3, H 10.6, N 5.4; found

C 65.0, H 10.7, N 5.2.

(\S,2S,5R)~1-[/V,/V-Bis(2-hydroxyethyl)-aminometh-

yl]-1-hydroxy-5-methyl-2-( 1-methylethyl)cyclohexane

2c: Yield: 98 % .1H NMR (360.13 MHz, CDCI3): 6 =0.76

(br t, 1 H, J = 12.9 Hz, 11-H ax.), 0.81 (m, 1H, 9-H ax.),

0.86 (d, J = 6.4 Hz„ 3 H, 14-H or 15-H), 0.87 (d, J =

7.0 Hz, 3 H, 12-H), 0.89 (d, J = 6.4 Hz, 3 H, 15-H or

14-H), 0.96 (ddd, J = 11.4, 4.8, 1.8 Hz, 1H, 7-H ax.),

1.45 (qd, J = 12.3, 3.3 Hz, 1 H, 8 -H ax.), 1.48 (m, 1H,

Syntheses o f terpene-derived oxiranes

(1R,2R,4R,6R)~ 1-Methyl-4-( 1-methylethenyl)-bicy-

clo[4.1.0]heptane-2-spiro-2’-oxirane le and (1R,2S,AR,

6R)-1-methyl-4-( 1-methylethenyl)-bicyclo[4.1.0]hept-

ane-2-spiro-2’-oxirane If: A solution of KOBuf (22.4 g,

0.20 mol) in dry DMSO (200 ml) was kept at 50 °C

under a vacuum (80 mmHg) for 2h. After cooling to

R. T., trimethylsulfoxonium iodide (44.0 g, 0.20 mol) was

added under nitrogen and the mixture stirred for 2 h. ( -) -

Carvone (15.0g, 0.10 mol) was then added and stirring

continued for 16 h. Water (300 ml) was added and the

mixture extracted with hexane (3 x 100ml). The com-

bined extracts were dried over Na2SC>4 and the solvent

removed under vacuum (15 mmHg). Kugelrohr distil-

lation (6 mmHg, 120 °C of the residue afforded 10.7 g

(60%) of a 2:1 mixture of le and If.

le: 1H NMR (360.13 MHz, CDC13): 6 = 0.34 (m, 1 H,

12-H), 0.39 (m, 1 H, 12-H), 0.72 (m, 1 H, 10-H), 0.88 (s,

3 H, 13-H), 1.70 (m, 1 H, 7-H), 1.71 (s, 3 H, 16-H), 1.84

(m, 1 H, 7-H), 1.85 (m, 1 H, 9-H), 1.87 (m, 1 H, 8-H), 1.90

Brought to you by | New York University Bobst Library Technical Services

Authenticated

Download Date | 8/6/15 3:14 PM

G. Wagner et al. • Chiral Silatranes Derived from Terpenes

35

1 H, 2-H), 3.62 (m, 2 H, 3-H or 5-H), 3.70 (m, 1 H, 3-H

or 5-H), 3.78 (m, 2 H, 3-H, 5-H), 4.74 (s, 2 H, 15-H).

- ^ C j'H } NMR (90.56MHz, CDC13): 6 = 14.0 (C-12),

20.0 (C-16), 20.3 (C-10), 21.3 (C-13), 22.5 (C -ll), 29.0

(C-7), 39.7 (C-8), 39.8 (C-9), 51.4 (C-4, C-6 ), 58.1 (C-2),

60.8 (C-3 or C-5), 62.8 (C-3 or C-5), 73.6 (C-l), 109.0

(C-15), 149.0 (C-14). - HPLC-ESI: m/z = 283 [M+], -

Ci6H29N03(283.41): calcd. C 67.8, H 10.3, N 4.9; found

C 67.5, H 10.0, N 5.2.

8-H eq.), 1.67 (m, 1H, 10-H ax.), 1.73 (dm, J = 12.1 Hz,

1 H, 9-H eq.), 2.01 (ddd, J = 13.2,3.3, 2.6 Hz, 1 H, 11-H

eq.), 2.07 (septd, J = 6 .6 , 1.8 Hz, 1 H, 13-H), 2.26 (d, J

= 14.3 Hz, 1 H, 2-H), 2.68 (ddd, J = 13.2, 5.5, 3.7 Hz, 2

H, 4-H, 6 -H), 2.79 (ddd, J = 13.6, 7.0, 4.0 Hz, 2 H, 4-H,

6 -H), 3.02 (d, J = 14.3 Hz, 1H, 2-H), 3.59 (ddd, 11.4,5.2,

4.0 Hz, 2 H, 3-H, 5-H), 3.68 (ddd, J = 11.4, 7.3, 3.7 Hz,

2 H, 3-H, 5H), 3.80 (br s, 3 H, OH). - ^ C ^ H } NMR

(90.56 MHz, CDC13): 6 = 18.0, 22.5 (C-14, C-15), 20.9

(C-8), 23.7 (C-12), 25.8 (C-13), 27.7 (C-10), 35.1 (C-9),

47.2 (C-l 1), 48.2 (C-7), 59.4 (C-4, C-6 ), 60.2 (C-3, C-5),

64.7 (C-2), 74.9 (C-l). - HPLC-ESI: m/z = 273 [M+], -

Ci5H3iN 0 3(273.42): calcd. C 65.9, H 11.4, N 5.1; found

C 65.6,H 11.6, N 4.9.

General procedure fo r the synthesis o f the

phenylsilatranes 3

To

a

solution of phenyltriethoxysilan (600 mg,

2.5 mmol) and the corresponding triethanolamine

(2.5 mmol) in 15 ml of toluene was added a catalytic

amount of KOH (20-50 mg). The mixture was refluxed

for 12h. The solvent was distilled off and the residue

chromatographed on silica gel with CH2C12 to give the

corresponding phenylsilatrane 3 as a white solid. From the

mixture of 3e and 3f, pure 3e crystallized from CH2C12-

diethyl ether (1:1) while 3f remained in the mother liquor

and was not further purified.

(3/?,65’,8/?)-5-Aza-3-methyl-6-(l-methylethenyl)-l-

phenyl-1-sila-2,12,13-trioxa-tricyclo[7.3.3.03,8]pentade-

cane 3a: Yield 40.2%. M.p. 144- 145°C. - [a ß 3 -4 5 .2

(c 0.99 in CHCI3). - R { [CH2C12] 0.40. - 'H NMR

(360.13 MHz, CDC13): 6 = 1.49 (s, 3 H, 11-H), 1.65 (m, 1

H, 8 -H eq.), 1.69 (m, 1 H, 7-H), 1.71 (m, 1 H, 7-H), 1.76

(m, 1 H, 10-H eq.), 1.78 (s, 3 H, 14-H), 1.99 (dm, J =

13.2 Hz, 1 H, 8 -H ax.), 2.05 (dm, J = 13.2 Hz, 1 H, 10-H

ax.), 2.46 (dd, J = 12.8, 4.0 Hz, 1 H, 6 -H), 2.56 (br s, 1

H, 9-H eq.), 2.62 (td, J = 12.1,6.9 Hz, 1 H, 4-H), 2.73 (br

d, J = 13.2 Hz, 1 H, 2-H ax.), 2.82 (dd, J = 12.5, 3.7 Hz,

1 H, 4-H), 3.05 (td, J = 12.1, 5.2 Hz, 1 H, 6 -H), 3.77 (m,

1H, 3-H), 3.83 (m, 2 H, 3-H, 5-H), 3.93 (dd, J = 10.6,

7.0 Hz, 1 H, 5-H), 4.88 (br s, 1 H, 13-H trans to 14), 4.98

(br s, 1 H, 13-H cis to 14), 7.24 (m, 3 H, 17-H, 18-H), 7.73

(d, J = 1.1 Hz, 2 H, 16-H). - 13C{1H} NMR (90.56 MHz,

CDCI3): 6 = 22.3 (C -ll), 22.6 (C-14), 24.4 (C-10), 25.1

(C-8 ), 38.9 (C-9), 39.7 (C-7), 47.8 (C-6 ), 51.5 (C-4), 57.9

(C-3), 58.1 (C-5), 60.7 (C-2), 73.7 (C-l), 111.1 (C-13),

126.9 (C-17), 127.3 (C-18), 134.0 (C-16), 142.4 (C-15),

145.9 (C-12). - C2oH29N 0 3Si(359.55): calcd. C 66.8, H

8.1, N 3.9; found C 66.8, H 8.3, N 3.8.

(6S,4Ä)-6-[/V,7V-Bis(2-hydroxyethyl)-aminomethyl]-

6 -hydroxy-1-methyl-4-( 1-methylethenyl)cyclohexene

2d: Yield: 92 %. 'H NMR (360.13 MHz, CDC13): <5 =

I.48 (t, J = 12.6 Hz, 1 H, 7-Htrans to 8-H), 1.72 (s, 3 H,

12-H), 1.74 (s, 3H, 15-H), 1.97 (m, 1H, 9-H), 2.10 (m,

1H, 9-H), 2.25 (d, J = 12.6 Hz, 1 H, 7-H cis to 8-H), 2.33

(m, 1H, 8-H), 2.73 (d, J = 12.2 Hz, 1 H, 2-H), 2.78 (d, J

= 12.2 Hz, 1 H, 2-H), 2.78 (m, 4H, 4-H, 6 -H), 3.62 (br s,

3 H, OH), 3.65 (m, 4H, 3-H, 5-H), 4.73 (br s, 1 H, 14-H),

4.75 (br s, 1 H, 14-H), 5.50 (m, 1 H, 10-H). - ^ C fH }

NMR (90.56 MHz, CDC13): 6 = 17.1 (C-12), 20.3 (C-15),

31.0 (C-9), 39.2 (C-7), 39.3 (C-8 ), 59.3 (C-4, C-6 ), 60.3

(C-3, C-5), 61.0 (C-2), 74.3 (C-l), 109.3 (C-14), 125.0

(C-10), 136.9 (C-l 1), 148.6 (C-13). - HPLC-ESI: m/z =

269 [M+], - Ci5H27N03(269.39): calcd. C 66.9, H 10.1,

N 5.2; found C 67.0, H 10.5, N 5.0.

(l/?,2/?,4/?,6/?)-2-[N,jV-Bis(2-hydroxyethyl)aminome-

thyl]-2-hydroxy-1-methyl-4-( 1-methylethenyl)bicyclo-

[4.1.0]heptane 2e and (l/?,2S,4/?,6/?)-2-[jV,jV-bis(2-hydr-

oxyethyl)aminomethyl]-2-hydroxy-l-methyl-4-(l-meth-

ylethenyl)bicyclo [4.1.0]heptane 2f (from the mixture of

le and If): Yield 8 8 %. 2e: *H NMR (360.13MHz,

CDCI3): 6 = 0.30 (m, 1 H, 12-H), 0.51 (m, 1 H, 12-

H), 0.86 (m, 1 H, 10-H), 1.23 (s, 3 H, 13-H), 1.25 (m,

1 H, 7-H), 1.40 (m, 1 H, 7-H), 1.58 (m, 1 H, 9-H), 1.69

(s, 3 H, 16-H), 1.78 (m, 1 H, 9-H), 1.88 (m, 1 H, 8-H),

2.60 (m, 1 H, 2-H), 2.81 (m, 4 H, 4-H, 6 -H), 2.92 (m, 1

H, 2-H), 3.65 (m, 2 H, 3-H or 5-H), 3.73 (m, 1 H, 3-H

or 5-H), 3.83 (m, 1 H, 3-H or 5-H), 4.72 (s, 2 H, 15-H).

-

13C{’H} NMR (90.56MHz, CDC13): 6 = 13.8 (C-12),

19.7 (C -l6 ), 20.4 (C-10), 21.3 (C-13), 25.1 (C -ll), 29.7

(C-7), 35.6 (C-8), 41.8 (C-9), 51.1 (C-4, C-6 ), 56.3 (C-2),

60.0 (C-3 or C-5), 64.2 (C-3 or C-5), 73.3 (C-l), 108.8

(C-15), 149.4 (C-14).

(1 ’/?,3S)-5-Aza-6 ’,6 ’-dimethyl-1-phenyl-1-sila-2,8,9-

trioxabicyclo[3.3.3]undecane-3-spiro-2’-bicyclo[3.1.1]-

heptane 3b: Yield 45.9%. M.p. 161 - 165°C. - [a]g +2.0

(c 2.0 in CHCI3). - R { [CH2C12] 0.40. - *H NMR

(360.13 MHz, CDCI3): 6 = 1.16 (s, 3 H, 14-H), 1.48 (s,

3 H, 13-H), 2.00 (d, J = 10.3 Hz, 1 H, 12-H anti to 13),

2.02 (m, 1 H, 10-H), 2.15 (m, 2 H, 11-H, 9-H), 2.19 (m,

1 H, 10-H), 2.23 (m, 1 H, 7-H), 2.38 (m, 1 H, 11-H), 2.44

(m, 1 H, 12-H syn to 13), 2.96 (m, 1 H, 4-H or 6 -H),

2f: *H NMR (360.13 MHz, CDC13): 6 = 0.42 (m, 2 H,

12-H), 0.84 (m, 1 H, 10-H), 1.10 (s, 3 H, 13-H), 1.28 (m,

1 H, 7-H), 1.58 (m, 1 H, 7-H), 1.62 (m, 1 H, 9-H), 1.70

(s, 3 H, 16-H), 1.72 (m, 1 H, 8-H), 1.78 (m, 1 H, 9-H),

2.66 (m, 1 H, 2-H), 2.81 (m, 4 H, 4-H and 6 -H), 2.86 (m,

Brought to you by | New York University Bobst Library Technical Services

Authenticated

Download Date | 8/6/15 3:14 PM

36

G. Wagner et al. • Chiral Silatranes Derived from Terpenes

2.99 (d, J = 12.8 Hz, 1 H, 2-H), 3.05 (m, 1 H, 6 -H or

4-H), 3.07 (m, 1 H, 4-H or 6 -H), 3.14 (d, J = 13.2 Hz, 1

H, 2-H), 3.15 (m, 1 H, 6 -H or 4-H), 3.92 (m, 1 H, 3-H

or 5-H), 4.04 (m, 3 H, 3-H, 5-H), 7.44 (m, 3 H, 17-H,

18-H), 7.95 (d, J = 8.1 Hz, 2 H, 16-H). - l3C{*H} NMR

(90.56MHz, CDC13): 6 = 23.5 (C-14), 25.0 (C-10), 27.2

(C-13), 27.3 (C-12), 34.3 (C-l 1), 37.4 (C-8 ), 40.1 (C-9),

53.6, 54.6 (C-4, C-6 ), 55.1 (C-l), 57.6, 57.8 (C-3, C-5),

64.7 (C-2), 76.5 (C-l), 126.8 (C-17), 127.0 (C-18), 134.1

(C -l6 ), 143.6 (C-15). - C2oH29N0 3Si(3 5 9 .5 5 ): calcd. C

6 6 .8 , H 8.1, N 3.9; found C 6 6 .6 , H 8.0, N 3.6.

(C-8 ), 41.8 (C-7), 54.3 (C-4 or C-6 ), 56.1 (C-6 or C-4),

56.5 (C-2), 57.9 (C-3 or C-5), 58.1 (C-5 or C-3), 74.0

(C-l), 109.2 (C-14), 124.6 (C-10), 126.9 (C-18), 127.2

(C-19), 134.1 (C-17), 137.9 (C-l 1), 142.9 (C-16), 148.2

(C-13). - C2iH29N 0 3Si(371.56): calcd. C 67.9, H 7.9, N

3.8; found C 68.0, H 7.7, N 4.0.

(3Jl?,2,/?,4,/?,6,/?)-5-Aza-r-methyl-4,-(l-methylethe-

nyl) - 1-phenyl-1-sila-2,8,9-trioxa-bicyclo[3.3.3]undeca-

ne-3-spiro-2’-bicyclo[4.1.0]heptane 3e: Yield 38%. M.p.

170- 172°C. - [a]ß -62.5 (c 0.2 in CHCI3). - 'H NMR

(360.13 MHz, CDCI3): 6 = 0.34 (m, 2 H, 12-H), 1.08 (m,

1 H, 10-H), 1.23 (s, 3 H, 13-H), 1.68 (m, 1 H, 9-H), 1.72

(s, 3 H, 16-H), 1.78 (m, 1 H, 9-H), 1.80 (m, 1 H, 7-H),

1.83 (m, 1 H, 8 -H), 1.88 (m, 1 H, 7-H), 2.95 (m, 1 H, 4-H

or 6 -H), 3.02 (s, 2 H, 2-H), 3.05 (m, 2 H, 4-H or 6 -H),

3.10 (m, 1 H, 4-H or 6 -H), 3.96 (m, 4 H, 3-H and 5-H),

4.71 (s, 2 H, 15-H), 7.30 (m, 3 H, 19-H and 20-H), 7.87

(d, J = 7.7 Hz, 2 H, 18-H). - 13C{*H} NMR (90.56MHz,

CDCI3): 6 = 13.1 (C-12), 20.4 (C-16), 21.6 (C-10), 22.9

(C-13), 25.8 (C -ll), 29.5 (C-7), 35.5 (C-8 ), 44.3 (C-9),

54.6 (C-4 or C-6 ), 56.0 (C-4 or C-6 ), 58.0 (C-3 or C-5),

58.1 (C-3 or C-5), 59.5 (C-2), 72.9 (C-l), 109.2 (C-15),

127.0 (C-19), 127.4 (C-20), 134.3 (C-18), 143.1 (C-17),

148.9 (C-14). - C22H3iN03Si(385.58): calcd. C 68.5, H

8.1, N 3.6; found C 68.5, H 8.0, N 3.5.

(3/?,2’5,4’/?,6’/?)-5-Aza-1’-methyl-4’-(1-methylethe-

nyl)-!-phenyl-l-sila-2,8 ,9-trioxabicyclo[3.3.3]undeca-

ne-3-spiro-2’-bicyclo[4.1.0]heptane 3f: Yield ca. 20%.

'H N M R (360.13 MHz, CDCI3): <5= 0.37 (m, 1 H, 12-H),

0.86 (m, 1 H, 10-H), 0.89 (m, 1 H, 12-H), 1.14 (s, 3 H,

13-H), 1.36 (m, 1 H, 9-H), 1.73 (s, 3 H, 16-H), 1.78 (m,

1 H, 7-H), 1.85 (m, 1 H, 8-H), 1.88 (m, 1 H, 7-H), 1.89

(m, 1 H, 9-H), 2.98 (m, 4 H, 4-H and 6 -H), 3.02 (m, 1

H, 2-H), 3.12 (m, 1 H, 2-H), 3.96 (m, 4 H, 3-H and 5-H),

4.73(s, 2 H, 15-H), 7.30 (m, 3 H, 19-H and 20-H), 7.78

(d, J = 7.9 Hz, 2 H, 18-H). - 13C{'H} NMR (90.56MHz,

CDCI3): 6 = 15.6 (C-12), 20.9 (C-16), 21.0 (C-10), 22.4

(C -ll), 23.3 (C-13), 27.0 (C-7), 35.9 (C-8 ), 42.6 (C-9),

54.3 (C-4 or C-6 ), 54.7 (C-4 or C-6 ), 57.6 (C-3 or C-5),

58.0 (C-3 or C-5), 59.1 (C-2), 73.5 (C-l), 108.4 (C-15),

127.0 (C-19), 127.4 (C-20), 134.1 (C-18), 142.8 (C-17),

149.3 (C-14). - C22H3iN 0 3Si(385.58): calcd. C 68.5, H

8.1, N 3.6; found C 68.9, H 8 .6 , N 3.8.

(3S,2'S,5 'R)-5-Aza-5’-methyl-2’-( 1-methylethyl)-1-

phenyl-l-sila-2,8 ,9-trioxabicyclo[3.3.3]undecane-3-spi-

ro-1’-cyclohexane 3c: Yield 34.1%. M.p. 185- 188°C. -

[a ß 3 +11.9 (c 0.3 in CHCI3). - R { [CH2C12] 0.38. - 'H

NMR (360.13 MHz, CDC13): 6 = 0.86 (d, J = 6 .6 Hz, 3

H, 14-H or 15-H), 0.88 (m, 1 H, 9-H ax.), 0.94 (m, 1 H,

11-H ax.), 0.97 (d, J = 7.0 Hz, 3 H, 12-H), 0.99 (d, J =

6 .6 Hz, 3 H, 15-H or 14-H), 1.02 (m, 1 H, 7-H ax.), 1.62

(m, 1 H, 8-H eq.), 1.80 (m, 1 H, 8 -H ax.), 1.83 (dm, J =

10.6 Hz, 1 H, 9-H eq.), 1.96 (m, 1 H, 10-H ax.), 2.06 (dm,

J = 12.8 Hz, 1 H, 11-Heq.), 2.13 (sept, J = 6 .6 Hz, 1 H,

13-H), 2.70 (d, J = 13.9 Hz, 1 H, 2-H anti to Pr1), 2.89

(ddd, J = 12.1, 10.6,6.2 Hz, 1 H, 4-H or 6 -H), 3.02 (ddd,

J = 12.1, 4.4, 2.2 Hz, 1 H, 4-H or 6 -H), 3.07 (m, 2 H,

6 -H or 4-H), 3.13 (d, J = 13.9 Hz, 1 H, 2-H syn to Pr1),

3.81 (td, J = 10.6, 4.4 Hz, 1 H, 3-H or 5-H), 3.88 (ddd,

J = 10.6, 6.2, 2.2Hz, 1 H, 3-H or 5-H), 3.95 (m, 2 H,

5-H or 3-H), 7.29 (t, J = 7.7 Hz, 2 H, 18-H), 7.30 (td, J

= 7.7, 1.8 Hz, 1 H, 19-H), 7.81 (dd, «7= 7.7, 1.8 Hz, 2 H,

17-H). - ^ C ^ H } NMR (90.56MHz, CDCI3): 6 = 17.9,

22.4 (C-14, C-15), 21.8 (C-8 ), 23.9 (C-12), 26.4 (C-13),

28.1 (C-10), 34.8 (C-9), 48.4 (C-7), 51.5 (C-l 1), 55.5 (C-

4 or C-6 ), 57.1 (C-6 or C-4), 58.3 (C-3 or C-5), 58.5 (C-5

or C-3), 60.0 (C-2), 75.6 (C-l), 127.0 (C-18), 127.4 (C-

19), 134.3 (C-17), 143.1 (C -16).-C 2iH33N03Si(375.59):

calcd. C 67.2, H 8.9, N 3.7; found C 67.0, H 8.9, N 3.5.

(35,5 'R)-5-Aza-2’-methyl-5 ’-(1 -methylethenyl)-1-

phenyl-l-sila-2,8 ,9-trioxabicyclo[3.3.3]undecane-3-spi-

ro -l’-(2-cyclohexene) 3d: Yield 42.2%. M.p. 60-64°C.

- [a]o -26.9 (c 0.8 in CHC13). - R { [CH2C12] 0.37. -

*H NMR (360.13MHz, CDCI3): 6 = 1.94 (s, 3 H, 15-H),

1.99 (s, 3 H, 12-H), 2.07 (t, J = 13.2 Hz, 1 H, 7-Htrans to

8 -H), 2.13 (m, 1 H, 9-H), 2.24 (d, J = 12.8 Hz, 1 H, 7-H

cis to 8-H), 2.27 (m, 1 H, 9-H), 2.51 (m, 1 H, 8 -H), 2.80

(d, J = 14.0 Hz, 1 H, 2-H syn to C-10), 3.04 (m, 1 H, 4-H

or 6 -H), 3.06 (m, 1 H, 4-H or 6 -H), 3.16 (m, 2 H, 6 -H or

4-H), 3.26 (d, J = 14.0 Hz, 1 H, 2-H anti to C-10), 4.03

(m, 2 H, 3-H and 5-H), 4.07 (m, 1 H, 3-H or 5-H), 4.12

General procedure fo r the synthesis o f the

methylsilatranes 4

A mixture of trichloro-methylsilane (374 mg, 2.5 mmol),

acetic anhydride (775 mg, 7.6 mmol) and sodium acetate

(50 mg, 0.6 mmol) was kept at 60°C for 4 h. Acetyl chlo-

(m, 1 H, 3-H or 5-H), 4.95 (br s, 1 H, 14-H), 4.97 (br s, 1 ride and excess of acetic anhydride was distilled off at

6 mmHg. The residue was dissolved in CHCI3 (10 ml)

and cooled to 0°C. A solution of the corresponding tri-

ethanolamine derivative 2 (2.5 mmol) in CHCI3 (20 ml)

H, 14-H), 5.71 (br s, 1 H, 10-H), 7.45 (m, 3 H, 18-H, 19-

H), 7.97 (m, 2 H, 17-H). - 13C{'H} NMR (90.56MHz,

CDCI3): 6 = 16.7 (C-12), 20.1 (C-15), 30.6 (C-9), 39.0

Brought to you by | New York University Bobst Library Technical Services

Authenticated

Download Date | 8/6/15 3:14 PM

37

G. Wagner et al. • Chiral Silatranes Derived from Terpenes

clohexane 4c: Yield 44.7%. M.p. 131-133°C. - [a ß 3

+22.9 (c 0.9 in CHCI3). - Rf [CH2Cl2-ethyl acetate

(10:1)] 0 .3 9 .- 'H NMR (360.13 MHz, CDC13): 6 = -0.12

(s, 3 H, 16-H), 0.80 (td, J = 12.8, 3.3 Hz, 1 H, 11-H ax.),

0.80 (d, J = 6 .6 Hz, 3 H, 14-H or 15-H), 0.82 (m, 1 H,

9-H ax.), 0.84 (dm, J = 12.9 Hz, 1 H, 7-H ax.), 0.87 (d,

J = 7.0 Hz, 3 H, 12-H), 0.90 (d, J = 6 .6 Hz, 3 H, 15-

H or 14-H), 1.46 (dq, J = 12.9, 3.3 Hz, 1 H, 8-H eq.),

1.62 (qd, J = 12.9, 3.3 Hz, 1 H, 8-H ax.), 1.70 (dm, J =

12.9 Hz, 1 H, 9-H eq.), 1.78 (m, 1 H, 10-H), 2.01 (sept,

J = 6 .6 Hz, 1 H, 13-H), 1.93 (ddd, J = 12.8, 3.3, 2.2 Hz,

1 H, 11-H eq.), 2.58 (d, J = 13.9 Hz, 1 H, 2-H anti to Pr1),

2.74 (ddd, J = 12.2, 10.3, 6.3 Hz, 1 H, 4-H or 6 -H), 2.93

(ddd, J = 12.5, 4.0, 1.8 Hz, 1 H, 4-H or 6 -H), 2.95 (d,

J = 13.9 Hz, 1 H, 2-H syn to Pr1), 2.96 (m, 2 H, 6 -H or

4-H), 3.68 (td, J = 10.6, 4.0 Hz, 1 H, 3-H or 5-H), 3.72

(ddd, J = 10.6, 6.3, 1.8 Hz, 1 H, 3-H or 5-H), 3.78 (m, 2

H, 5-H or 3-H). - l3C{'H} NMR (90.56MHz, CDC13):

6 = -1 .2 (C-l 6 ), 17.7,22.4 (C-14, C-15), 21.6 (C-8 ), 23.8

(C -l2), 26.2 (C-13), 28.0 (C-10), 34.8 (C-9), 48.2 (C-7),

51.4 (C-l 1), 55.3 (C-4 or C-6), 56.8 (C-6 or C-4), 58.2

(C-3 or C-5), 58.4 (C-5 or C-3), 60.0 (C-2), 75.2 (C-l).

- Ci6H3iN03Si(313.52): calcd. C 61.3, H 10.0, N 4.5;

found C 61.6, H 10.0, N 4.7.

was added dropwise within 30 min. The reaction mixture

was stirred at RT for 12 h, the solvent evaporated and the

residue chromatographed on silica gel with CH2CI2 / ethyl

acetate (10:1) to give the corresponding methylsilatrane

4 as a white solid. The properties of the pinene-derived

silatrane 4b have already been described [23],

(3R,6S,$R)-5-Aza-1,3-dimethyl-6-( 1-methylethenyl)-

l-sila-2,12,13-trioxatricyclo[7.3.3.03,8]pentadecane 4a:

Yield 44.4%. M.p. 112- 115°C. - [a]^3 -5 3 .4 (c 0.6 in

CHCI3). - Rf [CH2Cl2-ethyl acetate (10:1)] 0.30. - 'H

NMR (360.13 MHz, CDC13): 6 = -0.11 (s, 3 H, 15-H),

1.39 (s, 3 H, 11-H), 1.63 (m, 1 H, 7-H), 1.65 (m, 1 H,

7-H), 1.65 (m, 1 H, 8-H ax.), 1.73 (s, 3 H, 14-H), 1.73 (td,

J = 12.8, 5.5 Hz, 1 H, 10-Hax.), 1.94 (dm, J = 13.6 Hz,

1 H, 8-H eq.), 2.01 (ddd, J = 13.2,4.0, 2.2 Hz, 1 H, 10-H

eq.), 2.45 (dd, J = 12.9, 4.4 Hz, 1 H, 6 -H), 2.51 (br s, 1

H, 9-H), 2.55 (td, J = 12.1,7.0 Hz, 1 H, 4-H), 2.60 (dd, J

= 11.0, 2.6 Hz, 1 H, 2-Hax.), 2.78 (dd, J = 12.5, 3.8 Hz,

1 H, 4-H), 2.99 (td, J = 12.2, 7.0 Hz, 1 H, 6 -H), 3.64 (m,

1 H, 3-H), 3.68 (m, 1 H, 3-H), 3.73 (td, J = 12.1, 4.8 Hz,

1 H, 5-H), 3.81 (dd, J = 11.0, 6 .6 Hz, 1 H, 5-H), 4.83 (br

s, 1 H, 13-H trans to C-10), 4.93 (br s, 1 H, 13-H cis to

C-10). - 13C{‘H} NMR (90.56 MHz, CDC13): 6 = -1.1

(C-15), 22.2 (C-l 1), 22.6 (C-14), 24.6 (C-10), 25.2 (C-8 ),

39.0 (C-9), 39.7 (C-7), 47.7 (C-6), 51.5 (C-4), 57.9 (C-3),

58.1 (C-5), 60.4 (C-2), 73.8 (C-l), 111.1 (C-13), 146.0

(C -l2). - Ci5H27N03Si(297.47): calcd. C 60.6, H 9.2, N

4.7; found C 60.8, H 9.0, N 4.4.

Acknowledgement

We wish to thank Prof. Dr. Ivar Ugi, Technische Uni-

versität München, for general support. Financial support

by Fonds der Chemischen Industrie (Germany) is grate-

fully acknowledged.

(35,2’5,5 ’/?)-5-Aza-1,5’-dimethyl-2’-(1 -methylethyl)-

l-sila-2,8,9-trioxabicyclo[3.3.3]undecane-3-spiro-l’-cy-

[6] a) N. Prilezhaev, N. Prokopchuk, Zh. Obshch.

Khim. 3, 865 (1933); b) J. J. Ritter, K. L. Rus-

sell, J. Am. Chem. Soc. 58, 291 (1936); c) W. Hü-

ckel, E. Gelchsheimer, Liebigs Ann. Chem. 625, 12

(1959); d) R. K. Hill, J. W. Morgan, R. V. Shetty,

M. E. Synerholm, J. Am. Chem. Soc. 96, 4201

(1974).

[1] a) M. G. Voronkov, Pure Appl. Chem. 13, 35 (1966);

b) M. G. Voronkov, V. M. Dyakov, S. V. Kirpichenko,

J. Organomet. Chem. 233,1 (1982); c) S. N. Tandura,

M. G. Voronkov, N. V. Alekseev, Top. Curr. Chem.

131, 99 (1986); d) R. J. P. Corriu, J. Organomet.

Chem. 400, 81 (1990); e) J. G. Verkade, Coord.

Chem. Rev. 137, 233 (1994).

[7] S. A. Kozhin, V. V. Zaitsev, B. I. Ionin, Zh. Obshch.

Khim. 48, 203 (1978).

[8] G. Muller, D. Sainz, J. Organomet. Chem. 495, 103

(1995).

[9] E. J. Corey, M. Chaykovsky, J. Am. Chem. Soc. 87,

1353 (1965).

[2] a) R.-X. Zhuo, Z.-R. Lu, J. Liao, L.-F. Shen,

J. Organomet. Chem. 446, 107 (1994); b) Z.-R. Lu,

R.-X. Zhuo, L.-R. Shen, X.-D. Zhang, L.-F. Shen,

J. Organomet. Chem. 489, C38 (1995); c) X. Zhang,

S. Mao, L. Shen, C. Ye, R. Zhuo, Z. Lu, G. A. Webb,

J. Mol. Struct. 372, 249 (1995).

[10] a) R. G. Carlson, N. S. Behn, J. Org. Chem. 32,1363

(1967); b) J. D. Ballantine, P. J. Sykes, J. Chem. Soc.

C, 731 (1970).

[11] B. M. Trost, R. Humaus, Tetrahedron Lett. 30, 3893

(1989).

[3] M. Tasaka, M. Hirotsu, M. Kojima, S. Utsuno, Y. Yo-

shikawa, Inorg. Chem. 35, 6981 (1996).

[4] B. Pedersen, G. Wagner, R. Herrmann, W. Scherer,

K. Meerholz, E. Schmälzlin, C. Bräuchle, J. Or-

ganomet. Chem. 590, 129 (1999).

[12] M. Narayanaswamy, V. M. Sathe, A. S. Rao, Chem.

Ind. 27, 921 (1969).

[5] W. A. Nugent, R. L. Harlow, J. Am. Chem. Soc. 116,

6142(1994).

Brought to you by | New York University Bobst Library Technical Services

Authenticated

Download Date | 8/6/15 3:14 PM

38

G. Wagner et al. ■Chiral Silatranes Derived from Terpenes

[131 L. Pärkänyi, K. Simon, J. Nagy, Acta Crystallogr.

B38, 2328 (1974).

[23] B. Pedersen, G. Wagner, R. Herrmann, Elec-

tronic Conference on Heterocyclic Chemistry

(ECHET 98), Royal Society of Chemistry,

1998. ISBN 981-02-3594-1 (CD-ROM). See also:

http ://www.ch.ic.ac.uk/ectoc/echet 9 8 /pub/048/

[24] a) R. F. W. Bader, Acc. Chem. Res. 18, 9 (1985); b)

R. F. W. Bader, Chem. Rev. 91, 893 (1991); c) K. B.

Wiberg, R. F. W. Bader, C. D. H. Lau, J. Am. Chem.

Soc. 109, 985 (1987); d) R. F. W. Bader, P. L. A.

Popelier, T. A. Keith, Angew. Chem.,Int. Ed. Engl.

33, 620 (1994).

[14] M. J. Calhorda, P. E. M. Lopes, A. Schier, R. Herr-

mann, J. Organomet. Chem. 543, 93 (1997).

[15] M. W. Schmidt, K. K. Baldridge, J. A. Boatz, S. T.

Elbert, M. S. Gordon, J. H. Jensen, S. Koseki, M.

Matsunaga, K. A. Nguyen, S. J. Su, T. L. Windus,

M. Dupuis, J. A. Montgomery, J. Comput. Chem.

14,1347(1993).

[16] M. S. Gordon, M. T. Carroll, J. H. Jensen,

L. P. Davis, L. W. Burggraf, R. M. Guidry,

Organometallics 10, 2657 (1991).

[25] A. M. Torres, T. T. Nakashima, R. E. D. McClung,

J. Magn. Reson. 96, 103 (1992).

[17] M. W. Schmidt, T. L. Windus, M. S. Gordon, J. Am.

Chem. Soc. 117, 7480 (1995).

[18] D. Cremer, J. A. Pople, J. Am. Chem. Soc. 97, 1354

(1975).

[19] L. Pärkänyi, V. Fülöp, P. Hencsei, I. Koväcs, J. Or-

ganomet. Chem. 418, 173 (1991).

[26] Z. Otwinowski, W. Minor, Processing of X-ray

Diffraction Data Collected in Oscillation Mode, in

C. W. Carter (Jr.), R. M. Sweet (eds): Methods in

Enzymology, vol. 276, Academic Press; New York

(1997).

[20] T. Kemmit, W. Henderson, J. Chem. Soc., Perkin

Trans. 1,729(1997).

[21] L. Pärkänyi, P. Hencsei, L. Bihätsi, T. Müller, J. Or-

ganomet. Chem. 269, 1 (1984).

[22] G. I. Csonka, P. Hencsei, J. Mol. Struct. (Theochem)

362, 199(1996).

[27] A. Altomare, G. Cascarano, C. Giacovazzo, A. Gua-

gliardi, J. Appl. Crystallogr. 26, 343 (1993).

[28] G. M. Sheldrick, SHELXL-97, Program for Crystal

Structure Refinement, Universität Göttingen, 1997.

[29] A. L. Spek, Acta Crystallogr. A46, C-34 (1990).

Brought to you by | New York University Bobst Library Technical Services

Authenticated

Download Date | 8/6/15 3:14 PM

Article Doi

Synthesis and structure of chiral silatranes derived from terpenes

DOI: 10.1515/znb-2001-0105

Source and publish data:

Authors:

Article abstract of DOI:10.1515/znb-2001-0105

Full text of DOI:10.1515/znb-2001-0105

Products guided by the article

R&D Labs maybe for 338800-70-7

Relevant to this article

Hot Product