Sila-α-galbanone and analogues: Synthesis and olfactory characterization of silicon-containing derivatives of the galbanum odorant α-galbanone

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DOI:10.1002/ejic.201402597

Sila-α-galbanone and Analogues: Synthesis and Olfactory

Characterization of Silicon-Containing Derivatives of the

Galbanum Odorant α-Galbanone

Steffen Dörrich,^[a]Anna Ulmer,^[a]Christoph Mahler,^[a]

Christian Burschka,^[a]Johannes A. Baus,^[a]Reinhold Tacke,*^[a]

An Chai,^[b]Changming Ding,^[b]Yue Zou,^[b]Gerhard Brunner,^[c]

Andreas Goeke,^[c]and Philip Kraft*^[c]

Keywords: Silicon / Spiro compounds / Metathesis / Hydroformylation / Fragrances / Galbanum

Silicon compounds 1b–3b are sila-analogues of the galbanum

odorants α-galbanone (1a), α-spirogalbanone (2a), and nor-

α-galbanone (3a), respectively. Sila-α-galbanone (1b), sila-α-

spirogalbanone (2b), and sila-nor-α-galbanone (3b) were

synthesized in multistep syntheses in isomerically pure form,

starting from Me₂SiCl₂, (CH₂=CH)₂SiCl₂, and Me₂(CH₂=CH)-

SiCl, respectively. Hydroformylation of vinylsilanes, followed

by either ring-closing aldol condensation or ring-closing al-

kene metathesis, were the key steps in these syntheses. The

C/Si pairs 1a/1b, 2a/2b, and 3a/3b were studied for their ol-

factory properties. All compounds possess green-fruity gal-

banum-type odors with pineapple aspects and thus are olfac-

torily related. However, sila-analogues 1b–3b were found to

be weaker than the corresponding parent carbon compounds

1a–3a. This effect is most pronounced for the C/Si pair 2a/2b

as indicated by the odor thresholds of 0.023 ngL^–1air (2a)

and 3.8 ngL^–1air (2b). However, due to their higher molec-

ular mass, the silicon compounds are less volatile and thus

more substantive in functional applications. In contrast to the

stable 5-silacyclohex-1-enes 1b and 2b, the 4-silacyclopent-

1-ene 3b shows a limited chemical stability. For compound

3a an extremely low odor threshold of 0.0087 ngL^–1air was

measured, and the silicon analogue 3b with an odor thresh-

old of 0.085 ngL^–1air is the sila-odorant with the lowest odor

threshold measured so far.

the most successful odorants in perfumery in its own right.

α-Galbanone (α-dynascone, 1a) and its use in the ‘Galbex

183’ base was essential for the modernization of the Fou-

gère family, starting with Pierre Bourdon’s ‘Cool Water’

(Davidoff, 1988).^[2]A modern representative of such a Fou-

gère fragrance with its light and fizzy green–galbanum

freshness is, for instance ‘Eros’ (Versace, 2012) by Aurelien

Guichard. A distinct pineapple character is even essential in

such a woody-mossy composition as ‘Legend’ (Montblanc,

2011) that Olivier Pescheux and Céline Perdriel created

around Evernyl and Pomarose. Replacement of the gem-

dimethyl substituents of 1a by a ring system (Ǟ 2a) was

found to significantly enhance the substantivity of this

modern note and thus transposes the fruity-green galba-

num-pineapple freshness to the fond of a creation (Fig-

ure 1).^[3]Consequently, α-spirogalbanone (2a) brings par-

ticular advantages to laundry-care applications, where sub-

stantivity is a key feature, and long-lasting freshness is in

high demand. However, as ‘Hugo Red’ (Hugo Boss, 2013)

or Olivier Gillotin’s ‘Polo Red’ (Ralph Lauren, 2013) prove,

a long-lasting fresh green-metallic galbanum character can

also be of interest in fine fragrances. Most synthetic routes

to 1a and 2a lead to isomeric mixtures composed, in large

Introduction

α-Galbanone (α-dynascone, 1a) was discovered in 1972

by its powerful galbanum odor as a trace impurity in an

early α-damascone synthesis based on the cyclization of

pseudo-damascone (Figure 1).^[1]Resulting from allo-cycli-

zation of the 10-methyl-6-methyleneundeca-1,9-dien-4-yne

intermediate, the green, fruity-floral smelling homoallyl

ketone 1a that recalls galbanum resin, pineapples, and hya-

cinths, first led to the rejection of the early α-damascone

batches, but after its structure elucidation, olfactory evalu-

ation, and commercial synthesis in 1974 it became one of

[a] Universität Würzburg, Institut für Anorganische Chemie,

Am Hubland, 97074 Würzburg, Germany

E-mail: r.tacke@uni-wuerzburg.de

http://www-anorganik.chemie.uni-wuerzburg.de/

forschungsgruppen/prof_dr_reinhold_tacke/arbeitsgruppe_

research_group/

[b] Givaudan Fragrances (Shanghai) Ltd.,

Li Shi Zhen Road 298, 201203 Shanghai, China

[c] Givaudan Schweiz AG, Fragrance Research,

Überlandstrasse 138, 8600 Dübendorf, Switzerland

E-mail: philip.kraft@givaudan.com

http://ww w .givaudan.com

Supporting information for this article is available on the

WWW under http://dx.doi.org/10.1002/ejic.201402597.

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part, of the significantly weaker β-isomers 1aЈ and 2aЈ,

which are also far less typical in their galbanum character

(Figure 1).^[3,4]

Results and Discussion

Syntheses

Sila-α-galbanone (1b) was synthesized according to

Scheme 1, starting from dichlorodimethylsilane. Thus, reac-

tion of Me₂SiCl₂with vinylmagnesium chloride afforded di-

methyldivinylsilane (4, 86% yield),^[10]which upon rhodium-

catalyzed {[Rh(CO)₂acac]} hydroformylation under an at-

mosphere of hydrogen and carbon monoxide, in the pres-

ence of triphenylphosphine, furnished 3,3Ј-(dimethylsilane-

diyl)dipropanal (5, 17% yield). Intramolecular aldol con-

densation of 5 under acidic conditions (HCl/Et₂O) then fur-

nished

5,5-dimethyl-5-silacyclohex-1-ene-1-carbaldehyde

(6). To optimize the yield of 6, this compound was prepared

from 4 in a one-pot synthesis, without isolation of interme-

diate 5, to give 6 in 36% yield (relative to 4). Reaction of 6

with but-3-en-1-ylmagnesium bromide and subsequent

hydrolysis with water/ammonium chloride then afforded

1-(5,5-dimethyl-5-silacyclohex-1-en-1-yl)pent-4-en-1-ol (7,

Figure 1. Chemical structures of compounds 1a, 1aЈ, 1b, 2a, 2aЈ,

2b, 3a, and 3b.

Here we report the synthesis of silicon compounds 1b 92% yield). Oxidation of 7 with 1,1,1-tris(acetyloxy)-1,1-

(sila-α-galbanone) and 2b (sila-α-spirogalbanone), repre- dihydro-1,2-benziodoxol-3(1H)-one (Dess–Martin per-

senting sila-analogues of the galbanum odorants 1a and 2a iodinane, DMP) furnished sila-α-galbanone (1b) in 52%

(replacement of the quaternary carbon atoms by silicon yield.

atoms; Figure 1). We have succeeded in developing an ef-

Sila-α-spirogalbanone (2b) was synthesized according to

ficient synthetic strategy that exclusively leads to the desired Scheme 2, starting from dichlorodivinylsilane. Thus, reac-

α-isomers. The 5-silacyclohexene skeletons of 1b and 2b tion of (CH₂=CH)₂SiCl₂with 1,4-bis(bromomagnesio)-

were built up by hydroformylation of divinylsilanes, fol- butane afforded 1,1-divinylsilolane (8, 93% yield), which

lowed by an intramolecular aldol condensation.^[5,6]As we upon

rhodium-catalyzed

{[Rh(CO)₂acac]}

hydro-

found in our systematic investigations on silicon-based formylation under an atmosphere of hydrogen and carbon

odorants,^[7,8]a sila-substitution generally much decreases monoxide, in the presence of triphenylphosphine, furnished

the vapor pressure of odorants. Therefore, in addition to 3,3Ј-(silolane-1,1-diyl)dipropanal (9, 10% yield). Intramo-

the synthesis and olfactory characterization of the C/Si lecular aldol condensation of 9 under acidic conditions

pairs 1a/1b and 2a/2b, it was interesting to prepare the HCl/Et₂O) then furnished 5-silaspiro[4.5]dec-7-ene-7-car-

structurally related C/Si pair 3a/3b as well and to compare baldehyde (10). To optimize the yield of 10, this compound

its olfactory properties with those of the C/Si pairs 1a/1b was also prepared from 8 in a one-pot synthesis, without

and 2a/2b (Figure 1). nor-α-Galbanone (3a) was also pat- isolation of intermediate 9, to give 10 in 33% yield (relative

ented for use in perfumery compositions,^[9]but ascribed a to 8). Reaction of 10 with but-3-en-1-ylmagnesium bromide

strong, less distinct, aggressive fruity odor character remi- and subsequent hydrolysis with water/ammonium chloride

niscent of plum and pear scents.^[9]It was thus interesting to then afforded 1-(5-silaspiro[4.5]dec-7-en-7-yl)pent-4-en-1-ol

verify the odor description of 3a and to study the influence (11, 86% yield). Oxidation of 11 with DMP furnished 2b in

of the sila-substitution (Ǟ sila-nor-α-galbanone, 3b) on the 45% yield with a purity of 99.5%. Since further purification

odor profile.

of 2b could neither be achieved by chromatography nor by

Scheme 1. Synthesis of compound 1b.

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Scheme 2. Synthesis of compound 2b.

distillation, ketone 2b was converted by an acid-catalyzed reaction of Me₂(CH₂=CH)SiCl with 3-methylbut-2-en-1-yl-

(sulfuric acid) reaction with (2,4-dinitrophenyl)hydrazine to magnesium chloride afforded dimethyl(3-methylbut-2-en-1-

the corresponding (2,4-dinitrophenyl)hydrazone 12b (55% yl)vinylsilane (13, 74% yield), which upon rhodium-cata-

yield), which could be purified by recrystallization and then lyzed {[HRhCO(PPh₃)₃]} hydroformylation under an atmo-

transformed to 2b by treatment with acetone in the presence sphere of hydrogen and carbon monoxide, in the presence

of p-toluenesulfonic acid (p-TsOH). Thus, the olfactorily of triphenylphosphine, furnished 3-[dimethyl(3-methylbut-

pure target compound 2b was isolated in 72% yield (relative 2-en-1-yl)silyl]propanal (14, 63% yield). In the next step, an

to 12b).

α-methylenation with formaldehyde, catalyzed by pyr-

Sila-nor-α-galbanone (3b) was synthesized according to rolidine/propanoic acid,^[11]provided 2-{[dimethyl(3-meth-

Scheme 3, starting from chlorodimethylvinylsilane. Thus, ylbut-2-en-1-yl)silyl]methyl}acrylaldehyde (15, 42% yield).

Scheme 3. Synthesis of compound 3b.

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Subsequent reduction with lithium aluminum hydride, fol- 2b, the ketones 1a, 1b, and 2a were also transformed into

lowed by aqueous work-up, and treatment of the resulting the corresponding crystalline (2,4-dinitrophenyl)hydrazones

crude alcohol with acetyl chloride, in the presence of tri- 12a, 20a, and 20b (Figure 2), and the C/Si pairs 12a/12b and

ethylamine, furnished 2-{[dimethyl(3-methylbut-2-en-1-yl)- 20a/20b were structurally characterized by single-crystal X-

silyl]methyl}allyl acetate (16, 78% yield). Ruthenium-cata- ray diffraction (see section crystal structure analyses below).

lyzed (Zhan Cat 1B)^[12]ring-closing metathesis^[13]of 16 then Compounds 12a, 20a, and 20b were obtained by using the

afforded

(4,4-dimethyl-4-silacyclopent-1-en-1-yl)methyl same synthetic method as described above for the genera-

acetate (17, 62% yield). Reduction of 17 with lithium alumi- tion of 12b (see Scheme 2); for the characterizations of 12a,

num hydride, followed by aqueous work-up, furnished (4,4- 20a, and 20b, see the Supporting Information.

dimethyl-4-silacylopent-1-en-1-yl)methanol (18, 90% yield).

Subsequent Oppenauer oxidation using 4-nitrobenzalde-

Crystal Structure Analyses

hyde as the hydrogen acceptor, in the presence of aluminum

tri-sec-butoxide and acetic acid, afforded the corresponding

crude aldehyde. Treatment of the crude aldehyde with but-

3-en-1-ylmagnesium chloride, followed by aqueous work-

up, provided 1-(4,4-dimethyl-4-silacyclopent-1-en-1-yl)pent-

4-en-1-ol (19, 21% yield). Oppenauer oxidation with 4-

nitrobenzaldehyde, in the presence of aluminum tri-sec-

butoxide and acetic acid, finally afforded 3b (50% yield).

Compound 3b turned out to have only limited stability at

ambient conditions, and attempts to purify 3b by silica gel

chromatography led to partial decomposition. However,

compound 3b proved to be thermally stable under mild dis-

tillation conditions, and an olfactorily pure sample of 3b

could be obtained by bulb-to-bulb distillation, thus al-

lowing analytical characterization and olfactory evaluation

(for the synthesis and characterization of the parent carbon

compound 3a, see the Supporting Information).

Compounds 12a, 12b, 20a, and 20b were structurally

characterized by single-crystal X-ray diffraction.^[14]The

structures are depicted in Figures 3, 4, 5, and 6 (for further

details, see the Supporting Information). As can be seen

from superpositioning of the C/Si pairs 12/12b and 20a/20b

(Figures 7 and 8), the structural features of the molecular

skeletons of the respective C/Si analogues are similar; how-

ever, the different covalent radii of carbon and silicon also

result in some striking structural differences.

Compounds 1b, 2b, 3b, and 4–19 were isolated as color-

less or yellowish (3b and 19 only) liquids, whereas 12b was

obtained as a red crystalline solid. The chiral alcohols 7,

11, and 19 were obtained as racemates. At first glance, some

of the product yields appear somewhat unsatisfactory; how-

ever, it is important to note that we were aiming to prepare

olfactorily pure products for sensory evaluation, if neces-

sary, at the expense of the chemical yields. The identities of

1b, 2b, 3b, 4–11, 12b, and 13–19 were established by elemen-

tal analyses or high-resolution mass spectrometry and by

Figure 3. Molecular structure of 12a in the crystal.

Figure 7 shows the superposition of the molecular skel-

NMR spectroscopic studies. In addition, compound 12b etons of 12a with 12b-I and 12b-II. Both the cyclohexene

was structurally characterized by single-crystal X-ray dif- ring of 12a and the silacyclohexene rings of 12b-I and 12b-

fraction.

II adopt half-chair conformations, with the silicon-based

To get some information about the structures of the cy- ring system being flatter. The cyclopentane ring of 12a

clic and spirocyclic skeletons of the C/Si pairs 1a/1b and 2a/ adopts an envelope conformation, whereas the silacyclo-

pentane rings of 12b-I and 12b-II adopt half-chair confor-

mations, leading to significant changes in the shape and size

of the C/Si analogues.

Figure 8 shows the superpositions of the molecular skel-

etons of 20a-I and 20a-II with those of 20b-I and 20b-II,^[15]

clearly indicating the greater flexibility of the silacyclohex-

ene ring. Whereas the cyclohexene rings of 20a-I and 20a-

II are very similar and adopt a half-chair conformation,

both a half-chair (20b-I) and a boat conformation (20b-II)

were observed for the silacylohexene ring. Due to the longer

Si–C distances compared to the analogous C–C bond

lengths, the silacyclohexene ring is flatter than the cyclohex-

ene ring.

In conclusion, the crystal structure analyses of the C/Si

pairs 12a/12b and 20a/20b revealed some differences in the

Figure 2. Chemical structures of compounds 12a, 12b, 20a, and

20b.

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Figure 4. Molecular structures of the two crystallographically independent molecules in the crystal of 12b (molecule I, left; molecule II,

right).

Figure 5. Molecular structures of two of the eight crystallographically independent molecules in the crystal of 20a (molecule I, left;

molecule II, right). The structures of the other six molecules are very similar. One of these molecules is disordered (two different conforma-

tions of the olefinic side chain).

Figure 6. Molecular structures of two of the four crystallographically independent molecules in the crystal of 20b (molecule I, left;

molecule II, right). Molecules I and II are disordered (molecule I: two different conformations of the olefinic side chain, occupancy of

the depicted structure 62%; molecule II: two different conformations of the silacyclohexene ring, occupancy of the depicted structure

57%; two different conformations of the olefinic side chain, occupancy of the depicted structure 70%). The other two molecules are also

disordered, and the structures of the dominant conformers are very similar to those of the dominant conformers of molecules I and II,

respectively.

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Table 1. Olfactory properties of the C/Si pairs 1a/1b, 2a/2b, and 3a/

3b.

Olfactory properties

Odor threshold

[ngL^–1air]

1a Green-fruity, galbanum, pineapple, with a

herbal-floral hyacinth character, slightly oily

1b Green-fruity, galbanum, pineapple, with the

typical character of α-galbanone (1a), yet with-

out its hyacinth aspects, slightly fatty

0.027

0.094

2a Powerful, green, galbanum, fruity, pineapple,

slightly allylic

2b Green-fruity, galbanum, pineapple, with

metallic facets, close to α-galbanone (1a), yet

without its hyacinth aspects

0.023

3.8

Figure 7. Superpositions (atoms C/Si and C5–C9) of the molecular

skeletons of 12a (grey) and 12b-I (black, left) and 12a (grey) and

12b-II (black, right). Hydrogen atoms are omitted for clarity.

3a Powerful, fruity, pineapple, green, α-galbanone-

like, metallic, pungent, slightly sulfurous

3b Intense fruity-green, pineapple, α-galbanone-

like, pungent, slightly sulfurous

0.0087

0.085

ferring a fresh-fruity green galbanum–pineapple effect to

the dry-down of a fragrance or in fabric-care applications.

Its powerful odor profile is green, galbanum, fruity, pineap-

ple, and accompanied by slight allylic facets. The odor

threshold of 2a is drastically impaired by C/Si exchange

(Ǟ 2b). With an odor threshold of 3.8 ngL^–1air, silicon an-

alogue 2b is almost 170 times less potent than its parent

carbon compound 2a, although it still constitutes a reason-

able odorant. The structural differences in terms of shape

Figure 8. Superpositions (atoms C/Si, C1–C3, and C7) of the

molecular skeletons of the dominant conformers of 20a-I (grey)

and 20b-I (black, top left), 20a-I (grey) and 20b-II (black, top

right), 20a-II (grey) and 20b-I (black, bottom left), and 20a-II and size of the C/Si analogues 2a and 2b (see Figure 7)

(grey) and 20b-II (black, bottom right). Hydrogen atoms are omit-

ted for clarity.

likely impair the interactions of 2b with the hydrophobic

receptor binding pocket(s). Moreover, the relative position

and orientation of the endocyclic double bond relative to

molecular structures of the respective C/Si analogues. Anal-

the receptor binding site appears to be critically important.

ogous structural differences may play a role in dictating

Although the odor threshold is strongly affected, the odor

odor perception characteristics of the odorants 1a/1b and

2a/2b.

profile of 2a changes rather subtly upon sila-substitution

(Ǟ 2b). Sila-α-spirogalbanone (2b) also has a green-fruity

odor recalling galbanum resin and pineapples, close to α-

galbanone (1a), and also with metallic facets, yet without

its hyacinth aspects. With its considerably enhanced sub-

Olfactory Characterization

Compounds 1a, 1b, 2a, 2b, 3a, and 3b were studied for stantivity and adhesive power on textile fibers – possibly

their olfactory properties (Table 1). All compounds possess as a consequence of the enhanced lipophilicity of the sila-

green-fruity, galbanum-type odors with pineapple aspects analogue – silicon compound 2b shows good performance

and thus are olfactorily related.

in laundry applications (detergents, softeners), compensat-

With its hyacinth character, α-galbanone (1a) is the most ing to some extent for the poor odor threshold. The sub-

floral, hyacinth-like compound within the series investi- stantivity is thus enhanced both by replacement of the gem-

gated. It exhibits an additional slightly oily impression and dimethyl substituents with a spiro ring (1aǞ2a and

possesses an odor threshold of 0.027 ngL^–1air. Upon sila- 1bǞ2b) and by C/Si exchange (1aǞ1b and 2aǞ2b).

substitution (Ǟ 1b), the floral facets vanish, and the slightly

Such an enhancement of substantivity should be espe-

oily impression becomes somewhat more perceptible. As a cially useful for the α-galbanone homologue 3a. Contrary

result, the linear odor profile of sila-α-galbanone (1b) is to the strong, less distinct, aggressive fruity, plum- and

more pronounced green. With an odor threshold of pear-type odor ascribed in the patent literature,^[9]3a was

0.094 ngL^–1air, sila-α-galbanone (1b) is almost 3 times less found to possess a typical α-galbanone-like, fruity-green,

intense than α-galbanone (1a), but the increased molecular pineapple odor, accompanied by metallic, pungent facets,

mass of 1b leads to its enhanced substantivity in functional and slightly sulfurous aspects (Table 1). However, most

applications.

interesting was its extremely low odor detection threshold

α-Spirogalbanone (2a), with an odor threshold of of 0.0087 ngL^–1air, which is about three times lower than

0.023 ngL^–1air, is comparable with α-galbanone (1a), but that of the commercial α-galbanum odorants 1a and 2a.

due to its higher molecular mass it is even more substantive Indeed, sila-analogue 3b turned out to be very similar in

than sila-α-galbanone (1b) and is therefore useful in trans- odor profile, possessing an intense fruity-green, pineapple

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and galbanum odor with pungent facets, and slightly sulfu-

rous aspects. However, silicon compound 3b showed only a

limited stability at ambient conditions, which was not ob-

served for the less strained silacyclohexenes 1b and 2b. The

reasons for this instability will be further investigated. Thus,

an increased substantivity upon C/Si exchange could not be

taken advantage of. Again sila-analogue 3b turned out to

possess a significantly higher odor threshold than the par-

ent compound 3a, with 0.085 ngL^–1air being almost about

ten times higher than that of 3a (0.0087 ngL^–1air). Con-

cerning structure–odor correlations, silicon compound 3b

constitutes the most potent sila-odorant of the series, and

is, in fact, the sila-odorant with the lowest threshold mea-

sured thus far in our laboratory.^[7,8]

Experimental Section

General Methods: All syntheses in organic solvents were carried out

under dry argon. The organic solvents used were dried and purified

according to standard procedures and stored under dry nitrogen.

Starting materials and reagents were purchased from ABCR,

Acros, Aldrich, or Wacker and were used without further purifica-

tion. Filtrations were carried out by using silica gel (40–63 μm,

Merck). Flash chromatography (pressure, 1.5 bar) was performed

by using silica gel as the stationary phase (40–63 μm, Merck). Me-

dium pressure liquid chromatography (MPLC) was carried out as

follows: pressure, 16 bar; column, 50ϫ2.5 cm; stationary phase, sil-

ica gel (YMC SL12S15, 15 μm); detector, Knauer Variable Wave-

length Monitor. Compounds 1b and 2b were applied on the MPLC

column as solutions in their respective eluent through the sample

loop. Bulb-to-bulb distillations were performed by using a Büchi

Glass Oven B-580 apparatus. Melting points were determined by

differential scanning calorimetry using a Mettler Toledo DSC 823e

1

apparatus. The H, ¹³C, ¹⁵N (12b only) and ²⁹Si NMR spectra of

compounds 1b, 2b, 4–11, 12b, 20a, and 20b were recorded at 23 °C

with a Bruker Avance 500 NMR spectrometer (¹H, 500.1 MHz;

¹³C, 125.8 MHz; ¹⁵N, 50.7 MHz; ²⁹Si, 99.4 MHz) using C₆D₆as

Conclusions

Sila-α-galbanone (1b), sila-α-spirogalbanone (2b), and

sila-nor-α-galbanone (3b) are sila-analogues of the galba-

num odorants α-galbanone (1a), α-spirogalbanone (2a),

and nor-α-galbanone (3a), respectively. The silicon com-

pounds 1b–3b were prepared in multistep syntheses in iso-

merically pure form, starting from the silanes Me₂SiCl₂,

(CH₂=CH)₂SiCl₂, and Me₂(CH₂=CH)SiCl, respectively.

Hydroformylation of vinylsilanes, followed by either ring-

closing aldol condensations or ring-closing alkene metathe-

ses, were the key steps in these syntheses.

1

the solvent. The H and ¹³C NMR spectra of compounds 3b and

13–19 were recorded at ambient temperature with a Bruker AW

300 NMR spectrometer (¹H, 300.1 MHz; ¹³C, 75.5 MHz) using

C₆D₆(3b) or CDCl₃(13–19) as the solvent. Chemical shifts (ppm)

were determined relative to internal C₆HD₅(¹H, δ = 7.28 ppm;

C₆D₆), internal C₆D₆(¹³C, δ = 128.0 ppm; C₆D₆), internal CHCl₃

(¹H, δ = 7.24 ppm. CDCl₃), internal CDCl₃(¹³C, δ = 77.0 ppm.

CDCl₃), external H₂NC(O)H (90% in [D₆]DMSO) (¹⁵N, δ =

–268.0 ppm; C₆D₆), or external tetramethylsilane (²⁹Si, δ = 0 ppm;

C₆D₆). Assignment of the ¹H NMR spectroscopic data was sup-

ported by ¹H,¹H gradient-selected COSY, ¹H,¹H EXSY/NOESY

(mixing time, 500 ms; recycle delay, 2.0 s), ¹³C,¹H gradient-selected

HMQC and HMBC experiments, and DEPT-90 as well as DEPT-

135 experiments. Assignment of the ¹³C NMR spectroscopic data

was supported by the aforementioned ¹³C,¹H correlation experi-

ments. The ¹⁵N NMR spectra were obtained by using inverse corre-

lation ¹⁵N,¹H HSQC and HMBC experiments. The spin systems were

analyzed with the WIN-DAISY (version 4.05, Bruker)^[16]or

MestReNova software packages (version 9.0.0, Mestrelab Research

SL).^[17]Coupling constants are given as their absolute values. High

pressure liquid chromatography (HPLC) was performed as follows:

LC pump, Merck Hitachi LaChrom L-7100; column, 25 cm, i.d.

400 nm; stationary phase, silica gel (YMC SL 12S052504QT, 5 μm);

detector, Merck Hitachi L-4200 UV/Vis Detector. Elemental analy-

ses were performed with a VarioMicro apparatus (Elementar Ana-

lysensysteme GmbH) or a EURO EA Elemental Analyzer (Euro-

Vector). EI-MS spectra (70 eV) were recorded using an Agilent

MSD 5975 mass spectrometer. The selected m/z values given refer

to the isotopes ¹H, ¹²C, ¹⁶O, and ²⁸Si. HRMS spectra were recorded

with a Bruker MicrOTOF II (15. ESI) or a Finnigan MAT 95 mass

spectrometer (EI; 3b, 13, 14, 16–19).

The olfactory evaluations of the three C/Si pairs 1a/1b,

2a/2b, and 3a/3b once again demonstrated that the impact

of sila-substitution on the olfactory properties of odorants

is hardly predictable. Although the odor threshold of 1a is

affected very little upon sila-substitution, in the case of 2a

(Ǟ 2b) the receptor affinity, as indicated by the detection

odor threshold, decreased almost 170-fold. Also, in the case

of 3b, the odor threshold increased significantly, but only

by a factor of about 10. The odor profiles of the sila-ana-

logues 1b, 2b, and 3b and their parent carbon compounds

1a, 2a, and 3a are, however, clearly related, albeit the floral

hyacinth character of 1a and 2a was missing in the case of

their sila-analogues 1b and 2b. Taken together, these results

could indicate an interaction of 1a/1b, 2a/2b, and 3a/3b with

the same set of olfactory receptors, but with different steric

constraints within the hydrophobic binding pockets, espe-

cially with respect to the position of the endocyclic double

bonds. These effects are then multiplied by the steric expan-

sion in the case of sila-α-spirogalbanone (2b), yet are some-

what less relevant for the monocyclic compounds sila-α-gal-

banone (1b) and sila-nor-α-galbanone (3b). A surprising

finding was the extremely low odor threshold of

0.0087 ngL^–1air measured for nor-α-galbanone (3a). Im-

portantly, sila-nor-α-galbanone (3b), with an odor threshold

of 0.085 ngL^–1air, is the sila-odorant with the lowest odor

threshold measured by us thus far. The strong impact of

sila-substitution on odor thresholds reported in this study

again emphasizes the high potential of the C/Si switch strat-

egy in the exploration of structure–activity correlations.

1-(5,5-Dimethylcyclohex-1-en-1-yl)pent-4-en-1-one (α-Galbanone,

1a): This compound was synthesized according to ref.^[4]Odor de-

scription: green-fruity, galbanum, pineapple, with a herbal-floral

hyacinth character, slightly oily; odor threshold: 0.027 ngL^–1air.

1-(5,5-Dimethyl-5-silacyclohex-1-en-1-yl)pent-4-en-1-one

(Sila-α-

galbanone, 1b): 1,1,1-Tris(acetyloxy)-1,1-dihydro-1,2-benziodoxol-

3(1H)-one (Dess–Martin periodinane) (1.61 g, 3.80 mmol) was

added at 0 °C in a single portion to a stirred solution of 6 (800 mg,

3.80 mmol) in dichloromethane (60 mL), and the mixture was then

warmed to 20 °C within 1 h. A saturated aqueous sodium hydrogen

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carbonate solution (50 mL) was added, the organic layer was sepa-

rated, the aqueous layer was extracted with dichloromethane (3ϫ

50 mL) and discarded, the combined organic solutions were dried

with anhydrous sodium sulfate, and the solvent was removed under

reduced pressure. The residue was filtered through a pad of silica

gel (150 g), followed by elution with n-hexane/Et₂O (98:2 v/v). The

solvent of the filtrate (including the eluate) was removed under re-

duced pressure, and the residue was purified by twofold MPLC on

silica gel [eluent, n-hexane/Et₂O (99.5:0.5 v/v); flow rate,

65 mLmin^–1; detector wavelength, 230 nm], followed by bulb-to-

bulb distillation (oven temperature 115 °C, 0.01 mbar) to furnish

and filtered through a pad of silica gel (30 g), followed by elution

with n-hexane/Et₂O (95:5 v/v). The solvent of the filtrate (including

the eluate) was removed under reduced pressure, and the residue

was purified by flash chromatography on silica gel [eluent, n-hex-

ane/Et₂O (98:2 v/v)], followed by bulb-to-bulb distillation (oven

temperature 135 °C, 0.01 mbar) to furnish 2b as a colorless liquid

1

(450 mg, 1.92 mmol; 72% yield). H NMR (500.1 MHz, C₆D₆): δ

= 0.60 (δ_AAЈ), 0.63 (δ_BBЈ), 1.62 (δ_XXЈ), 1.65 (δ_YYЈ) [AAЈBBЈXXЈYYЈ

system, ²J(A,B) = ²J(AЈ,BЈ) = 14.8, ²J(X,Y) = ²J(XЈ,YЈ) = 12.9,

3

³J(A,X) = J(AЈ,XЈ) = 7.6, J(A,Y) = J(AЈ,YЈ) = 7.1, J(B,X) =

³J(BЈ,XЈ) = 7.1, ³J(B,Y) = ³J(BЈ,YЈ) = 7.6, ³J(X,XЈ) = 4.9, ³J(X,YЈ)

1

1b as a colorless liquid (410 mg, 1.97 mmol; 52% yield). H NMR

=

³J(XЈ,Y) = 7.7, ³J(Y,YЈ) = 5.0, ⁴J(A,XЈ) = ⁴J(AЈ,X) = 0.7,

(500.1 MHz, C₆D₆): δ = 0.04 (s, 6 H, SiCH₃), 0.56 (δ_AAЈ), 1.72 ⁴J(A,YЈ) = J(AЈ,Y) = 0.3, J(B,XЈ) = J(BЈ,X) = 0.4, J(B,YЈ) =

4

(δ_DDЈ), 2.21 (δ_HHЈ), 6.65 (δ_X) [AAЈDDЈHHЈX system, ²J(A,AЈ) = ⁴J(BЈ,Y) = 0.7 Hz, 8 H; SiCH_AH_BCH_XH_YCH_XЈH_YЈCH_AЈH_BЈ], 0.67

3

12.4, ²J(D,DЈ) = 12.4, ²J(H,HЈ) = 15.2, ³J(A,H) = J(AЈ,HЈ) = 6.1, (δ_AAЈ), 1.82 (δ_DDЈ), 2.23 (δ_HHЈ), 6.65 (δ_X) [AAЈDDЈHHЈX system,

3

4

³J(A,HЈ) = J(AЈ,H) = 7.8, J(H,X) = J(HЈ,X) = 5.3, J(D,X) = ²J(A,AЈ) = 11.0, ²J(D,DЈ) = 9.4, ²J(H,HЈ) = 13.6, ³J(A,H) =

⁴J(DЈ,X) = 1.4, J(D,H) = ⁵J(DЈ,HЈ) = 1.2, J(D,HЈ) = ⁵J(DЈ,H) = ³J(AЈ,HЈ) = 6.0, J(A,HЈ) = J(AЈ,H) = 7.8, J(H,X) = J(HЈ,X) =

5

3

1.8 Hz, 7 H; SiCH_AH_AЈCH_HH_HЈCH_X=CCH_DH_DЈ], 2.52 (δ_AAЈ), 5.3, ⁴J(D,X) = ⁴J(DЈ,X) = 1.4, ⁵J(D,H) = ⁵J(DЈ,HЈ) = 2.1, ⁵J(D,HЈ)

2.59 (δ_DDЈ), 5.06 (δ_F), 5.13 (δ_M), 5.93 (δ_X) [AAЈDDЈFMX

=

⁵J(DЈ,H) = 0.8 Hz, 7 H; SiCH_AH_AЈCH_HH_HЈCH_X=CCH_DH_DЈ],

2

3

system, J(A,AЈ) = 15.0, J(D,DЈ) = 16.8, J(F,M) = 2.0, J(A,D) 2.51 (δ_AAЈ), 2.58 (δ_DDЈ), 5.06 (δ_F), 5.13 (δ_M), 5.93 (δ_X)

=

³J(AЈ,DЈ)

³J(AЈ,X) = 6.6, ³J(F,X) = 10.2, ³J(M,X) = 17.1, ⁴J(A,F) =

1.2, ⁴J(A,M) ⁴J(AЈ,M)

1.6 Hz, 7 H;

CH_DH_DЈCH_AH_AЈCH_X=CH_FH_M] ppm. ¹³C NMR (125.8 MHz,

= = =

6.2, ³J(A,DЈ) ³J(AЈ,D) 8.8, ³J(A,X) [AAЈDDЈFMX system, J(A,AЈ) = 15.0, J(D,DЈ) = 16.8, J(F,M)

2

= 2.0, ³J(A,D) = ³J(AЈ,DЈ) = 6.2, ³J(A,DЈ) = ³J(AЈ,D) = 8.7,

⁴J(AЈ,F)

=

³J(A,X) = ³J(AЈ,X) = 6.6, ³J(F,X) = 10.2, ³J(M,X) = 17.1, ⁴J(A,F)

=

⁴J(AЈ,F) 1.2, ⁴J(A,M) ⁴J(AЈ,M)

= = = 1.6 Hz, 7 H;

C₆D₆): δ = –2.7 (SiCH₃), 9.2 (C-4), 10.8 (C-6), 23.7 (C-3), 29.2 CH_DH_DЈCH_AH_AЈCH_X=CH_FH_M] ppm.^{[19] 13}C NMR (125.8 MHz,

(CH₂CH=CH₂), 36.4 [C(O)CH₂], 114.9 (CH₂CH=CH₂), 138.3 C₆D₆): δ = 8.0 (C-10), 9.5 (C-6), 11.4 (C-1 and C-4), 23.9 (C-9),

(CH₂CH=CH₂), 139.6 (C-1), 140.4 (C-2), 199.0 (CO) ppm. ²⁹Si

NMR (99.4 MHz, C₆D₆): δ = –2.1 ppm. C₁₂H₂₀OSi (208.38): calcd.

C 69.17, H 9.67; found C 69.17, H 9.79; odor description: green-

fruity, galbanum, pineapple, with the typical character of α-gal-

banone (1a), yet without its hyacinth aspects, slightly fatty; odor

threshold: 0.094 ngL^–1air. For an alternative synthesis, see the

Supporting Information.

27.3 (C-2 and C-3), 29.2 (CH₂CH=CH₂), 36.4 [C(O)CH₂], 114.9

(CH₂CH=CH₂), 138.3 (CH₂CH=CH₂), 139.7 (C-7), 140.7 (C-8),

198.9 (CO) ppm. ²⁹Si NMR (99.4 MHz, C₆D₆): δ = 15.3 ppm.

C₁₄H₂₂OSi (234.41): calcd. C 71.73, H 9.46; found C 71.47, H 9.42;

odor description: green-fruity, galbanum, pineapple, with metallic

facets, close to α-galbanone (1a), yet without its hyacinth aspects;

odor threshold: 3.8 ngL^–1air.

1-(Spiro[4.5]dec-7-en-7-yl)pent-4-en-1-one (α-Spirogalbanone, 2a):

This compound was synthesized according to ref.^[3]Odor descrip-

tion: powerful, green, galbanum, fruity, pineapple, slightly allylic;

odor threshold: 0.023 ngL^–1air.

1-(4,4-Dimethyl-4-silacyclopent-1-en-1-yl)pent-4-en-1-one (Sila-nor-

α-galbanone, 3b): Aluminum tri-sec-butoxide (113 mg, 459 μmol)

was added at 20 °C to a stirred solution of 19 (300 mg, 1.53 mmol)

in tert-butyl methyl ether (30 mL), followed by the addition of ace-

tic acid (9.2 mg, 153 μmol). The resulting mixture was then stirred

at this temperature for 20 min, prior to evacuation of the system

and flushing twice with argon. Subsequently, 4-nitrobenzaldehyde

(924 mg, 6.11 mmol) was added at 20 °C in three portions, and the

reaction mixture was then stirred at this temperature for 30 min. n-

Hexane (30 mL) and anhydrous magnesium sulfate were added,

and the organic phase was separated by filtration. The solvent was

removed under reduced pressure at 20 °C, and the residue was puri-

fied by bulb-to-bulb distillation (oven temperature 80 °C,

0.015 mbar) to furnish 3b as a yellowish liquid (150 mg, 772 μmol;

50% yield). The product showed limited stability at ambient condi-

tions and decomposed when chromatographic purification on silica

gel was attempted. ¹H NMR (300.1 MHz, C₆D₆): δ = –0.03 (s, 6 H,

SiCH₃), 1.23 (δ_AAЈ), 1.62 (δ_DDЈ), 6.58 (δ_X) [AAЈDDЈX system,

1-(5-Silaspiro[4.5]dec-7-en-7-yl)pent-4-en-1-one

(Sila-α-spirogal-

banone, 2b). Method A: 1,1,1-Tris(acetyloxy)-1,1-dihydro-1,2-benz-

iodoxol-3(1H)-one (Dess–Martin periodinane) (17.1 g, 40.3 mmol)

was added at 0 °C in a single portion to a stirred solution of 10

(9.56 g, 40.4 mmol) in dichloromethane (400 mL), and the mixture

was then warmed to 20 °C within 1 h. A saturated aqueous sodium

hydrogen carbonate solution (150 mL) was added, the organic

phase was separated, the aqueous phase was extracted with di-

chloromethane (3ϫ 100 mL) and discarded, the combined organic

solutions were dried with anhydrous sodium sulfate, and the sol-

vent was removed under reduced pressure. The residue was filtered

through a pad of silica gel (200 g), followed by elution with n-hex-

ane/Et₂O (95:5 v/v). The solvent of the filtrate (including the eluate)

was removed under reduced pressure, and the residue was purified

by flash chromatography on silica gel [eluent, n-hexane/Et₂O

(98:2 v/v)], followed by MPLC on silica gel [eluent, n-hexane/acet-

one (99.8:0.2 v/v); flow rate, 50 mL min^–1; detector wavelength,

230 nm] and then by bulb-to-bulb distillation (oven temperature

135 °C, 0.01 mbar) to furnish 2b as a colorless liquid (4.30 g,

18.3 mmol; purity 99.5%; 45% yield). For the NMR spectroscopic

data, odor description, and odor threshold, see method B.

2

3

4

²J(AAЈ) = 17.5, J(DD)Ј = 17.5, J(DX) = J(DЈX) = 1.5, J(AD)

4

= J(AЈDЈ) = 1.8, J(ADЈ) = J(AЈD) = 1.7, J(AX) = J(AЈX) =

3.5 Hz, 5 H; SiCH_DH_DЈCH_X=CCH_AH_AЈ], 2.43 (δ_AAЈ), 2.49 (δ_BBЈ),

4.96 (δ_F), 5.03 (δ_M), 5.84 (δ_X) [AAЈBBЈFMX system, ²J(AAЈ) =

15.0, ²J(BBЈ) = 16.8, ²J(FM) = 2.0, ³J(AB) = ³J(AЈBЈ) = 8.8,

3

³J(ABЈ) = J(AЈB) = 6.2, J(AX) = J(AЈX) = 6.6, J(FX) = 10.2,

³J(MX) = 17.1, ⁴J(AF) = ⁴J(AЈF) = 1.2, ⁴J(AM) = ⁴J(AЈM) =

1.6 Hz, 7 H; CH_BH_BЈCH_AH_AЈCH_X=CH_FH_M] ppm. ¹³C NMR

(75.5 MHz, C₆D₆): δ = –2.2 (SiCH₃), 16.4 (C-5), 20.1 (C-3), 28.9

(CH₂CH=CH₂), 37.6 [C(O)CH₂], 114.9 (CH₂CH=CH₂), 138.3

(CH₂CH=CH₂), 142.2 (C-2), 145.3 (C-1), 198.1 (CO) ppm. EI-MS:

m/z (%) = 194 (10) [M]⁺, 179 (24), 165 (67), 153 (14), 135 (11), 111

Method B: A mixture of 12b (1.10 g, 2.65 mmol), p-toluenesulfonic

acid monohydrate (46 mg, 242 μmol), and acetone (50 mL) was

heated in a sealed tube at 60 °C for 65 h (for a similar method, see

ref.^[18]). The resulting mixture was then cooled to 20 °C within 1 h

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(17), 85 (14), 75 (100), 59 (15), 43 (8). HRMS (EI): m/z calcd. for flash chromatography on silica gel [eluent, n-hexane/Et₂O

C₁₁H₁₈OSi 194.1127, found 194.1120; odor description: intense

fruity-green, pineapple, α-galbanone-like, pungent, slightly sulf-

urous; odor threshold: 0.085 ngL^–1air.

(8:2 v/v)], followed by bulb-to-bulb distillation (oven temperature

70 °C, 0.01 mbar) to furnish 6 as a colorless liquid (7.50 g,

48.6 mmol; 36% yield). ¹H NMR (500.1 MHz, C₆D₆): δ = –0.02 (s,

6 H, SiCH₃), 0.51 (δ_AAЈ), 1.54 (δ_DDЈ), 2.17 (δ_HHЈ), 6.20 (δ_X)

Dimethyldivinylsilane (4):^[10]A 1.6 m solution of vinylmagnesium

chloride (1.07 L, 1.71 mol of CH₂=CHMgCl) was added dropwise

at 0 °C within 3 h to a stirred solution of dichlorodimethylsilane

(200 g, 1.55 mol) in Et₂O (600 mL), and the resulting mixture was

then heated under reflux for 2 h. The mixture was cooled to 20 °C

within 30 min, water (500 mL) was added, the organic phase was

separated, the aqueous phase was extracted with Et₂O (5ϫ

100 mL) and discarded, and the combined organic solutions were

dried with anhydrous sodium sulfate. The solvent was removed by

distillation at atmospheric pressure using a spinning band column,

and the residue was then purified by a further distillation at atmo-

spheric pressure with a spinning band column to furnish 4 as a

[AAЈDDЈHHЈX system, ²J(A,AЈ)

=

12.4, ²J(D,DЈ)

=

12.4,

²J(H,HЈ) = 15.2, J(A,H) = J(AЈ,HЈ) = 7.5, J(A,HЈ) = J(AЈ,H)

= 6.3, ³J(H,X) = ³J(HЈ,X) = 4.8, ⁴J(D,X) = ⁴J(DЈ,X) = 1.5,

⁵J(D,H) = ⁵J(DЈ,HЈ) = 2.0, ⁵J(D,HЈ) = ⁵J(DЈ,H) = 1.4 Hz, 7 H;

SiCH_AH_AЈCH_HH_HЈCH_X=CCH_DH_DЈ], 9.45 (CHO) ppm. ¹³C NMR

(125.8 MHz, C₆D₆): δ = –3.0 (SiCH₃), 8.4 (C-6), 9.4 (C-4), 21.1

(C-3), 141.2 (C-1), 152.4 (C-2), 194.0 (CHO) ppm. ²⁹Si NMR

(99.4 MHz, C₆D₆): δ = –3.6 ppm. C₈H₁₄OSi (154.28): calcd.

C 62.28, H 9.15; found C 62.15, H 9.15.

3

1-(5,5-Dimethyl-5-silacyclohex-1-en-1-yl)pent-4-en-1-ol

(7):

4-

Bromo-1-butene (11.4 g, 84.4 mmol) was added dropwise within

30 min to a suspension of magnesium turnings (2.60 g, 107 mmol)

in Et₂O (130 mL), causing the reaction mixture to boil under re-

flux. The mixture was heated under reflux for a further hour, co-

oled to 20 °C within 20 min, and then added dropwise at –10 °C

within 30 min to a stirred solution of 6 (8.70 g, 56.4 mmol) in Et₂O

(180 mL). The resulting mixture was warmed to 20 °C within

30 min and was then stirred at this temperature for a further hour,

a saturated aqueous solution of ammonium chloride (150 mL) was

added, the organic phase was separated, the aqueous phase was

extracted with Et₂O (3ϫ 100 mL) and discarded, and the combined

organic solutions were dried with anhydrous sodium sulfate. The

solvent was removed under reduced pressure, and the residue was

purified by flash chromatography on silica gel [eluent, n-hexane/

Et₂O (7:3 v/v)], followed by bulb-to-bulb distillation (oven tempera-

ture 130 °C, 0.01 mbar) to furnish 7 as a colorless liquid (10.9 g,

1

colorless liquid (150 g, 1.34 mol; 86% yield). B.p. 78 °C. H NMR

(500.1 MHz, C₆D₆): δ = 0.24 (s, 6 H, SiCH₃), 5.83 (δ_A), 6.06 (δ_B),

6.28 (δ_C) [ABC system, ²J(A,B) = 3.8, ³J(A,C) = 20.3, ³J(B,C) =

14.7 Hz, 6 H; CH_C=CH_AH_B] ppm. ¹³C NMR (125.8 MHz, C₆D₆):

δ = –3.2 (SiCH₃), 132.5 (CH₂), 138.1 (CH) ppm. ²⁹Si NMR

(99.4 MHz, C₆D₆):

δ = –13.8 ppm. C₆H₁₂Si (112.25): calcd.

C 64.20, H 10.78; found C 64.27, H 10.79.

3,3Ј-(Dimethylsilanediyl)dipropanal (5): A mixture of 4 (5.00 g,

44.5 mmol), triphenylphosphine (584 mg, 2.23 mmol), (acetyl-

acetonato)dicarbonylrhodium(I) (80 mg, 310 μmol), and benzene

(30 mL) was heated in an autoclave at 80 °C for 7 h under an atmo-

sphere of hydrogen (45 bar) and carbon monoxide (45 bar) and was

then cooled to 20 °C within 30 min. The mixture was filtered

through a pad of silica gel (30 g), followed by elution with n-hex-

ane/Et₂O (9:1 v/v). The solvent of the filtrate (including the eluate)

was removed under reduced pressure (5 mbar), and the residue was

suspended in a mixture of Et₂O (50 mL) and water (50 mL). The

organic phase was separated, the aqueous phase was extracted with

Et₂O (3ϫ 30 mL) and discarded, and the combined organic

solutions were dried with anhydrous sodium sulfate. The solvent

was removed under reduced pressure (5 mbar), the residue was

purified by a rapid bulb-to-bulb distillation (oven temperature

150 °C, 0.01 mbar), and the distillate was then further purified by

1

51.8 mmol; 92% yield). H NMR (500.1 MHz, C₆D₆): δ = 0.11 (s,

3 H, SiCH₃), 0.13 (s, 3 H, CH₃), 0.63–0.74 (m, 2 H, 4-H), 1.06–1.35

(m, 2 H, 6-H), 1.1 (br. s, 1 H, OH), 1.67–1.80 (m, 2 H, CH₂CHOH),

2.15–2.26 (m, 2 H, CH₂CH=CH₂), 2.24–2.31 (m, 2 H, 3-H), 3.93–

3.98 (m, 1 H, CHOH), 5.09–5.14 (m, 1 H, CH₂CH=CHH), 5.17–

5.23 (m, 1 H, CH₂CH=CHH), 5.68–5.73 (m, 1 H, 2-H), 5.91–6.01

(m, 1 H, CH₂CH=CH₂) ppm.^{[20] 13}C NMR (125.8 MHz, C₆D₆): δ

= –2.5 (SiCH₃), –2.4 (CH₃), 10.4 (C-4), 11.1 (C-6), 22.7 (C-3), 30.6

(CH₂CH=CH₂), 34.5 (CH₂CHOH), 77.6 (CHOH), 114.6

(CH₂CH=CH₂), 125.2 (C-2), 139.0 (CH₂CH=CH₂), 140.1 (C-1)

ppm. ²⁹Si NMR (99.4 MHz, C₆D₆): δ = –2.7 ppm. C₁₂H₂₂OSi

(210.39): calcd. C 68.51, H 10.54; found C 68.48, H 10.82.

a

second bulb-to-bulb distillation (oven temperature 95 °C,

0.01 mbar) to furnish 5 as a colorless liquid (1.30 g, 7.55 mmol;

17% yield). ¹H NMR (500.1 MHz, C₆D₆): δ = –0.14 (s, 6 H,

SiCH₃), 0.53 (δ_AAЈ), 1.91 (δ_DDЈ), 9.46 (δ_X) [AAЈDDЈX system,

²J(A,AЈ) = 17.1, ²J(D,DЈ) = 14.4, ³J(A,D) = ³J(AЈ,DЈ) = 5.5,

³J(A,DЈ) = ³J(AЈ,D) = 11.0, ³J(D,X) = ³J(DЈ,X) = 1.5 Hz, 10 H;

CH_AH_AЈCH_DH_DЈCH_X] ppm. ¹³C NMR (125.8 MHz, C₆D₆): δ =

–3.9 (SiCH₃), 6.4 (SiCH₂), 38.0 (CH₂CH), 200.9 (CHO) ppm. ²⁹Si

NMR (99.4 MHz, C₆D₆): δ = 4.3 ppm. C₈H₁₆O₂Si (172.30): calcd.

C 55.77, H 9.36; found C 55.60, H 9.55.

1,1-Divinylsilolane (8): A solution of 1,4-dibromobutane (124 g,

574 mmol) in tetrahydrofuran (150 mL) was added dropwise within

1 h to a suspension of magnesium turnings (28.0 g, 1.15 mol) in

tetrahydrofuran (100 mL), causing the reaction mixture to boil un-

der reflux. The mixture was heated under reflux for a further 2 h,

cooled to 20 °C within 30 min, and then added at 0 °C within 1 h

to a stirred solution of dichlorodivinylsilane (80.0 g, 523 mmol) in

tetrahydrofuran (250 mL). The resulting mixture was warmed to

5,5-Dimethyl-5-silacyclohex-1-ene-1-carbaldehyde (6): A mixture of

4 (15.3 g, 136 mmol), triphenylphosphine (1.80 g, 6.86 mmol), 20 °C within 20 min and stirred at this temperature for a further

(acetylacetonato)dicarbonylrhodium(I) (246 mg, 953 μmol), and

benzene (50 mL) was heated in an autoclave at 80 °C for 7 h under

an atmosphere of hydrogen (45 bar) and carbon monoxide (45 bar)

and was then cooled to 20 °C within 30 min. The resulting mixture

(containing 5 as an intermediate) was then added dropwise at 0 °C

within 1 h to a stirred 0.5 m solution of HCl in Et₂O (400 mL,

200 mmol of HCl), and the resulting mixture was then kept undis-

turbed at 20 °C for 18 h. The mixture was filtered through a pad

of silica gel (180 g), followed by elution with n-hexane/Et₂O

(1:1 v/v). The solvent of the filtrate (including the eluate) was re-

moved under reduced pressure, and the residue was purified by

2 h. Water (300 mL) was added, the organic phase was separated,

the aqueous phase was extracted with Et₂O (4ϫ 200 mL) and

discarded, and the combined organic solutions were dried with an-

hydrous sodium sulfate. The solvent was removed under reduced

pressure, and the resulting residue purified by distillation in vacuo

to furnish 8 as a colorless liquid (67.0 g, 485 mmol; 93% yield).

B.p. 84 °C/100 mbar. ¹H NMR (500.1 MHz, C₆D₆): δ = 0.85

(δ_{AAЈAЈЈAЈЈЈ}), 1.71 (δ_{XXЈXЈЈXЈЈЈ}

) [AAЈAЈЈAЈЈЈXXЈXЈЈXЈЈЈ system,

²J(A,AЈЈ) = ²J(AЈ,AЈЈЈ) = 14.6, ²J(X,XЈЈ) = ²J(XЈ,XЈЈЈ) = 11.1,

³J(A,X) = ³J(AЈ,XЈ) = 7.9, ³J(A,XЈЈ) = ³J(AЈ,XЈЈЈ) = 7.0, ³J(AЈЈ,X)

3

= J(AЈЈЈ,XЈ) = 6.4, J(AЈЈ,XЈЈ) = J(AЈЈЈ,XЈЈЈ) = 7.7, J(X,XЈ) =

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4

4.3, ³J(X,XЈЈЈ) = ³J(XЈ,XЈЈ) = 7.6, ³J(XЈЈ,XЈЈЈ) = 5.6, J(A,XЈ) = (δ_AAЈ), 0.55 (δ_BBЈ), 1.59 (δ_XXЈ), 1.60 (δ_YYЈ) [AAЈBBЈXXЈYYЈ sys-

⁴J(AЈ,X) = 1.5, ⁴J(A,XЈЈЈ) = ⁴J(AЈ,XЈЈ) = 0.6, ⁴J(AЈЈ,XЈ) =

tem, ²J(A,B) = ²J(AЈ,BЈ) = 10.3, ²J(X,Y) = ²J(XЈ,YЈ) = 13.2,

3

⁴J(AЈЈЈ,X) = 0.1, ⁴J(AЈЈ,XЈЈЈ) = ⁴J(AЈЈЈ,XЈЈ) = 0.1 Hz, 8 H; ³J(A,X) = J(AЈ,XЈ) = 7.7, J(A,Y) = J(AЈ,YЈ) = 6.7, J(B,X) =

SiCH_AH_AЈЈCH_XH_XЈЈCH_XЈH_XЈЈЈCH_AЈH_AЈЈЈ], 5.87 (δ_A), 6.08 (δ_B), ³J(BЈ,XЈ) = 7.0, ³J(B,Y) = ³J(BЈ,YЈ) = 7.8, ³J(X,XЈ) = 5.1, ³J(X,YЈ)

6.31 (δ_C) [ABC system, ²J(A,B) = 3.8, ³J(A,C) = 20.3, ³J(B,C) =

14.6 Hz, 6 H; CH_C=CH_AH_B] ppm.^{[19] 13}C NMR (125.8 MHz,

=

³J(XЈ,Y) = 7.8, ³J(Y,YЈ) = 4.8, ⁴J(A,XЈ) = ⁴J(AЈ,X) = 0.2,

⁴J(A,YЈ) = ⁴J(AЈ,Y) = 0.03, ⁴J(B,XЈ) = ⁴J(BЈ,X) = 0.01, ⁴J(B,YЈ) =

C₆D₆): δ = 11.1 (C-2 and C-5), 27.6 (C-3 and C-4), 133.4 ⁴J(BЈ,Y) = 0.4 Hz, 8 H; SiCH_AH_BCH_XH_YCH_XЈH_YЈCH_AЈH_BЈ], 0.60

(CH=CH₂), 136.2 (CH=CH₂) ppm. ²⁹Si NMR (99.4 MHz, C₆D₆): (δ_AAЈ), 1.64 (δ_DDЈ), 2.19 (δ_HHЈ), 6.21 (δ_X) [AAЈDDЈHHЈX system,

δ = 2.4 ppm. C₈H₁₄Si (138.28): calcd. C 69.49, H 10.20; found ²J(A,AЈ) = 12.4, ²J(D,DЈ) = 12.4, ²J(H,HЈ) = 15.2, ³J(A,H) =

3

C 69.49, H 10.30.

³J(AЈ,HЈ) = 6.3, J(A,HЈ) = J(AЈ,H) = 7.5, J(H,X) = J(HЈ,X) =

4.9, ⁴J(D,X) = ⁴J(DЈ,X) = 1.5, ⁵J(D,H) = ⁵J(DЈ,HЈ) = 2.0, ⁵J(D,HЈ)

=

⁵J(DЈ,H) = 1.3 Hz, 7 H; SiCH_AH_AЈCH_HH_HЈCH_X=CCH_DH_DЈ],

3,3Ј-(Silolane-1,1-diyl)dipropanal (9):

A mixture of 8 (8.00 g,

9.42 (s, 1 H, CHO) ppm.^{[19] 13}C NMR (125.8 MHz, C₆D₆): δ = 7.2

(C-6), 8.0 (C-10), 11.1 (C-1 and C-4), 24.5 (C-9), 27.2 (C-2 and C-

3), 141.4 (C-7), 152.5 (C-8), 193.8 (CHO) ppm. ²⁹Si NMR

(99.4 MHz, C₆D₆): δ = 13.9 ppm. C₁₀H₁₆OSi (180.32): calcd.

C 66.61, H 8.94; found C 66.38, H 9.02.

57.9 mmol), triphenylphosphine (760 mg, 2.90 mmol), (acetyl

acetonato)dicarbonylrhodium(I) (105 mg, 407 μmol), and benzene

(30 mL) was heated in an autoclave at 80 °C for 7 h under an atmo-

sphere of hydrogen (45 bar) and carbon monoxide (45 bar) and was

then cooled to 20 °C within 30 min. The mixture was filtered

through a pad of silica gel (15 g), followed by elution with n-hex-

ane/Et₂O (1:1 v/v). The solvent of the filtrate (including the eluate)

was removed under reduced pressure (5 mbar), and the residue was

suspended in a mixture of Et₂O (100 mL) and water (50 mL). The

organic phase was separated, the aqueous phase was extracted with

Et₂O (3ϫ 100 mL) and discarded, and the combined organic

solutions were dried with anhydrous sodium sulfate. The solvent

was removed under reduced pressure (5 mbar), the residue was

purified by a rapid bulb-to-bulb distillation (oven temperature

170 °C, 0.01 mbar), and the distillate was then further purified by

1-(5-Silaspiro[4.5]dec-7-en-7-yl)pent-4-en-1-ol (11): 4-Bromo-1-but-

ene (15.4 g, 114 mmol) was added dropwise within 30 min to a sus-

pension of magnesium turnings (3.70 g, 152 mmol) in Et₂O

(150 mL), causing the reaction mixture to boil under reflux. The

mixture was heated under reflux for a further hour, cooled to 20 °C

within 20 min, and then added at –10 °C within 30 min to a stirred

solution of 10 (13.7 g, 76.0 mmol) in Et₂O (250 mL). The resulting

mixture was warmed to 20 °C within 30 min and was then stirred

at this temperature for a further hour, a saturated aqueous solution

of ammonium chloride (200 mL) was added, the organic phase was

separated, the aqueous phase was extracted with Et₂O (3ϫ

a

second bulb-to-bulb distillation (oven temperature 120 °C,

0.01 mbar) to furnish 9 as a colorless liquid (1.20 g, 6.05 mmol;

10% yield). ¹H NMR (500.1 MHz, C₆D₆): δ = 0.44 (δ_{AAЈAЈЈAЈЈЈ}), 100 mL) and discarded, and the combined organic solutions were

1.55 (δ_{XXЈXЈЈXЈЈЈ}) [AAЈAЈЈAЈЈЈXXЈXЈЈXЈЈЈ system, ²J(A,AЈЈ) =

²J(AЈ,AЈЈЈ) = 14.4, ²J(X,XЈЈ) = ²J(XЈ,XЈЈЈ) = 11.3, ³J(A,X) =

³J(AЈ,XЈ) = 7.9, ³J(A,XЈЈ) = ³J(AЈ,XЈЈЈ) = 7.1, ³J(AЈЈ,X) =

dried with anhydrous sodium sulfate. The solvent was removed un-

der reduced pressure, and the residue was purified by flash

chromatography on silica gel [eluent, n-hexane/Et₂O (7:3 v/v)], fol-

³J(AЈЈЈ,XЈ) = 6.3, ³J(AЈЈ,XЈЈ) = ³J(AЈЈЈ,XЈЈЈ) = 7.8, ³J(X,XЈ) = 4.5, lowed by bulb-to-bulb distillation (oven temperature 170 °C,

³J(X,XЈЈЈ) = ³J(XЈ,XЈЈ) = 7.4, ³J(XЈЈ,XЈЈЈ) = 5.6, ⁴J(A,XЈ) =

⁴J(AЈ,X) = 1.5, ⁴J(A,XЈЈЈ) = ⁴J(AЈ,XЈЈ) = 0.6, ⁴J(AЈЈ,XЈ) =

0.02 mbar) to furnish 11 as a colorless liquid (15.5 g, 65.6 mmol;

86% yield). ¹H NMR (500.1 MHz, C₆D₆):

δ

=

0.63–0.74

⁴J(AЈЈЈ,X) = 0.1, ⁴J(AЈЈ,XЈЈЈ) = ⁴J(AЈЈЈ,XЈЈ) = 0.1 Hz, 8 H; (m, 4 H, 1-H and 4-H), 0.75–0.83 (m, 2 H, 10-H), 1.19–1.47 (m,

SiCH_AH_AЈЈCH_XH_XЈЈCH_XЈH_XЈЈЈCH_AЈH_AЈЈЈ], 0.59 (δ_AAЈ), 1.89 2 H, 6-H), 1.64–1.82 (m, 7 H, 2-H, 3-H, OH, and CH₂CHOH),

2

(δ_DDЈ), 9.43 (δ_X) [AAЈDDЈX system, J(A,AЈ) = 15.4, J(D,DЈ) =

2.13–2.33 (m, 4 H, 9-H and CH₂CH=CH₂), 3.95–4.00 (m, 1 H,

12.6,

=

³J(A,D)

=

³J(AЈ,DЈ)

=

5.5,

1.4 Hz, 10 H;

³J(A,DЈ) CHOH), 5.08–5.13 (m, 1 H, CH₂CH=CHH), 5.16–5.22 (m, 1 H,

³J(AЈ,D)

=

10.8, ³J(D,X)

=

³J(DЈ,X)

=

CH₂CH=CHH), 5.72–5.76 (m, 1 H, 8-H), 5.90–6.00 (m, 1 H,

CH_AH_AЈCH_DH_DЈCH_X] ppm.^{[20] 13}C NMR (125.8 MHz, C₆D₆): δ CH₂CH=CH₂) ppm.^{[20] 13}C NMR (125.8 MHz, C₆D₆): δ = 9.2 (C-

= 5.0 (CH₂CH₂CH), 10.1 (C-2 and C-5), 27.5 (C-3 and C-4), 38.4 10), 9.8 (C-6), 11.6 (C-1 or C-4), 11.7 (C-1 or C-4), 23.0 (C-9), 27.4

(CH₂CH), 200.6 (CHO) ppm. ²⁹Si NMR (99.4 MHz, C₆D₆): δ =

21.8 ppm. C₁₀H₁₈O₂Si (198.34): calcd. C 60.56, H 9.15; found

C 60.49, H 9.36.

(C-2 or C-3), 27.5 (C-2 or C-3), 30.6 (CH₂CHOH), 34.5

(CH₂CH=CH₂), 77.5 (CHOH), 114.7 (CH₂CH=CH₂), 125.6 (C-

8), 139.0 (CH₂CH=CH₂), 140.4 (C-7) ppm. ²⁹Si NMR (99.4 MHz,

C₆D₆): δ = 14.9 ppm. C₁₄H₂₄OSi (236.43): calcd. C 71.12, H 10.23;

found C 71.29, H 10.40.

5-Silaspiro[4.5]dec-7-ene-7-carbaldehyde (10):

A mixture of 8

(13.6 g, 98.3 mmol), triphenylphosphine (1.29 g, 4.92 mmol), (acet-

ylacetonato)dicarbonylrhodium(I) (178 mg, 690 μmol), and benz-

ene (50 mL) was heated in an autoclave at 80 °C for 7 h under an

atmosphere of hydrogen (45 bar) and carbon monoxide (45 bar)

and was then cooled to 20 °C within 30 min. The resulting mixture

(containing 9 as an intermediate) was then added dropwise at 0 °C

within 1 h to a stirred 0.5 m solution of HCl in Et₂O (300 mL,

150 mmol of HCl), and the resulting mixture was then kept undis-

turbed at 20 °C for 18 h. The mixture was filtered through a

pad of silica gel (180 g), followed by elution with n-hexane/Et₂O

(1:1 v/v). The solvent of the filtrate (including the eluate) was

removed under reduced pressure, and the residue was purified

by flash chromatography on silica gel [eluent, n-hexane/Et₂O

(7:3 v/v)], followed by bulb-to-bulb distillation (oven temperature

110 °C, 0.02 mbar) to furnish 10 as a colorless liquid (5.88 g,

32.6 mmol; 33% yield). ¹H NMR (500.1 MHz, C₆D₆): δ = 0.54

1-(5-Silaspiro[4.5]dec-7-en-7-yl)pent-4-en-1-one (2,4-Dinitrophenyl)-

hydrazone (12b): Sulfuric acid (11 mL), water (17 mL), and ethanol

(45 mL) were added sequentially at 20 °C in single portions to (2,4-

dinitrophenyl)hydrazine [5.58 g of a 50% suspension of (2,4-di-

nitrophenyl)hydrazine in water; 14.1 mmol of (2,4-dinitrophenyl)-

hydrazine], followed by dropwise addition of a solution of 2b

(3.00 g, 12.8 mmol; purity 99.5%) in ethanol (55 mL) at this tem-

perature within 45 min. The resulting precipitate was separated by

suction filtration and washed with water (5ϫ 25 mL) to furnish a

red solid, which was dried in vacuo (20 °C, 0.02 mbar, 2 h) and

then recrystallized from methanol (750 mL; slow cooling of a boil-

ing solution to 20 °C and crystallization over a period of 1 d). The

precipitate was isolated by suction filtration, washed with methanol

(–20 °C, 25 mL), and dried in vacuo (20 °C, 0.02 mbar, 4 h) to fur-

nish a red crystalline solid, which was again recrystallized from

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methanol until HPLC analysis indicated no more impurity. Com-

pound 12b was then isolated as a pure red crystalline solid (2.90 g,

7.00 mmol; 55% yield). M.p. 135 °C. ¹H NMR (500.1 MHz, C₆D₆):

3-[Dimethyl(3-methylbut-2-en-1-yl)silyl]propanal (14): A mixture of

carbonylhydridotris(triphenylphosphine)rhodium(I)

(510 mg,

555 μmol), triphenylphosphine (2.04 g, 7.78 mmol), 13 (60.0 g,

δ

=

0.74 (δ_AAЈ), 0.79 (δ_BBЈ), 1.73 (δ_XXЈ), 1.79 (δ_YYЈ

)

389 mmol), and toluene (20 mL) was heated in an autoclave to

[AAЈBBЈXXЈYYЈ system, ²J(A,B) = ²J(AЈ,BЈ) = 14.9, ²J(X,Y) = 80 °C for 3 h under an atmosphere of hydrogen (40 bar) and carbon

²J(XЈ,YЈ) = 12.9, J(A,X) = J(AЈ,XЈ) = 7.4, J(A,Y) = J(AЈ,YЈ)

=

monoxide (40 bar), and the reaction mixture was then cooled to

20 °C within 60 min. The solvent was removed under reduced pres-

sure, and the residue was purified by bulb-to-bulb distillation (oven

temperature 105 °C, 0.1 mbar) to furnish 14 as a colorless liquid

(45.0 g, 244 mmol; 63% yield). ¹H NMR (300.1 MHz, CDCl₃): δ =

3

7.1, ³J(B,X)

=

³J(BЈ,XЈ)

=

7.2, ³J(B,Y)

=

³J(BЈ,YЈ)

3

= 7.5, J(X,XЈ) = 4.9, J(X,YЈ) = J(XЈ,Y) = 7.6, J(Y,YЈ) = 4.8,

⁴J(A,XЈ) = ⁴J(AЈ,X) = 0.8, ⁴J(A,YЈ) = ⁴J(AЈ,Y) = 0.4, ⁴J(B,XЈ)

=

⁴J(BЈ,X) 0.5, ⁴J(B,YЈ) ⁴J(BЈ,Y)

= = = 0.8 Hz, 8 H;

SiCH_AH_BCH_XH_YCH_XЈH_YЈCH_AЈH_BЈ], 0.81 (δ_AAЈ), 2.06 (δ_DDЈ), 2.37 –0.02 (s, 6 H, SiCH₃), 0.75 (δ_AAЈ), 2.36 (δ_DDЈ), 9.72 (δ_X) [AAЈDDЈX

2

(δ_HHЈ), 6.26 (δ_X) [AAЈDDЈHHЈX system, ²J(A,AЈ) = 11.0, ²J(D,DЈ)

system, ²J(AAЈ) = 17.3, J(DD)Ј = 15.1, ³J(AD) = ³J(AЈDЈ) = 9.9,

= 8.5, ²J(H,HЈ) = 13.2, ³J(A,H) = ³J(AЈ,HЈ) = 5.9, ³J(A,HЈ) = ³J(ADЈ) = ³J(AЈD) = 5.1, ³J(DX) = ³J(DЈX) = 1.8 Hz, 5 H;

³J(AЈ,H) = 7.9, J(H,X) = J(HЈ,X) = 5.6, J(D,X) = J(DЈ,X) = CH_AH_AЈCH_DH_DЈCH_XO], 1.39 (d, ³J = 8.5 Hz, 2 H, CH₂CH=C),

3

4

1.0, ⁵J(D,H) = ⁵J(DЈ,HЈ) = 0.6, ⁵J(D,HЈ) = ⁵J(DЈ,H) = 1.6 Hz, 7 H;

SiCH_AH_AЈCH_HH_HЈCH_X=CCH_DH_DЈ], 2.19 (δ_AAЈ), 2.44 (δ_DDЈ), 5.12

1.54 (s, 3 H, CH₃C=CH), 1.67 (s, 3 H, CH₃C=CH), 5.10 (tspt, J

= 8.5, ⁴J = 1.3 Hz, 1 H, CH=C) ppm. ¹³C NMR (75.5 MHz,

CDCl₃): δ = –3.7 (SiCH₃), 6.7 (C-3), 16.9 [SiCH₂CH=C(CH₃)₂],

3

2

(δ_F), 5.21 (δ_M), 5.86 (δ_X) [AAЈDDЈFMX system, J(A,AЈ) = 13.1,

²J(D,DЈ) = 13.0, ²J(F,M) = 1.5, ³J(A,D) = ³J(AЈ,DЈ) = 6.1, 17.6 [CH=C(CH₃)_cis(CH₃)_trans], 25.7 [CH=C(CH₃)_cis(CH₃)_trans],

3

³J(A,DЈ) = J(AЈ,D) = 10.3, J(A,X) = J(AЈ,X) = 6.8, J(F,X) =

10.1, ³J(M,X) = 17.0, ⁴J(A,F) = ⁴J(AЈ,F) = 1.1, ⁴J(A,M) =

⁴J(AЈ,M) = 1.5 Hz, 7 H; CH_DH_DЈCH_AH_AЈCH_X=CH_FH_M], 7.70

(δ_A), 7.84 (δ_D), 8.95 (δ_M), 11.2 (δ_X) [ADMX system, ³J(A,D) = 9.5,

38.3

(C-2),

119.1

[CH=C(CH₃)_cis(CH₃)_trans],

129.3

[CH=C(CH₃)_cis(CH₃)_trans], 202.8 (CHO) ppm. EI-MS: m/z (%) =

184 (1) [M]⁺, 141 (2), 127 (3), 115 (100), 99 (14), 85 (35), 75 (7),

59 (31). HRMS (EI): m/z calcd. for C₁₀H₂₀OSi 184.1283, found

⁴J(D,M) = 2.6, ⁵J(D,X) = 0.7 Hz, 4 H; C₆H₃(NO₂)₂NH_X(3-H_M, 5- 184.1254.

H_D, 6-H_A)] ppm.^{[19] 13}C NMR (125.8 MHz, C₆D₆): δ = 8.6 [C-10,

2-{[Dimethyl(3-methylbut-2-en-1-yl)silyl]methyl}acrylaldehyde (15):

5-silaspiro[4.5]dec-7-en-7-yl (= 5-sila)], 11.3 (C-6, 5-sila), 11.6 (C-1

and C-4, 5-sila), 24.1 (C-9, 5-sila), 25.7 [C(N)CH₂], 27.4 (C-2 and

C-3, 5-sila), 30.5 (CH₂CH=CH₂), 116.0 [C-6, C₆H₃-

(NO₂)₂], 116.7 (CH₂CH=CH₂), 123.4 [C-3, C₆H₃(NO₂)₂], 129.57

[C-5, C₆H₃(NO₂)₂], 129.62 [C-2, C₆H₃(NO₂)₂], 134.5 (C-8, 5-sila),

136.1 (CH₂CH=CH₂), 136.8 (C-7, 5-sila), 138.1 [C-4, C₆H₃-

(NO₂)₂], 144.8 [C-1, C₆H₃(NO₂)₂], 157.2 [C(N)CH₂] ppm. ¹⁵N

NMR (50.7 MHz, C₆D₆): δ = –234.3 [C₆H₃(NO₂)₂NHN], –77.2

[C₆H₃(NO₂)₂NHN], –15.5 (NO₂), –13.2 (NO₂) ppm. ²⁹Si NMR

(99.4 MHz, C₆D₆): δ = 15.8 ppm. C₂₀H₂₆N₄O₄Si (414.54): calcd.

C 57.95, H 6.32, N 13.52; found C 58.08, H 6.24, N 13.74.

A mixture of 14 (45.0 g, 244 mmol) and a 36% (w/w) aqueous solu-

tion of formaldehyde (73.3 g, 880 mmol of CH₂O) was heated with

vigorous stirring to 70 °C. Subsequently, a mixture of pyrrolidine

(3.47 g, 48.8 mmol) and propanoic acid (4.34 g, 58.6 mmol) was

added dropwise within 10 min to the reaction mixture, and stirring

was continued at this temperature for a further 3 h. Water (50 mL)

was added, the organic phase was separated, the aqueous phase

was extracted with tert-butyl methyl ether (3ϫ 200 mL) and dis-

carded, and the combined organic solutions were dried with anhy-

drous magnesium sulfate. The solvent was removed under reduced

pressure, and the residue was purified by flash chromatography on

silica gel [eluent, isohexane/tert-butyl methyl ether (50:1 v/v)], fol-

lowed by bulb-to-bulb distillation (oven temperature 110 °C,

0.1 mbar) to furnish 15 as a colorless liquid (20.0 g, 102 mmol; 42%

Dimethyl(3-methylbut-2-en-1-yl)vinylsilane (13): A solution of 1-

chloro-3-methylbut-2-ene (66.7 g, 638 mmol) in tetrahydrofuran

(500 mL) was added dropwise within 45 min to a suspension of

magnesium turnings (16.9 g, 695 mmol) in tetrahydrofuran

(10 mL), causing the reaction mixture to boil under reflux. Sub-

sequently, chlorodimethylvinylsilane (70.0 g, 580 mmol) was added

at 20 °C within 15 min to the stirred reaction mixture. Upon cool-

ing to 0 °C, a saturated aqueous solution of ammonium chloride

(200 mL) was added, the organic phase was separated, and the

aqueous phase was extracted with ethyl acetate (3ϫ 100 mL) and

discarded. The combined organic solutions were washed with a sat-

urated aqueous solution of sodium chloride and dried with anhy-

drous magnesium sulfate. The solvent was removed under reduced

pressure, and the residue was purified by distillation under reduced

pressure to furnish 13 as a colorless liquid (66.5 g, 431 mmol; 74%

1

yield). H NMR (300.1 MHz, CDCl₃): δ = –0.05 (s, 6 H, SiCH₃),

3

1.40 (d, J = 8.3 Hz, 2 H, CH₂CH=C), 1.55 (s, 3 H, CH₃C=CH),

1.69 (br. s, 3 H, CH₃C=CH), 1.77 (br. s, 2 H, CH₂C=CH₂), 5.11

(tspt, ³J = 8.3, ⁴J = 1.3 Hz, 1 H, CH=C), 5.85 (m, 1 H,

C=CH_AH_B), 6.09 (m, 1 H, C=CH_AH_B), 9.47 (s, 1 H, CHO) ppm.

¹³C NMR (75.5 MHz, CDCl₃): δ = –3.6 (SiCH₃), 16.5 (C-3), 16.9

[SiCH₂CH=C(CH₃)₂], 17.6 [CH=C(CH₃)_cis(CH₃)_trans], 25.8

[CH=C(CH₃)_cis(CH₃)_trans], 119.1 [CH=C(CH₃)_cis(CH₃)_trans], 129.5

[CH=C(CH₃)_cis(CH₃)_trans], 131.5 (C=CH₂), 148.3 (C-2), 194.4

(CHO) ppm. EI-MS: m/z (%) = 196 (1) [M]⁺, 127 (100), 113 (5),

97 (10), 85 (7), 75 (12), 59 (16). HRMS (ESI): m/z calcd. for

C₁₁H₂₂NaOSi [M + Na]⁺219.1181, found 219.1357.

yield). B.p. 45–49 °C/5 mbar. ¹H NMR (300.1 MHz, CDCl₃): δ =

2-{[Dimethyl(3-methylbut-2-en-1-yl)silyl]methyl}allyl Acetate (16):

3

0.07 (s, 6 H, SiCH₃), 1.48 (d, J = 8.3 Hz, 2 H, CH₂CH=C), 1.58 Compound 15 (20.0 g, 102 mmol) was added at 0 °C within 15 min

(br. s, 3 H, CH₃C=CH), 1.72 (br. s, 3 H, CH₃C=CH), 5.16 (tspt, ³J

to a stirred suspension of lithium aluminum hydride (4.64 g,

122 mmol) in tetrahydrofuran (100 mL). The resulting mixture was

then stirred at this temperature for 3 h, water (20 mL) was added

dropwise, the organic phase was separated, and the aqueous phase

4

3

2

= 8.3, J = 1.4 Hz, 1 H, CH=C), 5.69 (dd, J = 20.0, J = 4.2 Hz,

1 H, CH=CH_cisH_trans), 5.96 (dd, ³J

1 H, CH=CH_cisH_trans), 6.17 (dd, ³J

=

14.7, ²J

20.0, ³J

=

4.2 Hz,

=

14.7 Hz,

1 H, CH=CH_cisH_trans) ppm. ¹³C NMR (75.5 MHz, CDCl₃): δ = was extracted with tert-butyl methyl ether (50 mL) and discarded.

–3.6 (SiCH₃), 17.3 [CH=C(CH₃)_cis(CH₃)_trans], 17.6 (CH₂), 25.7 The combined organic solutions were dried with anhydrous magne-

[CH=C(CH₃)_cis(CH₃)_trans], 119.4 [CH=C(CH₃)_cis(CH₃)_trans], 129.1 sium sulfate, and the solvent was removed under reduced pressure.

[CH=C(CH₃)_cis(CH₃)_trans], 131.5 (SiCH=CH₂), 139.0 (SiCH=CH₂) Dichloromethane (50 mL) and triethylamine (19.4 g, 192 mmol)

ppm. EI-MS: m/z (%) = 154 (13) [M]⁺, 139 (3), 126 (2), 111 (1), 98 were added to the residue, followed by dropwise addition of acetyl

(1), 85 (100), 73 (4), 59 (38), 43 (6). HRMS (EI): m/z calcd. for chloride (9.02 g, 115 mmol) at 0 °C within 5 min. The resulting

C₉H₁₈Si 154.1178, found 154.1184.

mixture was stirred at 20 °C for 3 h, water (50 mL) was added, the

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organic phase was separated, and the aqueous phase was extracted

with tert-butyl methyl ether (3ϫ 100 mL) and discarded. The com-

bined organic solutions were dried with anhydrous magnesium sulf-

ate, and the solvent was removed under reduced pressure. The resi-

due was purified by flash chromatography on silica gel [eluent,

isohexane/tert-butyl methyl ether (100:1 v/v)], followed by bulb-to-

bulb distillation (oven temperature 122 °C, 0.1 mbar) to furnish 16

as a colorless liquid (19.0 g, 79.0 mmol; 78% overall yield). ¹H

7 H; SiCH_DH_DЈCH_X=CCH_AH_AЈCH_MH_MЈO] ppm. ¹³C NMR

(75.5 MHz, CDCl₃): δ = –1.8 (SiCH₃), 17.8 (C-3), 18.0 (C-5), 66.2

(CH₂O), 125.6 (C-2), 143.2 (C-1) ppm. EI-MS: m/z (%) = 142 (1)

[M]⁺, 125 (2), 109 (7), 99 (3), 87 (2), 75 (100), 61 (4), 43 (5). HRMS

(EI): m/z calcd. for C₇H₁₄OSi 142.0814, found 142.0817.

1-(4,4-Dimethyl-4-silacyclopent-1-en-1-yl)pent-4-en-1-ol (19): Alu-

minum tri-sec-butoxide (727 mg, 2.95 mmol) was added at 20 °C to

a stirred solution of 18 (1.40 g, 9.84 mmol) in tert-butyl methyl

ether (100 mL), followed by the addition of acetic acid (53 mg,

883 μmol). The resulting mixture was then stirred at 0 °C for

10 min, 4-nitrobenzaldehyde (1.78 g, 11.8 mmol) was added, and

the reaction mixture was stirred at 20 °C for 2 h. Subsequently, n-

hexane (100 mL) and anhydrous magnesium sulfate were added,

and the organic phase was separated by filtration. The solvent was

removed under reduced pressure, n-hexane (10 mL) was added, and

the resulting supernatant was separated by filtration. The solvent

was removed under reduced pressure, and the residue was dissolved

in tetrahydrofuran (20 mL), followed by dropwise addition of a

0.90 m solution of but-3-en-1-ylmagnesium chloride [21.9 mL,

19.7 mmol of CH₂=CHCH₂CH₂MgCl; prepared from magnesium

turnings (7.40 g, 304 mmol) and 4-chloro-1-butene (25.2 g,

278 mmol) and then stored at 0 °C for different batches] at 0 °C

within 1 h. Subsequently, water (20 mL) was added dropwise, the

organic phase was separated, and the aqueous phase was extracted

with tert-butyl methyl ether (3ϫ 25 mL) and discarded. The com-

bined organic solutions were dried with anhydrous magnesium sulf-

ate, and the solvent was removed under reduced pressure. The resi-

due was purified by flash chromatography on silica gel [eluent,

isohexane/tert-butyl methyl ether (100:1 v/v)], followed by bulb-to-

bulb distillation (oven temperature 110 °C, 0.1 mbar) to furnish 19

as a colorless liquid (405 mg, 2.06 mmol; 21% overall yield). ¹H

NMR (300.1 MHz, CDCl₃): δ = 0.16 (s, 3 H, SiCH₃), 0.17 (s, 3 H,

SiCH₃), 1.06–1.35 [m, 4 H, CH(OH)CH₂, SiCH₂C=CH], 1.59–1.68

(m, 2 H, SiCH₂CH=C), 1.80 (br. s, 1 H, OH), 1.93–2.14 (m, 2 H,

CH₂CH=CH₂), 4.14 [br. t, ³J = 4.2 Hz, 1 H, CH(OH)CH₂], 4.94

3

NMR (300.1 MHz, CDCl₃): δ = 0.01 (s, 6 H, SiCH₃), 1.42 (d, J =

8.3 Hz, 2 H, CH₂CH=C), 1.55 (br. s, 5 H, CH₃C=CH,

CH₂C=CH₂), 1.69 (s, 3 H, CH₃C=CH), 2.09 [s, 3 H, CH₃C(O)O],

4.42 (s, 2 H, CH₂O), 4.72 (br. s, 1 H, C=CH_AH_B), 4.88 (m, 1 H,

3

C=CH_AH_B), 5.11 (tspt, J = 8.3, ⁴J = 1.3 Hz, 1 H, CH=C) ppm.

¹³C NMR (75.5 MHz, CDCl₃):

δ = –3.3 (SiCH₃), 17.1

[SiCH₂CH=C(CH₃)₂], 17.6 [CH=C(CH₃)_cis(CH₃)_trans], 20.9

[CH₃C(O)O], 22.0 (C-3), 25.7 [CH=C(CH₃)_cis(CH₃)_trans], 67.8

(CH₂O), 109.7 (C=CH₂), 119.2 [CH=C(CH₃)_cis(CH₃)_trans], 129.4

[CH=C(CH₃)_cis(CH₃)_trans], 141.5 (C-2), 170.5 [CH₃C(O)O] ppm.

EI-MS: m/z (%) = 240 (1) [M]⁺, 129 (12), 117 (100), 99 (6), 87 (7),

75 (58), 59 (9). HRMS (EI): m/z calcd. for C₈H₁₅O₂Si {[M – C₅H₉

(prenyl)]⁺} 171.0841, found 171.0815.

(4,4-Dimethyl-4-silacyclopent-1-en-1-yl)methyl Acetate (17): A solu-

tion of 16 (19.0 g, 79.0 mmol) and dichloro[1,3-bis(2,4,6-trimeth-

ylphenyl)-2-imidazolidinylidene]{5-[(dimethylamino)sulfonyl]-2-

(1-methylethoxy-O)phenyl}(methylene-C)ruthenium(II) (Zhan Cat-

alyst 1B; 1.16 g, 1.58 mmol) in 1,2-dichloroethane (100 mL) was

heated under reflux for 17 h. The reaction mixture was then cooled

to 20 °C, triethylamine (300 μL) was added in a single portion, and

the volatile components were removed under reduced pressure. The

residue was purified by flash chromatography on silica gel [eluent,

isohexane/tert-butyl methyl ether (99:1 v/v)], followed by bulb-to-

bulb distillation (oven temperature 85 °C, 0.1 mbar) to furnish 17

as a colorless liquid (9.00 g, 48.8 mmol; 62% yield). ¹H NMR

(300.1 MHz, CDCl₃): δ = 0.18 (s, 6 H, SiCH₃), 1.24 (δ_AAЈ), 1.31

2

(δ_DDЈ), 4.53 (δ_MMЈ), 5.79 (δ_X) [AAЈDDЈMMЈX system, J(AAЈ) =

17.5, ²J(DD)Ј = 17.5, ²J(MMЈ) = 14.0, ³J(DX) = ³J(DЈX) = 2.9,

⁴J(AD) = ⁴J(AЈDЈ) = 1.8, ⁴J(ADЈ) = ⁴J(AЈD) = 0.8, ⁴J(AM) =

⁴J(AЈMЈ) = ⁴J(AMЈ) = ⁴J(AЈM) = 0.1, ⁴J(AX) = ⁴J(AЈX) = 2.0,

⁴J(MX) = ⁴J(MЈX) = 0.6, ⁵J(DM) = ⁵J(DЈMЈ) = ⁵J(DMЈ) =

⁵J(DЈM) = 1.3 Hz, 7 H; SiCH_DH_DЈCH_X=CCH_AH_AЈCH_MH_MЈO],

2.08 [s, 3 H, CH₃C(O)O] ppm. ¹³C NMR (75.5 MHz, CDCl₃): δ =

–1.9 (SiCH₃), 18.1 (C-3), 18.2 (C-5), 20.8 [CH₃C(O)O], 67.0

(CH₂O), 128.6 (C-2), 138.2 (C-1), 170.7 [CH₃C(O)O] ppm. EI-MS:

m/z (%) = 184 (1) [M]⁺, 117 (74), 75 (100), 59 (8). HRMS (EI): m/z

calcd. for C₉H₁₆O₂Si 184.0920, found 184.0894.

3

2

4

(ddt, J = 10.2, J = 2.1, J = 1.2 Hz, 1 H, CH=CH_cisH_trans), 5.01

3

2

4

(ddt, J = 17.0, J = 2.1, J = 1.5 Hz, 1 H, CH=CH_cisH_trans), 5.76

3

(m, 1 H, CH=C), 5.82 (ddt, J = 17.0, J = 10.2, J = 6.6 Hz, 1 H,

CH=CH₂) ppm. ¹³C NMR (75.5 MHz, CDCl₃): δ = –1.9 (SiCH₃),

–1.8 (SiCH₃), 15.2 (C-5), 17.8 (C-3), 29.3 (CH₂CH₂CH=CH₂), 34.1

(CH₂CH₂CH=CH₂), 74.2 [CH(OH)], 114.6 (CH₂CH₂CH=CH₂),

126.3 (C-2), 138.5 (CH₂CH₂CH=CH₂), 145.6 (C-1) ppm. EI-MS:

m/z (%) = 196 (1) [M]⁺, 178 (4), 155 (3), 137 (20), 109 (7), 95 (3), 85

(3), 75 (100), 59 (13), 43 (4). HRMS (EI): m/z calcd. for C₁₁H₂₀OSi

196.1283, found 196.1275.

(4,4-Dimethyl-4-silacyclopent-1-en-1-yl)methanol (18): Compound

17 (2.00 g, 10.9 mmol) was added dropwise at 0 °C within 15 min

to a stirred suspension of lithium aluminum hydride (494 mg,

13.0 mmol) in tetrahydrofuran (100 mL). The resulting mixture was

then stirred at this temperature for 1 h, water (10 mL) was added

dropwise, the organic phase was separated, and the aqueous phase

was extracted with tert-butyl methyl ether (3ϫ 100 mL) and dis-

carded. The combined organic solutions were dried with anhydrous

magnesium sulfate, the solvent was removed under reduced pres-

sure, and the residue was purified by bulb-to-bulb distillation (oven

temperature 95 °C, 0.1 mbar) to furnish 18 as a colorless liquid

Olfactory Evaluation: The test compounds were evaluated on smell-

ing blotters by a panel of at least two expert perfumers as 10%

solutions in dipropylene glycol (DPG) and in ethanol. The blotters

were dipped 4 h and 8 h in advance and compared with the freshly

dipped samples for top, middle, and dry down odor character, lin-

earity of the smell as well as olfactory purity.

The detection odor thresholds were determined using GC-olfac-

tometry: different dilutions of the sample substance were injected

into a gas chromatograph in descending order of concentration un-

til the panelist failed to detect the respective substance at the sniff-

1

(1.40 g, 9.84 mmol; 90% yield). H NMR (300.1 MHz, CDCl₃): δ

= 0.18 (s, 6 H, SiCH₃), 1.27 (δ_AAЈ), 1.33 (δ_DDЈ), 4.10 (δ_MMЈ), 5.79 ing port. The panelist smelled in blind and pressed a button upon

(δ_X) [AAЈDDЈMMЈX system, ²J(AAЈ) = 17.5, ²J(DD)Ј = 17.5, perceiving an odor. If the recorded time matched the retention time,

3

²J(MMЈ) = 14.0, ⁴J(AD) = ⁴J(AЈDЈ) = 1.5, ³J(DX) = J(DЈX) = the sample was further diluted. The last concentration detected at

2.9, ⁴J(ADЈ) = ⁴J(AЈD) = 1.0, ⁴J(AM) = ⁴J(AЈMЈ) = ⁴J(AMЈ) = the correct retention time is the individual odor threshold. The

4

⁴J(AЈM) = 0.5, ⁴J(AX) = J(AЈX) = 2.0, J(MX) = ⁴J(MЈX) = 1.5,

reported threshold values are the geometrical means of the individ-

1.3 Hz, ual odor thresholds of at least three different panelists.

⁵J(DM)

=

⁵J(DЈMЈ)

=

⁵J(DMЈ)

=

⁵J(DЈM)

=

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[11] A. Erkkilä, P. M. Pihko, J. Org. Chem. 2006, 71, 2538–2541.

[12] Z.-Y. Zhan, PCT Int. Pat. Appl. WO 2007/003135 A1 (P. R.

China), July 3, 2006.

[13] For reviews on ring-closing metathesis, see: a) A. Michaut, J.

Rodriguez, Angew. Chem. Int. Ed. 2006, 45, 5740–5750; Angew.

Chem. 2006, 118, 5870–5881; b) V. B. Kurteva, C. A. M.

Afonso, Chem. Rev. 2009, 109, 6809–6857.

Supporting Information (see footnote on the first page of this arti-

cle): Alternative synthesis of 1b and syntheses of 3a, 12a, 20a, 20b,

and 21–28;

Acknowledgments

[14] Crystal structure analyses of 12a, 12b, 20a, and 20b: Suitable

single crystals were mounted in inert oil (perfluoropolyalkyl

ether, ABCR) on a glass fiber and then transferred to a cold

nitrogen gas stream of the diffractometer [Bruker Nonius

KAPPA APEX II (12a, 20a, and 20b; Montel mirror, Mo-K_α

radiation; λ = 0.71073 Å); Stoe IPDS (12b; graphite-monochro-

mated Mo-K_αradiation; λ = 0.71073 Å)]. The structures were

solved by direct methods (SHELXS-97) and refined by full-

matrix least-squares methods on F²for all unique reflections

(SHELXL-97 and SHELXL-2013).^[21]A riding model was em-

ployed for the CH hydrogen atoms. CCDC-1000185 (for 12a),

-1000186 (for 12b), -1000187 (for 20a), and -1000188 (for 20b)

contain the supplementary crystallographic data for this paper.

These data can be obtained free of charge from The Cambridge

Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_

request/cif. Selected data for 12a: single crystal of dimensions

0.48ϫ0.26ϫ0.22 mm obtained by crystallization from meth-

anol at 20 °C. C₂₁H₂₆N₄O₄; M_r= 398.46; analysis at 100(2) K;

The authors gratefully thank Alain E. Alchenberger and Domi-

nique Lelievre for carrying out the olfactory evaluations and Kata-

rina Grman and her panelists for the odor threshold determi-

nations.

[1] a) A. F. Morris, F. Näf, R. L. Snowden, Perfum. Flavor. 1991,

16, 33–35; b) A. Williams, Perfum. Flavor. 2002, 27, 18–31.

[2] P. Kraft, J. A. Bajgrowicz, C. Denis, G. Fráter, Angew. Chem.

Int. Ed. 2000, 39, 2980–3010; Angew. Chem. 2000, 112, 3106–

3138.

[3] For syntheses of 2a, see: B. Bourdin, G. Fráter, J. A. Bajgrow-

icz, Givaudan, EP Pat. Appl. 913383 A1, May 6, 1999.

[4] For syntheses of 1a, see: a) K.-H. Schulte-Elte, B. Willhalm, F.

Gautschi, Firmenich, US Pat. 4147672, April 3, 1979; b) W.

Bonrath, U. Letinois, J. Schütz, DSM, PCT Int. Pat. Appl. WO

2010/043522 A1, April 22, 2010.

[5] For selected publications dealing with the hydroformylation of

monovinylsilanes, see: a) R. Takeuchi, N. Sato, J. Organomet.

Chem. 1990, 393, 1–10; b) C. M. Crudden, H. Alper, J. Org.

Chem. 1994, 59, 3091–3097; c) V. L. K. Valli, H. Alper, Chem.

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J. J. Ziółkowski, I. Kownacki, B. Marciniec, J. Mol. Catal. A

2005, 237, 246–253.

[6] For a publication dealing with the hydroformylation of divin-

ylsilanes, see: L. Bärfacker, D. E. Tom, P. Eilbracht, Tetrahe-

dron Lett. 1999, 40, 4031–4034.

¯

triclinic; space group P1(no. 2); a = 9.2591(4), b = 10.2143(5),

c = 11.6545(6) Å; α = 78.913(2), β = 68.012(2), γ = 84.167(2)°;

V

= Z = 2; ρ_calcd.= μ =

1002.45(8) Å³; 1.320 gcm^–3;

0.093 mm^–1; F(000) = 424; 2θ_max= 56.818°; 24317 collected

reflections; 5026 unique reflections (R_int= 0.0293); 265 param-

eters; S = 1.033; 0 restraints; R₁= 0.0382 [IϾ2σ(I)]; wR₂(all

data) = 0.1050; max./min. residual electron density: +0.375/

–0.222 eÅ^–3. Selected data for 12b: single crystal of dimensions

0.3ϫ0.15ϫ0.1 mm obtained by crystallization from methanol

at 20 °C. C₂₀H₂₆N₄O₄Si; M_r= 414.54; analysis at 173(2) K;

¯

[7] For a review dealing with silicon-based odorants, see: R. Tacke,

S. Metz, Chem. Biodiversity 2008, 5, 920–941.

triclinic; space group P1 (no. 2); a = 10.743(3), b = 14.579(3),

c = 14.860(4) Å; α = 82.65(3), β = 73.58(3), γ = 70.58(3)°; V =

2104.0(9) Å³; Z = 4; ρ_calcd.= 1.309 gcm^–3; μ = 0.145 mm^–1;

F(000) = 880; 2θ_max= 52.04°; 23019 collected reflections; 7754

unique reflections (R_int= 0.0624); 531 parameters; S = 0.819;

0 restraints; R₁= 0.0410 [IϾ2σ(I)]; wR₂(all data) = 0.0904;

max./min. residual electron density: +0.443/–0.312 eÅ^–3.

Selected data for 20a: single crystal of dimensions

0.46ϫ0.43ϫ0.41 mm obtained by crystallization from meth-

anol at 20 °C. C₁₉H₂₄N₄O₄; M_r= 372.42; analysis at 100(2) K;

[8] For publications dealing with silicon-based odorants, see: a) R.

Tacke, T. Schmid, C. Burschka, M. Penka, H. Surburg, Orga-

nometallics 2002, 21, 113–120; b) R. Tacke, T. Schmid, M. Hof-

mann, T. Tolasch, W. Francke, Organometallics 2003, 22, 370–

372; c) T. Schmid, J. O. Daiss, R. Ilg, H. Surburg, R. Tacke,

Organometallics 2003, 22, 4343–4346; d) M. W. Büttner, M.

Penka, L. Doszczak, P. Kraft, R. Tacke, Organometallics 2007,

26, 1295–1298; e) L. Doszczak, P. Kraft, H.-P. Weber, R.

Bertermann, A. Triller, H. Hatt, R. Tacke, Angew. Chem. Int.

Ed. 2007, 46, 3367–3371; Angew. Chem. 2007, 119, 3431–3436;

f) M. W. Büttner, S. Metz, P. Kraft, R. Tacke, Organometallics

2007, 26, 3925–3929; g) M. W. Büttner, C. Burschka, K. Jun-

old, P. Kraft, R. Tacke, ChemBioChem 2007, 8, 1447–1454; h)

S. Metz, J. B. Nätscher, C. Burschka, K. Götz, M. Kaupp, P.

Kraft, R. Tacke, Organometallics 2009, 28, 4700–4712; i) J. B.

Nätscher, N. Laskowski, P. Kraft, R. Tacke, ChemBioChem

2010, 11, 315–319; j) A. Sunderkötter, S. Lorenzen, R. Tacke,

P. Kraft, Chem. Eur. J. 2010, 16, 7404–7421; k) J. B. G. Gluyas,

C. Burschka, P. Kraft, R. Tacke, Organometallics 2010, 29,

5897–5903; l) M. Geyer, J. Bauer, C. Burschka, P. Kraft, R.

Tacke, Eur. J. Inorg. Chem. 2011, 2769–2776; m) S. Dörrich,

J. B. Bauer, S. Lorenzen, C. Mahler, S. Schweeberg, C.

Burschka, J. A. Baus, R. Tacke, P. Kraft, Chem. Eur. J. 2013,

19, 11396–11408; n) B. Förster, R. Bertermann, P. Kraft, R.

Tacke, Organometallics 2014, 33, 338–346; o) J. Friedrich, S.

Dörrich, A. Berkefeld, P. Kraft, R. Tacke, Organometallics

2014, 33, 796–803.

¯

triclinic; space group P1 (no. 2); a = 17.6528(7), b = 21.4017(9),

c = 22.7819(10) Å; α = 63.3330(10), β = 86.908(2), γ =

84.006(2)°; V = 7649.2(6) Å³; Z = 16; ρ_calcd.= 1.294 gcm^–3; μ =

0.092 mm^–1; F(000) = 3168; 2θ_max= 49.478°; 144055 collected

reflections; 26087 unique reflections (R_int= 0.0398); 2013

parameters; S = 1.012; 5 restraints; R₁= 0.0396 [IϾ2σ(I)];

wR₂(all data) = 0.1065; max./min. residual electron density:

+0.602/–0.230 eÅ^–3. Selected data for 20b: single crystal of di-

mensions 0.5ϫ0.5ϫ0.5 mm obtained by crystallization from

methanol at 20 °C. C₁₈H₂₄N₄O₄Si; M_r= 388.50; analysis at

¯

296(2) K; triclinic; space group P1 (no. 2); a = 10.9364(9), b =

17.4897(14), c = 22.236(2) Å; α = 86.583(5), β = 84.257(5), γ =

72.568(4)°; V = 4035.5(6) Å³; Z = 8; ρ_calcd.= 1.279 gcm^–3; μ =

0.147 mm^–1; F(000) = 1648; 2θ_max= 55.202°; 128375 collected

reflections; 18586 unique reflections (R_int= 0.0384); 1184

parameters; S = 1.027; 296 restraints; R₁= 0.0475 [IϾ2σ(I)];

wR₂(all data) = 0.1462; max./min. residual electron density:

+0.394/–0.287 eÅ^–3.

[15] For the superposition analysis, the structures of those crystallo-

graphically independent molecules of 20a and 20b were chosen

that showed the greatest differences.

[9] W. Giersch, K. H. Schulte-Elte, G. Ohloff, Firmenich, Ger.

Offen. DE 2917450, May 11, 1978.

[10] For alternative synthetic methods, see: a) J. A. Soderquist, A.

Hassner, J. Organomet. Chem. 1978, 156, 227–233; b) R. I.

Damja, C. Eaborn, W.-C. Sham, J. Organomet. Chem. 1985,

291, 25–33; c) M. Stepp, Wacker, DE 10 2009 046 432 A1, July

22, 2010.

[16] a) Program PWIN-DAISY, v. 4.05, Bruker–Franzen GmbH,

Bremen, Germany, 1998; b) U. Weber, A. Germanus, H. Thiele,

Fresenius J. Anal. Chem. 1997, 359, 46–49.

Eur. J. Inorg. Chem. 0000, 0–0

13

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Pages: 15

www.eurjic.org

FULL PAPER

[17]

E. S. Magyar, J. Am. Chem. Soc. 1974, 96, 6112–6118; b) A.

Wu, D. Cremer, Int. J. Mol. Sci. 2003, 4, 158–192.

[20] Analysis of the spin system with the program WIN-DAISY

(v. 4.05) was not possible (more than ten spins in one system).

[21] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.

Received: June 27, 2014

Program MestReNova, v. 9.0.0, Mestrelab Research SL, Santi-

ago de Compostela, Spain, 2014.

[18] S. R. Maynez, L. Pelavin, G. Erker, J. Org. Chem. 1975, 40,

3302–3303.

[19] For spin-spin coupling constants of nonplanar ring systems,

see: a) J. B. Lambert, J. J. Papay, S. A. Khan, K. A. Kappauf,

Published Online: ᭿

Eur. J. Inorg. Chem. 0000, 0–0

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Pages: 15

www.eurjic.org

FULL PAPER

Sila-Galbanones

S. Dörrich, A. Ulmer, C. Mahler,

Sila-α-galbanone,

sila-α-spirogalbanone,

C. Burschka, J. A. Baus, R. Tacke,*

A. Chai, C. Ding, Y. Zou, G. Brunner,

A. Goeke, P. Kraft* ........................ 1–15

and sila-nor-α-galbanone (sila-analogues of

α-galbanone, α-spirogalbanone, and nor-α-

galbanone) were synthesized starting from

Me₂SiCl₂,

(CH₂=CH)₂SiCl₂,

and

Me₂(CH₂=CH)SiCl, respectively. These

sila-analogues proved to be less volatile and

thus more tenacious than the parent car-

bon compounds while also providing in-

sight into structure–odor correlations.

Sila-α-galbanone and Analogues: Synthesis

and Olfactory Characterization of Silicon-

Containing Derivatives of the Galbanum

Odorant α-Galbanone

Keywords: Silicon / Spiro compounds /

Metathesis

/ Hydroformylation / Fra-

grances / Galbanum

Eur. J. Inorg. Chem. 0000, 0–0

15

Article Doi

Sila-α-galbanone and analogues: Synthesis and olfactory characterization of silicon-containing derivatives of the galbanum odorant α-galbanone

DOI: 10.1002/ejic.201402597

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Article abstract of DOI:10.1002/ejic.201402597

Full text of DOI:10.1002/ejic.201402597

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