1,3-Diethynylallenes: Carbon-rich modules for three-dimensional acetylenic scaffolding

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Helvetica Chimica Acta Vol. 85 (2002)

1,3-Diethynylallenes: Carbon-Rich Modules for Three-Dimensional

Acetylenic Scaffolding

by Robert Livingston, Liam R. Cox, Severin Odermatt, and FranÁois Diederich*

Laboratorium f¸r Organische Chemie, ETH-Hˆnggerberg, HCI, CH-8093Z¸rich

Dedicated to Professor Dieter Seebach on the occasion of his 65th birthday

Regioselective Pd⁰-catalyzed cross-coupling of substrates, which bear bispropargylic leaving groups with

silyl-protected alkynes, has provided access to a variety of 1,3-diethynylallenes, a new family of modules for

three-dimensional acetylenic scaffolding. In enantiomerically pure form, these C-rich building blocks could

provide access by oxidative oligomerization to a fascinating new class of helical oligomers and polymers with

all-carbon backbones (Fig. 2). In the first of two routes, a bispropargylic epoxide underwent ring opening during

S_n2'-type cross-coupling, and the resulting alkoxide was silyl-protected, providing 1,3-diethynylallenes (Æ)-8,

(Æ)-12 (Scheme 3), and (Æ)-15 (Scheme 5). A more general approach involved bispropargylic carbonates or

esters as substrates (Scheme 6 8), and this route was applied to the preparation of a series of 1,3-

diethynylallenes to investigate how their overall stability against undesirable [2 2] cycloaddition is affected by

the nature of the substituents at the allene moiety. The investigation showed that the 1,3-diethynylallene

chromophore is stable against [2 2] cycloaddition only when protected by steric bulk and when additional p-

electron delocalization is avoided. The regioselectivity of the cross-coupling to the bispropargylic substrates is

entirely controlled by steric factors: attack occurs at the alkyne moiety bearing the smaller substituent

(Schemes 9 and 10). Oxidative Hay coupling of the terminally mono-deprotected 1,3-diethynylallene (Æ)-49

afforded the first dimer 50, probably as a mixture of two diastereoisomers (Scheme 12). Attempts to prepare a

silyl-protected tetraethynylallene by the new methodology failed (Scheme 13). Control experiments

(Schemes 14 16) showed that the Pd⁰-catalyzed cross-coupling to butadiyne moieties in the synthesis of this

still-elusive chromophore requires forcing conditions under which rapid [2 2] cycloaddition of the initial

product cannot be avoided.

1. Introduction. Oxidative coupling of small acetylenic modules has facilitated the

assembly of well-defined molecular architecture extending into one, two, and three

dimensions [1 3]. For example, (E)-diethynylethenes (1, DEEs, (E)-hex-3-ene-1,5-

diynes) and tetraethynylethenes (2, TEEs, 3,4-diethynylhex-3-ene-1,5-diynes) (Fig. 1)

have provided monodisperse rod-like poly(triacetylene) oligomers with lengths of up

to 18 nm, which have allowed insight into the chain-length dependency of extended

linear p-electron conjugation and hold promise as potential molecular wires [4].

Similarly, linear oligomers made from derivatives of 1,4-diethynyl- (3) and 1,1,4,4-

tetraethynylbutatriene (4) would also afford flat and rod-like structures. Acetylenic

scaffolding starting from (Æ)-1,3-diethynylallene ((Æ)-5; (Æ)-hepta-3,4-diene-1,6-

diyne) and 1,1,3,3-tetraethynylallene (6; Fig. 1), on the other hand, would provide

access to three-dimensional structures due to the inherent twist of the allene moiety.

Whereas silylated derivatives of peralkynylated butatriene 4 have been reported [5],

the ethynylated allenes (Æ)-5 and 6 have remained elusive, despite intensive efforts

aimed at their preparation [6]. During an attempted preparation of tetraethynyl-

methane, evidence for the formation of 1,1,3-triethynylallene in a mixture of products

was obtained [7]; also, mono-alkynylated allenes are well-known [8]. The major

Helvetica Chimica Acta Vol. 85 (2002)

3053

R

(±)-5

3

1

2

6

4

Fig. 1. Carbon-rich modules for acetylenic scaffolding

problems encountered in previous attempts to synthesize the novel C-rich building

blocks (Æ)-5 and 6 were their high tendency for rearrangement and facile [2 2]

cycloaddition, which occurred readily even at room temperature [6].

Here, we describe the synthesis of the first racemic 1,3-diethynylallenes, derivatives

of the parent compound (Æ)-5 (for a preliminary communication of parts of this work,

see [9]). We show that appropriate derivatives of (Æ)-5 possess sufficient stability for

terminal alkyne deprotection and subsequent oxidative coupling, generating the first

oligomeric derivatives. Due to the inherent 908 twist of the allene moiety, oxidative

coupling of these compounds in enantiomerically pure form promises to provide access

to a fascinating new class of three-dimensional helical oligomers and polymers. A

model of the helical structure of a dodecamer with (S)-1,3-diethynylallene repeating

units was generated by semi-empirical calculations (AM1, Austin model 1) [10]. As

shown in Fig. 2, substituents on the allene backbone (H-atoms in the model) are all

oriented toward the outside of the (P)-helix. This indicates possibilities such as helix

stabilization by attachment of substituents undergoing H-bonding or aromatic

interactions. Nonracemic helical polymers are attracting increasing interest for

potential applications ranging from materials exhibiting circularly polarized electro-

luminescence [11] to dopants for cholesteric liquid-crystalline phases [12]. Many

approaches to such advanced materials have relied upon side-chain chirality to induce

the desired helicity in a conformationally labile polymer backbone [13]. The

incorporation of rigid chiral units such as the 1,3-diethynylallenes directly into the

main chain offers the possibility for generating more-defined structures with a

stabilized helical conformation (for some recent examples, see [14]).

2. Results and Discussion. 2.1. Synthesis of 1,3-Dialkynylallenes. 2.1.1. Pd Catalysis

in the Formation of AlleneÀAcetylene C(sp²)ÀC(sp) Bonds. Pd⁰-catalyzed cross-

couplings of alkynes with suitably functionalized C(sp²)-centers have been well-

developed, and several particularly versatile protocols have seen widespread use [15].

Especially convenient are the Sonogashira conditions, under which the acetylene

partner is a Cu^Ispecies generated in situ from CuI and an amine base [16].

Most transition-metal-catalyzed cross-couplings proceed through initial oxidative

addition of, e.g., the vinyl or aryl halide to generate the intermediate Pd^IIspecies

(Scheme 1). For the coupling of allenyl (as opposed to vinyl) moieties, a variant

protocol involving S_n2'-type displacement of a propargylic leaving group can be

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Helvetica Chimica Acta Vol. 85 (2002)

Fig. 2. Views of the computer-generated (AM1) (P)-configured helical structure for a dodecamer obtained by

oxidative coupling of (S)-1,3-diethynylallene

employed [17]. This method has proven valuable in the preparation of alkynylallenes

from substrates bearing propargylic leaving groups such as halides, epoxides, acetates,

and carbonates [18 21]. Whether Pd⁰attack occurs syn or anti to the leaving group

(Scheme 1) is relevant when considering the transfer of stereochemical information

from the C-atom bearing the leaving group to the newly formed allene. Either mode

might occur through the more nucleophilic anionic Pd⁰complex as proposed by

Armatore and Jutand (shown for the anti mode) [22], while the syn mode would involve

prior precoordination of the metal to the acyl leaving group.

Given an appropriate regiochemical bias, application of these conditions to

bispropargylic precursors should yield the desired C₂-symmetric 1,3-diethynylallenes

(Scheme 2).

2.1.2. 1,3-Diethynylallenes by the Epoxide Route. In a first approach, we targeted the

bispropargylic epoxide (Æ)-7 (Scheme 3), which would undergo ring opening,

concomitant with the attack of the Pd⁰species, generating an allenylpalladium(II)

intermediate. In these experiments, the zinc acetylide (i-Pr)₃SiÀCꢀCÀZnCl was used

as the alkyne partner, thus generating an intermediate zinc alkoxide after coupling,

which could be silylated directly with (t-Bu)Me₂SiOTf (Tf SO₂CF₃) to give the

desired C₂-symmetrical allene [23]. In a higher-yielding protocol, the standard

Sonogashira conditions are employed, which formally generate the more-active Cu^I

acetylide in situ, allowing the coupling to proceed at room temperature and with short

reaction times. Under these more weakly basic conditions, the epoxide opening

Helvetica Chimica Acta Vol. 85 (2002)

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Scheme 1. Pd⁰-Catalyzed Cross-Coupling Modes of Vinyl and Allenyl Substrates

Standard Oxidative Addition

L

X

L

X

Pd⁰L₂

Pd^II

+

S_N2' Substitution

anti Mode

X

L

X

X^–

Pd^II

+

L

[Pd⁰L₂X]^–

MeO

O

Pd⁰L₂

L

OCOOMe

L

Pd^II

syn Mode

Scheme 2. Regioselectivity in the Cross-Coupling of Bispropargylic Substrates

Si(i-Pr)₃

R

Si(i-Pr)₃

(i-Pr)₃Si

C₂-Symmetric

Pd⁰

X

R

(i-Pr)₃Si

R

Si(i-Pr)₃

R

Si(i-Pr)₃

Unsymmetric

R

generates the alcohol (rather than the zinc alkoxide), so the addition of imidazole is

necessary to efficiently protect the newly created hydroxymethyl side chain as the (t-

Bu)Me₂Si ether (Scheme 3). Just 2 mol-% of [Pd(PPh₃)₄] as catalyst were sufficient to

produce 1,3-diethynylallene (Æ)-8 in 52% yield after 6 h at room temperature. In later

couplings of similar substrates, the use of higher catalyst loads (typically 5 mol-%)

resulted in significantly shorter reaction times and generally higher yields, so this result

should be considered nonoptimized.

A first synthesis of bispropargylic epoxide (Æ)-7 started with the formation of

bispropargylic alcohol (Æ)-9, which was obtained by two different routes. In one

approach, (t-Bu)Me₂SiOCH₂ÀCꢀCLi (prepared from the corresponding alkyne [24]

with BuLi in THF at À 788) was added to (i-Pr)₃SiÀCꢀCÀCHO [6b][25] in THF to

provide (Æ)-9 in 45% yield. Transmetallation of the lithiated alkyne with MgBr₂¥ OEt₂

did not enhance the yield of (Æ)-9. Alternatively, commercially available but-2-yne-1,4-

diol was monoprotected with (t-Bu)Me₂SiCl to give 10 [26]. Oxidation with MnO₂

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Helvetica Chimica Acta Vol. 85 (2002)

Scheme 3. Synthesis of 1,3-Diethynylallenes (Æ)-8 and (Æ)-12

a)

b), c)

HO

OSi(t-Bu)Me₂

OH

10

O

OH

d)

e)

OSi(t-Bu)Me₂

SiR₃

OSi(t-Bu)Me₂

(i-Pr)₃Si

(±)-9

11

O

Me₂(t-Bu)SiO

f) or g)

OSi(t-Bu)Me₂

(i-Pr)₃Si

OSi(t-Bu)Me₂

(±)-7

(i-Pr)₃Si

(±)-8 R = i-Pr

(±)-12 R = Me

a) (t-Bu)Me₂SiCl, NaH, THF, r.t.; 65%. b) MnO₂, Et₂O, r.t. c) (i-Pr)₃SiÀCꢀCLi, THF, À 788 ! r.t.; 34% (from

10). d) MnO₂, Et₂O, r.t.; 77%. e) MeLi ¥ LiBr, CH₂I₂, THF, À 788 ! r.t.; 79%. f) (i-Pr)₃SiÀCꢀCH, (i-Pr)₂NH,

[Pd(PPh₃)₄], CuI, CH₂Cl₂, r.t., then (t-Bu)Me₂SiCl, 1H-imidazole, r.t.; 52%. g) Me₃SiÀCꢀCH, (i-Pr)₂NH,

[Pd(PPh₃)₄], CuI, (CH₂Cl)₂, r.t., then (t-Bu)Me₂SiCl, 1H-imidazole, r.t.; 53%.

provided the corresponding propargylic aldehyde to which (i-Pr)₃SiÀCꢀCLi was

added to furnish (Æ)-9. Oxidation of (Æ)-9 afforded ketone 11, which was transformed

into epoxide (Æ)-7 with CH₂I₂/MeLi ¥ LiBr [27]. The C₂-symmetric 1,3-diethynylallene

(Æ)-8 was subsequently obtained in 52% yield as described above, and its structure was

established by X-ray crystallography [9]. Alternatively, coupling of (Æ)-7 with

Me₃SiÀCꢀCH afforded the differentially protected derivative (Æ)-12 in a similar yield.

In view of the rather modest yields obtained in the preparation of epoxide (Æ)-7, a

more direct and higher-yielding approach to this key intermediate was developed

(Scheme 4). Lewis acid-catalyzed acylation of differentially protected acetylene 13

(prepared in 90% yield from (i-Pr)₃SiÀCꢀCH and Me₃SiCl) with ClCH₂COCl gave

chloro ketone 14 [28] in nearly quantitative yield, without need for chromatographic

purification. Addition of (t-Bu)Me₂SiOCH₂ÀCꢀCLi gave the intermediate alkoxide,

and epoxide-ring closure was effected by addition of DMF to promote the nucleophilic

substitution. Addition of t-BuOK (0.5 equiv.) served to compensate for adventitious

H₂O in the DMF and to promote substitution by switching from Li to the less

coordinating K ion as the counterion. Conversion to epoxide (Æ)-7 was sufficiently

clean that only quick filtration through SiO₂was required to give material of reasonable

analytical purity.

Subsequently, we became interested in preparing the C₂-symmetric bis-Me₃Si-

protected allene (Æ)-15. We hoped to smoothly remove the more-labile Me₃Si

protecting groups in (Æ)-15 (as compared to the (i-Pr)₃Si groups in (Æ)-8) without

disturbing the (t-Bu)Me₂Si ether residues and thus allow the preparation of oligomeric

materials under the Glaser-Hay coupling conditions developed in our group for the

preparation of long poly(triacetylene) oligomers [4a][29]. However, the greater

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3057

Scheme 4. Alternative Synthesis of Epoxide (Æ)-7

O

a)

b)

Cl

(i-Pr)₃Si

SiMe₃

(i-Pr)₃Si

13

14

LiO

Cl

O

c)

OSi(t-Bu)Me₂

(i-Pr)₃Si

(±)-7

a) ClCH₂COCl, AlCl₃, CH₂Cl₂, 08 ! r.t.; 97%. b) (t-Bu)Me₂SiOCH₂ÀCꢀCLi, THF, À 788 ! r.t. c) t-BuOK,

DMF, r.t.; 82% (from 14).

lability of the Me₃Si protecting group also led to substantially reduced yields in the

preparation of the required epoxide (Æ)-16 by both routes described above.

Addition of (t-Bu)Me₂SiOCH₂ÀCꢀCLi to Me₃SiÀCꢀCÀCHO provided bispro-

pargylic alcohol (Æ)-17, which was oxidized with BaMnO₄[30] to the corresponding

ketone 18 (Scheme 5). As a result of the lability of the Me₃Si protecting group, ketone

18 was particularly susceptible to protodesilylation during chromatographic purifica-

tion. Oxirane formation as described above afforded (Æ)-16 in only 39% yield. By the

alternative route, chloro ketone 19 [31] was obtained in good yield, but the lability of

the Me₃Si group caused substantial problems in the epoxide-forming step, since this

reaction proceeds through an intermediate alkoxide, to which the silyl group is readily

transferred. Indeed, the isolated product mixture was found to include the desired

epoxide (Æ)-16, protodesilated epoxide (Æ)-20, and compound (Æ)-21 resulting from

incomplete epoxide formation. Once isolated, epoxide (Æ)-16 was readily converted to

1,3-diethynylallene (Æ)-15 under standard conditions.

2.1.3. A General Route to 1,3-Diethynylallenes. The structural limitations of the

epoxide-opening route could be circumvented with acetate or carbonate as the leaving

group for the formation of the allenylpalladium intermediate. This is illustrated by the

synthesis of (Æ)-22 in Scheme 6. Propargyl alcohol (Æ)-23 was oxidized to give ketone

24, to which lithiated oct-1-yne was added to provide bispropargylic alcohol (Æ)-25.

While the corresponding acetate (Æ)-26 could be formed under standard conditions in

69% yield, aliphatic amine bases or pyridine proved generally unsuitable for the

preparation of carbonates from bispropargylic alcohols. On the other hand, formation

of the lithium alkoxide with BuLi or LHMDS (lithium hexamethyldisilazide), followed

by addition of methyl chloroformate [18c], provided carbonate (Æ)-27 in good yield

(71%).

While acetate (Æ)-26 could be converted by Pd⁰-mediated cross-coupling to 1,3-

dialkynylallene (Æ)-22 in 66% yield after 4 h reflux in THF, carbonate (Æ)-27 provided

the target compound in 94% yield by stirring for 30 min at room temperature in CH₂Cl₂

(a better solvent for the catalyst at ambient temperature).

Upon isolation in pure form, (Æ)-22 became prone to the thermal [2 2]

cyclodimerization known to occur readily in allenes with extended p-electron

conjugation [32]. This process had not been observed with the sterically hindered

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Helvetica Chimica Acta Vol. 85 (2002)

Scheme 5. Synthesis of 1,3-Diethynylallene (Æ)-15

OH

OSi(t-Bu)Me₂

Me₃Si

SiMe₃

(±)-17

a)

c)

O

Cl

OSi(t-Bu)Me₂

Me₃Si

18

b)

O

19

d), e)

HO

Cl

O

Me₃Si

H

Me₃Si

OSi(t-Bu)Me₂

(±)-16

(±)-20

OSi(t-Bu)Me₂

(±)-21

OSi(t-Bu)Me₂

f)

SiMe₃

Me₂(t-Bu)SiO

OSi(t-Bu)Me₂

Me₃Si

(±)-15

a) BaMnO₄, CH₂Cl₂, r.t.; 93%. b) MeLi ¥ LiBr, CH₂I₂, THF, À 788 ! r.t.; 39%. c) ClCH₂COCl, AlCl₃, CH₂Cl₂,

08 ! r.t.; 78%. d) (t-Bu)Me₂SiOCH₂ÀCꢀCLi, THF, À 788 !À 408. e) t-BuOK, DMF, À 408 !À 208; 23 %

(16), 9% ((Æ)-20), 26% ((Æ)-21) (from 19). f) Me₃SiÀCꢀCH, (i-Pr)₂NH, [Pd(PPh₃)₄], CuI, CH₂Cl₂, r.t., then

(t-Bu)Me₂SiCl, 1H-imidazole, r.t.; 63%.

allene (Æ)-8, but, for (Æ)-22, the half-life was on the order of 1 2 d at room

temperature. Storage at low temperature did not entirely suppress the dimerization

although the monomer was stable over several months when diluted with hexane and

kept in the freezer at À 308. NMR Analysis indicated that the dimerized product

consists of several inseparable stereoisomers. That this material is a dimer of 1,3-

diethynylallene (Æ)-22 was established by mass spectrometry and microanalysis, but

since the inseparable mixture of isomers does not give clear structural data, further

rearrangements of the presumed initial [2 2] cycloadduct cannot be ruled out [6b].

To explore the influence of different substituents on the thermal stability against

[2 2] cycloaddition, the new route developed for (Æ)-22 was applied to the synthesis

of other 1,3-diethynylallenes. The preparation of (Æ)-28 started from 3-(4-methoxy-

phenyl)prop-1-yne (29) [3 3 ]S(cheme 7). The corresponding acetylide was added to

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Scheme 6. Synthesis of 1,3-Diethynylallene (Æ)-22

OH

a)

b)

CHO

(i-Pr)₃Si

(±)-23

OH

O

c)

(i-Pr)₃Si

24

(±)-25

d)

e)

OCOMe

OCOOMe

(i-Pr)₃Si

(±)-27

(±)-26

f)

g)

Si(i-Pr)₃

(i-Pr)₃Si

(±)-22

a) (i-Pr)₃SiÀCꢀCLi, THF, À 788 ! r.t.; 79%. b) Me₂SO, (COCl)₂, Et₃N, CH₂Cl₂, À 788; 94%. c)

Me(CH₂)₅CꢀCLi, THF, À 788 ! r.t.; 66%. d) Ac₂O, Et₃N, 4-(dimethylamino)pyridine (DMAP), CH₂Cl₂,

r.t.; 69%. e) BuLi, THF, À 788, then MeOCOCl, r.t.; 71%. f) (i-Pr)₃SiÀCꢀCH, (i-Pr)₂NH, [Pd(PPh₃)₄], CuI,

THF, D; 66%. g) (i-Pr)₃SiÀCꢀCH, (i-Pr)₂NH, [Pd(PPh₃)₄], CuI, CH₂Cl₂, r.t.; 94%.

Weinreb amide 30 to provide ketone 31. Addition of (i-Pr)₃SiÀCꢀCLi led to tertiary

alcohol (Æ)-32, which was transformed into methyl carbonate (Æ)-33. Allene formation

as described for (Æ)-22 gave the target compound (Æ)-28 in 52% yield. Intermediates

on the route to (Æ)-28 proved rather unstable to extended storage even at low

temperature, presumably because of the acidity of the doubly activated benzylic

groups. Also, the final 1,3-diethynylallene, which was isolated as a clear oil, showed only

borderline stability.

When the allene fragment is substituted by Ph residues, thereby further extending

its p-electron conjugation and reducing the steric shielding, the stability decreases

dramatically. The preparation of 1,3-diethynyl-1,3-diphenylallene (Æ)-34 proved quite

challenging due to instability of the intermediates in the synthetic route (Scheme 8).

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Helvetica Chimica Acta Vol. 85 (2002)

Scheme 7. Synthesis of 1,3-Diethynylallene (Æ)-28

MeO

O

OMe

O

N

MeO

30

a)

31

29

Si(i-Pr)₃

OMe

MeO

RO

MeO

b)

d)

OMe

Si(i-Pr)₃

(i-Pr)₃Si

(±)-28

(±)-32 R = H

(±)-33 R = COOMe

c)

a) BuLi, THF, À 788, then 30, À 788 ! r.t.; 67%. b) (i-Pr)₃SiÀCꢀCLi, THF, À 788 ! r.t.; 56%. c) LiHMDS,

THF, À 788, then MeOCOCl, À 788 ! r.t.; 71%. d) (i-Pr)₃SiÀCꢀCH, (i-Pr)₂NH, [Pd(PPh₃)₄], CuI, CH₂Cl₂,

r.t.; 52%.

Scheme 8. Synthesis of the Thermally Unstable 1,3-Diethynylallene (Æ)-34

OH

O

a)

b)

Ph

(i-Pr)₃Si

Ph

(±)-36

35

Si(i-Pr)₃

+

OBz

Ph

c)

Dimer

(i-Pr)₃Si

Ph

(±)-34

(±)-37

(i-Pr)₃Si

a) (i-Pr)₃SiÀCꢀCLi, THF, À 788 ! r.t.; 92%. b) BuLi, PhCOCl (BzCl), THF, À 788 ! r.t. c) (i-Pr)₃SiÀCꢀCH,

(i-Pr)₂NH, [Pd(PPh₃)₄], CuI, THF, D; 38% (combined yield of (Æ)-34 and dimer, starting from (Æ)-36).

Addition of (i-Pr)₃SiÀCꢀCLi to 1,3-diphenylprop-2-yn-1-one (35) [34] provided the

bispropargylic alcohol (Æ)-36. Both the methyl carbonate and the diethyl phosphate of

(Æ)-36 proved unstable in solution even at low temperatures. The corresponding

acetate and benzoate could not be isolated, but were sufficiently stable to be used in the

formation of the allene. Thus, benzoate (Æ)-37 was prepared in situ, followed by

immediate application of the cross-coupling conditions to give (Æ)-34. However, the

half-life of this allene with regard to cyclodimerization was only a few minutes in neat

form at room temperature, which precluded isolation in pure form. These experiments

clearly demonstrate that bulky side chains that do not extend the p-conjugation of the

allene system are required to prevent the approach of the two allene units and to

mitigate the undesired thermal [2 2] cycloaddition to an appreciable extent.

2.2. Regiochemical Studies. From the outset of this investigation, we assumed that

the primary factor in determining the regioselectivity (Scheme 2) in the formation of

the allenylpalladium intermediate and, ultimately, the 1,3-diethynylallene formed

Helvetica Chimica Acta Vol. 85 (2002)

3061

would be the difference in steric bulk between the two alkyne substituents rather than

the difference in electronic factors. Thus, attack of the Pd⁰species at (Æ)-7 (Scheme 3)

or (Æ)-16 (Scheme 5) occurs at the acetylene bearing the smaller (t-Bu)Me₂SiOCH₂

substituent and not at the silyl-protected ((i-Pr)₃Si or Me₃Si) alkyne. To test this

hypothesis further, we investigated 1,3-dialkynylallene formation starting from

carbonate (Æ)-38, in which the two alkynyl residues are substituted with (i-Pr)₃Si

and Me₃C groups, respectively. Starting from ketone 39 [35], we prepared by the

established protocol alcohol (Æ)-40 and carbonate (Æ)-38 (Scheme 9).

Scheme 9. Cross-Coupling of the Hindered Carbonate (Æ)-38

O

OH

a)

b)

(i-Pr)₃Si

(±)-40

39

Si(i-Pr)₃

OCOOMe

c)

(i-Pr)₃Si

(±)-38

(±)-41

(i-Pr)₃Si

a) (i-Pr)₃SiÀCꢀCLi, THF, À 788 ! r.t.; 89%. b) LiHMDS, THF, À 788, then MeOCOCl, À 788 ! r.t.; 94%.

c) (i-Pr)₃SiÀCꢀCH, (i-Pr)₂NH, [Pd(PPh₃)₄], CuI, (CH₂Cl)₂, 708; 32%.

The following cross-coupling reaction with (i-Pr)₃SiÀCꢀCH proved extremely

sluggish even after heating, with the Pd catalyst turning to a black, inactive precipitate

after low conversion. Air should be rigorously excluded to prevent oxidative coupling

of (i-Pr)₃SiÀCꢀCH, since the separation of the resulting buta-1,3-diyne from the

desired allene proved extremely difficult. The attack by Pd⁰occurred with complete

regioselectivity at the alkyne moiety substituted with the smaller Me₃C group, affording

the stable, C₂-symmetric 1,3-diethynylallene (Æ)-41 in 32% yield (92% based on

recovered starting material). The sluggish reaction and the low yield demonstrate,

however, that the increase in steric bulk at the site of Pd-attack is clearly hindering

formation of the allenylpalladium intermediate and subsequent cross-coupling.

To further explore the role of steric vs. electronic factors in the regioselectivity, we

replaced the (i-Pr)₃Si group in carbonate (Æ)-38 with the smaller Me₃Si group, which is

similar to the Me₃C group in steric bulk (Scheme 10). Preparation of carbonate (Æ)-42

was accomplished via the established route starting from ketone 39 [35] via alcohol

(Æ)-43, and cross coupling with Me₃SiÀCꢀCH in (CH₂Cl)₂at 708 proceeded smoothly

to complete conversion. The 1,3-diethynylallene products isolated in 71% yield

consisted of a ca. 5 :2 mixture of C₁-symmetric (Æ)-44 and C₂-symmetric isomer (Æ)-45.

This ratio is (qualitatively speaking) easily accounted for by the slightly reduced steric

demand imposed by the Me₃Si group with the longer C(sp)ÀSi bond and rules out any

significant electronic bias for attack in the cross-coupling.

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Helvetica Chimica Acta Vol. 85 (2002)

Scheme 10. Inverted Regioselectivity in the Cross-Coupling of Carbonate (Æ)-42

O

OH

OCOOMe

b)

a)

Me₃Si

(±)-43

(±)-42

39

Me₃Si

SiMe₃

c)

+

Me₃Si

(±)-45

(±)-44

ca. 5 : 2

a) (i-Pr)₃SiÀCꢀCLi, THF, À 788 ! r.t.; 72% (includes preparation of crude 39). b) LiHMDS, THF, À 788,

then MeOCOCl, À 788 ! r.t.; 90%. c) Me₃SiÀCꢀCH, (i-Pr)₂NH, [Pd(PPh₃)₄], CuI, (CH₂Cl)₂, 708; 71%

(combined yield).

While this result was satisfying in itself, it does place some constraints upon the

design of future systems, in which we would generally like to use bulkier side chains to

prevent allene dimerization, yet sterically less-demanding alkyne protection to allow

more-facile deprotection for subsequent oligomerization via oxidative coupling.

2.3. Chemical Transformations with 1,3-Diethynylallenes: Preparation of the First

Dimer. The first target in our investigations was the formation of a 1,3-diethynylallene

dimer, thereby establishing the feasibility of the oxidative acetylenic coupling required

to ultimately reach the new helical oligomers and polymers (Fig. 2). We initially chose

(Æ)-8 as the precursor in view of its stability and good accessibility via the epoxide route

(Scheme 4). However, (Æ)-8 bears silyl-protecting groups on the side chains as well as

the alkynyl moieties, which precludes straightforward alkyne deprotection, as required

for oxidative coupling. Therefore, we intended to exchange the silyl ether by another

O-protecting group (Scheme 11). The (t-Bu)Me₂Si group could, indeed, be removed

with TsOH in MeOH/Et₂O to yield diol (Æ)-46, which is stable only in very dilute

solution. Upon concentration, dimerization occurs within minutes. Therefore, the crude

diol, isolated as an oil after workup, was immediately trapped with pivaloyl chloride in

CH₂Cl₂in the presence of Et₃N. The first acylation seems to proceed rather smoothly

(TLC), but the second one is appreciably slower, and side products start to form with

increasing reaction time. Pure diacetylated allene (Æ)-47 was isolated, although its

instability prevented further use in alkyne deprotection and subsequent oxidative

coupling.

We subsequently decided to prepare the desired dimer starting from unsymmetri-

cally protected 1,3-diethynylallene (Æ)-48 (Scheme 12). Cross-coupling between

carbonate (Æ)-38 and Me₃SiÀCꢀCH provided (Æ)-48 as a stable compound that was

mono-deprotected with K₂CO₃in MeOH/THF to give ethynyl derivative (Æ)-49.

Oxidative coupling under Hay conditions proceeded slowly and afforded the desired

diallene 50 in 72% yield. The isolated product decomposes only slowly at ambient

Helvetica Chimica Acta Vol. 85 (2002)

3063

Scheme 11. Exchange of the O-Protecting Groups in 1,3-Diethynylallene (Æ)-8

Si(i-Pr)₃

Me₂(t-Bu)SiO

OH

a)

OSi(t-Bu)Me₂

HO

(±)-46

(i-Pr)₃Si

(±)-8

Si(i-Pr)₃

(t-Bu)COO

b)

OOC(t-Bu)

(±)-47

(i-Pr)₃Si

a) TsOH, MeOH/Et₂O, r.t. b) Me₃CCOCl, Et₃N, CH₂Cl₂, 08 ! r.t.; 49% (from (Æ)-8).

Scheme 12. Synthesis of Diallene 50

SiMe₃

OCOOMe

a)

b)

(i-Pr)₃Si

(±)-38

(±)-48

(i-Pr)₃Si

H

(i-Pr)₃Si

c)

Si(i-Pr)₃

50

(±)-49

(i-Pr)₃Si

(probably as a mixture

of two diastereoisomers)

a) Me₃SiÀCꢀCH, (i-Pr)₂EtN, [Pd(PPh₃)₄], CuI, (CH₂Cl)₂, 808. b) K₂CO₃, MeOH/THF 1:1, r.t.; 57% (from

(Æ)-38). c) CuCl, N,N,N',N'-tetramethylethylenediamine (TMEDA), air, molecular sieves (4 ä), CHCl₃, r.t.;

72%.

atmosphere to a much more-polar compound, but it does not dimerize. Stored in an

inert atmosphere, it seems completely stable.

Support for the formation of 50 was provided by the electron-impact mass spectrum

(EI-MS), which depicted the molecular ion M at m/z 710.5 (52%) as an intense ion,

besides characteristic fragment ions at 695.5 (11, [M À Me] ), 667.4 (16, [M À Pr] ),

653.4 (46, [M À t-Bu] ), 553.3 (5, [M À (i-Pr)₃Si] ), 57.1 (89, t-Bu ), and 44.0 (100,

Pr ). Starting from racemic (Æ)-49, the formation of two diastereoisomers, one meso

compound and one pair of enantiomers, was expected. However, the ¹H- and ¹³C-NMR

spectra (CDCl₃) show only one set of peaks (i.e., 13 ¹³C and two ¹H resonances). Also,

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Helvetica Chimica Acta Vol. 85 (2002)

all attempts to separate the diastereoisomers by HPLC have failed so far. Nevertheless,

we believe that the existence of only one set of NMR resonances is pure coincidence,

and that the isolated compound 50 is composed of a mixture of two diastereoisomers.

Full clarity will be reached in this matter when oxidative coupling is conducted with

enantiomerically pure 1,3-diethynylallenes, which is our next objective in this project.

2.4. Attempted Synthesis of Tetraethynylallene. Tetraethynylallene (6) and its

silylated derivatives have remained elusive despite intensive past efforts aimed at their

preparation in our group [6b]. These compounds are expected to be unstable toward

dimerization in analogy to the diphenyl derivative (Æ)-34, but we hoped that the newly

developed methodology described above would allow their synthesis and subsequent

characterization, at least in solution.

On the way to (i-Pr)₃Si-protected tetraethynylallene 51, we started from alcohol 52

[6b], which was transformed into carbonate 53 (Scheme 13). However, the carbonate

failed to react under the standard cross-coupling conditions at room temperature, and

heating gave incomplete conversion to two less-polar products, the minor of which

could be consistent with the dimer of 51, although no clean spectral data were obtained

to support this conclusion.

Scheme 13. Attempted Synthesis of Tetraethynylallene 51

OH

OCOOMe

a)

Si(i-Pr)₃

(i-Pr)₃Si

52

53

(i-Pr)₃Si

Si(i-Pr)₃

b)

(i-Pr)₃Si

51

a) LiHMDS, THF, À 788, then MeOCOCl, À 788 ! r.t.; 84%. b) (i-Pr)₃SiÀCꢀCH, (i-Pr)₂NH, [Pd(PPh₃)₄],

CuI, (CH₂Cl)₂, D.

In analyzing this failure, we note that two structural elements have been changed

from the previously used substrates. First, one of the three residues at the tertiary

center, which, in previous substrates, was generally an alkyl group, is now an additional

alkynyl group, making the leaving group trispropargylic. Second, the acetylene moiety

to undergo Pd-attack is now part of a buta-1,3-diyne fragment, and this might cause a

sufficiently large electronic perturbation to disfavor the attack. Preparing and cross-

coupling substrates that separate these two elements might give insight into the

problems encountered in the attempted preparation of tetraethynylallene.

The first target was trispropargylic carbonate 54, which was expected to give

triethynylallene 55 after coupling (Scheme 14). Ketone 56 [6b] was transformed into

alcohol 57 and subsequently into the desired carbonate, which proved to be unstable to

concentration and chromatography, but could be prepared cleanly in solution, then

taken directly to the cross-coupling step. This resulted in the formation of several

Helvetica Chimica Acta Vol. 85 (2002)

3065

products, including one likely candidate for the targeted triethynylallene, but this

largely decomposed to another product on attempted isolation. This behavior is

consistent with allene formation and dimerization, as observed with the diphenyl and

expected for the tetraethynyl derivative.

Scheme 14. Attempted Synthesis of Triethynylallene 55

O

OH

a)

b)

(i-Pr)₃Si

Si(i-Pr)₃

(i-Pr)₃Si

57

56

(i-Pr)₃Si

Si(i-Pr)₃

OCOOMe

c)

(i-Pr)₃Si

55

54

a) Me(CH₂)₃CꢀCLi, THF, À 788 ! r.t.; 75%. b) LiHMDS, THF, À 788, then MeOCOCl, À 788 ! r.t.

c) (i-Pr)₃SiÀCꢀCH, (i-Pr)₂NH, [Pd(PPh₃)₄], CuI, THF, D.

Carbonate 58 was subsequently prepared from propargyl alcohol 59 [36] via 60 to

test the reactivity of buta-1,3-diyne fragments in the cross-coupling reaction

(Scheme 15). Attack of Pd required heating to attain appreciable reaction rates.

However, once the reaction was initiated, conversion to product was clean and 1,1-

diethynylallene 61 was obtained in excellent (97%) yield.

Scheme 15. Synthesis of 1,1-Diethynylallene 61

OH

a)

b)

Si(i-Pr)₃

60

59

Si(i-Pr)₃

OCOOMe

c)

Si(i-Pr)₃

58

61

a) (i-Pr)₃SiÀCꢀCBr [37], NH₂OH ¥ HCl, PrNH₂, EtOH, CuCl, r.t.; 93%. b) LiHMDS, THF, À 788, then

MeOCOCl, À 788 ! r.t.; 71%. c) (i-Pr)₃SiÀCꢀCH, (i-Pr)₂NH, [Pd(PPh₃)₄], CuI, (CH₂Cl)₂, 708; 97%.

For direct comparison of the reaction rates for cross-coupling to acetylene and

butadiyne fragments, carbonate 62 was also prepared (via 63 ! 64 ! 62; Scheme 16). In

this case, cross-coupling proceeded readily at room temperature and alkynylallene 65

was isolated in 94% yield.

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Helvetica Chimica Acta Vol. 85 (2002)

Scheme 16. Synthesis of Alkynylallene 65

O

OH

a)

b)

63

64

Si(i-Pr)₃

OCOOMe

c)

62

65

a) Me(CH₂)₃CꢀCLi, THF, À 788 ! r.t. b) LiHMDS, THF, À 788, then MeOCOCl, À 788 ! r.t.; 67% (from

63). c) (i-Pr)₃SiÀCꢀCH, (i-Pr)₂NH, [Pd(PPh₃)₄], CuI, (CH₂Cl)₂, r.t.; 94%.

The comparison between the cross-coupling reactivity of 58 and 62 clearly shows

that attack of Pd at the butadiyne fragment is less favorable, compared with attack at an

acetylene moiety, requiring higher temperatures for conversion. This finding may also

explain why carbonate 53 (Scheme 13) is much less reactive than analog 54

(Scheme 14). Thus, the attempt to synthesize the most delicate tetraethynylallene

chromophore via this cross-coupling method appears disadvantageous: attack of Pd at

the butadiyne moiety requires forcing conditions, while the product, with its high

propensity to undergo [2 2] cycloaddition, is likely to exhibit extreme sensitivity to

heat.

3. Conclusions. Regioselective Pd⁰-catalyzed cross-coupling of substrates bearing

bispropargylic leaving groups with silyl-protected alkynes has provided access to a

variety of 1,3-diethynylallenes, a new family of C-rich modules for three-dimensional

acetylenic scaffolding. Extensive investigation showed that the 1,3-diethynylallene

chromophore is stable only against [2 2] cycloaddition, when protected by steric bulk,

and when additional p-electron delocalization is avoided. Compounds (Æ)-8 and (Æ)-

41 with bulky alkyl groups attached to the allene fragment are representatives of

thermally stable derivatives, whereas the diphenyl derivative (Æ)-34 is a good example

for an unstable derivative undergoing rapid [2 2] cycloaddition at ambient temper-

ature. Hay coupling of (Æ)-49 led to the first 1,3-diethynylallene dimer 50,

demonstrating that the formation of oligomers and polymers with a helical backbone

(Fig. 2) by oxidative oligomerization is in reach, once a protocol for the optical

resolution of the 1,3-diethynylallenes has been worked out. Attempts to apply the new

cross-coupling methodology to the formation of a silyl-protected tetraethynylallene

failed. Control experiments showed that the Pd⁰-catalyzed cross-coupling to butadiyne

moieties in the synthesis of this still-elusive chromophore requires forcing conditions

under which rapid [2 2] cycloaddition of the initial product cannot be avoided.

Now that the methods for preparing 1,3-diethynylallenes are well-established, the

focus will be on isolating them in enantiomerically pure form. One option for isolation

of enantiomerically pure compounds is derivatization of racemic material with chiral

Helvetica Chimica Acta Vol. 85 (2002)

3067

side chains, followed by separation of the diastereoisomers. An obvious candidate for

such experiments is diol (Æ)-46 (Scheme 11), which could be esterified with optically

active carboxy derivatives. Another option is to prepare enantiomerically pure

bispropargylic carbonates and attempt to transfer this atom-centered chirality to the

axial chirality of the allene according to the stereoselective modes of attack outlined in

Scheme 1. It is clear that such an endeavor will require many additional new methods.

But the prospect of preparing fascinating new helical oligomers and polymers (Fig. 2)

with promising chiroptical properties fully warrants these synthesis investments.

Experimental Part

General. Reagents and solvents were purchased as reagent-grade and used without further purification

unless otherwise stated. THF and Et₂O were freshly distilled from sodium benzophenone ketyl, and CH₂Cl₂was

freshly distilled from CaH₂. (i-Pr)₂NH and Et₃N were distilled over KOH and stored over activated molecular

sieves (4 ä). All reactions were performed in oven-dried or flame-dried glassware under an inert atmosphere

(N₂; for Pd-catalyzed reactions: Ar) unless otherwise stated. Evaporation and concentration in vacuo was

performed at ꢁ 308/ca. 10 Torr. Further drying of the new compounds was carried out at ca. 10^À2Torr.

Chromatography refers to flash chromatography (FC) on SiO₂60 (0.02 0.063mm) from Fluka; head pressure

of ca. 0.3bar. TLC: Polygram SIL G/UV₂₅₄SiO₂-coated plates from Macherey-Nagel; visualization by UV light

(254 nm) or by coloring with an anisaldehyde soln. (98% EtOH (198 ml), conc. H₂SO₄(7 ml), AcOH (2 ml),

and anisaldehyde (5 ml)). M.p.: B¸chi B-540 melting-point apparatus; uncorrected. UV/VIS (l_max[nm], (e

[m^À1cm^À1]): Varian-CARY 500 Scan spectrophotometer with a 1-cm cell at r.t. IR ([cm^À1], KBr or film): Perkin-

Elmer 1600 FT-IR spectrometer. NMR (¹H, ¹³C; d [ppm], J [Hz]): Varian Gemini 200, Varian Gemini 300, or

Bruker 500 MHz spectrometer at 298 K with residual solvent peaks as internal reference. MS (m/z (%)): EI

mass spectra were recorded on a VG-Tribid instrument operating at 70 eV, and HR-MALDI mass spectra on an

IonSpec Fourier Transform (FT) instrument. Elemental analyses were performed by the Mikrolabor at the

Laboratorium f¸r Organische Chemie at ETH Z¸rich.

(Æ)-6-[(tert-Butyl)dimethylsilyloxy]-1-(triisopropylsilyl)hexa-1,4-diyn-3-ol ((Æ)-9). Method A: BuLi

(1.71 ml of a 1.6m soln. in hexane, 2.73mmol) was added dropwise to ( t-Bu)Me₂SiOCH₂ÀCꢀCH [24]

(503mg, 2.96 mmol) in THF (10 ml) at À 788. After 30 min, (i-Pr)₃SiÀCꢀCÀCHO [6b][25] (478 mg,

2.28 mmol) in THF (2 ml) was added via cannula. After 45 min, the reaction was quenched by dropwise addition

of sat. aq. NH₄Cl soln. (1 ml) and allowed to warm to r.t. The mixture was partitioned between Et₂O and sat. aq.

NH₄Cl soln. (1:1, 50 ml), the phases were separated, and the aq. layer was extracted with Et₂O (3 Â 20 ml). The

combined org. phases were washed with sat. aq. NaCl soln. (10 ml), dried (MgSO₄), and concentrated in vacuo.

FC (SiO₂; CH₂Cl₂/hexane 1:1) afforded (Æ)-9 (393 mg, 45%). Clear oil. R_f(SiO₂; hexane/AcOEt 10 :1) 0.30. IR

(film): 3385, 2944, 2861, 2172, 1461, 1386, 1364, 1292, 1256, 1133, 1089, 1036, 997, 961, 883, 836, 778, 733, 672.

¹H-NMR (300 MHz, CDCl₃): 5.25 (dt, J 7.8, 1.8, 1 H); 4.36 (d, J 1.8, 2 H); 2.13( d, J 7.8, 1 H); 1.08 (s, 21 H);

0.91 (s, 9 H); 0.13( s, 6 H). ¹³C-NMR (75 MHz, CDCl₃): 103.7; 85.9; 82.9; 81.9; 52.6; 51.6; 25.8; 18.5; 18.2; 11.1;

À 5.1. EI-MS: 380.2 (M ). Anal. calc. for C₂₁H₄₀O₂Si₂(380.7): C 66.25; H 10.59; found: C 66.44, H 10.58.

Method B: MnO₂(15 g) was added at r.t. to 10 [26] (3.00 g, 15 mmol) in Et₂O (15 ml). After stirring

overnight, additional MnO₂(15 g) and Et₂O (10 ml) were added, and stirring was continued for 24 h. The

mixture was filtered through Celite, washing with Et₂O, and the filtrate was dried (MgSO₄). Evaporation in

vacuo gave 1.75 g of the propargylic aldehyde as a clear oil, which was used without further purification. BuLi

(8.69 ml of a 1.6m soln. in hexane, 13.9 mmol) was added at À 788 to (i-Pr)₃SiÀCꢀCH (2.96 ml, 13.2 mmol) in

THF (25 ml). After 15 min, the soln. was warmed to r.t. and stirred for another 15 min. After recooling to À 788,

the crude propargylic aldehyde (1.75 g, 8.8 mmol) in THF (10 ml) was added rapidly via syringe. After warming

to r.t., the mixture was partitioned between sat. aq. NH₄Cl soln. (50 ml) and Et₂O (50 ml), the aq. phase was

extracted with Et₂O (3 Â 50 ml), and the combined org. phases were dried (MgSO₄). Evaporation in vacuo and

FC (SiO₂; hexanes/AcOEt 5 :1) gave (Æ)-9 (1.95 g, 34%).

6-[(tert-Butyl)dimethylsilyloxy]-1-(triisopropylsilyl)hexa-1,4-diyn-3-one (11). MnO₂(3.8 g) was added at

r.t. to (Æ)-9 (1.90 g, 5.00 mmol) in Et₂O, and the mixture was stirred for 3h. Filtration through Celite,

evaporation in vacuo, and FC (SiO₂; hexanes/AcOEt 10 :1) gave 11 (1.46 g, 77%). Clear oil. R_f(SiO₂; hexanes/

AcOEt 10 :1) 0.53. IR (film): 2946, 2866, 2228, 2139, 1633, 1461, 1361, 1256, 1200, 1100, 983, 883, 833, 779.

3068

Helvetica Chimica Acta Vol. 85 (2002)

¹H-NMR (300 MHz, CDCl₃): 4.50 (s, 2 H); 1.11 (s, 18 H); 1.09 (s, 3H); 0.91 ( s, 9 H); 0.15 (s, 6 H). ¹³C-NMR

(75 MHz, CDCl₃): 159.9; 104.6; 97.5; 91.0; 84.9; 51.5; 25.6; 18.4; 18.1; 11.0; À 5.2. EI-MS: 378.2 (6, M ), 321.2

(100, [M À CMe₃] ). Anal. calc. for C₂₁H₃₈O₂Si₂(378.7): C 66.60, H 10.11; found: C 66.83, H 10.16.

(Æ)-2-[2-({[(tert-Butyl)dimethylsilyl]oxy}methyl)ethynyl]-2-[(triisopropylsilyl)ethynyl]oxirane ((Æ)-7).

Method A: MeLi ¥ LiBr (3.12 ml of a 1.5m soln. in Et₂O, 4.68 mmol) was added dropwise at À 788 to 11

(1.36 g, 3.60 mmol) and CH₂I₂(0.38 ml, 4.68 mmol) in THF (15 ml). The mixture was slowly warmed to r.t. over

2 h, while epoxide formation was monitored by TLC. After 1 h at r.t., the mixture was partitioned between sat.

aq. NH₄Cl soln. (25 ml) and Et₂O (25 ml), the aq. phase was extracted with Et₂O (2 Â 25 ml), and the combined

org. phases were dried (MgSO₄). Evaporation in vacuo and FC (SiO₂; hexanes/AcOEt 20 :1) provided (Æ)-7

(1.11 g, 79%). Pale-yellow, somewhat unstable oil. R_f(SiO₂; hexanes/AcOEt 10 :1) 0.49. IR (film): 2945, 2862,

2241, 2167, 1464, 1367, 1292, 1264, 1099, 929, 882, 837, 779, 678. ¹H-NMR (200 MHz, CDCl₃): 4.34 (s, 2 H); 3.14 (s,

2 H); 1.07 (s, 21 H); 0.90 (s, 9 H); 0.12 (s, 6 H). ¹³C-NMR (50 MHz, CDCl₃): 102.3; 84.9; 81.2; 80.8; 57.4; 51.6;

39.8; 25.7; 18.5; 18.2; 11.0; À 5.2. EI-MS: 392 (M ). Anal. calc. for C₂₂H₄₀O₂Si₂(392.7): C 67.28, H 10.27; found:

C 67.18, H 10.26.

Method B: BuLi (1.56 ml of a 1.6m soln. in hexane, 2.5 mmol) was added at À 788 to (t-Bu)Me₂-

SiOCH₂ÀCꢀCH (425 mg, 2.5 mmol) in THF (5 ml), and the soln. was stirred for 30 min at this temp. Ketone 14

(518 mg, 2.0 mmol) in THF (2 ml) was added rapidly via syringe, and the mixture was warmed to r.t. over 1 h.

Dry DMF (4 ml) and t-BuOK (100 mg, 1 mmol) were added, and the deep-red mixture was stirred 2 h at r.t. The

mixture was partitioned between sat. aq. NH₄Cl soln. (25 ml) and Et₂O (25 ml), the aq. phase was extracted with

Et₂O (2 Â 25 ml), and the combined org. phases were dried (MgSO₄). Evaporation in vacuo and filtration (SiO₂;

hexanes/AcOEt 10 :1) gave nearly pure (Æ)-7 (643mg, 82%).

(Æ)-3,5-Bis({[(tert-butyl)dimethylsilyl]oxy}methyl)-1,7-bis(triisopropylsilyl)hepta-3,4-diene-1,6-diyne ((Æ)-8).

A soln. of (Æ)-7 (785 mg, 2.0 mmol), (i-Pr)₃SiÀCꢀCH (0.67 ml, 3.0 mmol), and (i-Pr)₂NH (0.56 ml, 4.0 mmol)

in CH₂Cl₂(4 ml) was sparged with Ar. [Pd(PPh₃)₄] (46 mg, 0.04 mmol) and CuI (15 mg, 0.08 mmol) were added

sequentially with further sparging with Ar after each addition. After 6 h, 1H-imidazole (204 mg, 3.0 mmol) and

(t-Bu)Me₂SiCl (393 mg, 2.6 mmol) were added sequentially with additional CH₂Cl₂(5 ml). After 2 h, the

mixture was filtered through Celite with hexanes and the filtrate evaporated in vacuo. FC (SiO₂; hexanes/CH₂Cl₂

4 :1) yielded (Æ)-8 (720 mg, 52%). Clear oil, which solidified upon storage at À 308. R_f(SiO₂; hexanes/CH₂Cl₂

4 :1) 0.45. M.p. 56 578. IR (film): 2944, 2891, 2863, 2147, 1944, 1464, 1388, 1361, 1333, 1254, 1111, 994, 878, 833,

779, 667. ¹H-NMR (200 MHz, CDCl₃): 4.20 (s, 4 H); 1.07 (s, 42 H); 0.89 (s, 18 H), 0.08 (s, 12 H). ¹³C-NMR

(50 MHz, CDCl₃): 214.9; 98.7; 95.9; 95.1; 64.1; 25.7; 18.5; 18.1; 11.2; À 5.4; À 5.5. EI-MS: 688 (M ). Anal. calc.

for C₃₉H₇₆O₂Si₄(689.4): C 67.95, H 11.11; found: C 67.85, H 11.13. X-Ray: see [9].

(Æ)-3,5-Bis({[(tert-butyl)dimethylsilyl]oxy}methyl)-1-(triisopropylsilyl)-7-(trimethylsilyl)hepta-3,4-diene-

1,6-diyne ((Æ)-12). A soln. of (Æ)-7 (196 mg, 0.50 mmol), Me₃SiÀCꢀCH (206 ml, 0.75 mmol), and (i-Pr)₂NH

(140 ml, 1.0 mmol) in (CH₂Cl)₂(2.5 ml) was sparged with Ar. [Pd(PPh₃)₄] (29 mg, 0.025 mmol) and CuI (9.5 mg,

0.050 mmol) were added sequentially with further sparging with Ar after each addition. After 1 h, 1H-imidazole

(51 mg, 0.75 mmol) and (t-Bu)Me₂SiCl (98 mg, 0.65 mmol) were added sequentially. After 2 h, the mixture was

filtered through Celite with hexanes and the filtrate evaporated in vacuo. FC (SiO₂; hexanes/CH₂Cl₂4 :1)

afforded (Æ)-12 (161 mg, 53%). Clear oil. R_f(SiO₂; hexanes/CH₂Cl₂4 :1): 0.33. IR (film): 2957, 2891, 2859, 2149,

1

1943, 1463, 1387, 1359, 1251, 1112, 1004, 882, 841, 777, 677. H-NMR (300 MHz, CDCl₃): 4.21 (s, 2 H); 4.20 (s,

2 H); 1.07 (s, 21 H); 0.90 (s, 18 H); 0.18 (s, 9 H); 0.09 (s, 12 H). ¹³C-NMR (50 MHz, CDCl₃): 214.5; 98.5; 98.4;

96.8; 95.9; 95.6; 95.3; 64.3; 63.7; 25.8; 18.6; 18.2; 11.2; À 0.2; À 5.2; À 5.3; À 5.4. EI-MS: 604.3( M ). Anal. calc.

for C₃₃H₆₄O₂Si₄: C 65.49, H 10.66; found: C 65.76, H 10.81.

1-(Triisopropylsilyl)-2-(trimethylsilyl)acetylene (13) [28]. BuLi (32.8 ml of a 1.6m soln. in hexane,

52.5 mmol) was added at À 788 to (i-Pr)₃SiÀCꢀCH (11.2 ml, 50.0 mmol) in THF (50 ml). After stirring for

15 min at this temp. and 15 min at r.t., the mixture was recooled, and Me₃SiCl (6.98 ml, 55.0 mmol) was added

via syringe. After stirring 1 h at À 788, the mixture was warmed to r.t. and stirred an additional 2 h before being

partitioned between H₂O (100 ml) and Et₂O (100 ml). The aq. phase was extracted with Et₂O (2 Â 100 ml), and

the combined org. phases were dried (MgSO₄) and evaporated in vacuo. Vacuum distillation afforded 13

(12.73g, 90%). Clear liquid. R_f(SiO₂; hexane) 0.52. IR (film) 2959, 2944, 2896, 2867, 1464, 1383, 1250, 996, 883,

859, 842, 767, 676. ¹H-NMR (200 MHz, CDCl₃): 1.07 1.05 (m, 21 H); 0.17 (s, 9 H). ¹³C-NMR (50 MHz, CDCl₃):

116.2; 110.2; 18.6; 11.1; 0.0.

1-Chloro-4-(triisopropylsilyl)but-3-yn-2-one (14) [28]. Compound 13 (1.27 g, 5.0 mmol) and ClCH₂COCl

(0.40 ml, 5.0 mmol) in CH₂Cl₂(10 ml) were added over 10 min at 08 to AlCl₃(0.87 g, 6.5 mmol) in CH₂Cl₂

(20 ml). The mixture was stirred at r.t. for 30 min , then 1m HCl (25 ml) was added. The mixture was extracted

with Et₂O (3 Â 50 ml) and the combined extracts were dried (MgSO₄). Evaporation in vacuo provided nearly

Helvetica Chimica Acta Vol. 85 (2002)

3069

pure 14 (1.25 g, 97%), which was used without further purification in the next conversion. Yellow oil. R_f(SiO₂;

hexanes/AcOEt 10 :1): 0.47. IR (film) 2946, 2868, 2152, 1692, 1682, 1464, 1214, 1105, 995, 883, 858, 836, 788, 681.

¹H-NMR (200 MHz, CDCl₃): 4.21 (s, 2 H); 1.13 1.10 ( m, 21 H). ¹³C-NMR (50 MHz, CDCl₃): 178.5; 101.5;

101.3; 49.4; 18.3; 10.8.

(Æ)-6-[(tert-Butyl)dimethylsilyloxy]-1-(trimethylsilyl)hexa-1,4-diyn-3-ol ((Æ)-17). BuLi (10.1 ml of a 1.6m

soln. in hexane, 16.2 mmol) was added dropwise to (t-Bu)Me₂SiOCH₂ÀCꢀCH (2.98 g, 17.5 mmol) in THF

(60 ml) at À 788. After 30 min, Me₃SiÀCꢀCÀCHO (1.70 g, 13.5 mmol) in THF (12 ml) was added via cannula.

After 40 min, the reaction was quenched by dropwise addition of sat. aq. NH₄Cl soln. (5 ml) and allowed to

warm to r.t. The mixture was partitioned between Et₂O (100 ml) and sat. aq. NH₄Cl soln. (100 ml). The aq.

phase was extracted with Et₂O (3 Â 75 ml), and the combined org. phases were washed with sat. aq. NaCl soln.

(50 ml), dried (MgSO₄), and concentrated in vacuo. FC (SiO₂; CH₂Cl₂/hexane 7:3 ! 9 :1 gradient) afforded

(Æ)-17 (2.91 g, 73%). Pale-yellow oil. IR (film): 3383, 2956, 2928, 2889, 2856, 2178, 1464, 1367, 1294, 1250, 1133,

1089, 1042, 964, 839, 778, 761. ¹H-NMR (200 MHz, CDCl₃): 5.12 (dt, J 7.8, 1.8, 1 H); 4.37 (d, J 1.8, 2 H); 2.17

(d, J 7.8, 1 H); 0.91 (s, 9 H); 0.18 (s, 9 H); 0.13( s, 6 H). ¹³C-NMR (75 MHz, CDCl₃): 101.6; 89.6; 83.2; 81.8;

52.5; 51.6; 25.7; 18.1; À 0.5; À 5.3. EI-MS: 296.1 (M ). Anal. calc. for C₁₅H₂₈O₂Si₂(296.6): C 60.75, H 9.52;

found: C 60.94, H 9.42.

6-[(tert-Butyl)dimethylsilyloxy]-1-(trimethylsilyl)hexa-1,4-diyn-3-one (18). BaMnO₄(0.79 g, 90% tech.

grade, 2.75 mmol) was added in one portion to (Æ)-17 (0.164 g, 0.55 mmol) in CH₂Cl₂(7 ml) at r.t. After 3.5 h,

the mixture was filtered through a pad of Celite with hexane/CH₂Cl₂1:1 (200 ml). Concentration of the filtrate

in vacuo provided 18 (0.152 g, 93%), which was of sufficient purity for subsequent transformations. FC (SiO₂;

hexanes/CH₂Cl₂7:3) provided a sample for anal. characterization. Yellow oil. IR (film): 2958, 2930, 2891, 2858,

2228, 2147, 2097, 1633, 1472, 1361, 1256, 1200, 1106, 983, 839, 778, 722. ¹H-NMR (200 MHz, CDCl₃): 4.50 (s, 2 H);

0.92 (s, 9 H); 0.25 (s, 9 H); 0.15 (s, 6 H). ¹³C-NMR (75 MHz, CDCl₃): 160.2; 102.3; 99.6; 91.6; 84.9; 51.6; 25.6;

18.1; 1.1; À 5.4. EI-MS: 294.0 (0.5, M ), 237.1 (74, [M À Me₃C] ), 209.1 (100, [M À Me₃C À CO] ). The

tendency for protodesilylation during purification precluded collection of accurate microanalysis data.

1-Chloro-4-(trimethylsilyl)but-3-yn-2-one (19) [31]. A soln. of Me₃SiÀCꢀCÀSiMe₃(2.24 ml, 10 mmol) and

ClCH₂COCl (0.80 ml, 10 mmol) in CH₂Cl₂(10 ml) was added over 10 min at 08 to AlCl₃(1.33 g, 10 mmol) in

CH₂Cl₂(20 ml). After stirring at r.t. for 30 min, 1m HCl (25 ml) were added at 08. The mixture was extracted with

Et₂O (3 Â 50 ml) and the combined extracts were dried (MgSO₄). Evaporation in vacuo and bulb-to-bulb

distillation gave 19 (1.36 g, 78%). Clear oil. R_f(SiO₂; hexane/AcOEt 10 :1) 0.40. IR (film): 2964, 2892, 2155,

1698, 1677, 1398, 1254, 1215, 1106, 867, 847, 785, 763, 615. ¹H-NMR (200 MHz, CDCl₃): 4.22 (s, 2 H); 0.26 (s,

9 H). ¹³C-NMR (50 MHz, CDCl₃): 178.3; 103.3; 99.9; 49.5; À 1.0.

(Æ)-2-[2-({[(tert-Butyl)dimethylsilyl]oxy}methyl)ethynyl]-2-[(trimethylsilyl)ethynyl]oxirane ((Æ)-16).

Method A: MeLi ¥ LiBr (1.65 ml of a 1.5m soln. in Et₂O, 2.47 mmol) was added dropwise to 18 (519 mg,

1.77 mmol) and CH₂I₂(185 ml, 2.29 mmol) in THF (6 mol) at À 788. The soln. was allowed to warm to r.t over 3h

and, after 1.5 h at r.t., it was poured into sat. aq. NH₄Cl soln. (10 ml). The phases were separated, and the aq.

phase was extracted with Et₂O (3 Â 20 ml). The combined org. phases were washed with sat. aq. NaCl soln.

(10 ml), dried (MgSO₄), and concentrated in vacuo. FC (SiO₂; hexanes/CH₂Cl₂7:3) provided relatively

unstable (Æ)-16 (212 mg, 39%), which slowly decomposed at À 208 under N₂. Pale-yellow oil. IR (film): 2957,

2929, 2899, 2858, 2169, 1472, 1364, 1294, 1258, 1097, 1014, 931, 875, 839, 778, 761. ¹H-NMR (200 MHz, CDCl₃):

4.34 (s, 2 H); 3.18 3.10 (AB, J 6.6, 2 H); 0.91 (s, 9 H); 0.18 (s, 9 H); 0.13( s, 6 H). ¹³C-NMR (75 MHz, CDCl₃):

100.2; 88.5; 81.6; 80.6; 57.2; 51.6; 39.7; 25.7; 18.1; À 0.6; À 5.3. EI-MS: 308.2 (1.5, M ), 251.1 (93, [M À Me₃C] ),

205.1 (100, [M À Me₃CÀCH₂OÀO] ). Anal. calc. for C₁₆H₂₈O₂Si₂(308.6): C 62.28, H 9.15; found: C 61.09,

H 9.19.

Method B: BuLi (3.75 ml of a 1.6m soln. in hexane, 6.0 mmol) was added at À 788 to (t-Bu)Me₂-

SiOCH₂ÀCꢀCH (1.02 g, 6.0 mmol) in THF (10 ml), and the soln. was stirred for 30 min at this temp. After

rapid addition of 19 (874 mg, 5.0 mmol) in THF (2 ml) via syringe, the mixture was warmed to À 408 over

30 min. Dry DMF (5 ml) and t-BuOK (280 mg, 2.5 mmol) were added, and the mixture darkened to deep

reddish-brown as it was warmed to À 208. After stirring 30 min at À 208, the mixture was partitioned between

sat. aq. NH₄Cl soln. (50 ml) and Et₂O (50 ml). The aq. phase was extracted with Et₂O (3 Â 50 ml), and the

combined org. phases were dried (MgSO₄) and evaporated in vacuo. FC (SiO₂; hexanes/AcOEt 20 :1 ! 10 :1)

provided (Æ)-16 (357 mg, 23%) in addition to (Æ)-20 (111 mg, 9%) and (Æ)-21 (450 mg, 26%).

(Æ)-3,5-Bis({[(tert-butyl)dimethylsilyl]oxy}methyl)-1,7-bis(trimethylsilyl)hepta-3,4-diene-1,6-diyne ((Æ)-

15). A soln. of (Æ)-16 (62 mg, 0.20 mmol), Me₃SiÀCꢀCH (42 ml, 0.30 mmol) and (i-Pr)₂NH (56 ml, 0.40 mmol)

in CH₂Cl₂(1.0 ml) was sparged with Ar. [Pd(PPh₃)₄] (11.6 mg, 0.01 mmol) and CuI (3.8 mg, 0.02 mmol) were

added sequentially with further sparging with Ar after each addition. After 1 h, 1H-imidazole (20 mg,

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Helvetica Chimica Acta Vol. 85 (2002)

0.30 mmol) and (t-Bu)Me₂SiCl (39 mg, 0.26 mmol) were added sequentially. After 2 h, the mixture was filtered

through Celite with hexanes and the filtrate evaporated in vacuo. FC (SiO₂; hexanes/CH₂Cl₂4 :1) provided (Æ)-

15 (66 mg, 63%). Clear oil. R_f(SiO₂; hexanes/AcOEt 4 :1) 0.26. IR (film): 2958, 2929, 2897, 2856, 2151, 1944,

1472, 1360, 1251, 1111, 1006, 910, 841, 777, 759. ¹H-NMR (300 MHz, CDCl₃): 4.20 (s, 4 H); 0.90 (s, 18 H); 0.17 (s,

18 H); 0.09 (s, 12 H). ¹³C-NMR (50 MHz, CDCl₃) 214.6; 98.8; 96.6; 95.6; 63.8; 25.8; 18.3; À 0.2; À 5.3; À 5.4.

EI-MS; 520.4 (M ). Anal. calc. for C₂₇H₅₂O₂Si₄(521.1): C 62.24, H 10.06; found: C 62.51, H 10.04.

(Æ)-1-(Triisopropylsilyl)non-1-yn-3-ol ((Æ)-23). BuLi (6.56 ml of a 1.6m soln. in hexane, 10.5 mmol) was

added at À 788 to (i-Pr)₃SiÀCꢀCH (2.24 ml, 10.0 mmol) in THF (10 ml). The mixture was stirred for 15 min at

this temp., then warmed to r.t. and stirred for another 15 min. After recooling to À 788, heptanal (1.54 ml,

11.0 mmol) was added, and the mixture was stirred for 30 min at this temp. After warming to r.t., the mixture

was partitioned between sat. aq. NH₄Cl soln. (25 ml) and Et₂O, the org. phase was extracted with Et₂O (25 ml),

and the combined org. extracts were dried (MgSO₄). Evaporation in vacuo and bulb-to-bulb distillation gave

(Æ)-23 (2.33 g, 79%). Clear oil. R_f(SiO₂; hexanes/AcOEt 10 :1) 0.31. IR (film): 3333, 2933, 2862, 2164, 1462,

1385, 1333, 1264, 1123, 1041, 1015, 995, 918, 877, 677. ¹H-NMR (200 MHz, CDCl₃): 4.38 (q, J 6.1, 1 H); 1.77

1.65 (m, 3H); 1.51 1.28 ( m, 8 H); 1.07 (s, 21 H); 0.89 (t, J 6.6, 3H). ¹³C-NMR (50 MHz, CDCl₃): 109.1; 85.3;

63.0; 37.9; 31.7; 28.9; 25.1; 22.5; 18.5; 14.0; 11.1. EI-MS: 296 (M ). Anal. calc. for C₁₈H₃₆OSi (296.8): C 72.90, H

12.24; found: C 73.00, H 12.27.

1-(Triisopropylsilyl)non-1-yn-3-one (24). Me₂SO (0.65 ml, 9.1 mmol) was added at À 788 to (COCl)₂

(0.65 ml, 7.3mmol) in CH ₂Cl₂(15 ml), and the soln. was stirred for 10 min. A soln. of (Æ)-23 (1.80 g, 6.07 mmol)

in CH₂Cl₂(5 ml) was added dropwise over 10 min and, after stirring for 10 min, Et₃N (2.54 ml, 18.2 mmol) was

added. The mixture was stirred for 30 min at À 788 and 30 min at r.t. before being diluted with CH₂Cl₂(20 ml)

and washed with sat. aq. NH₄Cl soln. (20 ml). Evaporation in vacuo left a residue, which was taken up in Et₂O

(25 ml) and washed with H₂O (3 Â 10 ml). Drying (MgSO₄) and evaporation in vacuo gave nearly pure 24

(1.70 g, 94%). Pale-yellow oil. R_f(SiO₂; hexanes/AcOEt 20 :1) 0.44. IR (film) 2944, 2862, 2144, 1677, 1462, 1210,

1133, 1087, 1072, 1015, 995, 882, 677. ¹H-NMR (200 MHz, CDCl₃): 2.55 (t, J 7.5, 2 H); 1.73 1.62 ( m, 2 H);

1.35 1.28 (m, 6 H); 1.11 (s, 3 H); 1.10 (s, 18 H); 0.88 (t, J 6.4, 3H). ¹³C-NMR (50 MHz, CDCl₃): 188.1; 104.3;

95.3; 45.5; 31.4; 28.5; 24.1; 22.3; 18.3; 13.8; 10.9. EI-MS: 294 ( M ). Anal. calc. for C₁₈H₃₄OSi (294.6): C 73.40, H

11.63; found: C 73.43, H 11.54.

(Æ)-3-Hexyl-1-(triisopropylsilyl)undeca-1,4-diyn-3-ol ((Æ)-25). BuLi (3.71 ml of a 1.6m soln. in hexane,

5.93mmol) was added at À 788 to oct-1-yne (0.84 ml, 5.68 mmol) in THF (10 ml). After 15 min, the mixture was

warmed to r.t. and stirred for additional 15 min. After recooling to À 788, 24 (1.52 g, 5.16 mmol) in THF (5 ml)

was added, and the mixture was stirred for 30 min. After warming to r.t., the mixture was partitioned between

sat. aq. NH₄Cl soln. (50 ml) and Et₂O (50 ml), the aq. phase was extracted with Et₂O (3 Â 50 ml), and the

combined org. phases were dried (MgSO₄). Evaporation in vacuo and FC (SiO₂; hexanes/AcOEt 20 :1) gave

(Æ)-25 (1.37 g, 66%). Clear oil. R_f(SiO₂; hexanes/AcOEt 10 :1) 0.32. IR (film): 3456, 2933, 2862, 2236, 2164,

1467, 1379, 1323, 1067, 995, 877, 672. ¹H-NMR (200 MHz, CDCl₃): 2.35 (s, 1 H); 2.24 (t, J 6.8, 2 H); 1.93 1.84

(m, 2 H); 1.65 1.23( m, 16 H); 1.10 (s, 21 H); 0.91 (t, J 6.9, 6 H). ¹³C-NMR (50 MHz, CDCl₃): 108.5; 84.1;

83.5; 81.1; 64.1; 44.0; 31.6; 31.2; 28.9; 28.3; 24.6; 22.4; 18.5; 18.4; 13.9; 11.0 (3 resonances missing due to overlap).

EI-MS: 404 (M ). Anal. calc. for C₂₆H₄₈OSi: C 77.16, H. 11.95; found: C 76.87, H 11.77.

(Æ)-1-Hexyl-1-[(triisopropylsilyl)ethynyl]non-2-ynyl Acetate ((Æ)-26). Ac₂O (0.28 ml, 3.0 mmol) was

added at 08 to (Æ)-25 (405 mg, 1.0 mmol), Et₃N (0.7 ml, 5.0 mmol), and DMAP (ca. 5 mg) in CH₂Cl₂(3ml).

The mixture was stirred at r.t. for 12 h and then partitioned between sat. aq. NH₄Cl soln. (20 ml) and Et₂O

(20 ml). The aq. phase was extracted with Et₂O (2 Â 20 ml), and the combined org. phases were dried (MgSO₄).

Evaporation in vacuo and FC (SiO₂; hexanes/AcOEt 20 :1) gave (Æ)-26 (308 mg, 69%). Clear oil. R_f(SiO₂;

hexanes/AcOEt 20 :1) 0.30. IR (film): 2933, 2862, 2246, 2164, 1759, 1462, 1364, 1221, 1072, 1010, 918, 882, 677.

¹H-NMR (200 MHz, CDCl₃): 2.21 (t, J 6.9, 2 H); 2.05 1.97 (m, 2 H); 2.03( s, 3H); 1.64 1.18 ( m, 16 H); 1.06

(s, 21 H); 0.91 0.85 (m, 6 H). ¹³C-NMR (50 MHz, CDCl₃): 168.0; 104.6; 85.7; 85.6; 77.8; 68.4; 42.7; 31.6; 31.2;

28.8; 28.3; 28.2; 24.2; 22.4; 21.4; 18.6; 18.4; 13.9; 11.1 (2 resonances missing due to overlap). EI-MS: 446 ( M ).

Anal. calc. for C₂₈H₅₀O₂Si (446.8): C 75.27, H 11.28; found: C 75.26, H 11.14.

(Æ)-1-Hexyl-1-[(triisopropylsilyl)ethynyl]non-2-ynyl Methyl Carbonate ((Æ)-27). BuLi (0.34 ml of a 1.6m

soln. in hexane, 0.55 mmol) was added at À 788 to (Æ)-25 (202 mg, 0.50 mmol) in THF (2 ml). After stirring for

15 min at this temp., MeOCOCl (58 ml, 0.75 mmol) was added, and the mixture was stirred at r.t. for 30 min. The

mixture was partitioned between H₂O (25 ml) and Et₂O (25 ml), the aq. phase was extracted with Et₂O (2 Â

25 ml), and the combined org. phases were dried (MgSO₄). Evaporation in vacuo and FC (SiO₂; hexanes/

AcOEt 20 :1) gave (Æ)-27 (165 mg, 71%). Clear oil. R_f(SiO₂; hexanes/AcOEt 20 :1) 0.34. IR (film): 2934, 2862,

2247, 2174, 1770, 1464, 1436, 1253, 1144, 1075, 997, 952, 883, 788, 678. ¹H-NMR (200 MHz, CDCl₃): 3.78 (s, 3 H);

Helvetica Chimica Acta Vol. 85 (2002)

3071

2.24 (t, J 7.2, 2 H); 2.09 2.01 (m, 2 H); 1.67 1.28 (m, 16 H); 1.09 (s, 21 H); 0.90 (t, J 6.6, 6 H). ¹³C-NMR

(50 MHz, CDCl₃): 152.9; 104.0; 86.3; 77.3; 71.0; 54.4; 42.9; 31.6; 31.2; 28.7; 28.3; 28.1; 24.2; 22.4; 18.6; 18.4; 13.9;

11.0 (3resonances missing due to overlap). EI-MS: 462 ( M ). Anal. calc. for C₂₈H₅₀O₃Si (462.8): C 72.67, H

10.89; found: C 72.77, H 10.84.

(Æ)-3,5-Dihexyl-1,7-bis(triisopropylsilyl)hepta-3,4-diene-1,6-diyne ((Æ)-22). A soln. of (Æ)-27 (46 mg,

0.10 mmol), (i-Pr)₃SiÀCꢀCH (34 ml, 0.15 mmol) and (i-Pr)₂NH (28 ml, 0.20 mmol) in CH₂Cl₂(1.0 ml) was

sparged with Ar. [Pd(PPh₃)₄] (5.8 mg, 5.0 mmol) and CuI (1.9 mg, 10 mmol) were added sequentially with further

sparging with Ar after each addition. After stirring for 30 min, the yellow soln. was diluted with hexanes and

filtered through SiO₂. Evaporation in vacuo and FC (SiO₂; hexanes) provided (Æ)-22 (54 mg, 94%). Clear oil.

R_f(SiO₂; hexanes) 0.60. IR (film): 2927, 2851, 2133, 1933, 1464, 1380, 1154, 1072, 990, 883, 672. ¹H-NMR

(200 MHz, CDCl₃): 2.15 (t, J 7.1, 4 H); 1.58 1.43( m, 4 H); 1.40 1.22 (m, 12 H); 1.07 (s, 42 H); 0.88 (t, J 6.6,

6 H). ¹³C-NMR (50 MHz, CDCl₃): 216.2; 101.7; 92.6; 91.8; 34.1; 31.6; 28.2; 27.4; 22.4; 18.5; 14.0; 11.2. EI-MS:

568.6 (M ). Anal. calc. for C₃₇H₆₈Si₂(569.1): C 78.09, H 12.04; found: C 78.22, H 12.08.

N-Methoxy-N-methyl-2-(4-methoxyphenyl)acetamide (30). Pyridine (1.45 ml, 18.0 mmol) was added via

syringe to 2-(4-methoxyphenyl)acetyl chloride (1.22 ml, 8.0 mmol) and N,O-dimethylhydroxylamine hydro-

chloride (878 mg, 0.9 mmol) at 08 in CH₂Cl₂. After stirring for 1 h at r.t., the mixture was taken up in H₂O

(25 ml) and Et₂O (25 ml). The aq. phase was extracted with Et₂O (3 Â 25 ml), and the combined org. phases

were dried (MgSO₄). Evaporation in vacuo and bulb-to-bulb distillation provided 30 (1.48 g, 88%). Clear oil. R_f

(SiO₂; hexanes/AcOEt 1:1) 0.27. IR (film): 2933, 2831, 1662, 1610, 1508, 1462, 1380, 1246, 1174, 1031, 1005, 821,

790. ¹H-NMR (200 MHz, CDCl₃): 7.25 7.19 (m, 2 H); 6.87 6.83( m, 2 H); 3.77 (s, 3H); 3.70 ( s, 2 H); 3.60 (s,

3H); 3.17 ( s, 3 H). ¹³C-NMR (50 MHz, CDCl₃): 172.7; 158.5; 130.2; 126.9; 113.8; 61.1; 55.0; 38.2; 32.0. EI-MS:

209 (M ). Anal. calc. for C₁₁H₁₅NO₃(209.2): C 63.14, H 7.23, N 6.69; found: C 63.11, H 7.14, N 6.70.

1,5-Bis(4-methoxyphenyl)pent-3-yn-2-one (31). BuLi (4.69 ml of a 1.6m soln. in hexane, 7.5 mmol) was

added at À 788 to 29 [33] (1.02 g, 7.0 mmol) in THF (15 ml). After stirring for 15 min at this temp. and 15 min at

r.t., the mixture was recooled to À 788 and 30 (1.36 g, 6.5 mmol) in THF (2 ml) was added dropwise via syringe.

The mixture was immediately brought to 08 and, after stirring for 1 h, warmed to r.t. The mixture was partitioned

between sat. aq. NH₄Cl soln. (25 ml) and Et₂O (25 ml), the aq. phase was extracted with Et₂O (2 Â 25 ml), and

the combined org. phases were dried (MgSO₄). Evaporation in vacuo and FC (SiO₂; hexanes/AcOEt 5 :1) gave

31 (1.28 g, 67%). Pale-yellow oil which eventually solidified. R_f(SiO₂; hexanes/AcOEt 5 :1) 0.21. M.p. 76.5 778.

IR (film): 2995, 2954, 2841, 2210, 1667, 1611, 1513, 1456, 1303, 1250, 1178, 1033, 818. ¹H-NMR (200 MHz,

CDCl₃): 7.19 7.06 (m, 4 H); 6.91 6.79 (m, 4 H); 3 .80 (s, 6 H); 3 .77 (s, 2 H); 3.66 (s, 2 H). ¹³C-NMR (50 MHz,

CDCl₃): 185.5; 158.9; 158.7; 130.8; 128.9; 126.1; 125.1; 114.1; 114.0; 93.4; 81.9; 55.2; 55.1; 51.2; 24.3. EI-MS: 294

(100, M ). Anal. calc. for C₁₉H₁₈O₃(294.4): C 77.53, H 6.16; found: C 77.26, H 6.42.

(Æ)-3-(4-Methoxybenzyl)-6-(4-methoxyphenyl)-1-(triisopropylsilyl)hexa-1,4-diyn-3-ol ((Æ)-32). BuLi

(2.28 ml of a 1.6m soln. in hexane, 3.64 mmol) was added at À 788 to (i-Pr)₃SiÀCꢀCH (0.75 ml, 3.36 mmol)

in THF (10 ml). After 15 min, the mixture was warmed to r.t. and stirred for an additional 15 min. After

recooling to À 788, 31 (825 mg, 2.80 mmol) in THF (2 ml) was added via syringe, and the mixture was stirred for

30 min. After warming to r.t., the mixture was partitioned between sat. aq. NH₄Cl soln. (25 ml) and Et₂O

(25 ml), the aq. phase was extracted with Et₂O (3 Â 25 ml), and the combined org. phases were dried (MgSO₄).

Evaporation in vacuo and FC (SiO₂; hexanes/AcOEt 10 :1) gave (Æ)-32 (750 mg, 56%) besides recovered 31

(190 mg). Pale-yellow oil. R_f(SiO₂; hexanes/AcOEt 5 :1) 0.26. IR (film): 3448, 2943, 2865, 2236, 2164, 1611,

1

1513, 1464, 1249, 1177, 1036, 883, 824, 672. H-NMR (200 MHz, CDCl₃): 7.29 (d, J 8.7, 2 H); 7.19 (d, J 8.7,

2 H); 6.83( d, J 8.7, 2 H); 6.80 (d, J 8.7, 2 H); 3.80 (s, 3H); 3.79 ( s, 3H); 3.57 ( s, 2 H); 3.16 (s, 2 H); 2.58 (br. s,

1 H); 1.06 (s, 21 H). ¹³C-NMR (75 MHz, CDCl₃): 159.0; 158.5; 132.1; 129.0; 128.3; 127.3; 113.9; 113.4; 107.5;

85.2; 83.0; 82.6; 64.2; 55.2; 55.1; 48.8; 24.0; 18.4; 11.0. EI-MS: 476 (M ). HR-MALDI-MS: 499.2644 ([M

Na] , C₃₀H₄₀NaO₃Si ; calc. 499.2644).

(Æ)-1-(4-Methoxybenzyl)-4-(4-methoxyphenyl)-1-[(triisopropylsilyl)ethynyl]but-2-ynyl Methyl Carbonate

((Æ)-33). LHMDS (1.20 ml of a 1m soln. in hexane, 1.20 mmol) was added at À 788 to (Æ)-32 (477 mg,

1.00 mmol) in THF (5 ml). After stirring for 30 min at this temp., MeOCOCl (100 ml, 1.30 mmol) was added via

syringe. The mixture was warmed to r.t. and, after 30 min, partitioned between sat. aq. NH₄Cl soln. (25 ml) and

Et₂O (25 ml). The aq. phase was extracted with Et₂O (2 Â 25 ml), and the combined org. phases were dried

(MgSO₄). Evaporation in vacuo and FC (SiO₂; hexanes/AcOEt 10 :1) gave (Æ)-33 (380 mg, 71%). Pale-yellow

syrup. R_f(SiO₂; hexanes/AcOEt 5 :1) 0.32. IR (film): 2943, 2862, 2246, 2174, 1766, 1610, 1513, 1462, 1436, 1248,

1

1174, 1031, 990, 677. H-NMR (200 MHz, CDCl₃): 7.27 (d, J 8.3, 2 H); 7.16 (d, J 8.3, 2 H); 6.82 (d, J 8.7,

2 H); 6.77 (d, J 8.7, 2 H); 3.80 (s, 3H); 3.78 ( s, 3H); 2.77 ( s, 3H); 3.57 (− s×, 2 H); 3.31 (−s×, 2 H); 1.05 (s, 21 H).

¹³C-NMR (50 MHz, CDCl₃): 159.0; 158.4; 152.9; 132.3; 129.0; 128.0; 126.5; 113.8; 113.2; 103.2; 88.0; 85.2; 79.0;

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Helvetica Chimica Acta Vol. 85 (2002)

70.9; 55.2; 55.1; 54.5; 47.4; 24.1; 18.4; 11.0. EI-MS: 534.3 (M ). HR-MALDI-MS: 459.2717 ([M À MeOOCO] ,

C₃₀H₃₉O₂Si ; calc. 459.2719).

(Æ)-3,5-Bis(4-methoxybenzyl)-1,7-bis(triisopropylsilyl)hepta-3,4-diene-1,6-diyne ((Æ)-28). A soln. of (Æ)-

33 (160 mg, 0.30 mmol), (i-Pr)₃SiÀCꢀCH (101 ml, 0.45 mmol), and (i-Pr)₂NH (84 ml, 0.60 mmol) in CH₂Cl₂

(1.5 ml) was sparged with Ar. [Pd(PPh₃)₄] (17.3mg, 15.0 mmol) and CuI (5.7 mg, 30 mmol) were added

sequentially with further sparging with Ar after each addition. After stirring for 1 h, the yellow soln. was diluted

with hexanes and filtered through Celite. Evaporation in vacuo and FC (SiO₂; hexanes/AcOEt 20 :1) provided

(Æ)-28 (100 mg, 52%). Clear oil. R_f(SiO₂; hexanes/AcOEt 10 :1) 0.47. IR (film): 2943, 2851, 2133, 1939, 1611,

1512, 1464, 1303, 1248, 1174, 1039, 883, 815, 677. ¹H-NMR (300 MHz, CDCl₃): 7.00 (d, J 8.7, 4 H); 6.75 (d, J

8.7, 4 H); 3.78 (s, 6 H); 3.34 (−s×, 2 H); 3.33 (−s×, 2 H); 1.03( s, 42 H). ¹³C-NMR (75 MHz, CDCl₃): 216.9; 158.4;

130.2; 130.0; 113.6; 101.0; 93.9; 93.2; 55.1; 39.8; 18.4; 11.1. EI-MS: 640.3 (M ). HR-EI-MS: 640.4129 (M ,

C₄₁H₆₀O₂Si₂; calc. 640.4132).

1,3-(Diphenyl)prop-2-yn-1-one (35) [34]. BuLi (6.88 ml of a 1.6m soln. in hexane, 11.0 mmol) was added at

À 788 to phenylacetylene (1.10 ml, 10.0 mmol) in THF (20 ml). After 15 min, the mixture was warmed to r.t. and

stirred for additional 15 min. After recooling to À 788, PhCHO (1.22 ml, 12.0 mmol) was added via syringe.

After warming to r.t. and stirring for 30 min, the mixture was partitioned between sat. aq. NH₄Cl soln. (50 ml)

and Et₂O (50 ml). The aq. phase was extracted with Et₂O (3 Â 50 ml), and the combined org. phases were dried

(MgSO₄). Evaporation in vacuo provided the propargyl alcohol (2.30 g) containing an excess of PhCHO. The

alcohol was dissolved in Et₂O (20 ml), and MnO₂(5.0 g) was added at r.t. After stirring for 3h, the mixture was

filtered through Celite with Et₂O, and the filtrate was dried (MgSO₄). Evaporation in vacuo and application of

high vacuum (10^À2Torr) overnight gave 35 (2.05 g, 99%) as a liquid, which, on storage, crystallized. Pale-yellow

solid. R_f(SiO₂; hexanes/AcOEt 5 :1) 0.42. M.p. 45 478. IR (film): 2199, 1642, 1600, 1580, 1490, 1450, 1316, 1286,

1209, 1172, 1012, 996, 758, 698. ¹H-NMR (200 MHz, CDCl₃): 8.25 8.20 (m, 2 H); 7.69 7.36 (m, 8 H). ¹³C-NMR

(50 MHz, CDCl₃): 177.8; 136.7; 134.0; 132.9; 130.7; 129.4; 128.54; 128.48; 119.9; 92.9; 86.8.

(Æ)-1,3-Diphenyl-5-(triisopropylsilyl)penta-1,4-diyn-3-ol ((Æ)-36). BuLi (3.75 ml of a 1.6m soln. in hexane,

6.0 mmol) was added at À 788 to (i-Pr)₃SiÀCꢀCH (1.23ml, 5.5 mmol) in THF (10 ml). After 15 min, the

mixture was warmed to r.t. and stirred for an additional 15 min. After recooling to À 788, 35 (1.03g, 5.0 mmol)

in THF (5 ml) was added via syringe. After warming to r.t. and stirring for 30 min, the mixture was partitioned

between sat. aq. NH₄Cl soln. (50 ml) and Et₂O (50 ml). The aq. phase was extracted with Et₂O (3 Â 50 ml), and

the combined org. phases were dried (MgSO₄). Evaporation in vacuo and FC (SiO₂; hexanes/AcOEt 10 :1) gave

(Æ)-36 (1.79 g, 92%). Clear oil. R_f(SiO₂; hexanes/AcOEt 5 :1) 0.43. IR (film): 3539, 3447, 3067, 2943, 2865, 2226,

2174, 1490, 1450, 1063, 1015, 940, 883, 756, 693. ¹H-NMR (200 MHz, CDCl₃): 7.97 7.92 (m, 2 H); 7.53 7.33( m,

8 H); 3.01 (s, 1 H); 1.16 (s, 21 H). ¹³C-NMR (50 MHz, CDCl₃): 141.9; 131.9; 128.8; 128.6; 128.5; 128.3; 126.0;

122.2; 107.0; 89.4; 87.1; 84.7; 65.8; 18.5; 11.1. EI-MS: 388 (M ). Anal. calc. for C₂₆H₃₂OSi (388.6): C 80.36, H

8.30; found: C 80.45, H 8.32.

(Æ)-3,5-Diphenyl-1,7-bis(triisopropylsilyl)hepta-3,4-diene-1,6-diyne ((Æ)-34). BuLi (0.46 ml of a 1.6m soln.

in hexane, 0.75 mmol) was added at À 788 to (Æ)-36 (194 mg, 0.50 mmol) in THF (5 ml). After 15 min, the

mixture was warmed to r.t. and stirred for additional 15 min. PhCOCl (58 ml, 0.50 mmol) was added, and stirring

was continued for 30 min. Subsequently, (i-Pr)₃SiÀCꢀCH (168 ml, 0.75 mmol) and (i-Pr)₂NH (140 ml,

1.00 mmol) were added, and the soln. was purged with Ar. [Pd(PPh₃)₄] (29 mg, 25.0 mmol) and CuI (9.5 mg,

50 mmol) were added sequentially with further sparging with Ar after each addition. After heating to reflux for

3h in a preheated oil bath, the mixture was diluted with hexane and filtered through Celite. The bulk of the

solvent was evaporated in vacuo at r.t. and in the absence of light, and the residual few ml were quickly removed

under high vacuum (10^À2Torr). The residue was immediately purified by FC (SiO₂; hexanes/CH₂Cl₂10 :1) to

give, after solvent evaporation as above, (Æ)-34 (48 mg) and dimeric material (58 mg; 38% total cross-coupled

product). Immediate characterization of (Æ)-34 was required. R_f(SiO₂; hexanes/AcOEt 10 :1) 0.65. IR (film):

2944, 2862, 2144, 1944, 1595, 1492, 1462, 1385, 1241, 1062, 990, 882, 759, 676. ¹H-NMR (300 MHz, CDCl₃): 7.65

7.62 (m, 2 H); 7.40 7.27 (m, 8 H); 1.15 (s, 42 H). ¹³C-NMR (75 MHz, CDCl₃): 222.6; 132.7; 128.7; 128.2; 126.8;

98.7; 97.6; 97.3; 18.5; 11.2. EI-MS (dimer): 1104.7 ( M ). Anal. calc. for C₇₄H₁₀₄Si₄(1106.0; dimer): C 80.36, H

9.48; found: C 80.17, H 9.34.

2,2,6,6-Tetramethylhepta-4-yn-3-one (39) [35]. BuLi (3.43 ml of a 1.6m soln. in hexane, 5.5 mmol) was

added at À 788 to 3,3-dimethylbut-1-yne (0.62 ml, 5.0 mmol) in THF (5 ml). After 15 min, the mixture was

warmed to r.t. and stirred for an additional 15 min. After recooling to À 788, the soln. was transferred dropwise

via cannula into a rapidly stirring soln. of t-BuCOCl (1.85 ml, 15 mmol) and CuCl (50 mg, 0.5 mmol) in THF

(10 ml) at À 788. The mixture was stirred for 30 min at this temp., then warmed to 08. Sat. aq. NaHCO₃soln.

(10 ml) was added, and the mixture was extracted with Et₂O (4 Â 25 ml). The combined org. phases were

Helvetica Chimica Acta Vol. 85 (2002)

3073

washed with sat. aq. NaHCO₃soln. (50 ml) and dried (MgSO₄). Evaporation in vacuo and FC (SiO₂; hexanes/

AcOEt 20 :1) gave 39 (575 mg, 69%). Clear volatile oil. R_f(SiO₂; hexanes/AcOEt 20 :1) 0.31. IR (film): 2972,

2872, 2205, 1728, 1674, 1478, 1456, 1365, 1278, 1251, 1200, 1113, 1015, 900, 749. ¹H-NMR (200 MHz, CDCl₃): 1.29

(s, 9 H); 1.18 (s, 9 H). ¹³C-NMR (50 MHz, CDCl₃): 194.6: 103.0; 77.1; 44.6; 30.0; 27.8; 26.1.

(Æ)-3-(tert-Butyl)-6,6-dimethyl-1-(triisopropylsilyl)hepta-1,4-diyn-3-ol ((Æ)-40). BuLi (2.59 ml of a 1.6m

soln. in hexane, 4.15 mmol) was added at À 788 to (i-Pr)₃SiÀCꢀCH (0.85 ml, 3.80 mmol) in THF (5 ml). After

stirring for 15 min, the mixture was warmed to r.t. and stirred for an additional 15 min. The soln. was recooled to

À 788, and 39 (575 mg, 3.46 mmol) in THF (2 ml) was added via syringe. After 15 min, the mixture was allowed

to warm to r.t. and was partitioned between conc. aq. NH₄Cl soln. (50 ml) and Et₂O (50 ml). The aq. phase was

extracted with Et₂O (3 Â 50 ml), and the combined org. phases were dried (MgSO₄). Evaporation in vacuo gave

anal. pure (Æ)-40 (1.07 g, 89%). Clear oil. R_f(SiO₂; hexanes/AcOEt 10 :1) 0.44. IR (film): 3467, 2967, 2236, 2164,

1459, 1363, 1261, 1123, 1072, 1005, 973, 883, 749, 672. ¹H-NMR (200 MHz, CDCl₃): 2.23(br. s, 1 H); 1.21 (s, 9 H);

1.11 (s, 9 H); 1.08 (s, 21 H). ¹³C-NMR (50 MHz, CDCl₃): 107.7; 92.6; 84.3; 78.7; 71.0; 39.7; 30.7; 27.5; 24.8; 18.6;

11.2. EI-MS: 348.3 (M ). Anal. calc. for C₂₂H₄₀OSi (348.7): C 75.79, H 11.56; found: C 75.64, H 11.64.

(Æ)-1-(tert-Butyl)-4,4-dimethyl-1-[(triisopropylsilyl)ethynyl]pent-2-ynyl Methyl Carbonate ((Æ)-38).

LHMDS (1.76 ml of a 1m soln. in hexane, 1.76 mmol) was added at À 788 to (Æ)-40 (560 mg, 1.60 mmol) in

THF (5 ml). After stirring for 15 min at this temp. and 15 min at r.t., the soln. was recooled to À 788 and

MeOCOCl (148 ml, 1.92 mmol) was added via syringe. After 15 min, the mixture was warmed to r.t. and, after

30 min, partitioned between sat. aq. NH₄Cl soln. (25 ml) and Et₂O (25 ml). The aq. phase was extracted with

Et₂O (2 Â 25 ml), and the combined org. phases were dried (MgSO₄). Evaporation in vacuo and FC (SiO₂;

hexanes/AcOEt 20 :1) gave (Æ)-38 (610 mg, 94%). Colorless crystalline solid. R_f(SiO₂; hexanes/AcOEt 10 :1)

0.55. IR (film): 2966, 2862, 2236, 2174, 1769, 1462, 1436, 1364, 1254, 1149, 1072, 964, 908, 877, 672. ¹H-NMR

(200 MHz, CDCl₃): 3.76 (s, 3H); 1.21 ( s, 9 H); 1.15 (s, 9 H); 1.07 (s, 21 H). ¹³C-NMR (50 MHz, CDCl₃): 152.9;

103.1; 94.5; 86.9; 77.3; 75.0; 54.3; 40.4; 30.5; 27.5; 24.8; 18.5; 11.2. EI-MS: 406.4 (M ). Anal. calc. for C₂₄H₄₂O₃Si

(406.7): C 70.88, H 10.41; found: C 70.84, H 10.40.

(Æ)-3,5-Di(tert-butyl)-1,7-bis(triisopropylsilyl)hepta-3,4-diene-1,6-diyne ((Æ)-41).

A

soln. of (Æ)-38

(203mg, 0.50 mmol), (i-Pr) ₃SiÀCꢀCH (168 ml, 0.75 mmol), and (i-Pr)₂NH (140 ml, 1.00 mmol) in (CH₂Cl)₂

(2.5 ml) was sparged with Ar. [Pd(PPh₃)₄] (58 mg, 50 mmol) and CuI (9.5 mg, 50 mmol) were added sequentially

with further sparging with Ar. An Ar-flushed reflux condenser was added, and the dark-purple mixture was

heated to 708 in a preheated oil bath. After 1 h, conversion was less than 50%, but the Pd appeared to have

precipitated almost entirely as a black solid, so the reaction was halted to prevent oxidative dimerization of (i-

Pr)₃SiÀCꢀCH. The mixture was filtered through Celite with hexanes, and evaporation in vacuo, followed by FC

(SiO₂; hexanes), provided (Æ)-41 (82 mg, 32%) besides 132 mg recovered (Æ)-38. Colorless crystalline solid. R_f

(SiO₂; hexanes) 0.60. M.p. 106.5 1078. IR (film): 2963, 2866, 2141, 1460, 1359, 1241, 1118, 1072, 990, 882, 754,

718, 677. ¹H-NMR (200 MHz, CDCl₃): 1.13( s, 18 H); 1.08 (s, 42 H). ¹³C-NMR (50 MHz, CDCl₃): 213.3; 103.4;

100.6; 93.8; 35.2; 28.8; 18.5; 11.2. EI-MS: 512.3 (M ). Anal. calc. for C₃₃H₆₀Si₂(513.0): C 77.26, H 11.79; found: C

77.05, H 11.89.

(Æ)-3-(tert-Butyl)-6,6-dimethyl-1-(trimethylsilyl)hepta-1,4-diyn-3-ol ((Æ)-43). BuLi (5.0 ml of a 1.6m soln.

in hexane, 8.0 mmol) was added at À 788 to Me₃SiÀCꢀCH (1.06 ml, 7.5 mmol) in THF (10 ml). After stirring

for 15 min, the mixture was warmed to r.t. and stirred for additional 15 min. The soln. was recooled to À 788, and

crude 39 (737 mg, 4.43 mmol) in THF (2 ml) was added via syringe. After 15 min, the mixture was allowed to

warm to r.t. and was partitioned between conc. aq. NH₄Cl soln. (50 ml) and Et₂O (50 ml). The aq. phase was

extracted with Et₂O (3 Â 50 ml), and the combined org. phases were dried (MgSO₄). Evaporation in vacuo

followed by FC (SiO₂; hexanes/AcOEt 10 :1) gave (Æ)-43 (950 mg, 72% (including the preparation of crude

39). White waxy solid. M.p. 31 32.58. R_f(SiO₂; hexanes/AcOEt 10 :1) 0.36. IR (film): 3477, 2969, 2903, 2882,

1

2236, 2164, 1477, 1456, 1363, 1251, 1072, 973, 862, 843, 760. H-NMR (200 MHz, CDCl₃): 2.25 (s, 1 H); 1.22 (s,

9 H); 1.09 (s, 9 H); 0.17 (s, 9 H). ¹³C-NMR (50 MHz, CDCl₃): 105.5; 92.7; 87.8; 78.4; 70.9; 39.9; 30.7; 27.3; 24.7;

À 0.2. EI-MS: 249.3([ M À Me] ). Anal. calc. for C₁₆H₂₈OSi (264.5): C 72.66, H 10.67; found: C 72.69, H 10.70.

(Æ)-1-(tert-Butyl)-4,4-dimethyl-1-[(trimethylsilyl)ethynyl]pent-2-ynyl Methyl Carbonate ((Æ)-42).

LHMDS (1.1 ml, 1.1 mmol) was added at À 788 to (Æ)-43 (264 mg, 1.0 mmol) in THF (2 ml). Reaction with

MeOCOCl (93 ml, 1.2 mmol) and workup as described for (Æ)-38 afforded (Æ)-42 (290 mg, 90%). Colorless

crystalline solid. R_f(SiO₂; hexanes/AcOEt 10 :1) 0.41. M.p. 55 568. IR (film): 2970, 2892, 2872, 2246, 2164,

1770, 1440, 1364, 1253, 1152, 1074, 963, 909, 862, 844. ¹H-NMR (200 MHz, CDCl₃): 3.76 (s, 3 H); 1.21 (s, 9 H);

1.12 (s, 9 H); 0.16 (s, 9 H). ¹³C-NMR (50 MHz, CDCl₃): 153.0; 101.2; 94.4; 90.0; 77.1; 74.6; 54.3; 40.8; 30.5; 27.4;

24.8; À 0.3. EI-MS: 322.2 (M ). Anal. calc. for C₁₈H₃₀O₃Si (322.5): C 67.03, H 9.38; found: C 67.12, H 9.38.

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Helvetica Chimica Acta Vol. 85 (2002)

(Æ)-5-(tert-Butyl)-8,8-dimethyl-1,3-bis(trimethylsilyl)nona-3,4-diene-1,6-diyne ((Æ)-44) and (Æ)-3,5-Di-

(tert-butyl)-1,7-bis(trimethylsilyl)hepta-3,4-diene-1,6-diyne ((Æ)-45). A soln. of (Æ)-42 (161 mg, 0.50 mmol),

Me₃SiÀCꢀCH (106 ml, 0.75 mmol), and (i-Pr)₂NH (140 ml, 1.00 mmol) in (CH₂Cl)₂(2.5 ml) was sparged with

Ar. [Pd(PPh₃)₄] (58 mg, 50 mmol) and CuI (9.5 mg, 50 mmol) were added sequentially with further sparging with

Ar. An Ar-flushed reflux condenser was added, and the dark-purple mixture was heated to 708 in a preheated oil

bath. After 1 h, the mixture was filtered through Celite with hexanes. Evaporation in vacuo and FC (SiO₂;

hexanes) provided (Æ)-44 and (Æ)-45 as a 5 :2 mixture (ratio from ¹H-NMR; 123mg, 71% combined yield).

Careful additional FC (SiO₂; hexanes) allowed partial separation of the isomers for anal. purposes.

Data of (Æ)-44: Colorless oil. R_f(SiO₂; hexanes) 0.29. IR (film): 2966, 2903, 2872, 2135, 1913, 1477, 1460,

1362, 1250, 1051, 843, 758, 698, 638. ¹H-NMR (200 MHz, CDCl₃): 1.23( s, 9 H); 1.09 (s, 9 H); 0.18 (s, 9 H); 0.17 (s,

9 H). ¹³C-NMR (75 MHz, CDCl₃): 216.7; 103.2; 99.0; 97.5; 96.2; 86.9; 71.5; 34.5; 31.0; 29.0; 28.2; 0.0; À 2.0. EI-

MS: 344.2 (M ). Anal. calc. for C₂₁H₃₆Si₂(344.7): C 73.18, H 10.53; found: C 73.28, H 10.40.

Data of (Æ)-45: White Solid. R_f(SiO₂; hexanes) 0.32. M.p. 55 568. IR (film): 2964, 2892, 2871, 2142, 1917,

1476, 1460, 1363, 1249, 1116, 1082, 842, 758, 699, 639. ¹H-NMR (200 MHz, CDCl₃): 1.12 (s, 18 H); 0.18 (s, 18 H).

¹³C-NMR (75 MHz, CDCl₃): 212.2; 103.4; 98.6; 97.8; 35.4; 28.8; À 0.1. EI-MS: 344.2 (M ). Anal. calc. for

C₂₁H₃₆Si₂(344.7): C 73.18, H 10.53; found: C 73.20, H 10.60.

(Æ)-2,4-Bis[(triisopropylsilyl)ethynyl]pent-2,3-diene-1,5-diyl Bis(2,2-dimethylpropionate) ((Æ)-47). To (Æ)-

8 (245 mg, 0.36 mmol) in Et₂O (3ml) and MeOH (50 ml), a catal. amount of TsOH was added. After 2 h at r.t.,

the mixture was poured into sat. aq. NaHCO₃soln. and extracted with Et₂O (70 ml). After careful evaporation

in vacuo and rapid exposure to high vacuum, the resulting oil (crude (Æ)-46) was immediately taken up in

CH₂Cl₂(12 ml). The soln. was cooled to 08, and Et₃N (0.75 ml, 5.4 mmol) and t-BuCOCl (0.64 ml, 5.2 mmol)

were added. After 5 h at r.t., the mixture was washed with sat. aq. NH₄Cl soln. (2 Â 20 ml). The org. phase was

dried (filtered through cotton wool) and concentrated in vacuo. FC (SiO₂; hexane/CH₂Cl₂1:1) gave (Æ)-47

(111 mg, 49%). Unstable colorless oil. R_f(SiO₂; hexane/AcOEt 20 :1) 0.30. ¹H-NMR (300 MHz, CDCl₃): 4.61

(s, 4 H); 1.21 (s, 18 H); 1.07 (s, 42 H). ¹³C-NMR (75 MHz, CDCl₃): 214.6; 177.3; 96.7; 96.6; 92.5; 62.9; 38.8; 27.2;

18.6; 11.3. EI-MS: 627.7 (<1, [M À H] ), 57.1 (100, Me₃C ).

(Æ)-3,5-Di(tert-butyl)-1-(triisopropylsilyl)-7-(trimethylsilyl)hepta-3,4-diene-1,6-diyne ((Æ)-48). A soln. of

(Æ)-38 (0.60 g, 1.48 mmol) in (i-Pr)₂EtN (5 ml) and (CH₂Cl)₂(5 ml) was sparged with Ar. [Pd(PPh₃)₄] (0.17 g,

0.15 mmol), CuI (0.03g, 0.15 mmol), and a first portion of Me ₃SiÀCꢀCH (0.1 ml, 0.71 mmol) were added

sequentially with further Ar-sparging after each addition. An Ar-flushed reflux condenser was added, and the

dark mixture was heated to 808 in a preheated oil bath. During the reaction, additional Me₃SiÀCꢀCH (0.6 ml,

4.20 mmol) was added in portions of 0.1 or 0.05 ml. After 5 h, the mixture was diluted with hexanes (100 ml),

filtered through Celite, and concentrated in vacuo. FC (SiO₂; hexanes) yielded a pale-yellow oil. For anal.

characterization, Me₃SiÀCꢀCÀCꢀCÀSiMe₃, formed by oxidative homocoupling, was partially separated by

careful FC (ca. 72% estimated yield of (Æ)-48 determined by ¹H-NMR integration after subtracting the amount

of butadiyne). R_f(SiO₂; hexane) 0.40. UV/VIS (cyclohexane): 201 (24100), 236 (39700), 246 (41500). IR (film):

1

2963, 2866, 2141, 1460, 1391, 1362, 1250, 1117, 1084, 996, 874, 842, 760, 714, 675. H-NMR (300 MHz, CDCl₃):

1.14 (s, 9 H); 1.12 (s, 9 H); 1.08 (s, 21 H); 0.20 (s, 9 H). ¹³C-NMR (75 MHz, CDCl₃): 212.0; 103.7; 102.8; 100.3;

97.5; 94.0; 35.6; 35.4; 28.9 (2Â); 18.7; 11.4; 0.2. EI-MS: 428.4 (17, M ), 385.4 (100, [M À Pr] ), 372.4 (64, [M À

Me₃C] ). Anal. calc. for C₂₇H₄₈Si₂(428.9): C 75.62, H 11.28; found: C 75.68, H 11.37.

(Æ)-3,5-Di(tert-butyl)-1-(triisopropylsilyl)hepta-3,4-diene-1,6-diyne ((Æ)-49). To (Æ)-48 (243mg,

0.57 mmol) in THF (6 ml), K₂CO₃(88 mg, 0.64 mmol) and MeOH (6 ml) were added, and the mixture was

stirred at r.t. for 2 h under N₂. The soln. was diluted with CH₂Cl₂and washed with sat. aq. NH₄Cl soln. The org.

layer was filtered through cotton wool and evaporated in vacuo. The resulting pale-yellow oil was purified via

FC (SiO₂; hexanes) to give (Æ)-49 (157 mg, 57% from (Æ)-38). Colorless oil. R_f(SiO₂; hexanes) 0.32. UV/VIS

(hexane): 198 (sh, 18100), 225 (30300), 233 (34600), 243 (sh, 19400). IR (film): 3314, 2964, 2866, 2143, 1461,

1392, 1362, 1243, 1223, 1108, 1070, 1018, 996, 883, 864, 756, 679, 641. ¹H-NMR (300 MHz, CDCl₃): 2.98 (s, 1 H);

1.14 (s, 9 H); 1.14 (s, 9 H); 1.08 (s, 21 H). ¹³C-NMR (75 MHz, CDCl₃): 212.3; 104.1; 101.7; 99.9; 94.3; 80.1; 77.6;

35.4; 35.4; 29.0; 28.9; 18.8; 11.4. EI-MS: 356.3 (14, M ), 313.2 (100, [M À Pr] ). Anal. calc. for C₂₄H₄₀Si (356.67):

C 80.82, H 11.30; found: C 80.94, H 11.29.

3,5,10,12-Tetrakis(tert-butyl)-1,14-bis(triisopropylsilyl)tetradeca-3,4,10,11-tetraene-1,6,8,13-tetrayne (50).

To (Æ)-49 (21 mg, 0.059 mmol) in CHCl₃(3ml), a few grains of molecular sieves (4 ä), TMEDA (13 ml,

0.082 mmol), and CuCl (3mg, 0.030 mmol) were added. The mixture was stirred at r.t. under air, while

evaporated solvent was replaced. After 30 h, CH₂Cl₂(25 ml) was added, and the mixture was washed with sat.

aq. NH₄Cl soln. (3 Â 20 ml). The org. layer was filtered through cotton wool and concentrated in vacuo. FC

(SiO₂; hexanes) yielded 50 (15 mg, 72%). White solid. R_f(SiO₂; hexane) 0.49. M.p. 110 1188. UV/VIS

Helvetica Chimica Acta Vol. 85 (2002)

3075

(hexane): 222 (sh, 40900), 249 (sh, 75400), 255 (sh, 80300), 261 (85400), 277 (25700), 296 (26300), 316 (22400).

IR (KBr): 2963, 2865, 2142, 1464, 1394, 1363, 1241, 1108, 1069, 1018, 996, 883, 863, 754, 678. ¹H-NMR (500 MHz,

CDCl₃): 1.14 (s, 36 H); 1.08 (s, 42 H). ¹³C-NMR (125 MHz, CDCl₃): 214.2; 104.6; 102.4; 99.6; 94.9; 76.9; 75.3;

35.9; 35.5; 29.0; 28.9; 18.7; 11.3. EI-MS: 710.5 (52, M ), 695.5 (11, [M À CH₃] ), 667.4 (16, [M À C₃H₇] ), 653.4

(46, [M À Me₃C] ), 57.1 (89, Me₃C ), 44.0 (100, C₃H₇). Anal. calc. for C₄₈H₇₈Si₂(711.3): C 81.05, H 11.05;

found: C 81.03, H 11.16.

Methyl 5-(Triisopropylsilyl)-1,1-bis[(triisopropylsilyl)ethynyl]penta-2,4-diynyl Carbonate (53). LHMDS

(0.60 ml of a 1m soln. in hexane, 0.60 mmol) was added at À 788 to 52 [6b] (300 mg, 0.50 mmol) in THF (5 ml).

Reaction with MeOCOCl (50 ml, 0.65 mmol) and workup as described for (Æ)-38 provided 53 (275 mg, 84%).

Colorless oil. R_f(SiO₂; hexanes/AcOEt 20 :1) 0.39. IR (film): 2944, 2862, 2226, 2102, 1772, 1464, 1257, 1221, 1137,

1019, 995, 918, 883, 785, 679. ¹H-NMR (300 MHz, CDCl₃): 3.81( s, 3 H); 1.08 (s, 63 H). ¹³C-NMR (75 MHz,

CDCl₃): 152.0; 99.25; 88.4; 88.3; 69.8; 69.3; 55.1; 18.5; 11.2; 11.1 (3 alkynyl resonances missing due to overlap).

EI-MS; 654.5 (M ). HR-MALDI-MS: 579.4241 ([M À MeOCOO] , C₃₆H₆₃Si₃; calc. 579.4243).

1-Triisopropylsilyl-3-[(triisopropylsilyl)ethynyl]nona-1,4-diyn-3-ol (57). BuLi (1.0 ml of a 1.6m soln. in

hexane, 1.6 mmol) was added at À 788 to hex-1-yne (0.17 ml, 1.5 mmol) in THF (5 ml). Reaction with 56 [6b]

(0.40 g, 1.0 mmol) and workup as described for (Æ)-32 provided 57 (353 mg, 75%). Clear oil. R_f(SiO₂; hexanes/

AcOEt 10 :1) 0.37. IR (film): 3456, 2943, 2866, 2236, 2174, 1464, 1159, 1072, 1017, 918, 883, 677. ¹H-NMR

(200 MHz, CDCl₃): 2.70 (s, 1 H); 2.24 (t, J 6.6, 2 H); 1.34 1.60 (m, 4 H); 1.08 (s, 42 H); 0.90 (t, J 7.1, 3H ) .

¹³C-NMR (50 MHz, CDCl₃): 104.8; 83.9; 83.7; 78.5; 54.6; 30.1; 21.7; 18.5; 18.3; 13.5; 11.1. EI-MS: 472.4 (M ).

Anal. calc. for C₂₉H₅₂OSi₂(472.9): C 73.66, H 11.08; found: C 73.65, H 11.11.

5-Ethynylnonan-5-ol (59) [3 6]. HCꢀCÀMgBr (10 ml of a 0.5m soln. in Et₂O, 5.0 mmol) was added at À 788

to nonan-5-one (0.86 ml, 5.0 mmol) in THF (50 ml). After stirring for 15 min, the mixture was warmed to r.t.

and stirring was continued for 1 h. Sat. aq. NH₄Cl soln. (50 ml) was added, and the mixture was extracted with

Et₂O (4 Â 50 ml). The combined org. phases were dried (MgSO₄) and evaporated in vacuo. Bulb-to-bulb

distillation gave 680 mg (81% crude yield) of the product containing only traces of an impurity with higher R_f-

value. FC (SiO₂; hexanes/AcOEt 5 :1) gave pure 59 (420 mg, 50%). R_f(SiO₂; hexanes/AcOEt 5 :1) 0.41. IR

(film): 3408, 3311, 2956, 2867, 2107, 1468, 1459, 1379, 1259, 1139, 1036, 996, 899, 625. ¹H-NMR (200 MHz,

CDCl₃): 2.42 (s, 1 H); 1.98 (s, 1 H); 1.69 1.25 (m, 12 H); 0.92 (t, J 7.1, 6 H ) . ¹³C-NMR (50 MHz, CDCl₃): 87.0;

72.1; 71.1; 41.5; 26.2; 22.8; 14.0.

5-Butyl-1-(triisopropylsilyl)nona-1,3-diyn-5-ol (60). A soln. of 59 (420 mg, 2.5 mmol), NH₂OH ¥ HCl

(347 mg, 5.0 mmol), and PrNH₂(0.82 ml, 10 mmol) in 95% EtOH (10 ml) was sparged at r.t. with Ar for 5 min.

CuCl (25 mg, 0.25 mmol) and (i-Pr)₃SiÀCꢀCÀBr [37] (732 mg, 2.8 mmol) were added sequentially, and

sparging with Ar was continued for several min. After stirring for 12 h, H₂O (50 ml) was added, and the mixture

was extracted with Et₂O (4 Â 50 ml). The combined extracts were dried (MgSO₄), and evaporation in vacuo

followed by FC (SiO₂; hexanes/AcOEt 10 :1), gave 60 (810 mg, 93%). Colorless crystals. R_f(SiO₂; hexanes/

AcOEt 10 :1) 0.36. M.p. 74 758. IR (film): 3328, 2943, 2863, 2215, 2098, 1460, 1382, 1230, 1142, 1113, 1042, 992,

880, 672. ¹H-NMR (200 MHz, CDCl₃): 2.07 (s, 1 H); 1.70 1.61 (m, 4 H); 1.54 1.26 (m, 8 H); 1.08 (s, 21 H); 0.92

(t, J 7.1, 6 H ) . ¹³C-NMR (50 MHz, CDCl₃): 89.1; 84.1; 79.6; 71.7; 69.5; 41.5; 26.2; 22.7; 18.4; 13.8; 11.2. EI-MS:

348.2 (M ). Anal. calc. for C₂₂H₄₀OSi (348.7): C 75.79, H 11.56; found: C 75.95, H 11.59.

1,1-Dibutyl-5-(triisopropylsilyl)penta-2,4-diynyl Methyl Carbonate (58). LHMDS (1.43ml of a 1 m soln. in

hexane, 1.43mmol) was added at À 788 to 60 (454 mg, 1.30 mmol) in THF (5 ml). Reaction with MeOCOCl

(120 ml, 1.56 mmol) and workup as described for (Æ)-38 provided 58 (376 mg, 71%) besides 52 mg of recovered

60. Colorless oil. R_f(SiO₂; hexanes/AcOEt 10 :1) 0.52. IR (film): 2958, 2862, 2092, 1758, 1462, 1441, 1380, 1253,

1112, 995, 882, 790, 677. ¹H-NMR (200 MHz, CDCl₃): 3.76 (s, 3H); 2.05 1.82 ( m, 4 H); 1.52 1.23( m, 8 H); 1.08

(s, 21 H); 0.92 (t, J 7.1, 6 H ) . ¹³C-NMR (50 MHz, CDCl₃): 153.3; 88.9; 85.2; 80.8; 75.0; 71.6; 54.4; 37.9; 25.9;

22.6; 18.5; 13.9; 11.2. EI-MS: 406.3 (M ). Anal. calc. for C₂₄H₄₂O₃Si (406.7): C 70.88, H 10.41; found: C 70.73, H

10.54.

5-Butyl-1-(triisopropylsilyl)-3-[(triisopropylsilyl)ethynyl]nona-3,4-dien-1-yne (61). A soln. of 58 (122 mg,

0.30 mmol), (i-Pr)₃SiÀCꢀCH (101 ml, 0.45 mmol), and (i-Pr)₂NH (84 ml, 0.60 mmol) in (CH₂Cl)₂(1.5 ml) was

sparged with Ar. [Pd(PPh₃)₄] (17.3mg, 15 mmol) and CuI (5.7 mg, 30 mmol) were added sequentially with

further sparging with Ar. An Ar-flushed reflux condenser was added, and the mixture was heated to 708 in a

preheated oil bath. After 30 min, the mixture was diluted with hexanes and filtered through SiO₂. Evaporation

in vacuo and FC (SiO₂; hexanes) provided 61 (150 mg, 97%). Colorless oil. R_f(SiO₂; hexanes) 0.42. IR (film):

2944, 2862, 2155, 1933, 1464, 1382, 1241, 1191, 1073, 996, 883, 675. ¹H-NMR (200 MHz, CDCl₃): 2.06 (t, J 6.6,

4 H); 1.51 1.26 (m, 8 H); 1.09 1.07 (m, 42 H); 0.89 (t, J 7.1, 6 H ) . ¹³C-NMR (75 MHz, CDCl₃): 214.3; 108.4;

3076

Helvetica Chimica Acta Vol. 85 (2002)

100.6; 90.1; 77.7; 32.1; 29.3; 22.0; 18.6; 13.9; 11.3. EI-MS: 512.4 (M ). Anal. calc. for C₃₃H₆₀Si₂: C 77.26, H 11.79;

found: C 77.15, H 11.72.

5-Butylundec-6-yn-5-ol (64). BuLi (4.06 ml of a 1.6m soln. in hexane, 6.5 mmol) was added at À 788 to hex-

1-yne (0.67 ml, 6.0 mmol) in THF (10 ml). Reaction with 63 (0.86 ml, 5.0 mmol) and workup as described for

(Æ)-32 (but no FC needed) provided 64 (1.02 g, 91%) as an oil, which was used without further purification. R_f

(SiO₂; hexanes/AcOEt 10 :1) 0.31. IR (film): 3415, 2957, 2935, 2862, 2236, 1467, 1379, 1328, 1139, 1028, 995.

¹H-NMR (200 MHz, CDCl₃): 2.19 (t, J 6.9, 2 H); 1.84 (br. s, 1 H); 1.62 1.54 (m, 4 H); 1.52 1.27 (m, 15 H);

0.91 (t, J 7.2, 6 H). ¹³C-NMR (75 MHz, CDCl₃): 84.6; 83.2; 71.3; 42.0; 30.8; 26.5; 22.9; 21.9; 18.3; 14.0; 13.5. EI-

MS: 224.2 (M ). Anal. calc. for C₁₅H₂₈O (224.4): C 80.29, H 12.58; found: C 80.31, H 12.49.

1,1-Dibutylhept-2-ynyl Methyl Carbonate (62). LHMDS (1.1 ml of a 1m soln. in hexane, 1.1 mmol) was

added at À 788 to 64 (224 mg, 1.0 mmol) in THF (2 ml). Reaction with MeOCOCl (93 ml, 1.2 mmol) and workup

as described for (Æ)-38 provided 62 (190 mg, 67%; from 63). Colorless oil. R_f(SiO₂; hexanes/AcOEt 10 :1) 0.44.

IR (film): 2958, 2934, 2867, 2242, 1756, 1463, 1440, 1379, 1252, 1155, 1128, 962, 941, 880, 791. ¹H-NMR (200 MHz,

CDCl₃): 3.71 (s, 3H); 2.21 ( t, J 6.8, 2 H); 2.01 1.78 (m, 4 H); 1.56 1.24 (m, 12 H); 0.891 (t, J 7.2, 6 H);

0.886 (t, J 7.2, 3H). ¹³C-NMR (50 MHz, CDCl₃): 153.4; 87.0; 81.6; 79.2; 54.0; 38.2; 30.6; 26.2; 22.7; 21.8; 18.4;

14.0; 13.5. EI-MS: 205.3 (M À H À MeOOCO] ). Anal. calc. for C₁₇H₃₀O₃(282.4): C 72.30, H 10.71; found: C

72.43, H 10.76.

3,5-Dibutyl-1-(triisopropylsilyl)nona-3,4-diene-1-yne (65).

A soln. of 62 (85 mg, 0.3 0 mmol),

(i-Pr)₃SiÀCꢀCH (101 ml, 0.45 mmol), and (i-Pr)₂NH (84 ml, 0.60 mmol) in (CH₂Cl)₂(1.5 ml) was sparged

with Ar. [Pd(PPh₃)₄] (17.3mg, 15 mmol) and CuI (5.7 mg, 30 mmol) were added sequentially with further

sparging with Ar. After stirring for 30 min at r.t., the yellow soln. was diluted with hexanes and filtered through

SiO₂. Evaporation in vacuo and FC (SiO₂; hexanes) provided 65 (110 mg, 94%). Clear oil. R_f(SiO₂; hexanes)

0.62. IR (film): 2957, 2864, 2142, 1946, 1464, 1380, 1073, 1015, 996, 883, 675. ¹H-NMR (200 MHz, CDCl₃): 2.08 (t,

J 7.3, 2 H); 2.00 1.94 (m, 4 H); 1.52 1.29 (m, 12 H); 1.08 1.06 (m, 21 H); 0.901 (t, J 7.2, 6 H); 0.889 (t, J

7.2, 3H). ¹³C-NMR (50 MHz, CDCl₃): 206.8; 105.5; 104.4; 90.6; 89.6; 33.8; 32.3; 30.2; 29.7; 22.2; 22.0; 18.6; 14.0;

13.9; 11.4. EI-MS: 388.4 (M ). Anal. calc. for C₂₆H₄₈Si (388.8): C 80.33, H 12.44; found: C 80.28; H 12.39.

We thank the ETH Research Council, F. Hoffmann-La Roche AG, Basel, and the Fonds der Chemischen

Industrie for support of this work. We acknowledge the participation of S. Hannemann in preliminary

explorations. We thank Dr. C. Thilgen for help with the nomenclature.

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Received May 15,2002

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1,3-Diethynylallenes: Carbon-rich modules for three-dimensional acetylenic scaffolding

DOI: 10.1002/1522-2675(200210)85:10<3052::AID-HLCA3052>3.0.CO;2-4

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Full text of DOI:10.1002/1522-2675(200210)85:10<3052::AID-HLCA3052>3.0.CO;2-4

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