Asymmetric diels - Alder reactions with chiral acetylenic carbene complexes as dienophiles

TETRAHEDRON

Pergamon

Tetrahedron 56 (2000) 4951±4965

Asymmetric Diels±Alder Reactions with Chiral Acetylenic

Carbene Complexes as Dienophiles

Annette Rahm,^aArnold L. Rheingold^band William D. Wulff ^{a, ,²}

*

^aDepartment of Chemistry, Searle Chemistry Laboratory, The University of Chicago, Chicago, IL 60637 USA

^bDepartment of Chemistry, The University of Delaware, Newark, DE 19716 USA

Received 6 January 2000; accepted 16 February 2000

AbstractÐA new synthetic method is developed for the asymmetric Diels±Alder reactions of acetylenic dienophiles. Acetylenic Fischer

carbene complexes with chiral pyrrolidines as the heteroatom stabilizing substituent were anticipated to block three of the four possible

approaches of a diene and lead to selective asymmetric cycloadditions. A series of complexes of the type (CO)₅MvC((C₄H₇N)CR₂OMe)-

CuCH (MCr, W; RH, Me, Ph) were prepared by aminolysis of the corresponding methoxy complexes that have the terminal acetylene

protected as a silane. Michael addition is completely suppressed if the alkyne is protected as a triisopropylsilyl group and after aminolylsis by

1,2-addition of a pyrrolidine the terminal alkynyl carbene complexes can be obtained predominately as E-isomers upon protodesilylation.

The cycloadditions of the E-isomers (but not Z-isomers) of these complexes occur with signi®cant asymmetric induction with 2-tri-

isopropylsiloxy-1,3-pentadiene (66±73% de) but not with cyclopentadiene and a-triisopropylsiloxyvinyl cyclohexene. A model is presented

to account for the observed stereoselectivities. q 2000 Published by Elsevier Science Ltd.

Introduction

the dienophile and electronically favoring either an endo or

exo approach (2 or 3 vs. 1 or 4, Scheme 1). All four possible

approaches (excluding the different approaches giving rise

to regioisomers) lead to four different products. For

reactions with acetylenic dienophiles, the picture is very

different. Due to the presence of two orthogonal p-systems

in the acetylenic dienophile, it has been suggested that both

p-bonds in the acetylene may be reacting.^2aIn addition, no

secondary p-orbital overlap to the carbonyl carbon is

possible between the diene and dienophile, thus removing

Asymmetric Diels±Alder reactions with ole®nic dieno-

philes have been investigated extensively and many excel-

lent systems have been developed for both stoichiometric

and catalytic processes.¹However, reports of asymmetric

Diels±Alder reactions with acetylenic dienophiles are

rare.²The asymmetric induction for most Diels±Alder

reactions with ole®nic dienophiles is achieved by sterically

blocking one side (approaches 1 or 2 vs. 3 or 4, Scheme 1) of

Scheme 1.

Keywords: chiral ®scher carbene complex; asymmetric Diels±Alder reaction; chromium; tungsten; acetylenic dienophile.

* Corresponding author; e-mail: wulff@cem.msu.edu

Current address: Department of Chemistry, Michigan State University, East Lansing, MI 48864 USA.

²

0040±4020/00/$ - see front matter q 2000 Published by Elsevier Science Ltd.

PII: S0040-4020(00)00209-X

4952

A. Rahm et al. / Tetrahedron 56 (2000) 4951±4965

Scheme 2.

a valuable control element for stereoselection.³There are

eight possible directions for the diene to approach the dieno-

phile (excluding the different approaches giving rise to

regioisomers), which lead to only two different products

(approaches 1, 3, 5 and 8 give one product, approaches 2,

4, 6 and 7 give the other, Scheme 1).

reactions,⁴(2) chiral aminocarbene complexes had been

employed in a number of reactions with good asymmetric

inductions,⁵(3) it has been shown that the metal penta-

carbonyl fragment of Fischer carbene complexes is an

effective substitute for the carbonyl group of electron poor

dienophiles in Diels±Alder reactions,⁶and (4) due to the

strong resonance stabilization (.25 kcal mol²¹)⁷in amino-

carbene complexes, isomerization of E- and Z-rotamers of

these complexes will not be expected even at elevated

temperatures. We anticipated that the large size of the

metal fragment may prevent the diene from approaching

from two of the remaining four possible sides (approaches

2 and 3, Scheme 3). By tuning the size of the chiral amine

moiety in E-3 to block approach 1, we hoped to design a

system that would undergo Diels±Alder reactions with high

asymmetric induction.

Design

To better understand the reactivity of the two p-systems in

an acetylenic dienophile, the molecular orbitals of propynal

1 and diene 2 have been calculated as model compounds

with the CAChe program (Scheme 2). As one might have

expected, the results suggest that the p-system in conjuga-

tion with the carbonyl group is more reactive. This implies

that four of the above mentioned approaches are disfavored

(5, 6, 7 and 8, Scheme 1).

Results

Encouraged by this result, we anticipated that chiral

alkynyl(amino)carbene complexes of type E-3 (Scheme 3)

could serve as useful acetylenic dienophiles in asymmetric

Diels±Alder reactions. This expectation is based on several

facts as follows: (1) terminal alkynyl(amino)carbene

complexes have been made in our laboratory and found to

be reactive enough to serve as dienophiles in Diels±Alder

Preparation and trial studies with non-chiral cyclic

aminocarbene complexes

For the asymmetric Diels±Alder reactions on mono-

substituted alkynyl aminocarbene complexes of type 3, we

planned to use pyrrolidines 4, 5, and 6 as chiral auxiliaries

Scheme 3.

Scheme 4.

A. Rahm et al. / Tetrahedron 56 (2000) 4951±4965

4953

Scheme 5.

carbene complexes which failed to give the cycloadducts

even at elevated temperature.^12,13Thus, while it was

expected that the tungsten and chromium complexes 9a

and 9b should be competent dienophiles, we were nonethe-

less delighted to ®nd that these complexes would both react

with the diene 11 to give good yields (75%, in each case) of

the desired Diels±Alder adducts 14a and 14b (Scheme 7).

Preparation of chiral complexes by aminolysis

Scheme 6.

Following these trial studies, we examined the aminolysis of

the trimethylsilyl and triisopropylsilylalkynyl complexes

7a±7d with the with chiral amines 4, 5 and 6. It had been

shown previously that the reaction of an amine with an

alkynyl carbene complex has two competitive pathways:

1,2-addition and 1,4-addition.¹⁴It has been established,

that the addition reaction can be directed to 1,2-addition

product formation (avoiding the 1,4-addition pathway) by

choosing lower reaction temperatures,¹⁴increasing the size

of the substituent on the acetylene,^15,16and decreasing the

size of the incoming amine.¹⁶

for the acetylenic aminocarbene complexes. Enantio-

merically pure pyrrolidine 4 is commercially available,

and 5 and 6 were easily synthesized in enantiomerically

pure form following the route developed by Enders

(Scheme 4).⁸

Prior to the preparation of chiral carbene complexes form

amines 4±6, we decided to prepare and evaluate the Diels±

Alder activity of the achiral pyrrolidinyl complexes 9a and

9b. These could be prepared in excellent yield from the

acetylenic methoxycarbene complexes 7.⁹The aminolysis

was performed at 21008C using one equivalent of pyrroli-

dine to generate the aminocarbene complexes. The proto-

desilylation was performed by a protocol that has previously

been established (Scheme 5).^4,10

The reaction is further complicated when non-C₂-symme-

trical chiral amines are employed, because of the possible

formation of two rotamers as products. Considering the

design of our system, it is not only important to avoid 1,4-

addition, but also crucial to have high selectivity for the

correct rotamer of the 1,2-adduct. Reaction with the

`wrong' rotamer (as Z-3, Scheme 3) is expected to give

low asymmetric induction, because the chiral moiety is on

the side opposite to the acetylene group. Furthermore, it is

expected that it will not be possible to thermally isomerize

the `wrong' rotamer and thus recycle it to the useful rotamer

given the higher thermal barrier to rotation about the

nitrogen±carbene carbon bond that has been reported for

amino carbene complexes.⁷The distribution of the rotamers

in the 1,2-addition is believed to be determined kineti-

cally¹⁷. However, it does not appear as if there is a generally

reliable method for the prediction of the kinetically favored

product. If the ratio was determined only by steric factors,

The dienes to be employed in the present study include

cyclopentadiene and the acylic dienes 11 and 13. These

dienes were synthesized in analogy to the commonly used

method (Scheme 6): an a,b-unsaturated ketone is deproto-

nated, and the enolate is subsequently trapped with triiso-

propylsilyl tri¯uoromethanesulfonate.¹¹

We have previously shown that dimethylamino analogs of

the unsubstituted alkynyl pyrrolidinyl 9a and 9b will

undergo Diels±Alder reaction with cyclopentadiene at

room temperature in 24 h to give good yields of the cyclo-

adducts.⁴This is in contrast to previous attempts to conduct

Diels±Alder reactions with substituted alkynyl amino-

Scheme 7.

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A. Rahm et al. / Tetrahedron 56 (2000) 4951±4965

Table 1. Aminolysis of carbene complexes 7a±7d

M

R¹

Carbene complex

R

Amine Temp (8C) 1,2-adduct % Yield 1,2-adduct

E:Z

1,4-adduct % Yield 1,4-adduct Total yield

Cr SiMe₃

7a

7c

H

4

5

6

2100

278

2150

25

278

15

16

17

18

94

15

10

81

98

±

16:1

E only

4:1

48:1

±

23

24

25

26

±

60

64

±

94

75

74

81

98

±

Me

Ph

Si(iPr)₃

278 to 125

W

SiMe₃

7b

7d

H

4

5

6

5

2100

278

2100

278 to 25

278

19

20

21

22

94

58

88

±

2:1

14:1

43:1

±

27

28

29

30

±

24

1

17

±

94

82

89

17

93

Me

Ph

Me

Si(iPr)₃

93

7:1

we would expect that the predominate product from reaction

with a chiral, non C₂-symmetrical amine would be the one

where the bulky substituent is directed away from the metal

pentacarbonyl moiety, thus leading to the desired E-isomers

of 3 (Scheme 3).

Pyrrolidine 6 is too large to be reactive in a 1,2-addition

(Table 1, entries 6 and 10), and only small amounts of a

product, tentatively assigned as Michael adduct 29 was

obtained. While the smallest pyrrolidine 4 does not lead to

Michael adducts (Table 1, entries 1 and 7), the medium

sized pyrrolidine 5 does. In the case of the trimethylsilyl-

acetylene chromium complex 7a, Michael addition was the

major reaction pathway and occurred even at low tempera-

ture (Table 1, entries 2 and 3). However, when the tri-

isopropyl substituted ethynyl complex 7c was used,

Michael addition was disfavored even at room temperature

(Table 1, entries 4 and 5). In addition, tungsten complexes

give much less Michael addition than do chromium

complexes (entries 2 vs. 8).

The aminolysis reactions of complexes 7 with the chiral

pyrrolidine derivatives 4, 5 and 6 were investigated at

different temperatures. As indicated in Table 1, we were

able to synthesize several of desired 1,2-adducts with high

selectivities and high yields. All the products formed in each

reaction were separable, making it possible to continue the

work with pure individual E and Z-rotamers. The assign-

ment of the E and Z-diastereomers was done by comparison

1

of their H NMR and ¹³C NMR spectra according to the

method of Fischer^13,18,19and con®rmed in one case by

X-ray diffraction after a Diels±Alder reaction (vide infra).

The proton and carbon atoms located in proximity to the

metal pentacarbonyl are observed to appear at lower ®eld

than the those more distant from the metal.^13,18,19We were

able to observe considerable effects of reaction temperature,

the size of the silyl substituent, and the size of the amine on

the regio- and stereoselectivity of the aminolysis reactions.

Proto-desilylation to give chiral mono-substituted

alkynyl aminocarbene complexes

The pure E and Z isomers of chiral amino carbene

complexes were subjected to proto-desilylation (Table

2).^4,10No rotamer inter-conversion was detected by ¹H

NMR spectroscopy in the terminal acetylenic carbene

complexes (Table 2). As discussed above, the geometry of

Table 2. Proto-desilylation of alkynyl carbene complexes

Silyl alkyne complex

M

R⁰

R

Terminal alkyne complex

Z-isomer

E-isomer

Z-isomer

E-isomer

% Yield

E-15

E-17

E-19

E-20

E-22

Cr

W

SiMe₃

Si(iPr)₃

SiMe₃

Si(iPr)₃

SiMe₃

Si(iPr)₃

H

Me

H

Me

H

E-31

E-32

E-33

E-34

74

84

91

74

84

40

Z-19

Z-22

Z-33

Z-34

Me

A. Rahm et al. / Tetrahedron 56 (2000) 4951±4965

4955

pentadiene because, as depicted in Scheme 8, the acyclic

dienes 11 and 13 have a larger spatial difference between the

two sides of the axis `connecting' the two terminal sp²

carbon atoms of the diene than does cyclopentadiene. In

addition, dienes 11 and 13 are substituted in the 2 and/or

3 positions and thus should extend further into regions 1 and

4 in Scheme 3 and also should have more serious negative

interactions in regions 2 and 3. Therefore, the size differen-

tiation in the approach of an acyclic diene should be much

more unambiguous and result in a higher selection between

approaches 3, 4 vs. 1, 2 (Scheme 3).

Scheme 8.

1

the rotamers was assigned by comparing the H NMR and

¹³C NMR spectra of E- and Z- complexes.

The Diels±Alder reactions were carried out in neat diene

and took 2 to 4 days at room temperature. The results of the

reactions of complexes E-31±E-34 with dienes 11, 13 and

35 are summarized in Schemes 9 and 10. In the cases of

cycloadducts 38±40, the major stereoisomer (A) could be

separated from the minor stereoisomer (B). In the

other cases, a mixture of stereoisomers was isolated. No

Asymmetric Diels±Alder reactions

The Diels±Alder reaction of complexes E-31, E-33, E-32

and E-34 with dienes 11, 13 and cyclopentadiene were

studied. We anticipated that the reactions with dienes 11

and 13 would give higher induction than those with cyclo-

Scheme 9.

Scheme 10.

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A. Rahm et al. / Tetrahedron 56 (2000) 4951±4965

Scheme 11.

inter-conversion of the rotamers was observed in the

conversion of starting carbene complex to the product

carbene complex in the cycloaddition.

actual Diels±Alder reaction (38A/38B6.3:1), but

remained the same (38A/38B1.5:1). This indicates that

the Diels±Alder reaction is not reversible under these

reaction conditions.

The assignment of the stereochemistry of the products was

complicated in some cases because the major isomers of the

Diels±Alder reaction underwent double bond isomerization

to complexes of type 43 in CDCl₃in the NMR tube. We

followed the double bond isomerization of complex 39A in

the NMR tube and assigned structure 43 by ¹H NMR,

COSEY, and ¹³C NMR spectra (Scheme 11). Interestingly,

the corresponding minor stereoisomer 39B was not

observed to undergo double bond isomerization.

In the second control experiment (Scheme 11), we tested our

assumption that the Z-rotamers of the unsubstituted alkynyl

carbene complexes, which have the chiral substituent point-

ing towards the metal fragment, would not be effective in

asymmetric induction. Rotamer Z-33 was subjected to the

Diels±Alder reaction with diene 11 and indeed, the ratio of

diastereomers in the product Z-37 was determined to be 1:1.

The relative stereochemistry of the chiral center formed in

the Diels±Alder reaction was assigned by X-ray crystallo-

graphic analysis of the major diastereomer 38A (Fig. 1). The

stereochemistry observed is consistent with what we

expected from our design, namely the approach of the

diene through quadrant 4 (Scheme 3). Additionally, the

X-ray structure determination con®rmed our NMR assign-

ments about the nitrogen-carbene carbon bond: the bulky

substituent of the pyrrolidine moiety points away from the

metal fragment.

Control experiments

Two control experiments were performed. It was shown that

the product ratio did not re¯ect a thermodynamic product

distribution. A sample of the Diels±Alder product enriched

with the minor isomer (38A/38B1.5:1) was subjected to

the same reaction conditions (Scheme 11). After stirring

4 days with excess diene 11 and 258C it was found that

the products had not equilibrated to re¯ect the ratio in the

Figure 1. ORTEP picture of major isomer 38A.

A. Rahm et al. / Tetrahedron 56 (2000) 4951±4965

4957

This is a clear indication that the Z-isomers of these

complexes are not effective for chiral Diels±Alder reactions

as was predicted by the model in Scheme 3.

E-31±E-34 with diene 11 (Scheme 9). Furthermore, due to

the larger size of tungsten and the resulting longer bond

length to the carbene carbon, it was expected that the tung-

sten carbene complexes would be sterically less congested.

Therefore, the stereoselectivity in their reactions was

expected to be lower than in the reactions of their chromium

counterparts. However, it was found that the carbene

complexes from both metals gave the same diastereomeric

ratios. It is not clear why this expectation was not realized,

but in other Diels±Alder reactions where differences in

stereoselectivity between the two metals has been seen the

differences have been small.⁶

Discussion

The results described above reveal that the Diels±Alder

reactions of complexes E-31±E-34 with dienes 11, 13 and

cyclopentadiene proceed to give asymmetric inductions

roughly in accord with the model presented in Scheme 3.

The optimal complex in terms of yield and induction in the

tungsten dimethylmethoxylmethylpyrrolidine complex

E-34. Its reaction with diene 11 gives the cycloadduct 39

in 73% yield and 76% diastereoselectivity. Furthermore, the

stereoisomeric products 39A and 39B are separable, and

therefore the cycloadduct 39A is available in enantiomeri-

cally pure form.

It has been shown above that the outcome of both the regio-

and the stereoselectivity in the Diels±Alder reactions were

predicted correctly from the model in Scheme 3. The direc-

tion of induction in these reactions was determined via the

X-ray structure determination of major isomer of 38. The

structure determination reveals that the major isomer has the

stereochemistry indicated in 38A and the formation of this

isomer as the major product is consistent with a favored

approach of the diene through quadrant 4 (Scheme 3 and

Fig. 2, view A). Another factor anticipated to affect the

stereoselectivity is the size of the chiral auxiliary. In all

The in¯uence of the metal was expected to be twofold. Due

to the greater stability of tungsten unsubstituted alkynyl

aminocarbene complexes, it was expected that their

reactions would give higher yields than their chromium

analogs. This was observed for the reactions of complexes

Figure 2. Space ®lling models of minimized structures of complexes E-31 and E-32.

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A. Rahm et al. / Tetrahedron 56 (2000) 4951±4965

cases in which the chiral aminocarbene complex is derived

from the more bulky pyrrolidine 5 (complexes E-32 and

E-34, Scheme 9), the diastereoselectivities obtained are

higher than in the cases of aminocarbene complexes derived

from pyrrolidine 4 (complexes E-31 and E-33, Scheme 9).

This observation is in good agreement with the design

outlined in Scheme 3. The model indicates that approach

of the diene through quadrant 1 should be more impeded in

the case of the dimethyl substituted complex E-32 than in

the case of the less bulky complex E-31 (Fig. 2, view B).

The data suggest that while the phenyl group was too large

to incorporate into the pyrrolidine in the carbene complex,

the induction does increase with the size of the substituent R

(Table 1). Perhaps other groups larger than methyl (or

methoxy) would lead to increase inductions over those of

complex E-32 and E-34 in Scheme 9.

dinyl carbene complexes can be used as chiral synthons for

the Diels±Alder reactions of acetylenic dienophiles. The

Diels±Alder products could serve as building blocks in

organic synthesis since a variety of methods are available

to oxidatively cleave the metal fragment²⁰to produce the

corresponding aldehydes and amides. In a recent report, it

has been demonstrated that aminocarbene complexes can be

reduced to amines in a procedure employing tri¯ic acid and

NaBH₄.²¹In addition, since the Diels±Alder products

furnish alkenyl aminocarbene complexes, it was recognized

that their transformation in a benzannulation reaction would

lead to synthetically interesting products.

Experimental

General information

The topology of the diene is also important in determining

the stereoselectivity. The Diels±Alder reactions of cyclo-

pentadiene and diene 13 was observed to give quite low

asymmetric induction (Scheme 10). The result of the reac-

tions with cyclopentadiene can be explained by the spatial

properties of the diene illustrated in Scheme 8. The reason

for the low induction in the reaction with diene 13 relative to

diene 11 is less obvious. However considering the space

®lling models of quadrants 3 and 4 (Fig. 2, view A and

C), it becomes apparent that the methylene groups of the

pyrrolidine moiety are spatially demanding. The pyrrolidine

methylenes would be expected to have little effect on the

approach of diene 11. Its approach to the acetylenic moiety

in the dienophile is most favored through quadrant 4 as the

methyl substituent on the diene can be accommodated

between the pyrrolidine (marked in Fig. 2, view C with

!) and the metal carbonyl moiety while the diene moiety

containing the large triisopropylsilyoxy group in the 2-posi-

tion would not be expected to interact with the pyrrolidine

ring. However, the situation is quite different for diene 13.

The model indicates that the interaction between the

methylene groups of the pyrrolidine moiety in the carbene

complex (marked in Fig. 2, view C with !) and the

methylene groups of the cyclohexyl moiety of diene 13

(marked in Fig. 2, view C with )) should be signi®cant

in the approach from quadrant 4. This unfavorable situation

makes an approach of diene 13 to the carbene complex from

quadrant 3 more likely.

Unless otherwise indicated all common reagents and

solvents were used as obtained from commercial suppliers

without further puri®cation. Tetrahydrofuran (THF) and

diethylether were distilled from sodium/benzophenone;

methylene chloride was distilled from calcium hydride

prior to use. All reactions were carried out under either an

argon or nitrogen atmosphere. Flash chromatography was

carried out on Merck silica gel grade 60, 230±400 mesh,

Ê

60 A. Elemental analyses were performed by Galbraith

Laboratories in Knoxville, Tennessee.

Triisopropylethynyl(methoxy)carbene complexes 7c and

7d. These complexes were prepared following a procedure

reported for 7a.⁹A solution of triisopropylsilyl acetylene

(2.24 mL, 10 mmol) in 80 mL diethylether was cooled to

2788C and n-butyllithium in hexane (6.24 mL, 10 mmol,

1.6 M) was added. After stirring for 15 min at 2788C, the

cold bath was removed and the solution was allowed to

warm for 15 min. This reaction mixture was transferred

via canula into a slurry of chromium hexacarbonyl (2.2 g,

10 mmol) in 100 mL THF. After stirring for 1 h, the mixture

was concentrated and brie¯y dried under high vacuum. The

remaining oil was dissolved in 60 mL methylene chloride

and cooled to 08C. Methyl tri¯uoromethanesulfonate

(1.36 mL, 12 mmol) was added to the solution. It was

quenched after 15 min with sat. NaHCO₃and washed with

water and brine. After drying with MgSO₄, the solution was

®ltered and concentrated. The crude product was puri®ed by

column chromatography (pentane). Carbene complex 7c

(2.54 g, 6.1 mmol) was isolated as a dark red oil in 45%

Our design is based on the assumption that the Diels±Alder

reaction proceeds via a concerted mechanism rather than a

stepwise mechanism involving formal Michael addition

followed by intra-molecular trapping. No experiments to

probe this point have been done to date. The only comment

that can be made at this time is that the Diels±Alder reaction

of complex Z-33 with diene 11 (Scheme 11) proceeds to

give the product Z-37 without loss of stereochemistry about

the nitrogen-carbene carbon bond. It seems plausible that in

a stepwise mechanism, once intermediate 44 is formed, the

amine would rotate to release steric compression (Scheme

11). However, this argument is only valid if the rotation

occurs faster than the intra-molecular trapping step. In

order to answer this question more conclusively, further

experiments are planned to address this issue.

1

yield. Spectral data for 7c: H NMR (500 MHz, CDCl₃) d

4.36 (s, 3H), 1.27±1.19 (m, 3H), 1.15 (d, 18H, J6.9 Hz);

¹³C NMR (75 MHz, CDCl₃) d 318.0, 225.6, 216.0, 140.0,

106.5, 65.9, 18.5, 11.2; IR (thin ®lm) 2947±2868m, 2064s,

1997m, 1944s, 1463±1436w, 1224m, 1153m, 1063s,

882w cm²¹; mass spectrum (EI) m/z (% intensity) 416

(M¹, 17), 360 (M¹22CO, 13), 332 (M¹23CO, 7), 304

(M¹24CO, 73), 276 (M¹25CO, 94), 234 (67), 204 (12),

192 (42), 177 (5), 162 (13), 150 (25), 135 (15), 120 (16), 105

(17), 93 (12), 80 (14), 52 (100). Anal. Calcd for

C₁₈H₂₄O₆SiCr: C, 51.91; H, 5.81. Found: C, 51.91; H, 5.86.

Carbene complex 7d was obtained as a dark yellow±brown

oily solid in 50% from W(CO)₆following the above proce-

1

dure. Spectral data for 7d: H NMR (400 MHz, CDCl₃) d

The results described in this work show that chiral pyrrol-

A. Rahm et al. / Tetrahedron 56 (2000) 4951±4965

4959

3.68 (s, 3H), 1.12 (s, 21H); ¹³C NMR (75 MHz, C₆D₆) d

197.5, 136.1, 106.4, 57.5, 18.8, 11.6 (C_carband C_trans±CO

were not detected, even with various delay times); IR (thin

®lm) 2957±2866s, 2143m, 2071s, 2023m, 1992m, 1953s,

(8), 75 (22), 59 (23). Anal. calcd for C₁₇H₃₂OSi: C, 72.79; H,

11.50. Found: C, 72.62; H, 11.73.

Trimethylsilylethynyl pyrrolidinecarbene metalpenta-

carbonyl complexes 8a and 8b. Methoxy carbene complex

7b⁹(905 mg, 1.95 mmol) was dissolved in 20 mL diethyl

ether and cooled to 21008C. Pyrrolidine (0.174 mL,

147.8 mg, 1.95 mmol) was added and the solution was

stirred for 20 min at 21008C. The solution was poured

into a separatory funnel containing water and was washed

with water and brine. The aqueous phase was extracted with

diethyl ether. The combined extract was dried with MgSO₄,

®ltered and concentrated. Puri®cation by column chromato-

graphy (Et₂O/CH₂Cl₂/hexane; 1:1:10) afforded 8b (883.8

mg, 1.76 mmol) as a yellow solid in 90% yield. Spectral

1463m, 1224m, 1169w, 1102m, 1070w, 996w, 883m cm²¹

;

mass spectrum (EI) m/z (% intensity) 548 (M¹, 3, ¹⁸⁴W),

492 (M¹22CO, 2, ¹⁸⁴W), 464 (M¹23CO, 4, ¹⁸⁴W), 448

(100), 418 (M¹25CO, 3, ¹⁸⁴W), 279 (15), 145 (45), 117

(49), 103 (17), 89 (72), 75 (58), 55 (43).

2-(Triisopropyl)silyloxy-1,3-pentadiene 11. Commercially

available 3-pentene-2-one (containing 30% 3-methyl-3-

pentene-2-one, Aldrich) was puri®ed by column chromato-

graphy (pentane:Et₂O16:1) and concentrated on a rotary

evaporator at 08C. The ratio of pentane, Et₂O and 3-pentene-

2-one was determined by ¹H NMR integration. This

3-pentene-2-one solution (27.9 mmol) and 2,6-lutidine

(3.89 mL, 3.58 g, 33.5 mmol) were dissolved in 300 mL

THF and cooled to 08C. After addition of triisopropylsilyl

tri¯ouromethane sulfonate (6.6 mL, 7.52 g, 24.6 mmol), the

solution was stirred for 30 min at 08C and 30 min at 258C.

The reaction mixture was poured into a separation funnel

containing sat. NaHCO₃and pentane and then the oragnic

layer washed with water and brine. After drying with

MgSO₄and ®ltration, the solution was concentrated. The

crude product was ®ltered through a small column of NEt₃

treated silica gel and was washed with pentane. Concentra-

tion of the ®ltrate afforded 11 (4.26 g, 17.7 mmol) as a clear

liquid. Spectral data for 11: ¹H NMR (500 MHz, CDCl₃) d

6.06 (dd, 1H, J6.8, 15.0 Hz), 5.9 (dd, 1H, J1.3, 15.3 Hz),

4.19 (s, 1H), 4.14 (s, 1H), 1.79 (d, 3H, J6.7 Hz), 1.29±1.22

(m, 3H), 1.13 (d, 18H, J7.3 Hz); ¹³C NMR (75 MHz,

CDCl₃) d 155.4, 129.3, 126.2, 92.5, 18.1, 17.6, 12.9; IR

(thin ®lm) 2963±2868s, 1589m, 1465m, 1320s, 1027s,

959m, 883m cm²¹. Anal. calcd for C₁₄H₂₈OSi: C, 69.93;

H, 11.74. Found: C, 70.33; H, 11.93.

1

data for 8b: mp 78±808C; H NMR (500 MHz, CDCl₃) d

3.98 (t, 2H, J6.3 Hz), 3.85 (t, 2H, J6.2 Hz), 2.15 (m,

4H), 0.28 (s, 9H); ¹³C NMR (75 MHz, CDCl₃) d 224.1,

204.1, 198.6 (J_CW128 Hz), 131.1, 106.8, 59.9, 56.4,

25.4, 20.6; IR (thin ®lm) 2973±2880w, 2062s, 1974

shoulder, 1939±1899s, 1493m, 1448m, 1251m, 1067m,

849m cm²¹; mass spectrum (EI) m/z (% intensity) 503

(M¹, ¹⁸⁴W), 475 (M¹2CO, 2, ¹⁸⁴W), 447 (M¹22CO, 82,

¹⁸⁴W), 419 (M¹23CO, 76, ¹⁸⁴W), 391 (M¹24CO, 92,

¹⁸⁴W), 363 (M¹25CO, 100, ¹⁸⁴W), 346 (24), 330 (33),

316 (30), 277 (32), 263 (28), 249 (13), 180 (12), 165 (3),

149 (2), 73 (2). Anal. calcd for C₁₅H₁₇NO₅SiW: C, 35.80; H,

3.40; N, 2.78. Found: C, 35.59; H, 3.52; N, 2.60.

Trimethylsilylacetylene pyrrolidine chromium carbene

complex 8a was made from 7a⁹following this procedure

in 96% yield. Spectral data for 8a: H NMR (500 MHz,

1

CDCl₃) d 3.98 (t, 2H, J6 Hz), 3.84 (t, 2H, J6 Hz),

2.18±2.13 (m, 4H), 0.28 (s, 9H).

Ethynyl pyrrolidinecarbene metalpentacarbonyl com-

plexes 9a and 9b. Carbene complex 8b (200 mg,

0.398 mmol) was dissolved in 25 mL diethyl ether and

cooled to 2788C. Tetrabutylammonium ¯uoride

(0.400 mL, 1 M, 0.400 mmol) in THF was added and the

solution was stirred for 1 h at 2788C. The reaction was

quenched with water and washed with water and brine.

After drying with MgSO₄and ®ltration, the solution was

concentrated. Puri®cation with column chromatography

(Et₂O/CH₂Cl₂/hexane, 1:1:10) afforded 9b (156.9 mg,

0.364 mmol) as a yellow solid in 91% yield. Complex 9a

was made from 8a following this procedure in 75% yield.

a-(Triisopropyl)silyloxyvinylcyclohexene 13. Diisopropyl-

amine (0.77 mL, 505 mg, 4.94 mmol) was dissolved in

10 mL THF and cooled to 2788C. n-Butyllithium

(3.15 mL, 1.6 M, 5.04 mmol) in hexane was added and

after stirring for 10 min, acetylcyclohexene (0.578 mL,

558 mg, 4.5 mmol) was added dropwise over 3 min. This

solution was stirred at 2788C for 10 min and triisopropyl-

silyl

tri¯ouromethanesulfonate

(1.814 mL,

2.07 g,

6.75 mmol) was added quickly. After stirring for 10 min,

the reaction mixture was allowed to warm to room tempera-

ture and stirred for 45 min. The solution was diluted with

20 mL pentane and washed with dilute NaHCO₃, water and

brine. After drying with MgSO₄and ®ltration, the solution

was concentrated. The crude product was ®ltered through a

small column of Et₃N treated silica gel and was washed with

pentane. Concentration of the ®ltrate afforded 13 (2.99 g,

10.69 mmol) as a clear liquid in 36% yield. Spectral data for

13: ¹H NMR (500 MHz, CDCl₃) d 6.30 (s, 1H), 4.30 (s, 1H),

4.18 (s, 1H), 2.17±2.15 (m, 4H), 1.71±1.66 (m, 2H), 1.61±

1.57 (m, 2H), 1.29±1.23 (m, 3H), 1.13 (d, 18H, J7.3 Hz);

¹³C NMR (75 MHz, CDCl₃) d 157.0, 133.2, 125.1, 88.5,

25.5, 25.1, 22.8, 22.2, 18.1, 12.9; IR (thin ®lm) 2964±

2833s, 1590w, 1465w, 1288m, 1261m, 1089w, 1017m

cm²¹; mass spectrum (EI) m/z (% intensity) 280 (M¹, 72),

237 (100), 195 (12), 167 (7), 131 (11), 115 (11), 103 (13), 87

1

Spectral data for 9b: mp 77±798C; H NMR (500 MHz,

CDCl₃) d 5.47 (s, 1H), 4.02 (t, 2H, J6 Hz), 3.87 (t, 2H,

J6 Hz), 2.18 (m, 4H); ¹³C NMR (75 MHz, CDCl₃) d 224.4

1

(s), 203.9 (s), 198.4 (s), 110.0 (d, J_CH254 Hz), 86.7 (d,

²J._CH47 Hz), 60.3 (t), 56.7 (t), 25.4 (t); IR (thin ®lm)

3299w, 2981±2880w, 2070m, 1974shoulder, 1902s,

1498m, 1447m cm²¹; mass spectrum (EI) m/z (% intensity)

431 (M¹, 49, ¹⁸⁴W), 375 (M¹22CO, 56, ¹⁸⁴W), 347

(M¹23CO, 92, ¹⁸⁴W), 319 (M¹24CO, 100, ¹⁸⁴W), 291

(M¹25CO, 95, ¹⁸⁴W), 262 (42), 234 (29), 208 (14), 145

(13), 106 (8), 91 (11), 55 (7). Anal. calcd for

C₁₂H₉NO₅W: C, 33.44; H, 2.10; N, 3.25; W, 42.65.

Found: C, 34.22; H, 2.12; N, 3.02; W, 42.60.

Diels±Alder adducts 14a and 14b. Carbene complex 9b

(87.1 mg, 0.202 mmol) was dissolved in 0.5 mL diene 11

4960

A. Rahm et al. / Tetrahedron 56 (2000) 4951±4965

and stirred for 69 h at 258C. The reaction mixture was

loaded directly onto to a silica gel column and eluted with

a 1:1:10 mixture of ether, methylene chloride and hexane to

afford 14b (101.1 mg, 0.152 mmol) as a yellow solid in 75%

yield. Diels±Alder adduct 14a was obtained in 75% yield

from 9a following this procedure. Spectral data for 14b: mp

226.0 (s), 204.2 (s), 198.2 (s, J_CW128 Hz), 131.9 (s), 106.3

(s), 76.6 (t), 72.0 (d), 66.4 (t), 60.4 (q), 28.0 (t), 23.2 (t),

20.8 (q); IR (thin ®lm) 2964±2815w, 2061m, 1964m,

1901s, 1483m, 1446m, 1251m, 845m cm²¹; mass spectrum

(EI) m/z (% intensity) 547 (M¹, 43, ¹⁸⁴W), 519 (M¹2CO, 5,

¹⁸⁴W), 491 (M¹22CO, 78, ¹⁸⁴W), 463 (M¹23CO, 37,

¹⁸⁴W), 435 (M¹24CO, 9, ¹⁸⁴W), 407 (M¹25CO, 95,

¹⁸⁴W), 392 (97, ¹⁸⁴W), 364 (30), 349 (27), 335 (25), 321

(30), 293 (42), 277 (46), 263 (33), 238 (18), 222 (5), 204

(7), 180 (7), 155 (5), 135 (6), 111 (7), 97 (15), 73 (100), 59

(4). Anal. calcd for C₁₇H₂₁NO₆SiW: C, 37.31; H, 3.87; N,

2.56; W, 33.59. Found: C, 37.72; H, 3.94; N, 1.91; W, 33.84.

Spectral data for Z-19: ¹H NMR (500 MHz, CDCl₃) d 4.61±

4.52 (m, 1H), 4.07±3.96 (m, 1H), 3.81±3.70 (m, 1H), 3.62

(d, 2H, J8 Hz), 3.37 (s, 3H), 2.29±2.07 (m, 4H), 0.25 (s,

9H); ¹³C NMR (75 MHz, CDCl₃) d 224.3 (s), 203.7 (s),

198.5 (s, J_CW128 Hz), 132.2 (s), 107.2 (s), 76.6 (t), 73.1

(d), 59.3 (q), 55.9 (t), 27.0 (t), 22.7 (t), 20.7 (q); IR (thin

®lm) 2962±2851w, 2062m, 1976m, 1917s, 1483w, 1449w,

1260m, 847m cm²¹; mass spectrum (EI) m/z (% intensity)

547 (M¹, 24, ¹⁸⁴W), 519 (M¹2CO, 30, ¹⁸⁴W), 491

(M¹22CO, 43, ¹⁸⁴W), 463 (M¹23CO, 60, ¹⁸⁴W), 435

(M¹24CO, 7, ¹⁸⁴W), 407 (M¹25CO, 87, ¹⁸⁴W), 392

(100, ¹⁸⁴W), 363 (28), 347 (21), 321 (23), 306 (27), 265

(26), 249 (14), 224 (5), 204 (7), 182 (8), 155 (4), 120 (5),

97 (10), 83 (40), 70 (85), 55 (23). Anal. calcd for

C₁₇H₂₁NO₆SiW: C, 37.31; H, 3.87; N, 2.56; W, 33.59.

Found: C, 37.45; H, 4.20; N, 2.55; W, 34.68.

1

100±1038C; H NMR (CDCl₃) d 4.93 (m, 1H), 4.47±4.44

(m, 1H), 3.99±3.92 (m, 1H), 3.64±3.55 (m, 1H), 3.47±3.37

(m, 1H), 2.92±2.77 (m, 3H), 2.68±2.56 (m, 1H), 1.31±0.87

(m, 25H of which at 1.15 (d, 21H, J1.75 Hz)), 0.78 (d, 3H,

J7.17 Hz); ¹³C NMR (C₆D₆, 75 MHz) d 251.6, 203.6,

199.6, 153.7, 147.8, 110.0, 106.4, 61.7, 54.8, 34.8, 30.3,

25.0, 24.4, 20.6, 18.2, 13.0; IR (thin ®lm) 2947±2867w,

2059m, 1967m, 1908s, 1687w, 1502w, 1452w, 1381w,

1210w, 1147w, 883w cm²¹; mass spectrum (EI) m/z (%

intensity) 671 (M¹, 3, ¹⁸⁴W), 643 (M¹2CO, 9, ¹⁸⁴W), 615

(M¹22CO, 7, ¹⁸⁴W), 585 (16, ¹⁸⁴W), 555 (M¹24CO, 4,

¹⁸⁴W), 527 (M¹25CO, 12, ¹⁸⁴W), 508 (2), 488 (4), 458

(4), 416 (2), 370 (1), 347 (47), 304 (6), 276 (100), 233

(17), 205 (7), 177 (9), 124 (16), 103 (14), 84 (33), 59

(37). Anal. calcd for C₂₆H₃₇NO₆SiW: C, 46.50; H, 5.55;

N, 2.09; W, 27.38. Found: C, 46.44; H, 5.76; N, 1.61; W,

27.80.

Trimethylsilylethynyl (S)-methoxymethylpyrrolidine car-

bene complexes 15 and 19. The chromium carbene

complex 7a⁹(332.3 mg, 1 mmol) was dissolved in 10 mL

diethyl ether and cooled to 21008C. (S)-Methoxymethyl-

pyrrolidine 4 (0.160 mL, 149.3 mg, 1.3 mmol) was added.

After stirring for 15 min, the solution was poured into a

separatory funnel containing water and the organic layer

was washed with water and brine. The aqueous phase was

extracted with diethyl ether. The combined oragnic layer

was dried with MgSO₄, ®ltered and concentrated. Puri®ca-

tion by silica gel chromatography with a 1:1:10 mixture of

ether, methylene chloride and hexanes as eluent afforded

E-15 (352.3 mg, 0.882 mmol) as a yellow solid in 88%

yield and Z-15 (21.7 mg, 0.054 mmol) as a yellow solid in

Preparation of trimethylsilylethynyl (S)-dimethyl-

methoxymethylpyrrolidine carbene complexes 16 and

20. The chromium carbene complex 7a⁹(156 mg,

0.5 mmol) was dissolved in 5 mL diethyl ether and cooled

to 2788C and then pyrrolidine 5⁸(78.3 mg, 0.55 mmol) was

added. After stirring for 2 h at 2788C, the solvent was

removed and puri®cation of the crude reaction mixture by

column chromatography on silica gel (Et₂O,CH₂Cl₂,

hexanes:1:1:10) afforded E-16 (33.3 mg, 0.075 mmol) in

15% yield and the Michael adduct 24 (142.7 mg,

0.3 mmol) in 64% yield both as yellow solids. The same

procedure at 21508C afforded E-16 (21.1 mg,

0.048 mmol) in 10% yield and 24 (151.1 mg, 0.318 mmol)

in 64% yield. Spectral data for E-16: mp 87±908C, ¹H NMR

(500 MHz, CDCl₃) d 4.68±4.66 (m, 1H), 4.40±4.35 (m,

1H), 4.21±4.15 (m, 1H), 3.18 (s, 3H), 2.27±2.24 (m, 2H),

2.04±2.00 (m, 2H), 1.22 (s, 3H), 1.14 (s, 3H), 0.27 (s, 9H);

¹³C NMR (75 Hz, CDCl₃) d 247.0, 224.4, 217.4, 134.0,

105.8, 78.0 (s), 76.1 (d), 58.4 (t), 49.1 (q), 24.5, 23.1,

21.9, 20.8; IR (thin ®lm) 2973±2957w, 2054m,

1922s cm²¹; mass spectrum (EI) m/z (% intensity) 443

(M¹, 7), 387 (M¹22CO, 16), 359 (M¹23CO, 18), 331

(M¹24CO, 36), 303 (M¹25CO), 273 (45), 220 (33), 195

(61), 180 (64), 149 (21), 125 (16), 97 (16), 83 (15), 73 (55),

52 (18). Anal. calcd for C₁₉H₂₅NO₆SiCr: C, 51.46; H, 5.68;

N, 3.16. Found: C, 51.42; H, 5.84; N, 2.93. Spectral data for

24: (approx. 2:1 mixture of isomers A and B); mp 113±

1

5% yield. Spectral data for E-15: mp. 62±638C; H NMR

(500 MHz, CDCl₃) d 4.68±4.62 (m, 1H), 4.35±4.22 (m,

2H), 3.63±3.52 (m, 2H), 3.36 (s, 3H), 2.32±2.22 (m, 1H),

2.22±2.08 (m, 3H), 0.28 (s, 9H); ¹³C NMR (75 MHz,

CDCl₃) d 247.0 (s), 224.1 (s), 217.4 (s), 135.3 (s), 104.4

(s) 72.3 (t), 67.5 (d), 59.1 (q), 58.2 (t), 27.8 (t), 23.5 (t), 20.8

(q); IR (thin ®lm) 2054m, 1979w, 1919s, 1448w,

846w cm²¹; mass spectrum (EI) m/z (% intensity) 415

(M¹, 7), 359 (M¹22CO, 12), 331 (M¹23CO, 13), 303

(M¹24CO, 22), 275 (M¹25CO, 100), 260 (8), 245 (6),

230 (3), 206 (4), 194 (9), 180 (23), 147 (22), 133 (7), 97

(10), 83 (12), 73 (18), 52 (11). Anal. calcd for

C₁₇H₂₁NO₆SiCr: C, 49.15; H, 5.09; N, 3.37. Found: C,

1

48.95; H, 5.19; N, 3.09. Spectral data for Z-15: H NMR

(500 MHz, CDCl₃) d 4.67±4.70 (m, 1H), 4.17±4.07 (m,

1H), 3.86±3.79 (m, 1H), 3.67±3.63 (m, 2H), 3.39 (s, 3H),

2.32±2.05 (m, 4H), 0.29 (s, 9H).

1

The tungsten carbene complex 19 was prepared in a similar

manner from complex 7b.⁹Upon separation of isomers E-19

was obtained as a yellow solid in 60% yield and Z-19 as a

yellow oil in 34% yield. Spectral data for E-19: mp: 73±

1178C; H NMR (300 MHz, CDCl₃) d 6.90 (s, 1H, A),

6.53 (s, 1H, B), 4.29 (s, 3H, A), 4.29 (s, 3H, B), 4.25±

4.16 (m, 2H, B), 3.96±3.94 (m, 1H, B), 3.69±3.66 (m,

1H, A), 3.52±3.40 (m, 2H, A), 3.16 (s, 3H, A), 3.13 (s,

3H, B), 2.08±1.66 (m, 8H, A1B), 1.20 (s, 3H, A), 1.18

(s, 3H, A), 1.05 (s, 3H, B), 1.01 (s, 3H, B), 0.29 (s, 9H,

A), 0.28 (s, 9H, B); ¹³C NMR (75 MHz, CDCl₃) d 281.1,

1

758C; H NMR (500 MHz, CDCl₃) d 4.57±4.53 (m, 1H),

4.02±3.98 (m, 2H), 3.58±3.520 (m, 2H), 3.37 (s, 3H), 2.30±

2.09 (m, 4H), 0.28 (s, 9H); ¹³C NMR (75 MHz, CDCl₃) d

A. Rahm et al. / Tetrahedron 56 (2000) 4951±4965

4961

279.4, 224.4 (2 peaks), 219.5 (2 peaks), 175.8, 168.3, 125.8

(2 peaks), 78.7, 77.8, 70.4, 67.7, 63.1, 62.4, 57.7, 56.0, 49.1

(2 peaks), 25.2, 24.7, 23.8, 23.6, 22.0, 21.4, 21.0, 18.3, 2.2

(2 peaks); IR (thin ®lm) 2982±2837w, 2044m, 1963

shoulder, 1907s, 1428m cm²¹; mass spectrum (EI) m/z (%

intensity) 475 (M¹, 3), 419 (M¹22CO, 1), 391 (M¹23CO),

363 (M¹24CO, 13), 335 (M¹25CO, 44), 292 (16), 252

(34), 224 (73), 194 (43), 162 (17), 141 (5), 111 (34), 89

(26), 73 (100), 52 (38).

0.012 mmol) in 2% yield. The same reaction run at room

temperature gave E-17 (171.3 mg, 0.325 mmol) in 65%

yield and Z-17 (42.6 mg, 0.081 mmol) in 16% yield after

isolation. Spectral data for E-17: ¹H NMR (400 MHz,

CDCl₃) d 4.73 (d, 1H, J6.4 Hz), 4.44±4.38 (m, 1H),

4.24±4.16 (m, 1H), 3.17 (s, 3H), 2.24±2.19 (m, 2H),

2.04±1.97 (m, 2H), 1.56 (s, 3H), 1.25 (s, 3H), 1.14±1.04

(m, 21H); ¹³C NMR (75 MHz, CDCl₃) d 246.8(s), 224.3(s),

217.4(s), 129.8(s), 107.7(s), 77.9(s), 76.3(d), 58.6(t),

49.4(q), 24.5(t), 23.1(t), 21.7(2q), 18.6(q), 11.3(d); IR

(thin ®lm) 2997±2841m, 2054m, 1977w, 1926s, 1717m,

1472m, 1445w, 1231w, 1083w cm²¹; mass spectrum (EI)

m/z (% intensity) 527 (M¹, 2), 471 (M¹22CO, 5), 456 (13),

443 (M¹23CO, 5), 415 (M¹24CO, 8), 387 (M¹25CO,

92), 355 (17), 335 (7), 304 (16), 279 (79), 264 (100), 231

(6), 209 (7), 194 (5), 175 (12), 153 (15), 139 (8), 111 (16),

97 (8), 83 (13), 73 (23), 59 (7). Anal. calcd for

C₂₅H₃₇NO₆SiCr: C, 56.91; H, 7.07; N, 2.65; Cr, 9.85.

Found: C, 56.95; H, 7.28; N, 2.60; Cr, 10.53. Spectral

The tungsten complex 20 was prepared in a similar manner

from complex 7b.⁹Upon separation of isomers E-20 was

obtained as an orange solid in 53% yield, Z-20 as an orange

oil in 5% yield and the Michael adduct 28 was obtained in

24% yield. The same procedure at 21008C afforded a

mixture of E-20:Z-20 (2.6:1) (20.6 mg, 0.036 mmol) in

7% yield, pure Z-20 (233.4 mg, 0.406 mmol) in 81% yield

and 28 (4.2 mg, 0.007 mmol) in 1% yield. Spectral data for

1

E-20: mp 101±1048C; H NMR (500 MHz, CDCl₃) d 4.59

1

(d, 1H, J7.4 Hz), 4.26±4.22 (m, 1H), 4.02±3.96 (m, 1H),

3.19 (s, 3H), 2.31±2.20 (m, 2H), 2.06±1.98 (m, 2H), 1.24 (s,

3H), 1.13 (s, 3H), 0.27 (s, 9H); ¹³C NMR (75 MHz, CDCl₃)

d 226.8, 204.7, 198.6 (J_CW130 Hz), 107.8, 94.0, 77.9 s,

75.0 d, 60.6 t, 49.1 q, 24.8, 22.9, 22.2, 21.9, 20.8; IR (thin

®lm) 2979±2960w, 2062m, 1974w, 1915s, 1487w,

846w cm²¹; mass spectrum (EI) m/z (% intensity) 575

(M¹, 44, ¹⁸⁴W), 547 (M¹2CO, 3, ¹⁸⁴W), 519 (M¹22CO,

88, ¹⁸⁴W), 491 (M¹23CO, 6, ¹⁸⁴W), 462 (5), 437 (100), 435

(M¹25CO, 89, ¹⁸⁴W), 420 (83), 402 (21), 364 (20), 349

(18), 331 (13), 291 (18), 277 (17), 263 (10), 249 (4), 220

(2), 180 (3), 149 (3), 83 (3), 73 (13), 55 (5). Anal. calcd for

C₁₉H₂₅NO₆SiW: C, 39.66; H, 4.38; N, 2.43. Found: C,

data for Z-17: H NMR (500 MHz, CDCl₃) d 4.58 (d, 1H,

J6.4 Hz), 4.49±4.43 (m, 1H), 3.68±3.62 (m, 1H), 3.20 (s,

3H), 2.18±1.92 (m, 4H), 1.28 (s, 3H), 1.22 (s, 3H), 1.18±

1.04 (m, 21H); ¹³C NMR (75 MHz, CDCl₃) d 244.8, 223.8,

217.8, 107.6, 77.8, 76.9, 57.2, 48.93, 24.3, 23.4, 21.1, 21.0,

18.6, 11.2 (one of the acetylenic C's could not be detected);

IR (thin ®lm) 2992±2867w, 2054m, 1977w, 1920s, 1476±

1448w cm²¹; mass spectrum (EI) m/z (% intensity) 527

(M¹, 1), 471 (M¹22CO, 2), 456 (3), 443 (M¹23CO, 2),

415 (M¹24CO, 2), 387 (39), 355 (6), 304 (7), 279 (100),

262 (8), 237 (9), 209 (10), 175 (6), 139 (7), 111 (13), 96 (8),

73 (68), 59 (18). Anal. calcd for C₂₅H₃₇NO₆SiCr: C, 65.91;

H, 7.07; N, 2.65. Found: C, 56.73; H, 7.07; N, 2.48.

1

39.49; H, 4.55; N, 2.16. Spectral data for Z-20: H NMR

(500 MHz, CDCl₃) d 4.48 (d, 1H, J8.5 Hz), 4.43±4.38 (m,

1H), 3.68±3.63 (m, 1H), 3.18 (s, 3H), 2.29±2.23 (m, 1H),

2.18±2.12 (m, 1H), 2.04±1.96 (m, 1H), 1.32 (s, 3H), 1.29 (s,

3H), 0.29 (s, 9H); IR (thin ®lm) 2082m, 1914s cm²¹; MS

(EI) m/z (% intensity) 575 (M¹, 5, ¹⁸⁴W), 547 (M¹2CO, 28,

¹⁸⁴W), 519 (M¹22CO, 14, ¹⁸⁴W), 491 (M¹23CO, 21,

¹⁸⁴W), 435 (M¹25CO, 85, ¹⁸⁴W), 420 (50, ¹⁸⁴W), 404

(16), 364 (14), 349 (12), 291 (13), 277 (14), 263 (9), 249

(6), 220 (11), 197 (3), 180 (5), 155 (4), 111 (7), 89 (28), 73

(100), 55 (31). Spectral data for 28: tentative assignment,

The tungsten carbene complex 22 was prepared in a similar

manner from 7d. Separation of the isomers gave E-22 in

58% yield as an orange oil and Z-22 in 26% yield as an

1

orange oil. Spectral data for E-22: H NMR (400 MHz,

CDCl₃) d 4.64 (d, 1H, J7.7 Hz), 4.28±4.20 (m, 1H),

4.04±3.95 (m, 1H), 3.16 (s, 3H), 2.29±2.13 (m, 2H),

2.06±1.92 (m, 2H), 1.23 (s, 3H), 1.14 (s, 3H), 1.18±1.06

(m, 3£1H), 1.10±1.08 (m, 6£3H); ¹³C NMR (75 MHz,

CDCl₃) d 226.5 (s), 204.4 (s), 198.7 (s), 126.6 (s), 109.5

(s), 77.8 (s), 75.2 (d), 60.8 (t), 49.0 (q), 24.7 (t), 22.8 (t), 21.9

(q), 21.6 (q), 18.6 (q), 11.3 (d); IR (thin ®lm) 2945m,

2892w, 2868m, 2061m, 1974m, 1918s, 1482m, 1444w,

1131w, 1683m, 1046w cm²¹; mass spectrum (EI) m/z (%

intensity) 659 (M¹, 2, ¹⁸⁴W), 631 (M¹2CO, 7, ¹⁸⁴W), 603

(M¹22CO, 5, ¹⁸⁴W), 575 (M¹23CO, 8, ¹⁸⁴W), 519

(M¹25CO, 15, ¹⁸⁴W), 502 (12), 475 (4), 448 (5), 432 (4),

415 (2), 392 (2), 362 (3), 328 (4), 303 (5), 264 (10), 182 (3),

139 (11), 111 (13), 96 (12), 70 (100), 59 (23). Anal. calcd

for C₂₅H₃₇NO₆SiW: C, 45.53; H, 5.65; N, 2.12. Found: C,

1

isolated as a 2:1 mixture of two isomers A:B; H NMR

(500 MHz, CDCl₃) d 6.89 (s, 1H, A), 6.57 (s, 1H, B),

4.19 (s, 3H, B), 4.17±4.13 (m, 1H, A or B), 4.08 (s, 3H,

A), 3.99±3.94 (m, 1H, A or B), 3.69±3.63 (m, 1H, A or B),

3.52±3.49 (m, 1H, A or B), 3.47±3.39 (m, 1H, A or B), 3.18

(s, 3H, A), 3.15 (s, 3H, B), 2.12±1.73 (m, 8H, A1B), 1.21

(s, 3H, A), 1.19 (s, 3H, A), 1.07 (s, 3H, B), 1.03 (s, 3H, B),

0.33 (s, 9H, B), 0.32 (s, 9H, A).

1

Triisopropylsilylethynyl (S)-dimethylmethoxymethyl-

pyrrolidine carbene complexes 17 and 22. A solution of

chromium complex 7c (208 mg, 0.500 mmol) in 5 mL

diethyl ether was cooled to 2788C and pyrrolidine 5⁸

(86 mg, 0.600 mmol) was added. After 2 h, TLC indicated

that the reaction was not complete. Additional 5 (15 mg,

0.105 mmol) was added and the reaction was complete

after an additional 45 min. After concentration, the residue

was loaded onto a silica gel column and eluted with a 1:30

mixture of ether and pentane to two red±orange oils, E-17

(253.3 mg, 0.480 mmol) in 96% yield and Z-17 (6.3 mg,

45.63; H, 5.86; N, 2.10. Spectral data for Z-22: H NMR

(400 MHz, CDCl₃) d 4.49 (d, 1H, J6.7 Hz), 4.48±4.37 (m,

1H), 3.68±3.57 (m, 1H), 3.18 (s, 3H), 2.29±2.21 (m, 1H),

2.21±2.12 (m, 1H), 2.06±1.96 (m, 2H), 1.26 (s, 3H), 1.25 (s,

3H), 1.24±1.09 (m, 3£1H, 6£3H); ¹³C NMR (75 MHz,

CDCl₃) d 224.4 (s), 203.6 (s), 199.0 (s), 127.3 (s), 109.5

(s), 78.4 (d), 55.6 (t), 48.9 (q), 24.1 (t), 23.3 (t), 21.1 (q),

20.6 (q), 18.8 (q), 11.2 (d), one C-atom under CDCl₃peak;

¹³C NMR (75 MHz, C₆D₆) d 224.9 (s), 203.4 (s), 199.0 (s),

110.2 (s), 78.6 (d), 77.7 (s), 56.0 (t), 48.5 (q), 24.2 (t), 23.3

(t), 20.8 (q), 20.5 (q), 18.8 (q), 11.5 (d), one C-atom under

4962

A. Rahm et al. / Tetrahedron 56 (2000) 4951±4965

C₆D₆peak; IR (thin ®lm) 2945m, 2893w, 2867m, 2062s,

1974m, 1919s, 1473m, 1448w, 1208w, 1131w, 1083m,

1045w cm²¹; mass spectrum (EI) m/z (% intensity) 659

(M¹, 3, ¹⁸⁴W), 631 (M¹2CO, 27, ¹⁸⁴W), 603 (M¹22CO,

11, ¹⁸⁴W), 575 (M¹23CO, 29, ¹⁸⁴W), 547 (M¹24CO, 2,

¹⁸⁴W), 519 (M¹25CO, 56, ¹⁸⁴W), 502 (37,,W), 475 (16),

433 (13), 391 (7), 361 (8), 327 (11), 304 (12), 264 (15), 238

(3), 203 (3), 182 (3), 139 (12), 111 (13), 96 (15), 70 (100),

59 (44). Anal. calcd for C₂₅H₃₇NO₆SiW: C, 45.53; H, 5.65;

N, 2.12. Found: C, 45.41; H, 5.76; N, 2.52.

¹⁸⁴W), 291 (24), 265 (23), 237 (15), 209 (7), 168 (7), 145

(3), 120 (1), 69 (15). Anal. calcd for C₁₄H₁₃NO₆W: C, 35.39;

H, 2.76; N, 2.95; Found: C, 35.03; H, 2.99; N, 3.07.

Chromium complex E-32. Yellow solid, 84% yield from

E-17. Spectral data for E-32: mp: 78±828C (decomp); H

1

NMR (400 MHz, CDCl₃) d 5.74 (s, 1H), 4.66 (m, 1H),

4.42±4.35 (m, 1H), 4.27±4.13 (m, 1H), 3.16 (s, 3H),

2.25±2.18 (m, 2H), 2.05±1.92 (m, 2H), 1.19 (s, 3H), 1.15

(s, 3H); ¹³C NMR (75 MHz, CDCl₃) d 247.6, 224.2, 217.2,

1

2

113.5 (d, J_CH256 Hz), 85.6 (d, J._CH49 Hz), 80.0 (s),

76.4 (d), 58.9 (t), 49.1 (q), 24.6, 23.2, 21.9, 21.8; IR (thin

®lm) 3307w, 2988±2776w, 2054m, 1973m, 1920s, 1496m,

1082m cm²¹; mass spectrum (EI) m/z (% intensity) 371

(M¹, 23), 315 (M¹22CO, 17), 287 (M¹23CO, 13), 259

(M¹24CO, 26), 231 (M¹25CO, 90), 220 (100), 199 (25),

175 (11), 164 (13), 148 (26), 136 (15), 119 (13), 100(65), 80

(87), 73 (33), 52 (97). Anal. calcd for C₁₆H₁₇NO₆Cr: C,

51.76; H, 4.61; N, 3.77. Found: C, 51.93; H, 4.86; N, 3.63.

Preparation of complexes 31±34 by protodesilylation:

chromium complex E-31. The chromium carbene complex

E-15 (139.8 mg, 0.35 mmol) was dissolved in 20 mL

diethyl ether and cooled to 2788C. Tetrabutylammonium

¯uoride (0.350 mL, 1 M, 0.35 mmol) in THF was added

and the solution was stirred for 1 h at 2788C. The reaction

was quenched with water and washed with water and brine.

After drying with MgSO₄and ®ltration, the solution was

concentrated. Puri®cation by column chromatography on

silica gel (Et₂O/CH₂Cl₂/hexanes, 1:1:10) afforded E-31

(89.4 mg, 0.26 mmol) as a yellow solid in 74% yield. Spec-

tral data for E-31: mp 39±418C, ¹H NMR (500 MHz,

CDCl₃) d 5.84 (s, 1H), 4.67 (m, 1H), 4.24±4.22 (m, 2H),

3.59 (d,2H, J5.6 Hz), 3.36 (s, 3H), 2.33±2.14 (m, 4H); ¹³C

NMR (75 MHz, CDCl₃) d 247.5, 223.8, 217.2, 114.5, 84.3,

72.6, 67.9, 59.3, 58.6, 27.7, 23.5; IR (thin ®lm) 3298m,

2988±2834m, 2056s, 1979shoulder, 1911s, 1482m,

1449m, 1120w, 654m cm²¹; mass spectrum (EI) m/z (%

intensity) 343 (M¹, 27), 315 (M¹2CO, 3), 287

(M¹22CO, 45), 259 (M¹23CO, 22), 231 (M¹24CO,

73),220 (83), 203 (M¹25CO, 100), 188 (22), 173 (24),

158 (14), 147 (47), 133 (18), 119 (49), 108 (87), 92 (13),

80 (100), 70 (100). Anal. calcd for C₁₄H₁₃NO₆Cr: C, 48.99;

H, 3.82; N, 4.08. Found: C, 46.79; H, 4.40; N, 4.08.

Tungsten complex E-34. Yellow solid, 74% yield from E-20

and 74% from E-22 Spectral data for E-34: mp 88±978C

(decomp.); H NMR (400 MHz, CDCl₃) d 5.47 9 (d, 1H,

1

J7.6 Hz); 4.25±4.21 (m, 1H), 4.04±3.98 (m, 1H), 3.16 (s,

3H), 2.26±2.20 (m, 2H), 2.01±1.96 (m, 2H), 1.20 (s, 3H),

1.16 (s, 3H); ¹³C NMR (75 MHz, C₆D₆) d 226.7 (s), 204.5

(s), 199.1 (sd, J_WC127.8 Hz), 110.7 (s), 87.7 (s), 77.9 (s),

75.6 (d), 61.4 (t), 48.8 (q), 24.6 (t), 22.8 (t), 22.1 (q), 21.3

(q); IR (thin ®lm): 3298w, 3023±2800w, 2083m, 1978w,

1897s, 1881s, 1496m, 1085w cm²¹; mass spectrum (EI)

m/z (% intensity) 503 (M¹, 47, ¹⁸⁴W), 475 (M¹2CO, 4,

¹⁸⁴W), 447 (M¹22CO, 57, ¹⁸⁴W), 419 (M¹23CO, 13,

¹⁸⁴W), 391 (M¹24CO, 4, ¹⁸⁴W), 363 (M¹25CO, 100,

¹⁸⁴W), 331 (27), 292 (29), 263 (21), 237 (17), 209 (8), 181

(6), 149 (5), 110 (7), 96 (8), 73 (94), 55 (47). Anal. calcd for

C₁₆H₁₇NO₆W: C, 38.19; H, 3.41; N, 2.78. Found: C, 38.27;

H, 3.42; N, 2.71.

Tungsten complex E-33. Yellow solid, 91% yield from

E-19. Spectral data for E-33: mp: 40±428C; ¹H NMR

(300 MHz, CDCl₃) d 5.56 (s, 1H), 4.59±4.57 (m, 1H),

4.02 (m, 2H), 3.58 (d, 2H, J5.2 Hz), 3.35 (s, 3H), 2.26±

2.09 (m, 4H); ¹³C NMR (75 MHz, CDCl₃) d 226.3 (s), 204.0

Tungsten complex Z-34. Yellow oil, 40% yield from Z-22.

Spectral data for Z-34: ¹H NMR (400 MHz, CDCl₃) d 5.50

(s, 1H), 4.51 (d, 1H, J6.8 Hz), 4.44±4.38 (m, 1H), 3.70±

3.63 (m, 1H), 3.16 (s, 3H), 2.28±2.23 (m, 1H), 2.16±2.12

(m, 1H), 2.03±1.94 (m, 2H), 1.26 (s, 3H), 1.25 (s, 3H); ¹³C

NMR (125 MHz, CDCl₃) d 225.1 (s), 203.5 (s), 198.9 (s),

110.6 (d), 87.2 (s), 77.5 (d), 56.0 (t), 48.9 (q), 24.1 (t), 23.2

(t), 21.1 (q), 20.7 (q); IR (thin ®lm) 3299w, 2950±2850w,

1

(s), 198.4 (s, J_CW128 Hz), 111.2 (d, J_CH265 Hz), 86.2

(d, ²J._CH52 Hz), 72.3 (t), 66.7 (d), 60.8 (t), 59.3 (q), 28.0

(t), 23.2 (t); IR (thin ®lm) 3298w, 2979±2837w, 2063m,

1977shoulder, 1904s, 1486w cm²¹; MS (EI) m/z (% inten-

sity) 475 (M¹, 47, ¹⁸⁴W), 447 (M¹2CO, 4, ¹⁸⁴W), 419

(M¹22CO, 28, ¹⁸⁴W), 391 (M¹23CO, 48, ¹⁸⁴W), 363

(M¹24CO, 58, ¹⁸⁴W), 335 (M¹25CO, 100, ¹⁸⁴W), 278

(27), 237 (18), 211 (9), 168 (6), 145 (4), 120 (3), 96 (3),

70 (22). Anal. calcd for C₁₄H₁₃NO₆W: C, 35.39; H, 2.76; N,

2.95; W, 38.70. Found: C, 34.58; H, 2.95; N, 2.88; W, 38.88.

2083m, 1976m, 1905s, 1487m, 1446w, 1082w cm²¹

.

Diels±Alder reactions of the (S)-methoxymethylpyrroli-

dine carbene complexes E-31 and E-33 with siloxy

diene 11.

Tungsten complex Z-33. Yellow solid, 84% yield from Z-19.

Spectral data for Z-33: mp 46±498C; ¹H (500 MHz, CDCl₃)

d 5.55 (s, 1H), 4.62±4.56 (m, 1H), 4.05±3.98 (m, 2H),

3.66±3.62 (m, 2H), 3.38 (s, 3H), 2.31±2.08 (m, 4H); ¹³C

NMR (75 MHz, CDCl₃) d 224.5 (s), 203.4 (s), 198.3 (s),

111.3 (d), 87.7 (d), 73.1 (t), 69.9 (d), 59.3 (q), 56.3 (t), 27.1

(t), 22.7 (t); IR (thin ®lm) 3296w, 2992±2837w, 2064m,

1977 shoulder, 1907s, 1485w cm²¹; mass spectrum (EI)

m/z (% intensity) 475 (M¹, 40, ¹⁸⁴W), 447 (M¹2CO, 7,

¹⁸⁴W), 419 (M¹22CO, 25, ¹⁸⁴W), 391 (M¹23CO, 51,

¹⁸⁴W), 363 (M¹24CO, 55, ¹⁸⁴W), 335 (M¹25CO, 100,

Cycloadduct 36. The chromium carbene complex E-31

(570.1 mg, 1.67 mmol) was dissolved in 1.5 mL diene 11

and stirred for 28 h at room temperature. The crude reaction

mixture was directly loaded onto a silica gel column and

eluted with a 20:1 mixture of hexane and ether to give

carbene complex 36 (467.3 mg, 0.802 mmol) as a yellow

oil 48% yield. This product was obtained as a 5:1 mixture

of diastereomers and the major isomer was assigned as A on

the basis of a comparison of the NMR data with 38A. The

following spectral data was obtained on the mixture of

isomers and the NMR data for 36A was extracted from

A. Rahm et al. / Tetrahedron 56 (2000) 4951±4965

4963

the spectrum of the mixture. Spectral data for 36A: ¹H NMR

(500 MHz, CDCl₃) d 4.98 (s, 1H), 4.86 (s, 1H), 4.36±4.33

(m, 1H), 4.16±4.12 (m, 1H), 3.72±3.71 (m, 1H), 3.39 (d,

1H, J6.1 Hz), 3.33 (s, 3H), 2.95±2.89 (m, 1H), 2.78±2.73

(m, 1H), 2.30±2.26 (m, 1H), 2.18±2.10 (m, 2H), 1.92±1.88

(m, 1H), 1.22±1.61 (m, 3H), 1.11 (d, 18H, J6.5 Hz), 0.94

(d, 3H, J7.2 Hz); ¹³C NMR (C₆D₆, 75 MHz) d 273.0,

224.4, 218.9, 151.8, 147.7, 110.4, 106.5, 73.2, 66.6, 59.3,

58.8, 34.0, 30.2, 26.8, 21.7, 20.2, 18.2, 13.0; IR (thin ®lm)

2960±2868w, 2050m, 1967m, 1915s, 1688w, 1491±1456w,

1211m, 884w cm²¹; mass spectrum (EI) m/z (% intensity)

527 (M¹22CO, 36), 495 (3), 471 (M¹24CO, 17), 443

(M¹25CO, 100), 413 (24), 391 (92), 346 (87), 330 (18),

277 (100), 235 (32), 218 (18), 197 (22), 165 (100), 135 (91),

105 (92), 75 (100). Anal. calcd for C₂₈H₄₁NO₇SiCr: C,

57.62; H, 7.08; N, 2.40; Cr, 8.91. Found: C, 55.76; H,

7.86; N, 2.37; Cr, 9.17. The methoxy singlet of the minor

isomer 36B is at d3.30 ppm.

pure sample of 38A (122.5 mg, 0.200 mmol) as a yellow

solid in 14% yield. Repuri®cation of the mixed fraction

by a second silica gel column gave 20.9 mg of pure 38B

for spectral analysis. Spectral data for 38A: mp: 69±728C;

¹H NMR (500 MHz, CDCl₃) d 5.24 (s, 1H), 4.84 (s, 1H),

4.37±4.21 (m, 2H), 4.08 (d, 1H), 3.60±3.53 (m, 1H), 3.20 (s,

3H), 2.96±2.87 (m, 1H), 2.82±2.73 (m, 1H), 2.23±2.12 (m,

2H), 2.02±1.93 (m, 1H), 1.93±1.82 (m, 1H), 1.25±1.03 (m,

21H), 1.21 (s, 3H), 1.13 (s, 3H), 0.88 (d, 3H); ¹³C NMR

(75 MHz, C₆D₆) d 274.0, 224.4, 218.7, 151.3, 147.8, 112.6,

106.7, 76.7, 74.5, 60.9, 48.7, 34.1, 30.5, 24.2, 22.4, 22.2,

21.5, 20.6, 18.2, 13.4; IR (thin ®lm) 2945±2868w, 2049m,

1966w, 1941s, 1488w, 1465w, 1383w, 1206m, 1081w,

884w cm²¹; mass spectrum (EI) m/z (% intensity) 555

(M¹22CO, 6), 471 (M¹25CO, 20), 437 (5), 418 (4), 402

(4), 346 (37), 324 (8), 277 (100), 193 (67), 161 (18), 131

(30), 103 (28), 87 (15), 75 (42), 59 (41). Spectral data for

38B: ¹H NMR (500 MHz, CDCl₃) d 5.64 (t, 1H, J3.6 Hz),

4.80 (d, 1H, J2.9 Hz), 4.33±4.26 (m, 1H), 4.18±4.08 (m,

1H), 3.91 (d, 1H, J8.2 Hz), 3.19 (s, 3H), 3.08±3.03 (m,

1H), 2.76±2.71 (m, 1H), 2.57±2.54 (m, 1H), 2.22±2.17 (m,

2H), 1.99±1.95 (m, 1H), 1.87±1.83 (m, 1H), 1.29 (d, 3H,

J7.3 Hz), 1.28 (s, 3H), 1.17 (s, 3H), 1.11 (d, 18H,

J6.8 Hz), 1.22±1.01 (m, 3H); ¹³C NMR (75 MHz, C₆D₆)

d 280.0, 224.1, 218.5, 153.2, 148.8, 120.5, 107.4, 77.4, 74.5,

61.0, 48.7, 36.3, 30.2, 24.5, 23.4, 22.9, 22.1, 21.7, 18.1,

13.0; IR (thin ®lm) 29.45±2868m, 2050m, 1968w, 1918s,

1465w, 1450w, 1207w, 883w cm²¹; mass spectrum (EI) m/z

(% intensity) 555 (M¹22CO, 7), 496 (3), 471 (M¹25CO),

453 (9), 435 (7), 419 (7), 404 (15), 388 (6), 362 (9), 346

(39), 330 (8), 309 (3), 277 (73), 241 (33), 231 (83), 197

(100), 177 (15), 161 (23), 131 (56), 103 (58), 87 (28), 75

(87), 59 (71).

Cycloadduct 37. The tungsten carbene complex E-33

(98.2 mg, 0.207 mmol) was dissolved in 0.5 mL diene 11

and stirred for 43 h at room temperature. The crude reaction

mixture was directly loaded onto a silica gel column and

eluted with a 1:1:20 mixture of ether, methylene chloride

and hexanes to give carbene complex 37 (84.0 mg,

0.117 mmol) as a yellow oil 57% in yield. This product

was obtained as a 5:1 mixture of diastereomers and the

major isomer was assigned as A on the basis of a compari-

son of the NMR data with 38A. The following spectral data

was obtained on the mixture of isomers and the NMR data

for 37A was extracted from the spectrum of the mixture.

1

Spectral data for 37A: H NMR (500 MHz, CDCl₃) d 5.02

(m, 1H), 4.87 (m, 1H), 4.34±4.29 (m, 1H), 4.11±4.01 (m,

2H), 3.77±3.72 (m, 1H), 3.42±3.39 (m, 2H), 3.34 (s, 3H),

2.98±2.91 (m, 1H), 2.82±2.73 (m, 1H), 2.30±2.12 (m, 3H),

1.95±1.87 (m, 1H), 1.22±1.07 (m, 21H), 0.95 (d, 3H,

J7.2 Hz); ¹³C NMR (75 MHz, CDCl₃) d 254.7, 203.8,

199.1 (J_CW128 Hz), 151.9, 147.5, 111.1, 106.5, 73.3 t,

65.2 d, 61.2 t, 59.2 q, 33.8, 29.9, 27.1, 21.7, 20.0, 17.9,

12.6; IR (thin ®lm) 2945±2868w, 2059m, 1967m, 1910s,

1686w, 1492w, 1455m, 1210m, 884w cm²¹; mass spectrum

(EI) m/z (% intensity) 687 (M¹2CO, 35, ¹⁸⁴W), 659

(M¹22CO, 31 ¹⁸⁴W), 631 (M¹23CO, 43, ¹⁸⁴W), 603

(M¹24CO, 8, ¹⁸⁴W), 601 (11), 575 (M¹25CO, 47, ¹⁸⁴W),

560 (57), 519 (8), 488 (20), 458 (20), 416 (15), 391 (100),

346 (100), 278 (100), 218 (75), 157 (55), 103 (90), 87 (82),

73 (98), 59 (100). Anal. calcd for C₂₈H₄₁NO₇SiW: C, 47.00;

H, 5.77; H, 1.96; W, 25.69. Found: C, 46.54; H, 5.92; N,

1.55; W, 17.94. The methoxy singlet of the minor isomer

37B is at d3.30 ppm.

Cycloadduct 39. The tungsten carbene complex E-34

(157.1 mg, 0.312 mmol) was stirred with 1 mL of diene

11 in 1 mL diethyl ether for 48 h at room temperature.

The resulting mixture was concentrated and separation of

the isomers by silica gel column chromatography (pentane:

diethyl ether20:1) led to 39B (20.1 mg, 0.027 mmol) from

the ®rst fraction in 9% yield and 39A (127.3 mg,

0.171 mmol) from the second fraction in 55% yield. Both

complexes are bright yellow oils. Spectral data for 39A: ¹H

NMR (300 MHz, CDCl₃) d 5.22 (m, 1H), 4.82 (d, 1H,

J2.4 Hz), 4.33±4.25 (m, 1H), 4.12±4.03 (m, 1H), 4.01

(d, 1H, J7.8 Hz), 3.59 (bq, 1H, J7.3 Hz), 3.17 (s, 3H),

2.91 (ddd, 1H, J22 Hz, J7.4 Hz, J4.0 Hz), 2.19±2.05

(m, 2H), 1.98±1.87 (m, 1H), 1.87±1.76 (m, 1H), 1.16 (s,

3H), 1.09 (s, 3H), 1.17±1.10 (m, 3£1H), 1.06 (d, 6£3H,

J6.4 Hz), 0.84 (d, 3H, J7.3 Hz); ¹³C NMR (75 MHz,

C₆D₆) d 225.4 (s), 204.1 (s), 199.8 (s), 151.7 (s), 148.0

(s), 113.7 (d), 106.7 (d), 76.5 (s), 73.4 (d), 63.0 (t), 48.7

(q), 34.3 (d), 24.4 (t), 22.6 (q), 21.9 (t), 21.5 (q), 20.5 (q),

18.2 (q), 13.0 (d); IR (thin ®lm) 2962±2868m, 2058s,

1966m, 1905s, 1689w, 1491±1445m, 1206m 1081w,

884w cm²¹; mass spectrum (EI) m/z (% intensity) 743

(M¹, 0.3, ¹⁸⁴W), 715 (M¹2CO, 4, ¹⁸⁴W, 687 (M¹22CO,

1, ¹⁸⁴W), 659 (M¹23CO, 3, ¹⁸⁴W), 603 (M¹25CO, 4,

¹⁸⁴W), 584 (2), 545 (11, ¹⁸⁴W), 517 (2), 487 (2), 457 (2),

419 (10), 387 (15), 346 (100), 325 (5), 303 (6), 278 (100),

235 (25), 191 (26), 165 (20), 124 (100), 105 (66), 73 (100),

59 (100). Anal. calcd for C₃₀H₄₅NO₇SiW: C, 48.46; H, 6.10;

N, 1.88; W, 24.72. Found: C, 48.51; H, 6.11; N, 1.45; W,

Diels±Alder reactions of the (S)-dimethylmethoxy-

methylpyrrolidine carbene complexes E-32 and E-34

with siloxy diene 11.

Cycloadduct 38. The chromium carbene complex E-32

(515.1 mg, 1.387 mmol) was dissolved in 1.5 mL diene 11

and stirred at room temperature for 52 h. The products were

puri®ed by directly loading the crude reaction mixture on a

silica gel column and elution with a 20:1 mixture of pentane

and ether. The ®rst fraction was found to be a 4:1 mixture of

38A and 38B (256.2 mg, 0.419 mmol, 30% yield) and was

obtained as a yellow oil. The second fraction provided a

4964

A. Rahm et al. / Tetrahedron 56 (2000) 4951±4965

24.43. Spectral data for 39B: ¹H NMR (300 MHz, CDCl₃) d

5.55 (t, 1H, J3.7 Hz), 4.78 (dd, 1H, J2.7 Hz, J1.2 Hz),

4.17±4.00 (m, 2H), 3.84 (d, 1H, J7.9 Hz), 3.15 (s, 3H),

3.16±3.05 (m, 1H), 273 (t, 1H, J5.0 Hz), 2.59±2.50 (m,

1H), 2.27±2.11 (m, 2H), 1.99±1.76 (m, 2H), 1.29 (d, 3H,

J6.9 Hz), 1.11±1.01 (m, 3£1H), 1.06 (d, 6£3H,

J6.6 Hz); ¹³C NMR (75 MHz, C₆D₆) d 261.2 (s), 204.0

(s), 199.9 (s), 153.2 (s), 148.8 (s), 121.6 (d), 107.2 (d), 77.2

(s), 73.5 (d), 63.2 (t), 48.7 (q), 36.0 (d), 30.8 (t), 24.7 (t),

24.0 (q), 22.7 (t), 22.3 (q), 21.6 (q), 18.1 (q), 12.9 (d); IR

(thin ®lm) 2946m, 2893w, 2868m, 2059s, 1967m, 1917s,

1687w, 1466m, 1449m, 1382w, 1239w, 1207m, 1163w,

459 (7), 434 (3), 386 (32), 359 (17), 317 (75), 280 (15), 237

(40), 187 (14), 131 (42), 103 (25), 70 (100), 55 (10). Anal.

calcd for C₃₃H₄₉NO₇SiW: C, 50.58; H, 6.30; N, 1.79. Found:

C, 52.48; H, 6.71; N, 1.40. Spectral data for 40B: ¹H

(500 MHz, CDCl₃) d 5.50 (t, 1H, J3.4 Hz), 4.17±4.09

(m, 1H), 4.04±3.98 (m, 1H), 3.87 (d, 1H, J8.2 Hz), 3.15

(s, 3H), 3.20±3.11 (m, 1H), 3.05±2.99 (m, 1H), 2.86±2.77

(m, 1H), 2.35±2.14 and 2.00±1.78 and 1.74±1.55 and 1.49±

1.40 (m, 10H), 1.13±1.03 (m, 27H); ¹³C NMR (125 MHz,

CDCl₃) d 261.7 (s), 204.2 (s), 199.3 (s), 151.5 (s), 138.7 (s),

120.6 (d), 115.2 (s), 77.2 (s), 73.3 (d), 62.9 (t), 49.1 (q), 44.2

(d), 35.8 (t), 30.9 (t), 27.7 (t), 26.5 (t), 26.4 (t), 24.9 (t), 22.8

(t), 22.4 (q), 21.9 (q), 18.0 (q), 12.2 (d); IR (thin ®lm) 2942±

2866w, 2058m, 1966w, 1914s, 1448w cm²¹; mass spectrum

(EI) m/z (% intensity) 783 (M¹, 0.04, ¹⁸⁴W), 755 (M¹2CO,

0.18, ¹⁸⁴W), 727 (M¹22CO, 0.51, ¹⁸⁴W), 699 (M¹23CO,

0.19, ¹⁸⁴W), 643 (M¹25CO, 0.26, ¹⁸⁴W), 628 (0.24), 585

(3), 493 (3), 434 (3), 386 (32), 359 (6), 317 (100), 275 (24),

230 (26), 187 (7), 131 (27), 103 (19), 70 (100), 55 (10).

1082m, 884w cm²¹

.

Structure determination of Diels±Alder adduct 38A. A

weakly diffracting thin yellow±brown plate was mounted

on a glass ®ber and the unit-cell parameters determined

from the angular settings of 25 re¯ections. From these

data and systematic absences in the diffraction data, the

space group was uniquely assigned. A semi-empirical corre-

lation for absorption was required to compensate for the

20% variation in transmission seen in azimuthal scans.

The structure was solved using an automated Patterson

routine. Limitations in the number of data available allowed

anisotropic re®nement of only the Cr, Si, N and O atoms.

Hydrogen atoms were treated as idealized, updated contri-

bution. A Roger's handedness test showed that the reported

coordinates are preferred (n1.2(3)).

Diels±Alder reaction of the (S)-methoxymethylpyrroli-

dine carbene complexes E-31 with cyclopentadiene. The

chromium carbene complex E-31 (74 mg, 0.216 mmol) was

dissolved in 0.5 mL cyclopentadiene (freshly cracked from

its dimer). The solution was stirred for 48 h at room

temperature and then concentrated. The residue was loaded

onto a silica gel column and eluted with a 1:1:10 mixture of

ether, methylene chloride and hexanes to give carbene

complex 41 (37.7 mg, 0.092 mmol) as a yellow oil in 43%

yield as a mixture of isomers (A/B15:1). Spectral data for

41: ¹H NMR (500 MHz, CDCl₃) d 6.91±6.79 (m, 4H,

A1B), 5.74 (broad d, 1H, J2.2 Hz, A), 5.67 (broad s,

1H, B), 4.25±4.08 (m, A1B), 3.73 (m, 2H, A1B), 3.59

(d, 2H, J19.0 Hz, A1B), 3.35±3.18 (m, A1B), 3.35 (s,

3H, A), 3.27 (s, 3H, B), 2.30±1.56 (m, A1B); ¹³C NMR

(75 MHz, C₆D₆) d 269.4, 268.4, 223.8, 223.5, 218.4, 218.3,

164.8, 164.4, 143.6, 142.9, 141.3, 124.9, 122.1, 122.0, 72.3,

72.1, 71.9, 65.4, 64.3, 59.0, 58.7, 55.3, 55.2, 50.8, 50.6,

27.0, 22.1, 21.8, four carbon atoms from mixture not

identi®ed; IR (thin ®lm) 2985±2874w, 2051m, 2007w,

1969m, 1907s, 1483w, 1415w, 1300w, 1121w cm²¹; mass

spectrum (EI) m/z (% intensity) 381 (M¹2CO, 32), 353

(M¹22CO, 100), 325 (M¹23CO, 18), 321 (26), 297 (52),

269 (100), 230 (87), 203 (35), 148 (100), 117 (93), 80 (60).

Anal. calcd for C₁₉H₁₉NO₆Cr: C, 55.75; H, 4.68; N, 3.42;

Cr, 12.70. Found: C, 55.51; H, 4.86; N, 3.08; Cr, 13.05.

Crystal data for C₃₀H₄₅CrNO₇Si: f.w.611.8, orthorhom-

Ê

bic, P2₁2₁2₁, a8.385(3), b9.329(4), c43.126(5) A,

Ê ³

V3374(17) A , Z4, 2133 data collected; 1332 observed

from 2133 independent re¯ections. R(F)9.61% and

R(wF)12.31%. shelxtl (4.2) software was used for

re®nement (G. Sheldrick, Siemens XRD, Madison, WI).

Lists of the atomic coordinates, thermal parameters, bond

distances and bond angles have been deposited with the

Cambridge Crystallographic Database, Cambridge,

England.

Diels±Alder reaction of the (S)-dimethylmethoxymethyl-

pyrrolidine carbene complexes E-34 with siloxy diene 13.

The tungsten carbene complex E-34 (323.4 mg,

0.322 mmol) was dissolved in 1 mL diene 13 and stirred

for 89 h at room temperature. The resultant crude reaction

mixture was loaded directly onto a silica gel column chro-

matography and eluted with a 20:1 mixture of hexane and

ether. Cycloadduct 40B (66.3 mg, 0.085 mmol) was

obtained from the ®rst fraction in 26% yield as a sticky

foam and 40A (96.3 mg, 0.123 mmol) was obtained from

the second fraction in 38% yield as a yellow solid. Spectral

data for 40A: mp 108±1168C decomp, ¹H (500 MHz,

CDCl₃) d 5.18±5.15 (m 1H), 4.32±4.26 (m, 1H), 4.09±

4.01 (m, 2H), 3.37±3.28 (m, 2H), 3.16 (s, 3H), 3.07±3.01

(m, 1H), 3.01±2.91 (m, 1H), 2.86±2.77 (m, 1H), 2.14±2.07

(m, 4H), 1.98±1.88 (m, 2H), 1.82±1.67 (m, 4H), 1.16 (s,

3H), 1.10±1.02 (m, 24H); ¹³C NMR (125 MHz, C₆D₆) d

255.1, 204.0, 200.0, 151.2, 139.2, 114.7, 112.8, 76.4, 73.3,

62.9, 48.7, 42.4, 33.1, 30.7, 27.0, 26.8, 26.6, 24.6, 22.7,

21.8, 21.6, 18.2, 13.5; IR (thin ®lm) 2942±2866w, 2058m,

1966w, 1912s cm²¹; mass spectrum (EI) m/z (% intensity)

783 (M1, 0.4, ¹⁸⁴W), 755 (M¹2CO, 1, ¹⁸⁴W), 699

(M¹23CO, 1, ¹⁸⁴W), 643 (M1, 5CO, 0.6, ¹⁸⁴W), 585 (2),

Diels±Alder reaction of the (S)-dimethylmethoxymethyl-

pyrrolidine carbene complexes E-32 with cyclopenta-

diene.

The chromium carbene complex E-32 (55.7 mg,

0.15 mmol) was dissolved in 0.4 mL cyclopentadiene

(freshly cracked from its dimer). The solution was stirred

for 42 h at room temperature and then concentrated. The

residue was loaded onto a silica gel column and eluted

with a 1:1:10 mixture of ether, methylene chloride and

hexanes to give carbene complex 42 (39.4 mg, 0.090

mmol) as a yellow oil in 60% yield as a mixture of isomers

1

(A/B2.7:1). Spectral data for 42: H (500 MHz) d 6.82

(broad s, 2H, A), 6.71 (broad s, 2H, B), 6.0 (broad s,

A1B), 4.44 (broad s, 1H, B), 4.34 (m, 1H, A), 4.19 (m,

2H, A), 3.97 (m, 2H, B), 3.70 (m), 3.54±3.36 (broad m),

A. Rahm et al. / Tetrahedron 56 (2000) 4951±4965

4965

3.18 (s, 3H, A), 3.14 (s, 3H, B), 2.37±1.70 (3m, 8H, A1B),

References

1.15 (s, 3H, A), 1.09 (s, 3H, A), 1.01 (broad s, 6H, B); ¹³C

NMR (75 MHz, C₆D₆) d 269.1, 224.3, 224.1, 218.6, 166.6,

166.0, 144.2, 141.4, 141.2, 77.1, 76.8, 74.7, 73.3, 72.6, 59.9,

56.1, 56.0, 55.3, 51.2, 50.9, 48.7, 24.5, 24.2, 22.8, 22.1, 21.4

(10 C atoms of mixture not identi®ed, partially due to

solvent peak); ¹³C NMR (75 MHz, CDCl₃) d 268.8, 223.9,

223.7, 217.9, 166.1, 165.5, 143.9, 143.7, 141.2, 140.9,

128.0, 127.4, 76.7, 74.9, 74.4, 72.5, 72.4, 72.2, 59.6, 55.7,

54.9, 50.8, 50.5, 49.0, 48.9, 24.5, 24.2, 22.7, 21.7, 21.5, 21.0

(4 C atoms not detected); IR (thin ®lm) 2983±2835w,

2050m, 2005w, 1969w, 1909s, 1479w, 1448w cm²¹; mass

spectrum (EI) m/z (% intensity) 409 (M¹2CO, 7), 381

(M¹22CO, 32), 353 (M¹23CO, 2), 325 (M¹24CO, 14),

311 (3), 297 (100), 265 (25), 252 (6), 237 (12), 225 (10), 214

(15), 189 (47), 169 (27), 148 (72), 119 (100), 103 (7), 91

(23), 73 (43), 65 (12).

1. (a) Oh, T.; Reilly, M. Org. Prep. Proc. Int. 1994, 26, 129.

(b) Dias, L. C. J. Brazil. Chem. Soc. 1997, 8, 289.

2. (a) Evans, D. A.; Chapman, K. T.; Bisaha, J. J. Am. Chem. Soc.,

1998, 110, 1238. (b) Maruoka, K.; Concepcion, A. B.; Yamamoto,

H. Bull. Chem. Soc. Jpn 1992, 65, 3501. (c) Ishihara, K.; Kondo, S.;

Kurihara, H.; Yamamoto, H.; Ohashi, S.; Inagaki, S. J. Org. Chem.,

1997, 62, 3026. (d) Corey, E. J.; Lee, T. W. Tetrahedron Lett.

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Matt, P. J. Am. Chem. Soc. 1999, 121, 7559. (f) Buckle, R. N.;

Burnell, D. J. Tetrahedron, 1999, 55, 14829.

3. It has recently been suggested that secondary orbital overlap

can occur between the C-2 position of the diene and the carbonyl

oxygen giving rise to stereoelectronic control over the addition

even though endo and exo cycloadduts are not possible.^2cIn the

presence case, secondary overlap to the chromium atom is

expected to be sterically hindered by the presence of the carbonyl

ligands.

Isomerization of Cycloadduct 39A. A sample of 39A in

CDCl₃was left in the NMR tube overnight. A new

compound was formed was assigned the structure of the

double-bond isomer 43 on the basis of the following spectral

4. Rahm, A.; Wulff, W. D.; Rheingold, A. L. Organometallics

1993, 12, 597.

5. Wulff, W. D. Organometallics 1998, 17, 3116.

1

data: H NMR (400 MHz, CDCl₃) d 5.33±5.25 (m, 2H),

6. For citations to the literature, see: (a) Powers, T. S.; Jiang, W.;

Su, J.; Wulff, W. D.; Waltermire, B. E.; Rheingold, A. L. J. Am.

Chem. Soc. 1997, 119, 6438. (b) Wulff, W. D.; Bauta, W. E.;

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4.38±4.30 (m, 2H), 4.22 (d, 1H, 7.7 Hz) 4.10±4.00 (m,

1H), 3.16 (s, 3H), 2.27±2.07 (m, 4H), 1.98±1.80 (m, 2H),

1.15 (s, 3H), 1.08±1.2 (m, 3H, 6£3H), 0.89 (d, 2H, 7.2 Hz);

¹³C NMR (125 MHz, CDCl₃) d 256.2 (s), 204.0 (s), 199.0

(s), 153.1 (s), 144.8 (s), 115.9 (d), 101.5 (d), 76.9 (s), 73.4

(d), 62.2 (t), 49.0 (q), 38.8 (t), 34.5 (d), 24.6 (t), 22.7 (q),

22.3 (t), 22.1 (q), 17.9 (q), 16.9 (q), 12.5 (d).

7. (a) Moser, E.; Fischer, E. O. J. Organomet. Chem. 1968, 13,

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1976, 8, 761.

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Bhushan, V. Bull. Soc. Chim. Belg. 1988, 97, 691.

Diels±Alder reaction of the (S)-methoxymethylpyrroli-

dine carbene complexes Z-33 with siloxy diene 11.

Carbene complex Z-33 (100.0 mg, 0.211 mmol) was stirred

with 0.5 mL diene 11 for 14 h at room temperature. The

resulting mixture was loaded directly onto a silica gel

column and eluted with a 1:1:20 mixture of ether, methylene

chloride and hexanes to give Z-37A and Z-37B as a 1:1

mixture (54.2 mg, 0.076 mmol) in 36% yield. Spectral

data for mixture of Z-37A and Z-37B: ¹H NMR

(500 MHz, CDCl₃) d 4.88±4.78 (m, 4H), 4.63±4.55 (m,

2H), 4.36±4.30 (m, 1H), 4.01±3.96 (m, 1H), 3.91±3.79

(m, 3H), 3.69±3.62 (m, 4H) 3.42 (s, 3H), 3.36 (m, 3H),

2.99±2.85 (m, 2H), 2.82±2.70 (m, 2H), 2.31±2.05 (m,

6H), 2.01±1.78 (m, 2H), 1.23±1.16 (m, 6H), 1.13±1.05

(m, 36H), 0.98 (d, 3H, J7.3 Hz), 0.95 (d, 3H,

J7.2 Hz); ¹³C NMR (75 MHz, C₆D₆) d 252.5, 250.5,

203.7, 203.3, 200.1, 199.8, 154.7, 154.0, 147.8, 110.9,

108.6, 106.3, 106.0, 74.9, 74.3, 69.8, 69.4, 58.9, 58.8,

55.7, 53.9, 35.1, 35.0, 30.3, 30.1, 26.6, 25.8, 23.6, 23.1,

20.4, 18.2, 13.0 (4 C atoms not detected); IR (thin ®lm)

2945±2868w, 2059m, 1967w, 1912s, 1687w, 1494w,

9. Chan, K. S.; Wulff, W. D. J. Am. Chem. Soc. 1986, 108, 5229.

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1051.

È

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Abel, E. W., Stone, R. G. A., Wilkinson, G. Eds.; Pergamon Press:

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1463w, 1210m, 837w cm²¹

.

Acknowledgements

21. Baldoi, C.; Del Buttero, P.; Licandro, E.; Maiorana, S.;

Papagni, A.; Zanotti-Gerosa, A. Synlett 1994, 677.

This work was supported by a grant from the National

Institute of Health (PHS-GM 33589).

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Asymmetric diels - Alder reactions with chiral acetylenic carbene complexes as dienophiles

DOI: 10.1016/S0040-4020(00)00209-X

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