On the reduction of α,β-unsaturated (Group 6) carbene complexes by NaBH4

TETRAHEDRON

Pergamon

Tetrahedron 56 (2000) 4893±4905

On the Reduction of a,b-Unsaturated (Group 6) Carbene

Complexes by NaBH₄

1

*

Â Â Â

Mar Gomez-Gallego, Marõa J. ManchenÄo, Pedro Ramõrez, Carmen PinÄar and Miguel A. Sierra

Â Â Â

Departamento de Quõmica Organica I, Facultad de Quõmica, Universidad Complutense, 28040 Madrid, Spain

Received 22 November 1999; accepted 29 December 1999

AbstractÐChromium and tungsten styryl Fischer carbene complexes 12 and 15 were transformed into Z-vinyl ether 13 and E-allyl ether 14

by NaBH₄reduction in EtOH. Deuterium labeling experiments demonstrate that the reaction occurs by the initial addition of the hydride to

the carbene carbon atom, followed by a 1,3-rearrangement of the M(CO)₅fragment. The process could involve the participation of an h³-allyl

chromium intermediate. The reaction is general and has been applied to a series of a,b-unsaturated alkoxy and aminocarbene complexes. In

the case of chromium and tungsten alkynyl carbenes 38 and 39, NaBH₄reduction exclusively yields E-allyl ether 14. The intermediacy of an

allenyl complex 41 obtained after the 1,3-rearrangement of the metal center is con®rmed by deuterium labeling experiments. q 2000 Elsevier

Introduction

with no essential changes in the nature of the reaction

products with respect to those described for organic esters.

Logically, when the metal takes an active role in the

process, (like in Dotz's benzannulation)⁵, new types of

products, unknown for their organic counterparts, were

obtained. In this context, the behavior of a,b-unsaturated

alkoxychromium(0) carbenes and a,b-unsaturated organic

esters towards the addition of nucleophiles, should be

similar. The competition between 1,2- and 1,4-addition of

dimethylamine to alkynylcarbene complexes of chromium

and tungsten, was reported in 1972 by Fischer,¹⁰but the

factors controlling the chemoselectivity of these processes

are not yet fully understood. As an example, in an early

report, Casey¹¹stated that the conjugate addition of enolate

anions to vinyl carbene complexes is controlled mainly by

steric effects, while more recent work¹²describes the

preferred conjugated addition, in spite of unfavorable steric

effects. On the other hand, the decisive in¯uence of the

reagent in the chemoselectivity of the reaction is exempli-

®ed by the addition of ZnEt₂and ArLi to alkynyl complexes,

to yield 1,2-adducts exclusively.¹³Our own ®ndings¹⁴in this

®eld have shown that heteronucleophiles may form either

1,4- or 1,2-adducts depending on the case, and that factors

other than the steric hindrance may control the chemo-

selectivity of these processes. Among many other examples

the reaction of complex 1 with phosphorous ylides 2 gave

exclusively 1,2-adducts 3, while the conjugated addition of

sulfur ylides 4 to give cyclopropanes 5, is strongly depen-

dent on the ylide stabilization and the reaction conditions

(Scheme 1).^14d

Although the knowledge about the reactivity of group 6

metal carbene complexes has grown exponentially during

the last 20 years,²our understanding of the mechanisms of

the reactions involved do not parallel these results. Due to

the seminal work of Bernasconi, processes like a-deproto-

nation,³or addition of nucleophiles to the carbene carbon

atom on simple chromium complexes,⁴are now more

intimately known. However, the reaction mechanism for

other processes such as the cocyclization of an a,b-unsatu-

È

rated chromium carbene complex and an alkyne (Dotz reac-

tion),⁵in difference the most thoroughly studied reaction of

this kind of complexes, is still under a passionate debate. In

other cases, the well accepted mechanisms are based mainly

on indirect evidence. This is the case, for example, of the

photochemical carbonylation of chromium carbene

complexes, that it is believed to generate metal-bounded

ketenes.^2j,6aNevertheless, the sole reported attempt, made

to detect the formation of such intermediates, occurred with

no success.^6b

The isolobal analogy principle⁷states that a,b-unsaturated

alkoxychromium(0) carbenes should behave as a,b-unsatu-

rated organic esters in processes taking place outside of the

coordination sphere of the metal.²In consequence, such

complexes may be regarded as a kind of super-esters, with

their reactivity enhanced due to the presence of a metal in

their structures. Processes such as Diels±Alder,⁸1,3-di-

polar,^2land [212] cycloadditions⁹have been reported

An additional variable to be taken into consideration in the

addition of nucleophiles to a,b-unsaturated carbene

complexes, is the possibility of the active participation of

Keywords: organometallic mechanism; metal carbenes; hydride reduction;

1,3-metal migration.

* Corresponding author. E-mail: sierraor@eucmax.sim.ucm.es

PII: S0040-4020(00)00204-0

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M. Gomez-Gallego et al. / Tetrahedron 56 (2000) 4893±4905

4894

Scheme 1.

the metal in the process. Although 1,2 and 1,3-migrations of

metal fragments have been reported, these processes are not

frequent in Fischer carbene complexes. The 1,2-migration

of a M(CO)₅fragment was ®rst proposed by Fischer to

account for the cyclodimerization of ethynyl tungsten

distinct compounds upon quenching with different electro-

philes (Scheme 2).

Taking into account the precedents above mentioned, it is

predictable that the mechanism of the addition of simple

nucleophiles to a,b-unsaturated chromium(0) carbenes,

will be not as simple as in the case of their organic counter-

parts (namely, a,b-unsaturated esters and amides). In this

context, we decided to study the reaction of group 6

a,b-unsaturated alkoxy and amino Fischer carbene

complexes with NaBH₄. The addition of hydrides offers

an exceptional opportunity to combine reagent simplicity

with the possibility of isotopic labeling, (using either a

reagent or a deuterated solvent). Proofs for the exclusive

1,2-addition of the hydride to the carbene carbon atom,

followed by 1,3-allylic or propargylic migration of the

metal moiety, will be presented.

carbenes by ArLi reagents.¹⁵An analogous observation

13

È

was made by Dotz and Knochel in the reaction of such

complexes and Et₂Zn. More recently, Iwasawa¹⁶has

reported the preparation of different compounds, taking

advantage of the migration of the M(CO)₅in the intermedi-

ates 6 obtained by reaction of complexes 7 and alkynyl-

lithiums. Other similar migration processes have been

described by Barluenga, in the reaction of a,b-unsaturated

group 6 metal carbenes with 4-amino-1-azadienes, imines,

and sodium methoxide.¹⁷Much more unusual are 1,3 migra-

tions of the metal fragment. The ®rst example of one of such

processes through a diazaallyl system, was found in the

reaction of an alkoxy-carbene with diazobenzene.¹⁸This

early work was followed by other analogous processes, all

involving a migration through heteroatom substituted

systems.¹⁹The ®rst example describing the migration of

the M(CO)₅fragment in a fully carbonated system was

reported by Barluenga while this work was in progress.^17d,20

This author described the migration of an W(CO)₅moiety in

an intermediate of type 6 (R¹R³Ph; R²(2)menthyl), to

yield the allenyl tungsten derivative 8. This species led to

The reactivity of group 6 metal±carbene complexes towards

reducing agents has been scarcely studied. Hydrogenation

of Cr± and W±carbene complexes promotes the loss of the

metal moiety and the formation of the corresponding hydro-

carbon, in a process thought to occur by addition of hydro-

gen to the CvM bond and subsequent extrusion of the metal

moiety.²¹Complex [(CO)₅WC(OMe)Ph] reacts sequentially

with KHB(OiPr₂)₃and BrNEt₄to yield the salt 9 as a stable,

Scheme 2.

Scheme 3.

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M. Gomez-Gallego et al. / Tetrahedron 56 (2000) 4893±4905

4895

Table 1.

Complex

Reagent/Solvent

13 Yield^a(%)

14 Yield^a(%)

13/14^b

12 (MCr)

15 (MW)

NaBH₄/EtOH

NaBD₄/EtOH

NaBH₄/CD₃OD

NaBH₄/EtOH

13a R¹R²H (56)

13b R¹D R²H (59)

13c R¹H R²D (59)

13a R¹R²H

14a R¹H (12)

14b R¹D (12)

14b R¹D (16)

14a R¹H

80:20

85:15

83:17

89:11

^aIn pure, isolated compound.

^bDetermined by integration of well resolved signals in the reaction crude prior to any puri®cation. The value given is the average of three separate runs.

crystalline solid.²²This compound forms unstable carbene

complex 10 upon acid treatment. The HLi reduction of

[(CO)₅MoC(OMe)SiMePh₂] to [(CO)₅MoC(SiMePh₂)H],

was observed as a competitive process during the addition

of BuLi to the alkoxy carbene.²³1,4-Dihydropyridines

reduced complexes [(CO)₅MC(OEt)Me] (MCr, W) to

ylides 11, again through the initial addition of an hydride

to the carbene carbon atom.²⁴It should be noted that all of

these results are fully compatible with those expected for the

addition of simple nucleophiles to esters. Finally, not many

data about the reactivity of hydrides and metal carbene

complexes other than group 6, can be found in the literature,

but they follow essentially the same patterns previously

mentioned (Scheme 3).²⁵

thus, we undertook the task of determining the possible par-

ticipation of the metal in the process. Complex 12 was

reduced using NaBD₄/EtOH and monodeuterated

compounds 13b and 14b were obtained. On the other

hand, the reaction with CD₃OD as solvent, yielded mono-

deuterated 13c and 14b (in this case, quenching was by

addition of D₂O). A control experiment was done by submit-

ting ethyl cinnamate to analogous reaction conditions,

yielding unreacted material with only traces of ethyl 3-

phenylpropanoate, even after prolonged reaction times.

Changing the metal in the a,b-unsaturated complex does

not make any relevant difference. So, the reduction of tung-

sten carbene 15 under the same conditions yielded a mixture

of ethers 13a and 14a in an 89:11 ratio (Table 1).

These results clearly pointed to an involvement of the

M(CO)₅in the reduction process. Hydride addition takes

place on the carbene carbon atom to form intermediate 16,

from which the formation of E-14a is immediate. An alter-

native evolution for 16 could be the 1,3-migration of the

M(CO)₅moiety, that would lead to complex 17. This is the

key feature of the process and explains the formation of

Z-13a as the main reaction product. Both pathways are

consistent with the deuteration experiments. The incorpora-

tion of deuterium from the reagent takes place during the

hydride addition step, whereas in the CD₃OD experiment,

the deuterium transfer occurs during the protonation step

(Scheme 4).

Results and Discussion

Reduction of alkoxy a,b-unsaturated (group 6) carbene

complexes

We started this study by reducing a cooled (2208C) solution

of complex 12 in EtOH with the equimolar amount of

NaBH₄. This reaction yielded, after oxidation, a mixture

of Z-vinyl ether 13a and E-allyl ether 14a in a 80:20 ratio.

The reaction was almost quantitative and except for a little

oxidation product (the corresponding organic ester)

obtained in some cases, no other by-products could be

detected in the reaction mixtures. It was obvious that

compounds 13a and 14a could not be derived from the

standard hydride addition-alkoxide elimination sequence,²²

Extension of this reaction to a series of p-substituted penta-

carbonyl[(ethoxy)(styryl)carbene]chromium(0) complexes

Scheme 4.

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4896

Table 2.

Complex

19 Yield^a(%)

20 Yield^a(%)

19/20^b

18a XMe

18b XOMe

18c XCl

45

48

42

53

17

14

9

80:20

87:13

90:10

100:0^c

18d XCN

±

^aIn pure, isolated compound.

^bDetermined by integration of well resolved signals in the reaction crude prior to any puri®cation.

^c8% of Ethyl p-cyanocinnamate was also obtained.

18 was searched next. Exception made of 18d, mixtures of

ethers 19 and 20 were obtained. The reaction times

remained essentially unaltered and neither notable modi®-

cations in the structure, nor in the stereochemistry of the

reaction products were observed. However, a steady

increase of the ratio of vinyl ether 19 was observed with

the electron withdrawing nature of the substituents. In

fact, the reaction of the cyano-substituted complex 18d

exclusively gave vinyl ether 19d (Table 2).

labeling experiments were carried out. Reduction of

complex 21a with NaBD₄gave the corresponding mono-

deuterated vinyl ether 22b together with the trideuterated

alcohol 23b, while when the reaction was carried out with

NaBH₄/CD₃OD, monodeuterated vinyl ether 22c and mono-

deuterated alcohol 23c were obtained (Table 3).

The major reduction product, vinyl ether 22a, should arise

from the initial 1,2-hydride addition to the carbene complex

21a, followed by 1,3-allylic migration of the Cr(CO)₅frag-

ment and subsequent protonation, as is proposed in Scheme

5. Again, the key feature of the process is the allylic

rearrangement of the metal fragment and this is supported

by the deuteration experiments, in which the reagent trans-

fers the labeling during the reduction process and the

solvent in the protonation step. The formation of the second-

ary product, the alcohol 23a, could be justi®ed by alkoxide

elimination²²on intermediate 24, that would lead to unstable

carbene complex 25. By hydrolysis, this complex would be

transformed into the corresponding aldehyde,²⁶but only

E-3-(2-N-methylpyrrolyl)-2-propenal has been detected

during the NaBH₄reduction of the pyrrole substituted

complex 21c, the less reactive of the series. On the other

hand, the complete reduction of an a,b-unsaturated

aldehyde under these conditions does not take place,²⁷there-

fore it could be considered that saturated alcohol 23a is

a,b-Unsaturated complexes 21 having heterocyclic sub-

stituents were also studied. In these cases the presence of

an electron rich aromatic ring may alter the 1,3-allylic

migration step. Interestingly, a clear difference in reactivity

was found depending on the nature of the heterocycle. The

most reactive towards hydride reduction was the furyl

complex 21a that was instantaneously reduced with

NaBH₄in EtOH at 2788C, followed by the thiophene

substituted complex 21b whose reduction required several

hours at the same temperature. Finally, the reduction of

pyrrole substituted complex 21c was afforded at 2208C.

In the case of furyl substituted complex 21a the analysis

of the reaction crude showed a 80:20 mixture of the

expected Z-vinyl ether 22a together with a new compound

that was identi®ed as the saturated alcohol 23a. In order to

establish the outcome of the reaction in this case, deuterium

Table 3.

Complex

Reagent/Solvent

22 Yield^a(%)

23 Yield^a(%)

22/23^b

21a (XO)

21b (XS)

21c (XNMe)

NaBH₄/EtOH

NaBD₄/EtOH

NaBH₄/CD₃OD

NaBH₄/EtOH

22a R¹R²H (55)

22b R¹D R²H (50)

22c R¹H R²D (53)

22d R¹R²H (77)

22e R¹R²H (45)

23a R¹R²H (13)

80:20

83:17

85:15

23b R¹D R²H (12)

23c R¹H R²D (11)

±

100:0

c

^aIn pure, isolated compound.

^bDetermined by integration of well resolved signals in the reaction crude prior to any puri®cation. The value given is the average of three separate runs.

^cIn this case, a 80:20 mixture of 22e and E-3-(2-N-methylpyrrolyl)-2-propenal was obtained.

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4897

Scheme 5.

formed after overreduction and hydrolysis of 25. The

behavior of carbene complexes like 25 towards nucleophiles

is currently under study in our laboratories. Thiophene

derivative 21b yields vinyl ether 22d as the sole reaction

product, indicating that the replacement of an oxygen by a

sulfur atom bene®ts the 1,3-M(CO)₅migration and perhaps,

suggesting an extra stabilization of intermediate 26 by coor-

dination of the metal and the sulfur of the thiophene ring.

nation to the ethoxy group on the same face of the allylic

grouping, where H²is being delivered, may force the

chromium moiety to migrate through the opposite face of

the 3-carbon unit. This possibility has to be discarded

because the reduction of complex 12 with Me₄NBH₄gave

the expected mixture 13a/14a and again, 13a was obtained

with Z-stereochemistry exclusively. The participation of an

h³-allyl metal intermediate like 27 (MCr, W), in the

1,3-allylic rearrangement is suggested by the results

obtained by effecting the reduction process under a CO

atmosphere (Scheme 6).

Some features of the reactions previously discussed warrant

additional debate. First, the exquisite E/Z selectivity

observed on the newly formed CvC double bond of vinyl

ethers 13, 19 and 22, arising from the 1,3-migration path.

Second, the participation of an h³-allyl chromium inter-

mediate in these processes.²⁸The selectivity of the process

could be consequence of the chelation of the basic alkoxy

oxygen to the metal center, once the 1,3-rearrangement has

occurred. This chelation should impose the relative dispo-

sition of the metal and alkoxyde groups around the CvC

double bond and hence the observed stereochemistry. An

alternate explanation could derive from the participation of

the sodium cation in the reduction process. In fact, assuming

that through this paper we have depicted the more stable

conformer of the different alkenyl complexes, Na¹coordi-

It is clear that the migration of the M(CO)₅moiety from 16

to 17 should involve a decarbonylation-carbonylation

process that would be hampered under CO atmosphere.

When the reduction of complex 12 was carried out in a

CO-saturated EtOH solution, maintaining a positive CO

pressure during the reaction, the ratio of products 13a/14a

decreased from 4:1 to 2.7:1, while the stereochemistry of

13a remained unchanged. It was also observed that the

reactions were dirtier when CO was present, and variable

amounts of cinnamaldehyde were obtained. Clearly, a

partial inhibition of the 1,3-rearrangement process occurs

under such conditions, although the presence of CO does

Scheme 6.

Scheme 7.

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4898

Table 4.

Reagent/Solvent

33

34

33/34^a

NaBH₄/EtOH

NaBD₄/EtOH

NaBH₄/CD₃OD

33a R¹R²H

33c R¹H R²D

34a R¹H

34b R¹D

3:2

33b R¹D R²H

^aDetermined by integration of well resolved signals in the reaction mixtures.

not interfere with the hypothetical chelation of the metal by

the alkoxy group, which, as we propose, de®nes the vinyl

ether stereochemistry.

results (Scheme 8). Intermediate 35 was formed as a result

of the initial 1,2-addition of hydride to the aminocarbene 32.

1,3-Allylic migration of the metallic moiety in such species

yields the new complex 36 that after protonation, forms

enamine 37. The reduction of enamines by NaBH₄is a

known process²⁹and in this case explains the formation of

the totally saturated amine 33a as the main reaction product,

although all the attempts to detect the enamine 37 in the

reaction mixtures have been fruitless.

To complete the study, carbene complexes 28 and 30 having

an additional conjugated double bond, were submitted to

reaction with NaBH₄. 1,3-Allylic migration also occurred

in the case of biscarbene 28, that exclusively gave Z-di-

vinylether 29. In the case of the conjugated complex 30 it

could be expected a 1,5-M(CO)₅long range rearrangement.

However, only dienyl ether 31, resulting from the usual

1,3-allylic migration process, was obtained (Scheme 7).

Reduction of alkynyl (group 6) carbene complexes

Pentacarbonyl[(ethoxy)(phenylethynyl)carbene]chromium

(0) 38 was also reactive towards NaBH₄at 2208C, yielding

in a few minutes ether E-14a as the sole reaction product.

With NaBD₄/EtOH dideuterated derivative E-14c was

obtained. Finally, when CD₃OD was the solvent, the

reaction yielded dideuterated compound E-14d. Again the

reactions were almost quantitative and the results are

summarized on Table 5. The same result was obtained start-

ing from tungsten alkynyl carbene complex 39, that yielded

E-14a as the sole reaction product. To complete these

experiments, the NaBH₄/EtOH reduction of the analogous

organic ester, ethyl phenylpropiolate was checked, yielding

50% of a 2:1 mixture of E/Z-ethyl cinnamates and 50% of

unreacted starting material, after 48 h of reaction.

Reduction of a,b-unsaturated aminochromium carbene

complexes

a,b-Unsaturated aminochromium carbene complex 32 was

submitted to NaBH₄reduction. Due to the lower reactivity

of aminocarbenes towards nucleophiles the reaction

required room temperature to occur, leading to an unsepa-

rable 3:2 mixture of amines 33a and 34a. The formation of

totally reduced amine 33a resembles the results previously

obtained with furyl substituted complex 21a, although in

this case, compound 33a is the main reaction product.

Again deuteration experiments were carried out and the

results are summarized on Table 4.

A mechanism analogous to the proposed for the reduction of

alkenyl alkoxycarbenes, could explain the experimental

Again, it is dif®cult to understand the results obtained in the

reduction of complexes 38 and 39 without considering the

Scheme 8.

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4899

Table 5.

from these experiments is that the second hydride transfer

has to occur prior to the protonation step. The negative

charge in the allenyl complex 41 should be fully delocalized

across the coordination sphere of chromium, which renders

the anionic complex slightly basic (Scheme 9).

In conclusion, in this paper we have described an unprece-

dent 1,3-migration of a M(CO)₅fragment in the NaBH₄

reduction of a,b-unsaturated (group 6) metal carbene

complexes (MCr, W). We propose the participation of

an h³-allyl chromium intermediate in the process, as it is

suggested by the partial inhibition of the metal migration

when the reduction is carried out under CO atmosphere. The

exquisite E/Z-selectivity of the products obtained is also

determined during the rearrangement, possibly by chelation

of the metal center and the alkoxy group once the

1,3-M(CO)₅migration has occurred. The process is general

and can be observed either for styryl-type alkoxy and

aminocarbenes, or for propargyl alkoxy carbenes. The

proposed mechanisms are supported by the deuterium

labeling experiments and these reduction reactions can be

applied to the obtention of selectively deuterated Z-vinyl

and E-allyl ethers and amines.

Complex

Reagent/Solvent

14 Yield^a(%)

38 (MCr)

39 (MW)

NaBH₄/EtOH

NaBD₄/EtOH

NaBH₄/CD₃OD

NaBH₄/EtOH

14a R¹R²H (74)

14c R¹D R²H (74)

14d R¹H R²D (71)

14a R¹R²H (61)

^aIn pure isolated compound.

active participation of the metal in the process. The

1,3-migration of the M(CO)₅fragment in the NaBH₄

reduction processes seems to be a general behavior for

a,b-unsaturated complexes of different structures.

The initial 1,2-addition of hydride on the carbene carbon

atom of 38 and 39 would lead to intermediate 40. The ®rst

incorporation of deuterium occurs at this point when NaBD₄

is used as reagent. Alkynyl intermediate 40 may evolve to

allenyl complex 41³⁰by a 1,3-propargylic rearrangement.²⁰

The isolation of ethers 14 from the intermediate 41 requires

the addition of a new hydride ion at the end of the allenyl

system and justi®es the incorporation of the second

deuterium atom in 14c. This is remarkable, since the

addition of nucleophiles to allenes usually takes place at

the central allenic carbon.³¹Finally, diprotonation of

dianion 42 would yield the allyl ethers 14 and explains the

formation of dideuterated 14d when CD₃OD was used as

solvent. An alternative interpretation could be the proto-

nation of allenyl intermediate 41 before the addition of a

new hydride, to form free allene 43. The subsequent reduc-

tion of this compound would also lead to allyl ethers 14 in a

pathway fully compatible with the observed deuteration

pattern. To exclude this possibility, allene 43 was prepared

from 1-ethoxy-3-phenyl-2-propyne and BuLi,³²and treated

at 2208C with NaBH₄in EtOH. The compound was

recovered unchanged after several hours of reaction. This

lack of reactivity of allenes towards NaBH₄is in agreement

with previous literature reports.³³Finally, the reduction of

complex 38 was carried out with NaBH₄in anhydrous THF.

The reaction needed higher temperatures to occur but the

sole reaction product was again 14a. Under this conditions,

protonation of allenyl chromium intermediate 41 should be

precluded and hence, its evolution to the ®nal products

thorough a free allene may be discarded. The conclusion

Experimental

General procedures

¹H NMR and ¹³C NMR spectra were obtained in CDCl₃, on

a Varian XL-300S (299.94 MHz for ¹H and 75.43 MHz for

¹³C), a Bruker 250-AC (250.13 MHz for ¹H and 62.90 MHz

1

for ¹³C) or a Bruker 200-AC (200.132 MHz for H and

50.03 MHz for ¹³C) spectrometers. Chemical shifts are

given in ppm relative to TMS (¹H, 0.0 ppm), or CDCl₃

(¹³C, 76.9 ppm). IR spectra were recorded on a Perkin±

Elmer 781 spectrometer. Mass spectra were carried out

on a GC±MS HP-5989 (70 eV) mass spectrometer using

methanol as solvent. The degree of deuteration was deter-

minated by NMR and mass spectrometry (EI, 70 eV).

Flame-dried glassware and standard Schlenck techniques

were used for all the reactions. Merck silica-gel (230±

400 mesh) was used as the stationary phase for puri®cation

of crude reaction mixtures by ¯ash chromatography. TLC

analyses were performed using silica plates (Kiesegel 60F-

254) and were visualized using UV (254 nm) or iodine. All

commercially available compounds were used without

further puri®cation. Carbene±chromiun complexes 12,³⁴

15,³⁴21a,³⁴21b,³⁴21c,³⁵28,³⁴30,³⁴32,³⁶38³⁷and 39³⁷

Scheme 9.

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4900

were prepared according to literature methods. All new

compounds gave satisfactory microanalytical data.

Hydride reduction: general procedure

A suspension of NaBH₄in absolute EtOH at 2208C, was

placed in a ¯ame-dried airless ¯ask containing a magnetic

stirring bar, degassed by evacuation/back-®ll with argon

(3x). Then, a solution of the carbene in EtOH was added

by syringe at 2208C and the mixture was stirred at this

temperature until the complete disappearance of the starting

material (checked by TLC). After the addition of water at

2208C, the solvent was removed under reduced pressure

and the mixture dissolved in AcOEt, ®ltered through Celite,

diluted with one volume of hexane, and air oxidized under

sunlight. Then the solvent was removed in vacuo and the

residue was puri®ed by ¯ash column chromatography. For

the deuterium experiments the same procedure was

followed, using NaBD₄in EtOH or NaBH₄in CD₃OD as

solvent (in these cases, the reaction was quenched by

addition of D₂O instead of water).

Synthesis of styryl alkoxychromium(0)carbenes. To a

solution of pentacarbonyl [(ethoxy)(methyl)carbene]-

chromium(0) 44³⁸(5.0 mmol) and the aldehyde (5.0

mmol) in anhydrous Et₂O, were added 20 mmol of Et₃N.

Then, 15 mmol of TMSCl were added dropwise at room

temperature. The mixture was stirred until disappearance

of the starting material (checked by TLC). The solvent

was removed under reduced pressure and the product

puri®ed by ¯ash chromatography on silica gel.

Pentacarbonyl[(ethoxy)(p-tolylethenyl)carbene]chromium-

(0) (18a): From 1.32 g (5.0 mmol) of 44, 0.6 g (5.0 mmol)

of p-methylbenzaldehyde, 2.8 mL (20 mmol) of Et₃N and

2.3 mL (15.0 mmol) of TMSCl. After 48 h of reaction and

¯ash chromatography (hexane), 18a (1.33 g, 73%) was

1

obtained as a black crystalline solid. H NMR d1.63 (t,

3H, J7.0 Hz), 2.32 (s, 3H), 5.05 (q, 2H, J7.0 Hz),

6.90 (d, 1H, J15.4 Hz), 7.15 (d, 2H, J7.8 Hz), 7.44

(d, 2H, J7.8 Hz), 7.84 (d, 1H, J15.4 Hz); ¹³C NMR

d330.4, 224.2, 216.7, 141.4, 138.7, 131.4, 130.2,

129.7, 129.3, 76.9, 21.4, 15.0; IR (CHCl₃): 2056, 1940,

Reduction of pentacarbonyl[(ethoxy)(phenylethenyl)-

carbene]chromium(0) (12) with NaBH₄in EtOH. From

350 mg (0.99 mmol) of 12 and 37.4 mg (0.99 mmol) of

NaBH₄in absolute EtOH at 2208C. After 10 min of

reaction and further oxidation of the reaction mixture, a

colorless oil (120 mg) was obtained. The ¹H NMR spectrum

of the reaction crude showed a 80:20 mixture of ethers 13a

and 14a. The products were separated by ¯ash column chro-

matography (hexane/CH₂Cl₂8:1 to AcOEt). Z-1-Ethoxy-3-

phenyl-1-propene (13a), (90 mg, 56%) was obtained as a

1710 cm²¹

.

Pentacarbonyl[(ethoxy)(p-methoxyphenylethenyl)carbene]-

chromium(0) (18b): From 1.32 g (5.0 mmol) of 44 0.68 g

(5.0 mmol) of p-methoxybenzaldehyde, 2.8 mL (20.0

mmol) of Et₃N and 2.3 mL (15 mmol) of TMSCl. After

64 h of reaction and ¯ash chromatography (hexane/

CH₂Cl₂8:1), 18b (1.24 g, 65%) was obtained as a red

1

colorless oil. H NMR d1.22 (t, 3H, J6.9 Hz), 3.37 (d,

2H, J7.2 Hz), 3.77 (q, 2H, J6.9 Hz), 4.50 (dt, 1H, J₁

7.2 Hz, J₂6.0 Hz), 6.00 (d, 1H, J6.0 Hz), 7.11±7.24 (m,

5H); ¹³C NMR d145.2, 141.9, 128.3, 125.7, 105.5, 67.7,

30.2, 15.4; IR (®lm): 1662 (CvC), 1495, 1452 cm²¹; MS:

m/z (%): 162 (M¹, 78), 133 (42), 118 (18), 117 (23), 116

(15), 105 (100), 103 (23), 91 (38), 79 (28), 78 (28), 77 (39).

E-3-Ethoxy-1-phenyl-1-propene (14a), (20 mg, 12%) was

1

crystalline solid. H NMR d1.61 (t, 3H, J7.0 Hz), 3.79

(s, 3H), 5.02 (q, 2H, J7.0 Hz), 6.86 (d, 2H, J8.6 Hz),

6.93 (d, 1H, J15.2 Hz), 7.49 (d, 2H, J8.6 Hz), 7.77 (d,

1H, J15.2 Hz); ¹³C NMR d328.7, 224.2, 216.8, 162.2,

137.7, 131.2, 130.8, 126.7, 114.5, 75.6, 55.3, 15.0; IR

(CHCl₃): 2056, 1940, 1711 cm²¹

.

1

obtained as a colorless oil. H NMR d1.18 (t, 3H, J

6.9 Hz), 3.48 (q, 2H, J6.9 Hz), 4.07 (d, 2H, J6.0 Hz),

6.21 (dt, 1H, J₁15.9 Hz, J₂6.0 Hz), 6.54 (d, 1H, J

15.9 Hz), 7.12±7.33 (m, 5H); ¹³C NMR d136.7, 132.0,

128.4, 127.5, 126.3, 126.2, 71.2, 65.7, 15.3; IR (®lm):

1653 (CvC), 1495, 1448 cm²¹; MS: m/z (%): 162 (M¹,

41), 133 (39), 118 (26), 117 (51), 116 (25), 115 (58), 105

(100), 103 (22), 91 (36), 79 (26).

Pentacarbonyl[(p-chlorophenylethenyl)(ethoxy)carbene]-

chromium(0) (18c): From 1.32 g (5.0 mmol) of 44, 0.7 g

(5.0 mmol) of p-chlorobenzaldehyde, 2.8 mL (20.0 mmol)

of Et₃N and 2.3 mL (15.0 mmol) of TMSCl. After 66 h of

reaction and ¯ash chromatography (hexane), 18c (1.01 g,

1

52%) was obtained, as a black crystalline solid. H NMR

d1.55 (t, 3H, J7.0 Hz), 4.98 (q, 2H, J7.0 Hz), 6.70 (d,

1H, J15.4 Hz), 7.22 (d, 2H, J8.4 Hz), 7.36 (d, 2H,

J8.4 Hz), 7.74 (d, 1H, J15.4 Hz); ¹³C NMR d331.4,

224.2, 216.6, 139.7, 136.7, 133.0, 130.3, 129.3, 127.6, 76.3,

Reduction of pentacarbonyl[(ethoxy)(phenylethenyl)-

carbene]chromium(0) (12) with NaBD₄in EtOH. From

200 mg (0.57 mmol) of 12 and 24 mg (0.57 mmol) of

NaBD₄in absolute EtOH at 2208C. After 10 min of reac-

tion and further oxidation of the reaction crude, a colorless

15.1; IR (CHCl₃): 2057, 1942, 1711 cm²¹

.

1

Pentacarbonyl[(p-cyanophenylethenyl)(ethoxy)carbene]-

chromium(0) (18d): From 1.32 g (5.0 mmol) of 44, 0.68 g

(5.0 mmol) of p-cyanobenzaldehyde, 2.8 mL (20.0 mmol)

of Et₃N and 2.3 mL (15 mmol) of TMSCl. After 96 h of

reaction and ¯ash chromatography (hexane/CH₂Cl₂8:1),

18d (0.9 5g, 50%) was obtained as a green crystalline

oil (82 mg) was obtained. The H NMR spectrum of the

reaction crude showed a 85:15 mixture of ethers 13b and

14b. The products were separated by ¯ash column chroma-

tography (hexane/CH₂Cl₂8:1 to AcOEt). Z-1-Deutero-1-

ethoxy-3-phenyl-1-propene (13b), (55 mg, 59%) was

1

obtained as a colorless oil. H NMR d1.20 (t, 3H, J

1

solid. H NMR d1.56 (t, 3H, J7.0 Hz), 5.02 (q, 2H,

7.0 Hz), 3.36 (d, 2H, J7.4 Hz), 3.74 (q, 2H, J 7.0 Hz),

4.49 (t, 1H, J7.4 Hz), 7.06±7.24 (m, 5H); ¹³C NMR d

145.0 (t, J_C±D25.6 Hz), 142.0, 128.3, 125.7, 105.4, 67.7,

30.3, 15.4; IR (®lm) 1683(CvC), 1506, 1473 cm²¹; MS: m/

z (%): 163 (M¹, 100), 134 (44), 118 (28), 116 (24), 106 (76),

91 (22), 78 (23). E-3-deutero-3-ethoxy-1-phenyl-1-propene

J7.0 Hz), 6.62 (d, 1H, J15.4 Hz), 7.51 (broad s, 4H),

7.78 (d, 1H, J15.4 Hz); ¹³C NMR d332.4, 224.0,

216.1, 141.1, 139.1, 132.4, 129.2, 124.9, 118.2, 113.1,

75.6, 15.0; IR (CHCl₃): 2230 (CN), 2058, 1946,

1711 cm²¹

.

Â

M. Gomez-Gallego et al. / Tetrahedron 56 (2000) 4893±4905

4901

1

(14b), (11 mg, 12%) was obtained as a colorless oil. H

NMR d1.21 (t, 3H, J7.0 Hz), 3.49 (q, 2H, J7.0 Hz),

4.10 (broad d, 1H, J6.0 Hz), 6.23 (dd, 1H, J₁16.0 Hz,

J₂6.0 Hz), 6.54 (d, 1H, J16.0 Hz), 7.01±7.24 (m, 5H);

¹³C NMR d136.6, 132.1, 128.4, 127.4, 126.3, 126.1, 70.6

(t, J_C±D21.7 Hz), 65.4, 15.0; IR (®lm): 1652(CvC), 1506,

1448 cm²¹; MS: m/z (%): 163 (M¹, 77), 162 (14), 134 (52),

118 (63), 106 (100), 92 (22), 78 (18).

200 mg (0.55 mmol) of 18a and 20.8 mg (0.55 mmol) of

NaBH₄in absolute EtOH at 2208C. After 10 min of

reaction and further oxidation of the reaction mixture, a

colorless oil (109 mg) was obtained. The ¹H NMR spectrum

of the reaction crude showed a 80:20 mixture of 19a and

20a. The products were separated by ¯ash column chroma-

tography (hexane/CH₂Cl₂4:1 to AcOEt). Z-1-Ethoxy-3-

(p-tolyl)-1-propene (19a), (43 mg, 45%) was obtained as a

1

colorless oil. H NMR d1.20 (t, 3H, J7.1 Hz), 2.24 (s,

Reduction of pentacarbonyl[(ethoxy)(phenylethenyl)-

carbene]chromium(0) (12) with NaBH₄in CD₃OD.

From 206 mg (0.56 mmol) of 12 and 22 mg (0.56 mmol)

of NaBH₄in 10 mL of CD₃OD at 2208C. After 10 min of

reaction and further oxidation of the reaction mixture, a

colorless oil (90 mg) was obtained. The ¹H NMR spectrum

of the reaction crude showed a 83:17 mixture of ethers 13c

and 14b. The products were separated by ¯ash column

chromatography (hexane/CH₂Cl₂8:1 to AcOEt). Z-3-

Deutero-1-ethoxy-3-phenyl-1-propene (13c) (51 mg, 59%)

3H), 3.32 (d, 2H, J7.4 Hz), 3.76 (q, 2H, J7.1 Hz), 4.47

(td, 1H, J₁7.4 Hz, J₂6.3 Hz), 5.97 (dt, 1H, J₁6.3 Hz,

J₂1.45 Hz), 7.00 (d, 2H, J8.6 Hz), 7.05 (d, 2H, J

8.6 Hz); ¹³C NMR d145.2, 139.0, 135.2, 129.1, 128.3,

106.0, 67.8, 29.9, 21.1, 15.5; IR (CHCl₃): 1685 (CvC),

1618, 1610, 1515, 1419 cm²¹. E-3-Ethoxy-1-(p-tolyl)-1-

propene (20a), (17 mg, 17%) was obtained as a colorless

1

oil. H NMR d1.18 (t, 3H, J7.0 Hz), 2.26 (s, 3H), 3.48

(q, 2H, J7.0 Hz), 4.06 (dd, 2H, J₁6.1 Hz, J₂1.2 Hz),

6.18 (dt, 1H, J₁15.9 Hz, J₂6.1 Hz), 6.51 (d, 1H, J

15.9 Hz), 7.05 (d, 2H, J8.3 Hz), 7.22 (d, 2H, J8.3 Hz);

¹³C NMR d137.5, 134.1, 132.3, 129.3, 126.4, 125.3, 71.4,

1

was obtained as a colorless oil. H NMR d1.21 (t, 3H,

J7.0 Hz), 3.35 (broad d, 1H, J5.5 Hz), 3.74 (q, 2H,

J7.0 Hz), 4.49 (t, 1H, J6.7 Hz), 5.90 (dd, 1H, J₁

6.2 Hz, J₂1.1 Hz), 6.91±7.23 (m, 5H); ¹³C NMR d

65.7, 21.2, 15.3; IR (CHCl₃) 1514, 1465 cm²¹

.

145.2, 141.8, 128.3, 125.6, 105.4, 67.6, 29.9 (t, J_C±D

Reduction of pentacarbonyl[(ethoxy)(p-methoxyphenyl-

ethenyl)carbene]chromium(0) (18b) with NaBH₄in

EtOH. From 250 mg (0.66 mmol) of 18b and 25 mg

(0.66 mmol) of NaBH₄in absolute EtOH at 2208C. After

10 min of reaction and further oxidation of the reaction

20 Hz), 15.3; IR (®lm): 1662 (CvC), 1495, 1448 cm²¹

;

MS: m/z (%): 163 (M¹, 75), 134 (39), 119 (19), 118 (24),

106 (100), 104 (20), 92 (36), 79 (20), 78 (39), 77 (26). E-3-

Deutero-3-ethoxy-1-phenyl-1-propene (14b) (14 mg, 16%)

was obtained as a colorless oil.

1

mixture, a colorless oil (120 mg) was obtained. The H

NMR spectrum of the reaction crude showed a 87:13

mixture of 19b and 20b. The products were separated by

¯ash column chromatography (hexane/CH₂Cl₂4:1 to

AcOEt). Z-1-ethoxy-3-(p-methoxyphenyl)-1-propene (19b)

Reduction of pentacarbonyl[(ethoxy)(phenylethenyl)-

carbene]tungsten(0) (15) with NaBH₄in EtOH. From

200 mg (0.41 mmol) of 15 and 15.62 mg (0.41 mmol) of

NaBH₄in absolute EtOH at 2208C. After 1 h of reaction and

further oxidation of the reaction mixture, a yellow oil (140

1

(61 mg, 48%) was obtained as a colorless oil. H NMR

d1.20 (t, 3H, J7.1 Hz), 3.30 (d, 2H, J7.4 Hz), 3.71

(s, 3H), 3.76 (q, 2H, J7.1 Hz), 4.47 (q, 1H, J7.4 Hz),

5.99 (d, 1H, J6.3 Hz), 6.75 (d, 2H, J8.5 Hz), 7.07 (d,

2H, J8.5 Hz); ¹³C NMR d157.8, 145.1, 134.1, 129.3,

113.9, 106.1, 67.8, 55.4, 29.4, 15.4; IR (CHCl₃): 1662

(CvC), 1608, 1510, 1245 cm²¹. E-3-Ethoxy-1-(p-methoxy-

phenyl)-1-propene (20b), (17 mg, 13%) was obtained as a

1

mg) was obtained. The H NMR spectrum of the reaction

crude showed the presence of 13a and 14a in a 89:11 ratio.

Reduction of pentacarbonyl[(ethoxy)(phenylethenyl)-

carbene]chromium(0) (12) with Me₄NBH₄in EtOH.

From 250 mg (0.71 mmol) of 12 and 63.2 mg (0.71 mmol)

of Me₄NBH₄in absolute EtOH at 08C. After 10 min of

reaction and further oxidation of the reaction mixture, a

colorless oil (85 mg) was obtained. The ¹H NMR spectrum

of the reaction crude showed the presence of the isomers

13a and 14a in a 88:12 ratio.

1

colorless oil. H NMR d1.17 (t, 3H, J7.0 Hz), 3.47 (q,

2H, J7.0 Hz), 3.77 (s, 3H), 4.05 (d, 2H, J6.1 Hz), 6.10

(dt, 1H, J₁16.1 Hz, J₂6.1 Hz), 6.48 (d, 1H, J16.1 Hz),

6.83 (d, 2H, J8.8 Hz), 7.21 (d, 2H, J8.8 Hz); ¹³C NMR

d159.3, 144.3, 132.0, 127.7, 124.1, 114.0, 71.5, 65.6,

55.3, 15.3; IR (CHCl₃): 1606 (CvC), 1512, 1249 cm²¹

.

Reduction of pentacarbonyl[(ethoxy)(phenylethenyl)-

carbene]chromium(0) (12) under CO atmosphere with

NaBH₄in EtOH. The experiments were carried out by

bubbling a CO stream through a solution of 100 mg

(0.28 mmol) of 12 in absolute EtOH at 2208C, for about

30 min before the addition of 10.6 mg (0.28 mmol) of

NaBH₄. A CO ®lled balloon was placed at the top of the

¯ask to maintain the CO atmosphere during the reduction

process. After 10 min of reaction and further oxidation of

the reaction mixture, 85 mg of a colorless oil were obtained.

Reduction of pentacarbonyl[(p-chlorophenylethenyl)

(ethoxy)carbene]chromium(0) (18c) with NaBH₄in

EtOH. From 250 mg (0.52 mmol) of 18c and 19.6 mg

(0.52 mmol) of NaBH₄in absolute EtOH at 2208C. After

10 min of reaction and further oxidation of the reaction

mixture, a colorless oil (84 mg) was obtained. The ¹H

NMR spectrum of the reaction crude showed the presence

of the isomers 19c and 20c in a ratio of 90:10. The products

were separated by ¯ash column chromatography (hexane/

CH₂Cl₂4:1 to AcOEt). Z-1-Ethoxy-3-(p-chlorophenyl)-1-

propene (19c), (40 mg, 42%) was obtained as a colorless

1

The H NMR spectrum of the reaction crude showed the

presence of cinamaldehyde together with a mixture of 13a

and 14b in a 2.7:1 ratio.

1

oil. H NMR d1.20 (t, 3H, J7.1 Hz), 3.31 (dd, 2H,

J₁7.5 Hz, J₂1.34 Hz), 3.76 (q, 2H, J7.1 Hz), 4.44 (td,

1H, J₁7.5 Hz, J₂6.1 Hz), 5.99 (d, 1H, J6.1 Hz), 7.07

(d, 2H, J8.4 Hz), 7.16 (d, 2H, J8.4 Hz); ¹³C NMR

Reduction of pentacarbonyl[(ethoxy)(p-tolylethenyl)car-

bene]chromium(0) (18a) with NaBH₄in EtOH. From

Â

M. Gomez-Gallego et al. / Tetrahedron 56 (2000) 4893±4905

4902

d145.7, 140.5, 131.4, 129.8, 128.4, 105.4, 67.9, 29.7,

15.4; IR (CHCl₃): 1662 (CvC), 1491 cm²¹. E-3-Ethoxy-

1-(p-chlorophenyl)-1-propene (20c), (8 mg, 9%) was

ethoxy-3-(2-furyl)-1-propene (22b) (67 mg, 50%) was

1

obtained as a colorless oil. H NMR d1.19 (t, 3H, J

7.0 Hz), 3.37 (d, 2H, J7.2 Hz), 3.74 (q, 2H, J7.0 Hz),

4.47 (t, 1H, J7.2 Hz), 5.92 (m, 1H), 6.20 (m, 1H), 7.23 (m,

1H); ¹³C NMR d155.4, 141.0 (t, J_C±D26 Hz), 140.7,

110.0, 104.4, 101.4, 67.6, 23.0, 15.1; IR (®lm): 1647

(CvC), 1595, 1506 cm²¹; MS: m/z (%): 153 (M¹, 100),

124 (51), 109 (17), 96 (23), 81 (22), 68 (49). 1,1,2-Tri-

deutero-3-(2-furyl)propanol (23b) (16 mg, 12%) was

1

obtained as a colorless oil. H NMR d1.18 (t, 3H, J

7.0 Hz), 3.48 (q, 2H, J7.0 Hz), 4.06 (d, 2H, J6.0 Hz),

6.21 (dt, 1H, J₁15.9 Hz, J₂6.0 Hz), 6.54 (d, 1H, J

15.9 Hz), 7.29 (d, 2H, J8.6 Hz), 7.38 (d, 2H, J8.6 Hz);

¹³C NMR d143.1, 129.2, 128.7, 127.7, 127.1, 118.9, 71.0,

65.9, 15.2; IR (CHCl₃): 1637 (CvC), 1490 cm²¹

.

1

obtained as a colorless oil. H NMR d1.80 (m, 1H),

Reduction of pentacarbonyl[(p-cyanophenylethenyl)

(ethoxy)carbene]chromium(0) (18d) with NaBH₄in

EtOH. From 200 mg (0.53 mmol) of 18d and 20 mg

(0.53 mmol) of NaBH₄in absolute EtOH at 2208C. After

10 min of reaction and further oxidation of the reaction

2.66 (d, 2H, J8.1 Hz), 5.55 (m, 1H), 6.21 (m, 1H), 7.24

(m, 1H); ¹³C NMR d155.7, 140.8, 110.3, 105.1, 62.1 (m,

CD₂), 31.0 (t, J_C±D19.5 Hz), 24.3; IR (®lm): 3413 (OH)

cm²¹; MS: m/z (%): 129 (M¹, 27), 128 (15), 111 (31), 81

(100), 68 (10).

1

mixture, a colorless oil (119 mg) was obtained. The H

NMR spectrum of the reaction crude showed a 92:8 mixture

of 19d and ethyl p-cyanocinnamate. These products were

separated by ¯ash column chromatography (hexane/CH₂Cl₂

8:1 to AcOEt). Z-1-Ethoxy-3-(p-cyanophenyl)-1-propene

Reduction of pentacarbonyl[(ethoxy)[2-(2-furyl)ethenyl]-

carbene]chromium(0) (21a) with NaBH₄in CD₃OD.

From 300 mg (0.88 mmol) of 21a and 34 mg (0.88 mmol)

of NaBH₄in 10 mL of CD₃OD at 2788C. After 10 min of

reaction and further oxidation of the reaction mixture, a

colorless oil (93 mg) was obtained. The ¹H NMR spectrum

of the reaction crude showed a 85:15 mixture of 22c and

23c. The products were separated by ¯ash column chroma-

tography (hexane/CH₂Cl₂8:1 to AcOEt). Z-3-Deutero-1-

ethoxy-3-(2-furyl)-1-propene (22c) (71 mg, 53%) was

obtained as a colorless oil. ¹H NMR d1.18 (t, 3H,

J7.0 Hz), 3.38 (broad s, 1H), 3.73 (q, 2H, J7.0 Hz),

4.46 (t 1H, J7.31 Hz), 5.92 (m, 1H), 6.00 (dd, 1H, J₁

6.2 Hz, J₂1.47 Hz), 6.20 (m, 1H), 7.22 (m, 1H); ¹³C NMR

d155.4, 146.1, 140.9, 110.2, 104.6, 101.8, 67.9, 22.4 (t,

J_C±D20 Hz), 15.4; IR (®lm): 1662 (CvC), 1595,

1560 cm²¹; MS: m/z (%): 153 (M¹, 100), 124 (52), 109

(15), 96 (66), 82 (19), 68 (54). 3-Deutero-3-(2-furyl)propa-

1

(19d), (53 mg, 54%) was obtained as a colorless oil. H

NMR d1.20 (t, 3H, J7.1 Hz), 3.40 (d, 2H, J7.5 Hz),

3.78 (q, 2H, J7.1 Hz), 4.44 (td, 1H, J₁7.5 Hz, J₂

6.2 Hz), 6.04 (dt, 1H, J₁6.2 Hz, J₂1.34 Hz), 7.25 (d,

2H, J8.3 Hz), 7.48 (d, 2H, J8.3 Hz); ¹³C NMR

d147.6, 146.2, 132.0, 129.0, 119.1, 109.4, 103.2, 67.8,

30.3, 15.2; IR (CHCl₃): 2230 (CN), 1662 (CvC), 1608,

1505 cm²¹

.

Reduction of pentacarbonyl[(ethoxy)[2-(2-furyl)ethenyl]-

carbene]chromium(0) (21a) with NaBH₄in EtOH. From

200 mg (0.58 mmol) of 21a and 22 mg (0.58 mmol) of

NaBH₄in absolute EtOH at 2788C. After 10 min of

reaction and further oxidation of the reaction mixture, a

colorless oil (64 mg) was obtained. The ¹H NMR spectrum

of the reaction crude showed a 80:20 mixture of 22a and

23a. The products were separated by ¯ash column chroma-

tography (hexane/CH₂Cl₂8:1 to AcOEt). Z-1-Ethoxy-3-

(2-furyl)-1-propene (22a), (49 mg, 55%) was obtained as a

1

nol (23c) (12 mg, 11%) was obtained as a colorless oil. H

NMR d1.84 (m, 2H), 2.66 (t, 1H, J6.1 Hz), 3.63 (t, 2H,

J6.1 Hz), 5.95 (m, 1H), 6.22 (m, 1H), 7.24 (m, 1H); ¹³C

NMR d155.5, 140.9, 110.2, 105.0, 62.1, 31.0, 24.3 (t,

J_C±D25 Hz); IR (®lm): 3419 (OH) cm²¹; MS: m/z (%):

127 (M¹, 42), 109 (34), 108 (33), 96 (14), 81 (100), 68 (23).

1

colorless oil. H NMR d1.15 (t, 3H, J7.0 Hz), 3.37 (d,

2H, J7.2 Hz), 3.74 (q, 2H, J7.0 Hz), 4.47 (td, 1H,

J₁7.2 Hz, J₂6.2 Hz), 5.92 (m, 1H), 6.01 (d,t 1H,

J₁6.2 Hz, J₂1.55 Hz), 6.20 (m, 1H), 7.23 (m, 1H); ¹³C

NMR d155.3, 146.0, 140.9, 110.0, 104.5, 101.7, 67.7,

23.1, 15.4; IR (®lm): 1666 (CvC), 1596, 1550 cm²¹; MS:

m/z (%): 152 (M¹, 100), 123 (60), 108 (18), 95 (78), 81 (32),

67 (57). 3-(2-Furyl)propanol (23a), (10 mg, 13%) was

Reduction of pentacarbonyl[(ethoxy)[2-(2-thienyl)ethenyl]-

carbene]chromium(0) (21b) with NaBH₄in EtOH. From

175 mg (0.49 mmol) of 21b and 18.5 mg (0.49 mmol) of

NaBH₄in absolute EtOH at 2788C. After 5 h of reaction

and further oxidation of the reaction mixture, a colorless oil

1

(70 mg) was obtained. The H NMR spectrum of the reac-

1

obtained as a colorless oil. H NMR d1.84 (m, 2H),

tion crude only showed product, 22d. This product was

puri®ed by column chromatography (hexane/CH₂Cl₂4:1).

Z-1-Ethoxy-3-(2-thienyl)-1-propene (22d) (63.1 mg, 77%)

2.67 (t, 2H, J7.4 Hz), 3.62 (t, 2H, J6.2 Hz), 5.95 (m,

1H), 6.22 (m, 1H), 7.24 (m, 1H); ¹³C NMR d155.5,

140.9, 110.2, 105.0, 62.1, 31.0, 24.3; IR (CHCl₃): 3413

(OH) cm²¹; MS: m/z (%): 126 (M¹, 84), 108 (72), 95

(18), 81 (100), 79 (58), 65 (19).

1

was obtained as a colorless oil. H NMR d1.20 (t, 3H,

J7.1 Hz), 3.55 (d, 2H, J7.3 Hz), 3.77 (q, 2H, J

7.1 Hz), 4.54 (td, 1H, J₁7.3 Hz, J₂6.2 Hz), 5.99 (dt,

1H, J₁6.2 Hz, J₂1.22 Hz), 6.74 (m, 1H), 6.84 (m, 1H),

7.03 (m, 1H); ¹³C NMR d145.6, 145.1, 126.7, 123.9,

123.0, 104.8, 67.8, 24.6, 15.3; IR (CHCl₃): 1662 (CvC),

Reduction of pentacarbonyl[(ethoxy)[2-(2-furyl)ethenyl]-

carbene]chromium(0) (21a) with NaBD₄in EtOH. From

300 mg (0.88 mmol) of 21a and 37 mg (0.88 mmol) of

NaBD₄in absolute EtOH at 2788C. After 10 min of

reaction and further oxidation of the reaction mixture, a

colorless oil (86 mg) was obtained. The ¹H NMR spectrum

of the reaction crude showed a 83:17 mixture of 22b and

23b. The products were separated by ¯ash column chroma-

tography (hexane/CH₂Cl₂8:1 to AcOEt). Z-1-Deutero-1-

1438 cm²¹

.

Reduction of pentacarbonyl[(ethoxy)[2-(2-N-methyl-

pyrrolyl)ethenyl]carbene]chromium(0) (21c) with NaBH₄

in EtOH. From 170 mg (0.48 mmol) of 21c and 18.1 mg

(0.48 mmol) of NaBH₄in absolute EtOH at 2208C. After

1 h of reaction and further oxidation of the reaction mixture,

Â

M. Gomez-Gallego et al. / Tetrahedron 56 (2000) 4893±4905

4903

a brown oil (88 mg) was obtained. The ¹H NMR spectrum of

the reaction crude showed a 80:20 mixture of 22e and E-

3-(2-N-methylpyrrolyl)-2-propenal. The products were

separated by ¯ash column chromatography (hexane/

CH₂Cl₂8:1 to AcOEt). Z-1-Ethoxy-3-(2-N-methylpyrro-

lyl)-1-propene (22e) (36 mg, 45%) was obtained as a color-

NMR d2.59 (s, 3H), 3.48 (d, 2H, J7.0 Hz), 6.37 (dt,

1H, J₁15.8 Hz, J₂7.0 Hz), 6.55 (d, 1H, J15.8 Hz),

7.10±7.39 (m, 5H); ¹³C NMR d137.9, 126.7, 128.5,

128.7, 135.9, 120.3, 66.5, 50.8.

Reduction of pentacarbonyl[(1-N,N-dimethylamino)-

(phenylethylene)carbene]chromium(0) (32) with NaBD₄

in EtOH. From 256 mg (0.73 mmol) of 32 and 31 mg

(0.73 mmol) of NaBD₄in absolute EtOH at room tempera-

ture, after 3 h of reaction and further oxidation of the

reaction mixture, a yellow oil (93 mg) was obtained. The

¹H NMR spectrum of the reaction crude showed a 60:40

mixture of 33b and 34b. The separation of these products

was not possible by ¯ash column chromatography or by

distillation. The spectroscopical data are listed from a

pure mixture of both compounds: 1,1-Dideutero-3-phenyl-

1

less oil. H NMR d1.29 (t, 3H, J7.0 Hz), 3.36 (d, 2H,

J7.0 Hz), 3.52 (s, 3H), 3.81 (q, 2H, J7.0 Hz), 4.47 (td,

1H, J₁7.0 Hz, J₂6.0 Hz), 5.87 (m, 1H), 6.02 (dt, 1H,

J₁6.0 Hz, J₂1.4 Hz), 6.03 (m, 1H), 6.52 (m, 1H); ¹³C

NMR d145.0, 132.4, 121.2, 106.4, 105.6, 103.7, 67.7,

33.5, 21.5, 15.3; IR (CHCl₃): 1662 (CvC), 1492 cm²¹

.

E-3-(2-N-methylpyrrolyl)-2-propenal (11 mg, 17%) was

1

obtained as a brown oil. H NMR d3.69 (s, 3H), 6.18

(m, 1H), 6.39 (dd, 1H, J₁15.6 Hz, J₂7.8 Hz), 6.69 (m,

1H), 6.54 (m, 1H), 7.26 (d, 1H, J15.6 Hz), 9.49 (d, 1H,

J7.8 Hz); ¹³C NMR d193.1, 139.8, 136.9, 129.0, 123.6,

1

N,N-dimethylpropanamine (33b), H NMR d1.98 (t, 2H,

114.7, 110.2, 34.6; IR (®lm): 1660 (CHO) cm²¹

.

J7.6 Hz), 2.48 (s, 6H), 2.55 (t, 2H, J7.6 Hz), 7.10±7.38

(m, 5H); ¹³C NMR d140.8, 126.3, 128.4, 128.6, 64.2 (m,

CD₂), 51.3, 33.3, 25.4. E-1-Deutero-N,N-dimethyl-3-

Reduction of decacarbonyl-m-[1,4[phenylenebis(1-ethoxy-

2-propen-3-yl-1-yliden)]]di-chromium(0) (28) with

1

phenyl-2-propenamine (34b), H NMR d2.52 (s, 3H),

NaBH₄in EtOH. From 500 mg (0.8 mmol) of 28 and

60.5 mg (1.6 mmol) of NaBH₄in absolute EtOH at

2208C. After 6 h of reaction and further oxidation of the

reaction mixture, diene 29 (119 mg, 61%) was obtained as a

colorless oil. This product was puri®ed by vacuum distil-

3.47 (d, 1H, J7.0 Hz), 6.37 (dd, 1H, J₁15.9 Hz,

J₂7.0 Hz), 6.55 (d, 1H, J15.9), 7.10±7.38 (m, 5H); ¹³C

NMR d138.0, 135.9, 128.8, 128.5, 126.8, 120.3, 66.2 (t,

J_C±D20 Hz), 50.8.

1

lation. H NMR d1.20 (t, 3H, J7.1 Hz), 3.32 (dd, 2H,

Reduction of pentacarbonyl[(1-N,N-dimethylamino)-

(phenylethylene)carbene]chromium(0) (32) with NaBH₄

in CD₃OD. From 215 mg (0.61 mmol) of 32 and 23 mg

(0.61 mmol) of NaBH₄in 10 mL of CD₃OD at room

temperature, after 18 h of reaction and further oxidation of

the reaction mixture, a yellow oil (72.6 mg) was obtained.

The ¹H NMR spectrum of the reaction crude showed a 60:40

mixture of 33c and 34b. The separation of these products

was not possible by ¯ash column chromatography or distil-

lation. The spectroscopical data are listed from a pure

mixture of both compounds: 2,3-Dideutero-N,N-dimethyl-

J₁7.4 Hz, J₂1.35 Hz), 3.76 (q, 2H, J7.1 Hz), 4.47 (td,

1H, J₁7.4 Hz, J₂6.2 Hz), 5.96 (dt, 1H, J₁6.2 Hz, J₂

1.35 Hz), 7.06 (s, 4H); ¹³C NMR d145.0, 139.1, 128.2,

105.8, 67.6, 29.8, 15.3; IR (®lm): 1662 (CvC), 1510 cm²¹

.

Reduction of pentacarbonyl[(1-ethoxy)(E,E-5-phenyl-

2,4-pentadienylidene)]chromium(0) (30) with NaBH₄in

EtOH. From 200 mg (0.53 mmol) of 30 and 20 mg of

NaBH₄in absolute EtOH at 2788C. After 3 h of reaction

and further oxidation of the reaction mixture, diene 31

(87 mg (60%) was obtained as a colorless oil. This product

1

3-phenylpropanamine (33c), H NMR d1.91±2.01 (m,

1

was puri®ed by vacuum distillation. H NMR d1.20 (t,

1H), 2.49 (s, 7H), 2.71 (d, 2H, J8.7 Hz), 7.10±7.38 (m,

5H); ¹³C NMR d140.8, 128.6, 128.3, 126.3, 64.1, 51.4,

32.9 (t, J_C±D19 Hz), 25.0 (t, J_C±D20 Hz).

3H, J7.1 Hz), 2.93 (dd, 2H, J₁7.3 Hz, J₂6.3 Hz), 3.75

(q, 2H, J7.1 Hz), 4.37 (td, 1H, J₁7.3 Hz, J₂6.2 Hz),

5.97 (d, 1H, J6.2 Hz), 6.15 (dt, 1H, J₁15.9 Hz,

J₂6.3 Hz), 6.34 (d, 1H, J15.9 Hz), 6.88±7.29 (m, 5H);

¹³C NMR d145.3, 137.9, 129.4, 128.4, 126.7, 126.1,

125.9, 103.9, 67.6, 27.5, 15.3; This compound was unstable

and could not be obtained in analytically pure form.

Reduction of pentacarbonyl[(ethoxy)(phenylethynyl)-

carbene]chromium(0) (38) with NaBH₄in EtOH. From

250 mg (0.71 mmol) of 38 and 26.8 mg (0.71 mmol) of

NaBH₄in absolute EtOH at 2208C. After 10 min of reac-

tion and further oxidation of the reaction mixture, an oil

(85.2 mg) was obtained. The ¹H NMR spectrum of the reac-

tion crude showed product 14a exclusively. This product

was puri®ed by ¯ash column chromatography (hexane/

CH₂Cl₂4:1 to AcOEt) and was obtained as a colorless oil

(64 mg, 56%).

Reduction of pentacarbonyl[(N,N-dimethylamino)-

(phenylethylene)carbene]chromium(0) (32) with NaBH₄

in EtOH. From 143 mg (0.41 mmol) of 32 and 15.5 mg

(0.41 mmol) of NaBH₄in absolute EtOH at room tempera-

ture, after 3 h of reaction and further oxidation, a yellow oil

1

(46 mg) was obtained. The H NMR spectrum of the reac-

tion crude showed a 60:40 mixture of 33a and 34a. The

separation of these two products was not possible by ¯ash

column chromatography although a pure fraction of 33a

could be obtained by vacuum distillation. N,N-Dimethyl-3-

(phenyl)propanamine (33a), ¹H NMR d1.91±2.01 (m,

2H), 2.49 (s, 6H), 2.54 (t, 2H, J7.8 Hz), 2.71 (m, 2H),

7.10±7.39 (m, 5H); ¹³C NMR d140.7, 126.3, 128.3,

128.6, 64.2, 51.4, 33.3, 25.5; MS: m/z (%): 163 (M¹, 1),

91 (11), 58 (100). E-(3-Phenyl)-N,N-dimethyl-2-propene-

amine (34a), data taken from an enriched mixture: ¹H

Reduction of pentacarbonyl[(ethoxy)(phenylethynyl)-

carbene]chromium(0) (38) with NaBD₄in EtOH. From

200 mg (0.57 mmol) of 38 and 24 mg (0.57 mmol) of

NaBD₄in absolute EtOH at 2208C. After 10 min of reac-

tion and further oxidation of the reaction mixture, an oil

1

(69 mg) was obtained. The H NMR spectrum of the reac-

tion crude showed product 14c exclusively. This product

was puri®ed by ¯ash column chromatography (hexane/

CH₂Cl₂4:1 to AcOEt). E-3,3-Dideutero-3-ethoxy-1-phenyl-

1-propene (14c) (49 mg, 55%), colorless oil. ¹H NMR

Â

M. Gomez-Gallego et al. / Tetrahedron 56 (2000) 4893±4905

4904

Â

ManchenÄo, M. J.; Sierra, M. A.; Gomez-Gallego, M.; Ramirez, P.

Organometallics 1999, 18, 3252.

È

2. (a) Dotz, K. H.; Fischer, H.; Hofmann, P.; Kreissel, R.;

Schubert, U.; Weiss, K. Transition Metal Carbene Complexes;

d1.16 (t, 3H, J7.0 Hz), 3.44 (q, 2H, J7.0 Hz), 6.21 (d,

1H, J15.9 Hz), 6.53 (d, 1H, J15.9 Hz), 7.11±7.33 (m,

5H); ¹³C NMR d136.9, 132.4, 128.6, 127.6, 126.6, 126.3,

70.5 (m, CD₂), 65.6, 15.3; IR (®lm): 1654 (CvC), 1481,

1446 cm²¹. MS m/z: 164 (M¹, 45), 163 (12), 135 (43), 119

(62), 107 (100), 93 (22), 78 (22).

È

Verlag Chemie: Deer®eld Beach, Florida, 1983. (b) Dotz, K. H.

Angew. Chem., Int. Ed. Engl. 1984, 23, 587. (c) Wulff, W. D. In

Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.;

Pergamon: Oxford, 1991; Vol. 5, p 1065. (d) Schwindt, M. A.;

Miller, J. R.; Hegedus, L. S. J. Organomet. Chem. 1991, 413, 143.

(e) Rudler, H.; Audouin, M.; Chelain, E.; Denise, B.; Goumont, R.;

Massoud, A.; Parlier, A.; Pacreau, A.; Rudler, M.; Yefsah, R.;

Alvarez, C.; Delgado-Reyes, F. Chem. Soc. Rev. 1991, 20, 503.

Reduction of pentacarbonyl[(ethoxy)(phenylethynyl)-

carbene]chromium(0) (38) with NaBH₄in CD₃OD.

From 90 mg (0.26 mmol) of 38 and 9.8 mg (0.26 mmol)

of NaBH₄in 10 mL of CD₃OD at 2208C. After 10 min of

reaction and further oxidation of the reaction mixture, an oil

(30 mg) was obtained. The ¹H NMR spectrum of the

reaction crude showed 14d exclusively. This product was

puri®ed by ¯ash column chromatography (hexane/CH₂Cl₂

4:1 to AcOEt). E-1,2-Dideutero-3-ethoxy-1-phenyl-1-pro-

È

(f) Grotjahn, D. B.; Dotz, K. H. Synlett 1991, 381. (g) Wulff, W. D.

In Comprehensive Organometallic Chemistry II; Abel, E. W.,

Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford, 1995;

Vol. 12, p 470. (h) Hegedus, L. S. In Comprehensive Organo-

metallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson,

G., Eds.; Pergamon: Oxford, 1995; Vol. 12, p 549. (i) Harvey, D. F.;

Sigano, D. M. Chem. Rev. 1996, 96, 271. (j) Hegedus, L. S. Tetra-

hedron 1997, 53, 4105. (k) Aumann, R.; Nienaber, H. Adv. Orga-

nomet. Chem. 1997, 41, 163. (l) Alcaide, B.; Casarrubios, L.;

1

pene (14d) (24 mg 57%), colorless oil. H NMR d1.18

(t, 3H, J6.9 Hz), 3.48 (q, 2H, J6.9 Hz), 4.07 (s, 2H),

7.16±7.33 (m, 5H); ¹³C NMR d136.7, 131.5 (m), 128.4,

127.5, 126.3, 126.2 (m), 71.0, 65.6, 15.2; IR (®lm): 1655

(CvC), 1492, 1446 cm²¹; MS: m/z (%): 164 (M¹, 36), 163

(12), 135 (46), 120 (38), 119 (63), 118 (37), 117 (51), 108

(28), 107 (100), 106 (25).

Â

Domõnguez, G.; Sierra, M. A. Curr. Org. Chem. 1998, 2, 551.

3. (a) Bernasconi, C. F. Chem. Soc. Rev. 1997, 26, 299. (b)

Â Â

Bernasconi, C. F.; Leyes, A. E.; Garcõa-Rõo, L. Organometallics

1998, 17, 4940.

Reduction of pentacarbonyl[(ethoxy)(phenylethynyl)-

carbene]chromium(0) (38) with NaBH₄in THF. From

200 mg (0.57 mmol) of 38 and 22 mg (0.57 mmol) of

NaBH₄in anhydrous THF at room temperature. After 3 h

of reaction and further oxidation of the reaction mixture,

53 mg (59%) of a colorless oil were obtained. The ¹H

NMR spectrum of the reaction crude showed the presence

of 14a as the sole reaction product.

4. (a) Bernasconi, C. F.; Flores, F. X.; Sun, W. J. Am. Chem. Soc.

1995, 117, 4875. (b) Bernasconi, C. F.; Flores, F. X.; Kittredge,

K. W. J. Am. Chem. Soc. 1998, 120, 7983. (c) Bernasconi, C. F.;

Ali, M. J. Am. Chem. Soc. 1999, 121, 3039.

È

5. (a) Dotz, K. H. Angew. Chem., Int. Ed. Engl. 1975, 14, 644.

Some recent examples: (b) Wang, H.; Wulff, W. D. J. Am. Chem.

Soc. 1998, 120, 10573. (c) Pulley, S. R.; Carey, J. P. J. Org. Chem.

1998, 63, 5275. (d) Eastham, S. A.; Herbert, J.; Painter, J. E.; Patel,

P.; Quayle, P. Synlett 1998, 61. (e) Peterson, G. A.; Wulff, W. D.

Reduction of pentacarbonyl[(ethoxy)(phenylethynyl)-

carbene]tungsten(0) (39) with NaBH₄in EtOH. From

200 mg (0.41 mmol) of 39 and 15.7 mg (0.41 mmol) of

NaBH₄in absolute ethanol at 2208C. After 1 h of reaction

and further oxidation of the reaction mixture, 40 mg (61%)

of 14a were obtained as a yellow oil.

È

Tetrahedron Lett. 1997, 38, 5587. (f) Pfeiffer, J.; Nieger, M.; Dotz,

K. H. Chem. Eur. J. 1988, 4, 1843. (g) Wulff, W. D.; Su, J.; Tang,

P.-C.; Xu, Y.-C. Synthesis 1999, 415. For some different points of

È

view on the mechanism of Dotz's reaction: (h) Gleichmann, M. M.;

Dotz, K. H.; Hess, B. A. J. Am. Chem. Soc. 1996, 118, 10551. (i)

È

Á

Torrent, M.; Duran, M.; Sola, M. Chem. Commun. 1998, 999. (j)

Á

Torrent, M.; Duran, M.; Sola, M. Organometallics 1998, 14, 1492.

Reduction of 1-phenyl-1,2-propene (43) with NaBH₄in

EtOH. From 200 mg (1.25 mmol) of 43³²and 47.2 mg

(1.25 mmol) of NaBH₄in absolute EtOH at 2208C. After

4.5 h of reaction and further oxidation of the reaction

mixture, 87 mg of a brown oil were obtained. The ¹H

NMR spectrum of the reaction crude showed the starting

material unaltered.

(k) Fischer, H. Organometallics 1999, 18, 2590 and references

therein.

6. The participation of metal-bounded ketenes was proposed by

Hegedus, see: (a) Hegedus, L. S.; de Weck, G.; D'Andrea, S. J. Am.

Chem. Soc. 1988, 110, 2122. For the attempt to detect the metal-

ketene intermediate, see: (b) Gallagher, M. L.; Greene, J. B.;

Rooney. A. D. Organometallics 1997, 16, 5260.

7. (a) Hoffmann, R. Science 1981, 211, 995. (b) Hoffmann, R.

Angew. Chem., Int. Ed. Engl. 1982, 21, 711.

È

8. Weyershausen, B.; Nieger, M.; Dotz, K. H. J. Org. Chem. 1999,

64, 4206.

Acknowledgements

Support for this work under grants PB97-0323 and 2FD97-

Â

9. Wulff, W. D.; Faron, K. L.; Su, J.; Springer, J. P.; Rheingold,

A. L. J. Chem. Soc., Perkin Trans. I 1999, 197 and pertinent

references therein.

0314-CO2-02 from the Direccion General de EnsenÄanza

Â

Superior e Investigacion Cientõ®ca y Tecnica (MEC-

Spain) and the European Commission is acknowledged.

We wish to thank the Mass Spectrometry Service (UCM)

for the recording of the mass-spectra.

10. (a) Fischer, E. O.; Kreissl, F. R. J. Organomet. Chem. 1972,

35, C47. (b) Fischer, E. O.; Kalder, H. J. J. Organomet. Chem.

1977, 131, 57.

11. Casey, C. P.; Brunsvold, W. R. Inorg. Chem. 1977, 16, 391.

12. Examples: (a) Nakamura, E.; Tanaka, K.; Fujimura, T.; Aoki,

S.; Williard, P. G. J. Am. Chem. Soc. 1993, 115, 9015. (b)

References

Â

Barluenga, J.; Monserrat, J. M.; Florez, J.; Garcõa-Granda, S.;

Â

Martõn, E. Chem. Eur. J. 1995, 1, 236. (c) Iyoda, M.; Zhao, L.;

1. For a preliminary communication of a part of this work, see:

Â

M. Gomez-Gallego et al. / Tetrahedron 56 (2000) 4893±4905

4905

Matsuyama, H. Tetrahedron Lett. 1995, 36, 3699. (d) Barluenga,

Â

M. G. J. Chem. Soc. (A) 1971, 794. (b) Davinson, A.; Reger, D. L.

J. Am. Chem. Soc. 1972, 94, 9237. (c) Brunner, H.; Watcher, J.

J. Organomet. Chem. 1980, 201, 453. (d) Gibson, D. H.; Owens,

K.; Mandal, S. K.; Sattich, W. E.; Franco, J. O. Organometallics

1991, 10, 1203. (e) Gibson, D. H.; Owens, K. Organometallics

1991, 10, 1216.

Â Â

J.; Trabanco, A. A.; Florez, J.; Garcõa-Granda, S.; Martõn, E. J. Am.

Chem. Soc. 1996, 118, 13 099.

È

13. Dotz, K. H.; Christoffers, C.; Knochel, P. J. Organomet.

Chem. 1995, 489, C84.

Â

14. (a) Alcaide, B.; Dominguez, G.; Rodriguez-Lopez, J.; Sierra,

M. A. Organometallics 1992, 11, 1979. (b) Alcaide, B.;

Casarrubios, L.; Dominguez, G.; Sierra, M. A. Organometallics

1996, 15, 4612. (c) Alcaide, B.; Casarrubios, L.; Dominguez, G.;

26. This is a known behavior for group 6 metal carbene

complexes. See Ref. 4a.

27. Treatment of E-3-(2-furyl)-2-propenal with NaBH₄in ethanol

at 2788C quantitatively yielded E-3-(2-furyl)-2-propenol. The

same result was obtained when the reaction was carried out at

room temperature.

Â

Sierra, M. A.; Jimenez-Barbero, J. Organometallics 1994, 13,

2934. (d) Alcaide, B.; Casarrubios, L.; Dominguez, G.; Retamosa,

A.; Sierra, M. A. Tetrahedron 1996, 52, 13215. (e) Alcaide, B.;

Casarrubios, L.; Dominguez, G.; Sierra, M. A. J. Org. Chem. 1993,

58, 3886. For other examples, see: (f) Aumann, R.; Jasper, B.;

28. The formation of h3-complexes as intermediates in C±H

insertion processes of group 6 metal carbenes has been proposed

by several authors. Among other see: (a) Hoffmann, M.; Reissig,

H.-U. Synlett 1995, 625. (b) Harvey, D. F.; Lund, K. P. J. Am.

Chem. Soc. 1991, 113, 8916. (c) Buchert, M.; Reissig, H.-U.

Chem. Ber. 1992, 125, 2723.

È

Frohlich, R. Organometallics 1995, 14, 2447. (g) Aumann, R.;

Jasper, B.; Lage, M.; Krebs, B. Chem. Ber. 1994, 127, 2457.

È

15. Fischer, H.; Meisner, T.; Hofmann, J. Chem Ber. 1990, 123,

1799.

16. (a) Iwasawa, N.; Maeyama, K.; Saitou, M. J. Am. Chem. Soc.

1997, 119, 1486. (b) Iwasawa, N.; Maeyama, K. J. Org. Chem.

1997, 62, 1918. (c) Iwasawa, N.; Ochiai, T.; Maeyama, K.

Organometallics 1997, 16, 5137. (d) Iwasawa, N.; Ochiai, T.;

Maeyama, K. J. Org. Chem. 1998, 63, 3164.

Â

17. (a) Barluenga, J.; Tomas, M.; Ballesteros, A.; Santamaria, J.;

Â Â

Lopez-Ortiz, F.; Carbajo, R.; Garcõa-Granda, S.; Pertierra, P.

Â

Chem. Eur. J. 1996, 2, 88. (b) Barluenga, J.; Tomas, M.; Rubio,

Â Â

E.; Lopez-Pelegrin, J. A.; Garcõa-Granda, S.; Pertierra, P. J. Am.

29. Dally, J. W.; Witkop, B. J. Org. Chem. 1962, 27, 4104.

30. For the isolation and characterization of allenyl chromium

complexes, see: (a) Fischer, H.; Rindl, D.; Troll, C.; Leroux, F.

J. Organomet. Chem. 1995, 221. (b) Aumann, R.; Jasper, B.; Lage,

M.; Krebs, B. Chem. Ber. 1994, 127, 2475. Allenyl complexes

related to 41 are the postulated intermediates in the Michael

addition of nucleophiles to group 6 alkynylcarbene complexes.

See, for example: (c) de Meijere, A. Pure Appl. Chem. 1996, 68,

61. (d) Aumann, R.; Hinterding, P. Chem. Ber. 1993, 126, 421. (e)

Pipoh, R.; van Eldik, R.; Henkel, G. Organometallics 1993, 12,

Â

Chem. Soc. 1996, 118, 695. (c) Barluenga, J.; Rubio, E.; Lopez-

Â

Pelegrin, J. A.; Tomas, M. Angew. Chem., Int. Ed. 1999, 38, 1091.

Â Â

(d) Barluenga, J.; Tomas, M.; Rubio, E.; Lopez-Pelegrin, J. A.;

È

2236. (f) Aumann, R.; Jasper, B.; Lage, M.; Krebs, B. Organo-

metallics 1994, 13, 3502.

Â

Garcõa-Granda, S.; Perez-Priede, M. J. Am. Chem. Soc. 1999,

Â

31. The addition of nucleophiles to allenes usually takes place at

the central allenic carbon, see: Jacobs, T. L. In The Chemistry of

the Allenes; Landor, S.R., Ed.; Vol 2, Academic: London, UK,

1982. For aluminium hydride reductions of allenes see: (a)

Montury, M.; Gore, J. Tetrahedron Lett. 1980, 21, 51. (b) Baudouy,

R.; Gore, J. Tetrahedron 1975, 31, 383.

121, 3065.

18. (a) MCr, Hegedus, L. S.; Lundmark, B. J. Am. Chem. Soc.

1989, 111, 9194. (b) MW, Maxey, C. T.; Sleiman, H. F.; Maxey,

S. T.; McElwee-White, L. J. Am. Chem. Soc. 1992, 114, 5153.

19. Fischer, H.; Schlageter, A.; Bidell, W.; FruÈh, A. Organo-

metallics 1991, 10, 389.

33. The lack of reactivity of the allene system towards NaBH₄

reduction is in agreement with previous references: (a) Collman,

J. P.; Cawse, J. N.; Kang, J. W. Inorg. Chem. 1969, 12, 2574. (b)

Pasto, D. J.; Timmers, D. A.; Huang, N. Z. Inorg. Chem. 1984, 23,

4117.

Â

20. Barluenga, J.; Trabanco, A. A.; Florez, J.; Garcõa-Granda, S.;

Llorca, M. A. J. Am. Chem. Soc. 1998, 120, 12129.

21. Casey, C. P.; Neumann, S. M. J. Am. Chem. Soc. 1977, 99,

1651.

22. (a) Casey, C. P.; Polichnowski, S. W.; Tuinstra, H. E.; Albin,

L. D.; Calabrese, J. C. Inorg. Chem. 1978, 17, 3045. (b) Casey,

C. P.; Polichnowski, S. W.; Shucterman, A. J.; Jones, C. R. J. Am.

Chem. Soc. 1979, 101, 7282.

34. Aumann, R.; Heinen, H. Chem. Ber. 1987, 120, 537.

35. Wienand, A.; Reissig, H.-V. Chem. Ber. 1991, 124, 957.

36. Wulff, W. D.; Gilbert, A. M.; Hsung, R. P.; Rahm, A. J. Org.

Chem. 1995, 60, 4566.

23. Iwasawa, N.; Saitou, M. Chem. Lett. 1994, 231.

24. Cohen, F.; Goumont, R.; Rudler, H.; Daran, J. C.; Toscano,

R. A. J. Organomet. Chem. 1992, 431, C6.

37. Aumann, R.; Hinterding, P. Chem. Ber. 1993, 126, 421.

38. Hegedus, L. S.; McGuire, M. A.; Schultze, L. M. Org. Synth.,

Coll. Vol VIII, 217.

25. Examples: (a) Green, M. L. H.; Mitchard, L. C.; Swanwick,

Article Doi

On the reduction of α,β-unsaturated (Group 6) carbene complexes by NaBH4

DOI: 10.1016/S0040-4020(00)00204-0

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