Synthesis of chiral (7R)-[η6-5-(N,N-dimethylamino)-7-formyl-1,3-benzodioxole]-chromium complex and its application in the synthesis of optically active cis-β-lactam

Journal of Organometallic Chemistry 632 (2001) 27–40

www.elsevier.com/locate/jorganchem

Synthesis of chiral

(7R)-[h⁶-5-(N,N-dimethylamino)-7-formyl-1,3-benzodioxole]-

chromium complex and its application in the synthesis of optically

active cis-b-lactams

M. Filomena Costa ^a, M. Rute G. da Costa ^a,*, M.J. Marcelo Curto ^a, M. Magrinho ^a,

Ana M. Damas ^b,*, Luis Gales ^b

^aDepartamento de Tecnologia de Indu´strias Qu´ımicas, Instituto Nacional de Engenharia e Tecnologia Industrial, Estrada do Pac¸o do Lumiar 22,

1649-038 Lisbon, Portugal

^bInstituto de Cieˆncias Biome´dicas Abel-Salazar, Largo do Prof. Abel Salazar 2, 4050 Porto e Unidade de Estrutura Molecular,

Instituto de Biologia Molecular e Celular, Rua do Campo Alegre 823, 4050 Porto, Portugal

Received 18 February 2001; accepted 11 March 2001

Dedicated to Professor Alberto R. Dias honouring his pioneer contribution to organometallic chemistry in Portugal.

Abstract

Prochiral imine chromium complexes derived from the racemic (5-N,N-dimetylamino-7-formyl-1,3-benzodioxole)chromium

complex 4 and several amines reacted with acetoxylketene, generated from its corresponding acid chloride and triethylamine, to

produce the corresponding b-lactam complexes 6a, 6b and 6c with complete control of cis-diastereoselectivity. In a similar

manner, the imine condensation of the chiral imine complexes 11a and 11b, derived from the chiral aldehyde complex 4I, not only

provides complete cis-diastereoselection of the b-lactam complexes 12a and 12b, but remarkable enantioselectivities as well. X-ray

crystal structures of 4I and 12a were obtained and the mechanics implications within the context of the general mode proposed

Keywords: Chromium; Asymmetric synthesis; Imine complexes; Cycloadditions; b-Lactams

1. Introduction

known that the biological activity of b-lactams and

b-lactamase inhibitors most often is associated with a

single enantiomer [1d,2].

It is well known that the b-lactam skeleton is the key

structural element to a variety of antibiotics and a

versatile precursor of a great number of molecules of

diverse structures and different biological activities [1].

For many years the efforts of the organic synthetic

community have been directed towards searching for

new b-lactam antibiotics to meet the challenges of

bacterial resistance to the existing drugs and it is well

Ketenes are especially susceptible to [2+2] cycload-

ditions [3]; their reaction with imines, known as the

Staudinger reaction [4], has been studied extensively

and is now recognised as one of the most convenient

approaches to b-lactams [1b,5] due to its versatility and

stereochemical predictability [6]. This reaction, in con-

trast to the ester–enolate–imine condensation [1a,7]

(subjected to the limitations of enolate basicity [8]),

generally affords cis-b-lactams and is widely employed

in the synthesis of diverse monolactam antibiotics.

Some compounds of this particular class have potent

biological activity [1b,1d,9].

* Corresponding authors. Tel.: +351-2171-65141; fax: +351-

2171-68100.

E-mail address: rute.costa@mail.ineti.pt (M.R.G. da Costa).

PII: S0022-328X(01)00806-3

28

M. Filomena Costa et al. / Journal of Organometallic Chemistry 632 (2001) 27–40

2. Results and discussion

Planar chiral transition-metal p-complexes of ortho-

or meta-disubstituted arenes have emerged as useful

starting materials in asymmetric organic synthesis be-

cause the metal coordination enhances arene reactivity,

facilitating regio- and diastereoselective substitution of

positions on or adjacent to the aromatic ring (for

reviews see Ref. [10]). Therefore, planar chirality en-

ables new stereogenic centres to be formed and some

work involving the synthesis of b-lactam chromium

complexes has been developed [6c,11].

The ﬁrst outstanding contribution to the total re-

gioselectivity and asymmetric synthesis of the (5-N,N-

dimetylamino-1,3-benzodioxole)chromium

complex

derivative 4 (in our starting material dimethylaniline is

coupled to the dioxolane ring) to afford b-lactams with

high levels of enantioselectivity was based on early

ﬁndings reported on dimethylaniline and ortho- or

meta-disubstituted aldehyde complexes [5b,13], and on

both (1,3-benzodioxole) [14] and dimethylaniline com-

plexes [15], in which Schmalz and Simpkins, respec-

tively, have found that the metallation of those

complexes with some chiral bases gave disappointing

results. Secondly, our investigation was initiated with

the aim of establishing whether (5-N,N-dimetylamino-

1,3-benzodioxole-7-imine)chromium complexes are suit-

able chiral sources for the diastereoselective synthesis of

cis-[1%-(phenyl-substituted)-3%-acetoxy-4%-(5-N,N-di-

metylamino-1,3-benzodioxole)-azetidin-2%-one]chrom-

ium complexes (cis-b-lactams)¹via the Staudinger reac-

tion. Finally, the cis selectivity of b-lactams always

observed in our study, using acetoxyacetyl chloride as

ketene source and both prochiral and chiral imine

chromium complexes, can be accounted for by a two-

step mechanism involving ketenes+imines that has

been documented by experimental and theoretical cal-

culations [1b,16].

5-Amino-1,3-benzodioxole was chosen for several

reasons: (i) 1,3-benzodioxole is a subunit of a large

number of natural products [17] and there is a large

variety of its derivatives used in the pharmaceutical

industry [18]; (ii) the presence of the amino group at

C(5) and the OCH₂group in the fused dioxolane ring

of 1,3-benzodioxole could allow us to afford total

regioselectivity on 4 with reasonable yields; and (iii) to

introduce in the azetidin-2-one ring the 1,3-benzodiox-

ole as C(4%) substituent.

The development of methodology for the preparation

of monocyclic b-lactams has attracted considerable in-

terest from both academic and industrial points of view

and the concept of structural modiﬁcations at C(4) and

C(3) positions of the azetidin-2-one rings is of current

interest (for reviews on b-lactam antibiotics see Ref.

[12]). While abundant information on the diverse sub-

stitution patterns of optically active b-lactams exists,

the synthesis of these kinds of compound, in which

chemical manipulation at C(4) position of the azetidin-

2-one nucleus was introduced using chiral (5-amino-1,3-

benzodioxole)chromium complexes, is the subject of

this investigation. To check the feasibility of this reac-

tion, we ﬁrst examined the [2+2] cycloaddition reac-

tion between ketenes and imine complexes derived from

the aldehyde complex 4 in their racemic and optically

active forms providing the exclusive cis-azetidin-2-one

complexes. High enantioselectivities of b-lactams were

observed using the chiral complex 4I as starting mate-

rial. The X-ray crystal structures of 4I and 12a indi-

cated unambiguously their relative conﬁgurations as

(7R)-[h⁶-5-(N,N-dimethylamino)-7-formyl-1,3-benzo-

dioxole]tricarbonylchromium and (7R,3%R,4%S)-{1%-(4¦-

ﬂuorophenyl)-3%-acetoxy-4%-[h⁶-5-(N,N-dimethylamino)-

1,3-benzodioxole]azetidin-2%-one}tricarbonylchromium

complexes, respectively.

Conversion of 1 into its Cr(CO)₃complex was ac-

complished with the Cr(CO)₆ꢀBu₂O–THF reﬂux [19].

Facile formation of 2 was afforded in 86% yield after

recrystallisation and the complex was totally character-

ised (Scheme 1). The amino group of complex 2 was

methylated in the presence of NaH–MeI and complex 3

was obtained in 70% yield as yellow crystals after

column chromatography and recrystallisation. The

choice of solvents, base and temperature used in the

metallation/DMF sequence has been optimised, and the

best reaction conditions for the introduction of the

Scheme 1. Reagents: (i) Cr(CO)₆, (n-Bu)₂O–THF (10:1); (ii) NaH

(ﬁve equivalents); (iii) MeI (ﬁve equivalents); (iv) n-BuLi (1.5 equiva-

lents); and (v) DMF (ﬁve equivalents).

¹For clarity the azetidin-2-one ring atoms were numbered as N(1%),

C(2%), C(3%) and C(4%).

M. Filomena Costa et al. / Journal of Organometallic Chemistry 632 (2001) 27–40

29

azetidin-2%-one ring of the complexes was conﬁrmed

easily on the basis of their coupling constants (J_3%,4%

:

5.4 Hz), and is in line with what has been reported by

other authors for similar reactions [2b,6b,20]. These

complexes were isolated as single cis-diastereomers in

50, 60 and 45% yields, respectively, after column chro-

matography and recrystallisation. As the transforma-

tion acid chloridesketenes presents its own problems,

the use of these kinds of base as dehydrohalogenating

agents generates ammonium salts as interfering by-

products and the yields obtained could result from this

fact. The protocol mentioned above was extended to

imine 5d and the ¹H-NMR spectrum of the crude

mixture did not show traces of the corresponding b-lac-

tam complex, despite careful and repeated attempts to

isolate it. After puriﬁcation, complex 7 was isolated as

1

an orange powder in 50% yield and its H-NMR spec-

trum showed the presence of the CH₃COOCH₂CO

group, the two meta protons in the complexed arene

ring and the two non-equivalent CH₂proton singlets of

the dioxolane ring. The ¹³C-NMR spectrum also conﬁ-

rmed the presence of the CH₃COOCH₂CO group and

DEPT and the ¹H–¹³C heteronuclear experiments

(HMQC) allowed the structural assignment of 7. This

absence of cycloaddition [2+2] could be reasoned tak-

ing into account the presence of the NHPh group

attached to the iminic nitrogen on 5d. Presumably, the

nucleophilicity of the nitrogen lone pair of the imine

complex is strongly diminished by the electron-with-

drawing effect of the NHPh group attached to it [21],

which has precluded the cycloaddition reaction to the

ketene. Instead, abstraction of the acidic NH proton by

triethylamine could occur, allowing the reaction with

the acid chloride to proceed, and this route could access

complex 7.

Once the best reaction conditions to obtain the cis-b-

lactam complexes 6a, 6b and 6c were established,

phenylacetyl chloride was used to generate in situ the

corresponding ketene and the imine complex 5a was

allowed to react. Despite several runs, no traces of the

corresponding b-lactam complexes were detected in the

¹H-NMR spectral data. It is difﬁcult to anticipate how

aryl substituents such as phenyl would behave because

its conformation may vary [22] and, consequently, dif-

ferent results can occur from the interactions between

the ketene substituents and the substituents of the imine

complexes.

Scheme 2. Reagents: (i) RNH₂; Rꢁ4FꢀC₆H₄(a), CH₂Ph (b), Ph (c),

,

NHPh (d) and molecular sieves 4 A; (ii) Et₃N; (iii) CH₃CO₂COCl;

and (iv) hw/O₂. *Only one enantiomer is drawn.

aldehyde function in complex 3 were attained in the

presence of THF–Et₂O (1:1) as solvents at −30°C,

n-BuLi and DMF, and the expected exclusive function-

1

alisation at C(7) was observed. The H-NMR spectrum

of the racemic complex 4 shows H(4) and H(6) at l 4.64

and 5.47 with a meta coupling constant of 2.4 Hz and

the two non-equivalent CH₂proton singlets, as ob-

served in complexes 2 and 3 (Scheme 1). Imines 5a, 5b,

5c and 5d were prepared as yellow crystals by conden-

sation of 4 with 4-ﬂuoroaniline, benzylamine, aniline

and phenyl hydrazine in yields of 53, 60, 54 and 57%,

respectively (Scheme 2). These results were obtained

after several runs at different reaction conditions ac-

cording to the literature [1g,6b,6c,6i]. To check the

feasibility of the Staudinger reaction, the cycloaddition

reactions were examined between the reactive ketenes

generated in situ from acetoxyacetyl chloride and after-

wards from phenylacetyl chloride. Treatment of the

imine complexes 5a, 5b and 5c with acetoxyacetyl chlo-

ride and triethylamine in dichloromethane as solvent at

0°C led exclusively to the cis-b-lactam complexes 6a, 6b

Complexes 6a, 6b, 6c and 7 were subjected to decom-

plexation reactions by exposing ether solutions to air

and sunlight until the yellow colour of the solutions

disappeared. After puriﬁcation, the decomplexed cis-b-

lactams 8a, 8b, 8c and compound 9, respectively, were

afforded (Scheme 2).

1

and 6c, respectively. Inspection of the H-NMR spec-

tral data of their crude mixtures indicated that only one

stereoisomer had been formed and the cis disposition of

the vicinal methine protons at C(3%) and C(4%) in each

On the basis of these results, we now report our

results on the enantioselective synthesis of b-lactam

complexes using the chiral aldehyde complex 4I as

30

M. Filomena Costa et al. / Journal of Organometallic Chemistry 632 (2001) 27–40

forms was not achieved either by chromatography or

by recrystallisation. Treatment of 4 with (S)-(−)-(a)-

methylbenzylamine in Et₂O gave, after the usual work-

1

up, an orange solid and the H-NMR spectral data of

the crude mixture showed two imine complexes 10I and

10II in a 1:1 ratio. The d.e. of these imines were higher

1

than 95% by H-NMR measurements. Their separation

was only possible by recrystallisation and, ﬁrst, com-

plex 10I was afforded as red crystals. With no more

complex 10I in the solution, complex 10II recrystallised

as an orange powder and the total characterisation of

both the complexes was consistent with their presence.

Therefore, the chiral aldehyde required for our synthe-

sis of 4I was accessible by hydrolysis of 10I (Scheme 3).

All the spectral data of 4I were identical to those

observed on its racemic form but the determination of

its enantiomeric excess (e.e.), by both the ¹H-NMR

method using the chiral shift reagent Eu(hfc)₃[24] and

HPLC analysis using a chromatographic column Chi-

ralcel OJ [14], failed. Nevertheless, the X-ray crystal

structure determination of 4I conﬁrmed its relative

conﬁguration as (7R)-(5-N,N-dimethylamino-7-formyl-

1,3-benzodioxole)chromium complex and its speciﬁc ro-

tation indicated [h]²_D⁵= −364.

Two perspective views of 4I, with the atomic-la-

belling scheme, were obtained with ^ORTEP[25] and are

presented in Fig. 1. Interatomic distances and angles

are given in Table 1.

Scheme 3. Reagents: (i) (S)-(−)-(a)-methylbenzylamine, molecular

,

We can see the aldehyde function anti to the OCH₂

group from the dioxolane ring of 4I, which is in line

with the analogous complexes [23]. The Cr(CO)₃group

lies in an eclipsed conformation relative to the carbo-

cyclic ring. Also, the CrꢀC (ring) distance is maximum

relative to the amino substituent at C(5). The results

from an out-of-plane deformation of the carbocyclic

ring, with C(5) signiﬁcantly displaced out of the mean

plane in the opposite direction of the chromium atom,

have also been observed for other (amino-substituted

arene)chromium complexes [26]. A displacement of the

sieves 4 A; and (ii) HCl. Only complex 10I was hydrolised to obtain

4I.

starting material. Taking into account the literature,

chiral bases were not used according to the results of

Schmalz [14] and Simpkins [15] on (1,3-benzodioxole)

and (dimethylaniline)chromium complexes, respectively.

Therefore, the resolution of 4 was tested using three

different methods in which semioxamazone derivatives

[13a] and oxazolidines of valinol [23] were not success-

ful because the separation of their diastereoisomeric

Fig. 1. (a) Molecular structure of complex 4I. (b) View of molecule showing the relative positions of the carbonyl ligands to the carbocyclic ring.

M. Filomena Costa et al. / Journal of Organometallic Chemistry 632 (2001) 27–40

31

Table 1

by HPLC was higher than 95%. Complete cis

diastereoselectivity in b-lactam complexes was also

achieved using acetoxyacetyl chloride in the presence

of triethylamine and the optically active Schiff bases

11a and 11b. The e.e. determination of 12a and 12b

was not possible by HPLC because no acceptable ex-

perimental conditions were found to separate the

racemic complexes 6a and 6b. However, X-ray crystal

structure determination of 12a conﬁrmed its relative

conﬁguration as (7R,3%R,4%S)-{1%-(4¦-ﬂuorophenyl)-3%-

acetoxy-4%-[h⁶-5-(N,N-dimethylamino)-1,3-benzodi-

oxole]azetidin-2%-one}tricarbonylchromium complex in

which the cis-b-lactam complex carries three contigu-

ous chiral centres (Scheme 4); and the e.e. of the

decomplexed cis-b-lactams 13a and 13b were higher

than 90 and 85%, respectively, using a Lichrocart

column (n-hexane–2-propanol, 1:1).

Fig. 2 shows two perspective views of complex 12a

and the corresponding atomic-labelling scheme. The

interatomic distances and angles are presented in

Table 1. As for the aldehyde complex 4I, the Cr(CO)₃

group has an eclipsed conformation relative to the

carbocyclic ring and the CrꢀC (ring) distance is maxi-

mum in the case of C(5). An interesting structural

feature of complex 12a is the almost coplanar pyra-

midal disposition of the three valences of the nitrogen

atom at the 2-azetidin-2%-one ring, as reported in the

literature [27]. This latter aspect adds interest to this

b-lactams because it has been reported [28] that the

relative pyramidalisation of the nitrogen atom in both

monocyclic and bicyclic b-lactam antibiotics is di-

rectly related to their biological activity.

Selected geometric parameters for complexes 4I and 12a. Molecule 1

and molecule 2 of complexes 4I and 12a refer to the presence of two

molecules in the asymmetric unit

Complex 4I

Complex 12a

Molecule 1 Molecule 2 Molecule 1 Molecule 2

,

Bond lengths (A)

CrꢀC(10)

CrꢀC(11)

CrꢀC(12)

CrꢀC(3a)

CrꢀC(4)

CrꢀC(5)

CrꢀC(6)

1.732(6)

2.080(7)

1.773(7)

2.039(5)

2.122(6)

2.451(6)

2.429(6)

2.211(6)

2.057(5)

1.417(9)

1.779(6)

2.094(7)

1.693(7)

2.379(6)

2.525(5)

2.397(6)

2.027(6)

1.951(5)

2.113(6)

1.403(9)

1.757(6)

1.799(6)

1.797(8)

2.233(5)

2.267(5)

2.328(6)

2.239(5)

2.289(5)

2.285(4)

1.394(7)

1.426(7)

1.437(7)

1.791(6)

1.806(6)

1.817(7)

2.219(6)

2.274(6)

2.361(6)

2.247(6)

2.270(5)

2.263(5)

1.403(8)

1.413(8)

1.452(7)

1.427(7)

1.364(7)

1.408(7)

1.363(7)

1.452(8)

1.433(7)

1.393(6)

1.533(6)

1.408(6)

1.205(7)

1.423(6)

1.580(7)

1.496(7)

1.373(7)

1.453(6)

CrꢀC(7)

CrꢀC(7a)

C(3a)ꢀC(4)

C(4)ꢀC(5)

C(5)ꢀC(6)

C(6)ꢀC(7)

C(7)ꢀC(7a)

C(7a)ꢀC(3a)

C(3a)ꢀO(3)

O(3)ꢀC(2)

C(2)ꢀO(1)

O(1)ꢀC(7a)

C(7)ꢀC(13)

N(2)ꢀC(18)

C(14)ꢀO(4)

C(15)ꢀO(5)

C(13)ꢀC(15)

C(15)ꢀC(14)

C(14)ꢀN(2)

N(2)ꢀC(13)

1.566(10) 1.440(9)

1.436(8)

1.464(9)

1.469(9)

1.431(9)

1.453(8)

1.473(9)

1.524(9)

1.519(10) 1.440(6)

1.433(11) 1.369(6)

1.439(11) 1.407(6)

1.370(5)

1.527(10) 1.469(6)

1.420(8)

1.528(10) 1.474(10) 1.427(6)

1.407(7)

1.398(8)

1.385(5)

1.517(6)

1.421(6)

1.207(6)

1.422(6)

1.563(7)

1.498(7)

1.372(7)

1.456(6)

Bond angles (°)

C(10)ꢀCrꢀC(11)

C(11)ꢀCrꢀC(12)

C(10)ꢀCrꢀC(12)

O(5)ꢀC(15)ꢀC(14)

O(5)ꢀC(15)ꢀC(13)

C(14)ꢀC(15)ꢀC(13)

O(4)ꢀC(14)ꢀN(2)

O(4)ꢀC(14)ꢀC(15)

N(2)ꢀC(14)ꢀC(15)

C(14)ꢀN(2)ꢀC(18)

C(14)ꢀN(2)ꢀC(13)

C(18)ꢀN(2)ꢀC(13)

N(2)ꢀC(13)ꢀC(15)

N(2)ꢀC(13)ꢀC(7)

C(7)ꢀC(13)ꢀC(15)

87.8(3)

95.1(3)

95.5(3)

92.5(3)

87.3(3)

95.3(3)

86.4(3)

90.1(3)

84.5(3)

88.8(3)

89.0(3)

84.7(3)

The cis selectivity always observed in the present

study, using acetoxyacetyl chloride as the ketene

source and chiral imine chromium complexes to yield

the corresponding cis-azetidin-2-ones, can be ac-

counted for by a two-step mechanism in which the

ﬁrst step is a nucleophilic attack of the iminic nitro-

gen lone pair over the sp-hybridised carbon atom of

the ketene to form a zwitterionic intermediate accord-

ing to the exo mode. The second step of the reaction

is a conrotatory ring closure of the intermediate to

yield the corresponding four-membered ring (Scheme

5).

112.0(4)

115.9(4)

85.8(4)

113.1(5)

113.4(4)

85.7(4)

131.0(5)

136.6(5)

92.4(4)

133.7(5)

92.5(4)

132.6(4)

94.9(4)

131.7(4)

95.5(4)

131.6(4)

86.7(4)

131.5(4)

86.2(4)

113.8(4)

114.5(4)

114.8(4)

The acetoxy group in the synthesised cis-b-lactams

is suitable for its nucleophilic substitution [12c] and

can also be transformed easily into the amino func-

tion present in some mono b-lactam antibiotics [29],

with complete inversion of conﬁguration at the C(3%)

position of the b-lactam ring, not directly accessible

through the Staudinger reaction. Finally, earlier work

[30] would indicate that the 3%-acetoxy-b-lactams

might be attractive precursors of the a-amino acids

and related compounds.

Cr(CO)₃moiety with respect to the arene ring is also

observed. In fact, the chromium atom projection on

to the arene ring medium plan (see Fig. 1b) is shifted

from the barycentric of the ring towards atom C(7a).

Following the established protocol relative to the

racemic series of cis-b-lactam complexes, chiral imine

complexes 11 were prepared and the e.e. determined

32

M. Filomena Costa et al. / Journal of Organometallic Chemistry 632 (2001) 27–40

Scheme 5. Schematic representation of the possible initial approach

between the imine complex 11 and the non-symmetric acetoxyketene.

(ii) it was also demonstrated that the efﬁciency of this

process is dependent on the reactivity of both the imine

complex and the ketene used; (iii) it should be possible

to substitute the acetoxy group at C(3%) position and to

invert the stereochemistry at the C(3%) position of the

b-lactam complexes; and (iv) since methods for the

synthesis of a-amino acids in their (R) and (S) forms

are now abundant, the presence of the (1,3-benzodiox-

ole) subunit in this class of b-lactams opens up new

perspectives not only in the ﬁeld of b-lactam antibiotics,

but also in the chemistry that employs b-lactams as

chiral-starting materials. Further studies of the applica-

tions of other methodologies to the chemical synthesis

of b-lactams are in progress in our laboratory, includ-

ing the use of a nucleophile-catalysed reaction of elec-

tron-deﬁcient imines in order to develop a catalytic,

shuttle-base route to the optically active b-lactams.

Scheme 4. Reagents: (i) RNH₂; Rꢁ4FꢀC₆H₄(a), CH₂Ph, and (b)

,

molecular sieves 4 A; (ii) Et₃N; (iii) CH₃CO₂CH₂COCl; and (iv)

hw/O₂.

3. Concluding remarks

4. Experimental

From the results in the present study four key points

deserve to be mentioned: (i) (7R)-[h⁶-5-(N,N-dimethyl-

amino)-7-(N%-imino)-1,3-benzodioxole]tricarbonylchro-

mium complexes 11a and 11b are suitable chiral sources

for the development of new substitution patterns of

optically active b-lactams via the Staudinger reaction;

4.1. General procedures

Melting points (m.p.) were determined on a Reichert

Thermovar m.p. apparatus, and are uncorrected. In-

frared (IR) spectra were obtained on a Perkin–Elmer

Fig. 2. (a) Molecular structure of complex 12a. (b) View of molecule showing the relative positions of the carbonyl ligands to the carbocyclic ring.

M. Filomena Costa et al. / Journal of Organometallic Chemistry 632 (2001) 27–40

33

trast, the corresponding decomplexed b-lactams gave

all the ¹³C-NMR data. Due to instability of complex 7,

elemental analysis was only carried out in the decom-

plexed compound 9.

1725X FT-IR spectrometer using neat ﬁlms on NaCl

plates or KBr pellets. NMR spectra were recorded in

CDCl₃in a General Electric QE-300 P spectrometer

(operated at 300 MHz for ¹H and 75 MHz for ¹³C

spectra) or in a Bruker ARX spectrometer (operated at

4.2. (p⁶-5-Amino-1,3-benzodioxole)tricarbonylchromium

(2)

1

400 MHz for H and 100 MHz for ¹³C spectra). Chem-

ical shift values are given in parts per million (ppm)

relative to tetramethylsilane and J values are given in

Hertz. ¹H{¹³C} heteronuclear correlation experiments

(HETCORR, COLOC, HMQC or HMBC) were car-

ried out for most of the compounds and in some cases

(5b, 5d, 7, 9, 11b and 13b) the experiments were per-

formed at low temperature (5°C). Mass spectra were

acquired on a Kratos MS 25 RF instrument operating

at 70 eV. High-resolution mass spectra were determined

on an Extrell (Waters) FTMS 2001-DT S.T.I.C.R. mass

spectrometer. Elemental analyses were performed on a

Carlo Erba 1106 elemental analyser. Optical rotations

were recorded on a Perkin–Elmer 241 polarimeter.

X-ray diffraction studies were performed at room tem-

perature (r.t.) with a Stoe IPDS image plate equipped

A mixture of 5-amino-1,3-benzodioxole (1) (1.25 g,

9.12 mmol) and Cr(CO)₆(2.40 g, 10.91 mmol) in deoxy-

genated (n-Bu)₂O (50 ml)–THF (5 ml) was heated

under reﬂux for 5 days. The resulting solution was

cooled, ﬁltered through celite with Et₂O and concen-

trated under reduced pressure to afford complex 2.

Recrystallisation from CH₂Cl₂–n-hexane gave a yellow

powder (2.14 g, 86%), m.p. (dec.) 133–135°C. ¹H-NMR

(CDCl₃, 300 MHz): l=3.42 (s, 2H, NH₂), 4.38 (dd,

1H, J=1.8 and 6.6 Hz, ArH), 5.13 (d, 1H, J=1.8 Hz,

ArH), 5.61 (s, 1H, CH₂), 5.68 (d, 1H, J=6.6 Hz, ArH),

5.91 (s, 1H, CH₂). ¹³C-NMR (CD₃COCD₃, 75 MHz):

l=65.74 (Ar), 68.90 (Ar), 80.87 (Ar), 100.91 (CH₂),

120.81 (Ar, C_quat), 130.72 (Ar, C_quat), 134.35 (Ar, C_quat),

236.34 (CꢂO). FABMS; m/z (%): 274 ([MH⁺], 22), 273

([M⁺], 82), 217 (100), 189 (44). IR (KBr, cm⁻¹): w_max

3479 (NꢀH), 1942, 1872, 1849, 1814 (CꢂO). Anal.

Found: C, 43.68; H, 2.51; N, 4.96. Calc. for

C₁₀H₇O₅NCr (MW 273.17): C, 43.97; H, 2.58; N,

5.13%.

,

with Mo–K_aradiation (0.7107 A). The structures were

solved using ^SHELXS97 [31] and reﬁned with SHELXL97

[32]. HPLC analyses were carried out with a Spectra-

Physics apparatus using a chiral chromatographic

column (0.46 cm ID×25 cm) Chiralcel OJ. All separa-

tions were conducted at ambient temperature using an

isocratic solvent system, which was composed by n-hex-

ane–2-propanol (90:10, 80:20, 75:25, 70:30, 65:35,

60:40, 50:50; v/v). The complexes were detected by UV

absorption at 254 nm. The ﬂow rate for the resolution

of isomers of complex 5a was 0.7 ml min⁻¹(solvent:

n-hexane–2-propanol, 70:30; v/v). No acceptable sepa-

ration was found for the racemic mixtures 4, 6a and 8a

on this column. The decomplexed racemic mixtures 8a

and 8b were resolved on a Lichrocart column (0.4

ID×25 cm), using n-hexane–2-propanol, 50:50 as the

mobile phase and 0.7 ml min⁻¹as the ﬂow rate. All

reactions involving the preparation or utilisation of

(h⁶-arene)tricarbonylchromium complexes were per-

formed under a N₂atmosphere. Tetrahydrofuran and

Et₂O were distilled from sodium benzophenone ketyl

under N₂. Dichloromethane was distilled over CaH₂

under N₂. Dibutyl ether was dried over sodium and

distilled under an atmosphere of N₂prior to use.

Sodium hydride was obtained as 80% dispersion in oil,

from which the oil was removed by repeated washings

with n-hexane and drying under vacuum. All the other

reagents were used as received or puriﬁed by standard

methods [33]. Organic extracts were dried over anhy-

drous MgSO₄. Column chromatography was carried

out using Merck silica gel 60 (230–400 mesh). The

complexed b-lactams were not stable and, consequently,

all the ¹³C-NMR data could not be obtained. In con-

4.3. [p⁶-5-(N,N-Dimethylamino)-1,3-benzodioxole]-

tricarbonylchromium (3)

A suspension of NaH (1.19 g, 49.45 mmol) was

added to a solution of (h⁶-5-amino-1,3-benzodiox-

ole)tricarbonylchromium (2) (2.70 g, 9.89 mmol) in

THF (20 ml). When no further gas evolved, the mixture

was cooled to 0°C and methyl iodide was added (3.10 g,

49.45 mmol). After stirring the reaction for 2 h at 0°C

and for about 2 h at r.t., the resulting solution was

ﬁltered with CH₂Cl₂, ﬁrst through celite and then

through a silica column to yield complex 3. Recrystalli-

sation from CH₂Cl₂–n-hexane gave yellow crystals

(2.21 g, 70%), m.p. (dec.) 135–136°C. ¹H-NMR

(CDCl₃, 300 MHz): l=2.83 [s, 6H, N(CH₃)₂], 4.22 (dd,

1H, J=2.2 and 8.0 Hz, ArH), 5.09 (d, 1H, J=2.2 Hz,

ArH), 5.59 (s, 1H, CH₂), 5.68 (d, 1H, J=8.0 Hz, ArH),

5.88 (s, 1H, CH₂). ¹³C-NMR (CDCl₃, 75 MHz): l=

40.38 [N(CH₃)₂], 62.03 (Ar), 65.16 (Ar), 79.20 (Ar),

99.79 (CH₂), 119.62 (Ar, C_quat), 130.63 (Ar, C_quat),

133.04 (Ar, C_quat), 234.77 (CꢂO). IR (KBr, cm⁻¹): w_max

1943, 1850 (CꢂO). EIMS; m/z (%): 301 ([M⁺], 2), 245

(2), 217 (5), 165 (100). Anal. Found: C, 48.12; H, 3.77;

N, 4.44. Calc. for C₁₂H₁₁O₅NCr (MW 301.22): C,

47.85; H, 3.68; N, 4.65%.

34

M. Filomena Costa et al. / Journal of Organometallic Chemistry 632 (2001) 27–40

4.4. [p⁶-5-(N,N-Dimethylamino)-7-formyl-1,3-

benzodioxole]tricarbonylchromium (4)

1629 (CꢁN). Found: 422.03643. Calc. for C₁₉H₁₅O₅-

N₂CrF: 422.03646.

4.5.2. [p⁶-5-(N,N-Dimethylamino)-7-(N%-benzylimino)-

1,3-benzodioxole]tricarbonylchromium (5b)

n-Butyllithium (9.0 ml, 11.0 mmol) was added drop-

wise to a cooled solution (−30°C) of complex 3 (2.21

g, 7.34 mmol) in THF (20 ml) and Et₂O (20 ml) with

stirring for 1 h. N,N-Dimethylformamide (2.8 ml, 36.7

mmol) was added, the mixture was stirred for 1 h at

−30°C and the solution was allowed to react for 1 h at

r.t. The solution was washed with NH₄Cl (20 ml)–H₂O

(20 ml) and dried. Removal of the solvent and the

crude product washed with n-hexane gave complex 4.

Recrystallisation from CH₂Cl₂–n-hexane gave a red

powder (1.67 g, 70%), m.p. (dec.) 128–130°C. ¹H-NMR

(CDCl₃, 300 MHz): l=2.88 [s, 6H, N(CH₃)₂], 4.64 (d,

1H, J=2.4 Hz, ArH), 5.47 (d, 1H, J=2.4 Hz, ArH),

5.85 (s, 1H, CH₂), 6.11 (s, 1H, CH₂), 10.01 (s, 1H,

CHO). ¹³C-NMR (CDCl₃, 75 MHz): l=40.56

[N(CH₃)₂], 61.46 (Ar), 64.40 (Ar), 82.99 (Ar, C_quat),

101.50 (CH₂), 124.83 (Ar, C_quat), 128.14 (Ar, C_quat),

131.08 (Ar, C_quat), 185.96 (CꢁO), 233.37 (CꢂO). EIMS;

m/z (%): 329 ([M⁺], 2), 273 (2), 245 (5), 193 (100). IR

(KBr, cm⁻¹): w_max1946, 1891, 1847 (CꢂO), 1688 (CꢁO).

Anal. Found: C, 47.38; H, 3.63; N, 4.32. Calc.

C₁₃H₁₁O₆NCr (329.23): C, 47.43; H, 3.37; N, 4.25%.

Benzylamine (0.28 ml, 2.59 mmol) and complex 4

(0.17 g, 0.517 mmol) in CH₂Cl₂afforded 5b. Recrys-

tallisation from CH₂Cl₂–n-hexane gave an orange pow-

der (0.13 g, 60%), m.p. (dec.) 121–124°C. ¹H-NMR

(CDCl₃, 300 MHz): l=2.89 [s, 6H, N(CH₃)₂], 4.79–

4.92 (m, 3H, CH₂and ArH), 5.22 (d, 1H, J=2.1 Hz,

ArH), 5.78 (s, 1H, CH₂), 6.02 (s, 1H, CH₂), 7.26–7.40

(m, 5H, Ar%H), 8.40 (s, 1H, CHN). ¹³C-NMR (CDCl₃,

100 MHz): l=40.52 [N(CH₃)₂], 61.92 (Ar), 62.23 (Ar),

64.99 (CH₂), 87.99 (Ar, C_quat), 100.47 (CH₂), 121.04

(Ar, C_quat), 127.39 (Ar%), 128.41 (Ar%), 128.66 (Ar%),

129.89 (Ar, C_quat), 132.60 (Ar, C_quat), 138.04 (Ar%,

C_quat), 155.29 (CHN), 234.82 (CꢂO). EIMS; m/z (%):

334 ([M⁺−3CO], 1), 282 (100). IR (KBr, cm⁻¹): w_max

1938, 1870, 1844 (CꢂO), 1646 (CꢁN). Found:

418.05795. Calc. for C₂₀H₁₈O₅N₂Cr: 418.06153.

4.5.3. [p⁶-5-(N,N-Dimethylamino)-7-(N%-phenylimino)-

1,3-benzodioxole]tricarbonylchromium (5c)

Aniline (0.60 ml, 6.33 mmol) and complex 4 (0.42 g,

1.23 mmol) in THF afforded 5c. Recrystallisation from

CH₂Cl₂–n-hexane gave a red powder (0.28 g, 54%),

4.5. General method for synthesis of imine complexes 5

and 11

1

m.p. (dec.) 141–143°C. H-NMR (CDCl₃, 300 MHz):

l=2.94 [s, 6H, N(CH₃)₂], 5.03 (d, 1H, J=2.1 Hz,

ArH), 5.29 (d, 1H, J=2.1 Hz, ArH), 5.82 (s, 1H, CH₂),

6.06 (s, 1H, CH₂), 7.21–7.40 (m, 5H, Ar%H), 8.49 (s,

1H, CHN). ¹³C-NMR (CDCl₃, 75 MHz): l=40.52

[N(CH₃)₂], 61.88 (Ar), 62.55 (Ar), 87.24 (Ar, C_quat),

100.68 (CH₂), 120.93 (Ar%), 122.01 (Ar, C_quat), 126.59

(Ar%), 129.19 (Ar%), 129.73 (Ar, C_quat), 132.41 (Ar,

The required aniline (ﬁve equivalents) was added to a

,

solution of complex 4 containing 4 A molecular sieves

in THF (20 ml) or CH₂Cl₂(20 ml). The mixture was

stirred for 4 h. After ﬁltration through celite and evap-

oration of the solvent, the crude product washed with

n-hexane gave a compound which was identiﬁed as the

corresponding imine complex.

C

_quat), 151.06 (Ar%, C_quat), 153.68 (CHN), 234.52 (CꢂO).

EIMS; m/z (%): 404 ([M⁺], 6), 320 (13), 268 (100). IR

(KBr, cm⁻¹): w_max1933, 1868, 1841 (CꢂO), 1629 (CꢁN).

Anal. Found: C, 56.39; H, 4.22; N, 6.93. Calc. for

C₁₉H₁₆O₅N₂Cr (MW 404.35): C, 56.43; H, 3.99; N,

6.93%.

4.5.1. [p⁶-5-(N,N-Dimethylamino)-7-

(N%-4%-ﬂuorophenylimino)-1,3-benzodioxole]-

tricarbonylchromium (5a)

4-Fluoroaniline (0.70 ml, 7.16 mmol) and complex 4

(0.47 g, 1.43 mmol) in THF afforded 5a. Recrystallisa-

tion from CH₂Cl₂–n-hexane gave a red powder (0.32 g,

53%), m.p. (dec.) 144–145°C. ¹H-NMR (CDCl₃, 300

MHz): l=2.94 [s, 6H, N(CH₃)₂], 5.04 (d, 1H, J=1.2

Hz, ArH), 5.29 (d, 1H, J=1.2 Hz, ArH), 5.82 (s, 1H,

CH₂), 6.06 (s, 1H, CH₂), 7.05–7.24 (m, 4H, Ar%H), 8.47

(s, 1H, CHN). ¹³C-NMR (CDCl₃, 75 MHz): l=40.57

[N(CH₃)₂], 61.81 (Ar), 62.56 (Ar), 87.08 (Ar, C_quat),

100.72 (CH₂), 115.99 (d, 2Ar%, J=22.6 Hz), 122.02 (Ar,

4.5.4. [p⁶-5-(N,N-Dimethylamino)-7-(N%-phenylamino-

imino)-1,3-benzodioxole]tricarbonylchromium (5d)

Phenylhydrazine (0.60 ml, 5.62 mmol) and complex 4

(0.37 g, 1.13 mmol) in CH₂Cl₂afforded 5d. Recrystalli-

sation from CH₂Cl₂–n-hexane gave red crystals (0.27 g,

57%), m.p. (dec.) 139–142°C. ¹H-NMR (CDCl₃, 300

MHz): l=2.95 [(s, 6H, N(CH₃)₂], 5.02 (d, 1H, J=3.0

Hz, ArH), 5.13 (d, 1H, J=3.0 Hz, ArH), 5.79 (s, 1H,

CH₂), 6.04 (s, 1H, CH₂), 6.93–7.35 (m, 5H, Ar%H), 7.64

(s, 1H, CHN), 8.03 (s, 1H, NH). ¹³C-NMR (CDCl₃,

100 MHz): l=40.57 [N(CH₃)₂], 60.97 (Ar), 61.58 (Ar),

91.07 (CHN), 100.00 (CH₂), 112.84 (Ar%), 118.23 (Ar,

C_quat), 120.96 (Ar%), 127.80 (Ar, C_quat), 129.33 (Ar%),

130.11 (Ar, C_quat), 132.79 (Ar, C_quat), 143.34 (Ar%,

C_quat), 122.53 (d, 2Ar%, J=8.4 Hz), 129.76 (Ar, C_quat),

132.42 (Ar, C_quat), 147.12 (Ar%, C_quat), 153.52 (CHN),

161.61 (d, Ar%, J=243.6 Hz, C_quat), 234.51 (CꢂO).

EIMS; m/z (%): 422 ([M⁺], 1), 366 (9), 338 (17), 286

(100). IR (KBr, cm⁻¹): w_max1938, 1873, 1848 (CꢂO),

M. Filomena Costa et al. / Journal of Organometallic Chemistry 632 (2001) 27–40

35

C_quat), 235.20 (CꢂO). FABMS; m/z (%): 420 ([MH⁺],

13), 419 ([M⁺], 19), 363 (30), 335 (100), 283 (44). IR

(KBr, cm⁻¹): w_max3307 (NꢀH), 1939, 1867, 1822

(CꢂO), 1580 (CꢁN). Anal. Found: C, 54.79; H, 4.01; N,

9.87. Calc. for C₁₉H₁₇O₅N₃Cr (MW 419.36): C, 54.42;

H, 4.09; N, 10.2%.

J=2.1 Hz, ArH), 5.26 (d, 1H, J=5.1 Hz, CH), 5.44 (s,

1H, CH₂), 5.87 (s, 1H, CH₂), 6.15 (d, 1H, J=5.1 Hz,

CH), 7.28–7.57 (m, 5H, Ar%H). EIMS; m/z (%): 434

([M⁺−3CO], 1), 382 (100), 282 (46). IR (KBr, cm⁻¹):

w_max1937, 1871, 1851 (CꢂO), 1782, 1762 (CꢁO). Anal.

Found: C, 55.59, H, 4.26, N, 5.26. Calc. for

C₂₄H₂₂O₈N₂Cr (MW 518.44): C, 55.60; H, 4.28; N,

5.40%.

4.6. General method for synthesis of the i-lactam com-

plexes 6, 12, 13 and the imine complex 7

4.6.3. {1%-Phenyl-3%-acetoxy-4%-

To a stirred solution of the imine complex (one

equivalent) in CH₂Cl₂, Et₃N (six equivalents) previously

distilled and acetoxyacetyl chloride (three or six equiva-

lents) were added at 0°C. After 1 h, the reaction

mixture was allowed to warm up to r.t., and was

further stirred at this temperature for several hours.

When the reaction was completed (TLC), an aqueous

(aq.) solution of NH₄Cl (30 ml) was added and the aq.

layer was extracted with Et₂O (30 ml). The combined

organic extracts were dried, ﬁltered and concentrated to

give the crude product. Column chromatography (n-

hexane–Et₂O, 1:1) yielded the b-lactam complexes, in

some reactions the complexed and decomplexed ones

and the imine complex 7 were also obtained. The

compounds were recrystallised from Et₂O–n-hexane.

[p⁶-5-(N,N-dimethylamino)-1,3-benzodioxole]-

azetidin-2%-one}tricarbonylchromium (6c)

Imine 5c (0.17 g, 0.43 mmol), Et₃N (0.36 ml, 2.56

mmol) and acetoxyacetyl chloride (0.15 ml, 1.41 mmol)

after 20 h of reaction at r.t. afforded 6c. Recrystallisa-

tion yielded yellow crystals (0.092 g, 43%), m.p. (dec.)

1

142–144°C. H-NMR (CDCl₃, 300 MHz): l=2.06 (s,

3H, CH₃COO), 2.71 [s, 6H, (NCH₃)₂], 4.40 (s, 1H,

ArH), 5.09 (s, 1H, ArH), 5.47 (s, 1H, CH₂), 5.69 (d, 1H,

J=5.7 Hz, CH), 5.87 (s, 1H, CH₂), 6.45 (d, 1H, J=5.7

Hz, CH), 7.19–7.72 (m, 5H, Ar%H). EIMS; m/z (%):

504 ([M⁺], 6), 420 (13), 368 (41), 268 (100). IR (KBr,

cm⁻¹): w_max1935, 1850 (CꢂO), 1775, 1755 (CꢁO). Anal.

Found: C, 55.06; H, 3.99; N, 5.44. Calc. for

C₂₃H₂₀O₈N₂Cr (MW 504.42): C, 54.77; H, 4.00; N,

5.55%.

4.6.1. {1%-(4¦-Fluorophenyl)-3%-acetoxy-4%-

[p⁶-5-(N,N-dimethylamino)-1,3-benzodioxole]-

azetidin-2%-one}tricarbonylchromium (6a)

4.6.4. {p⁶-5-(N,N-Dimethylamino)-7-

[N%-(N¦-phenyl-acetoxyacetyl)imino]-1,3-benzodioxole}-

tricarbonylchromium (7)

Imine complex 5a (0.32 g, 0.76 mmol), Et₃N (0.64 ml,

4.56 mmol) and acetoxyacetyl chloride (0.25 ml, 2.28

mmol) after 20 h of reaction at r.t. afforded 6a. Recrys-

tallisation yielded yellow crystals (0.19 g, 50%), m.p.

Imine 5d (0.10 g, 0.24 mmol), Et₃N (0.20 ml, 1.43

mmol) and acetoxyacetyl chloride (0.15 ml, 1.43 mmol)

after 20 h of reaction at r.t. afforded 7. Recrystallisa-

tion yielded orange powder (0.060 g, 48%), m.p. (dec.)

1

(dec.) 138–140°C. H-NMR (CDCl₃, 300 MHz): l=

1

2.05 (s, 3H, CH₃COO), 2.72 [s, 6H, (NCH₃)₂], 4.37 (d,

1H, J=1.8 Hz, ArH), 5.11 (d, 1H, J=1.8 Hz, ArH),

5.46 (s, 1H, CH₂), 5.67 (d, 1H, J=5.4 Hz, CH), 5.88 (s,

1H, CH₂), 6.43 (d, 1H, J=5.4 Hz, CH), 7.13 (t, 2H,

J=9.0 Hz, Ar%H), 7.70 (m, 2H, Ar%H). EIMS; m/z (%):

386 ([M⁺−Cr(CO)₃], 10), 286 (29), 52 (100). IR (KBr,

cm⁻¹): w_max1947, 1880, 1862 (CꢂO), 1773, 1753 (CꢁO).

Anal. Found: C, 52.96; H, 3.62; N, 5.22. Calc. for

C₂₃H₁₉O₈N₂CrF (MW 522.41): C, 52.88; H, 3.67; N,

5.36%.

135–138°C. H-NMR (CDCl₃, 300 MHz): l=2.21 (s,

3H, CH₃COO), 2.91 [s, 6H, (NCH₃)₂], 4.66 (s, 1H,

ArH), 5.14 (s, 1H, ArH), 5.33 (dd, 2H, J=18.3 and

49.7 Hz, OCH₂), 5.66 (s, 1H, CH₂), 5.93 (s, 1H, CH₂),

7.23–7.59 (m, 5H, Ar%H). ¹³C-NMR (CDCl₃, 100

MHz): l=20.75 (CH₃), 40.46 [N(CH₃)₂], 60.90 (Ar),

61.46 (Ar), 62.34 (OCH₂), 87.18 (C_quat), 100.25 (CH₂),

119.60 (C_quat), 128.80 (Ar%), 130.05 (Ar%), 130.51 (Ar%),

132.74 (C_quat), 133.77 (C_quat), 135.82 (CHN), 167.96

(CꢁO), 170.98 (CꢁO), 234.57 (CꢂO). EIMS; m/z (%):

520 ([MH⁺], 7), 519 ([M⁺], 8), 463 (9), 435 (64), 383

(83), 327 (100). IR (KBr, cm⁻¹): w_max1946, 1857

(CꢂO), 1751, 1708 (CꢁO), 1578 (CꢁN).

4.6.2. {1%-Benzyl-3%-acetoxy-4%-

[p⁶-5-(N,N-dimethylamino)-1,3-benzodioxole]-

azetidin-2%-one}tricarbonylchromium (6b)

Imine complex 5b (0.13 g, 0.31 mmol), Et₃N (0.26 ml,

1.86 mmol) and acetoxyacetyl chloride (0.10 ml, 0.93

mmol) after 4 h of reaction at r.t. afforded 6b. Recrys-

tallisation yielded yellow crystals (0.096 g, 60%), m.p.

4.7. General procedure for the decomplexation of

i-lactams 6a–6d and complex 7

A solution of complexes 6 and 7 in ether was exposed

to air and sunlight at r.t. until TLC indicated that the

reaction had gone to completion. Filtration through

silica or celite and removal of the solvent gave decom-

plexed products which, when necessary, were further

1

(dec.) 123–126°C. H-NMR (CDCl₃, 300 MHz): l=

1.94 (s, 3H, CH₃COO), 2.50 [s, 6H, (NCH₃)₂], 3.88 (d,

1H, J=2.1 Hz, ArH), 4.44 (d, 1H, J=15.0 Hz,

NCH₂), 4.86 (d, 1H, J=15.0 Hz, NCH₂), 4.94 (d, 1H,

36

M. Filomena Costa et al. / Journal of Organometallic Chemistry 632 (2001) 27–40

puriﬁed by preparative layer chromatography (n-hex-

ane–Et₂O, 70:30) to afford products 8 and 9.

(Ar, C_quat), 148.57 (Ar%, C_quat), 161.80 (CꢁO), 168.69

(OCO). EIMS; m/z (%): 368 ([M⁺], 82), 268 (100), 249

(19), 207 (37). IR (ﬁlm, cm⁻¹): w_max1770, 1751 (CꢁO).

EIHRMS Found: 368.13667. Calc. for C₂₀H₂₀O₅N₂:

368.13669.

4.7.1. 1%-(4¦-Fluorophenyl)-3%-acetoxy-4%-[5-(N,N-

dimethylamino)-1,3-benzodioxole]azetidin-2%-one (8a)

Complex 6a (0.016 g, 0.043 mmol) afforded b-lactam

1

8a as a colourless oil (0.010 g, 60%). H-NMR (CDCl₃,

4.7.4. 5-(N,N-Dimethylamino)-7-

300 MHz): l=1.86 (s, 3H, CH₃COO), 2.82 [s, 6H,

(NCH₃)₂], 5.38 (d, 1H, J=4.8 Hz, CH), 5.80 (s, 1H,

CH₂), 5.90 (s, 1H, CH₂), 5.98 (d, 1H, J=4.8 Hz, CH),

6.01 (d, 1H, J=2.4 Hz, ArH), 6.37 (d, 1H, J=2.4 Hz,

ArH), 6.98 (t, 2H, J=8.4 Hz, Ar%H), 7.34 (m, 2H,

Ar%H). ¹³C-NMR (CDCl₃, 75 MHz): l=20.12 (CH₃),

41.56 [N(CH₃)₂], 57.48 (CH), 76.09 (CH), 96.51 (Ar),

101.21 (CH₂), 104.05 (Ar), 113.23 (Ar, C_quat), 115.97 (d,

2Ar%, J=22.6 Hz), 118.80 (d, 2Ar%, J=8.2 Hz), 133.25

(Ar%, C_quat), 138.13 (Ar, C_quat), 146.94 (Ar, C_quat),

148.56 (Ar, C_quat), 159.46 (d, Ar%, J=242.9 Hz, C_quat),

161.65 (CꢁO), 169.07 (OCO). EIMS; m/z (%): 386

([M⁺], 52), 286 (88), 43 (100). IR (ﬁlm, cm⁻¹): w_max

1762, 1637 (CꢁO). EIHRMS Found: 386.12724. Calc.

for C₂₀H₁₉O₅N₂F: 386.12725.

[N%-(N¦-phenyl-acetoxyacetyl)imino]-1,3-benzodioxole

(9)

Complex 7 (0.010 g, 0.019 mmol) afforded product 9

as a yellow powder (0.0064 g, 86%), m.p. (dec.) 160–

1

163°C. H-NMR (CDCl₃, 300 MHz): l=2.21 (s, 3H,

CH₃COO), 2.88 [s, 6H, (NCH₃)₂], 5.40 (s, 2H, CH₂),

5.88 (s, 2H, CH₂), 6.40 (d, 1H, J=2.4 Hz, ArH), 6.43

(d, 1H, J=2.4 Hz, ArH), 7.22 (m, 2H, Ar%H), 7.39 (s,

1H, CHN), 7.52 (m, 3H, Ar%H). ¹³C-NMR (CDCl₃, 100

MHz): l=20.87 (CH₃), 41.71 [N(CH₃)₂], 62.74

(OCH₂), 98.03 (Ar), 101.12 (CH₂), 101.34 (Ar), 115.38

(Ar, C_quat), 129.11 (Ar%), 129.79 (Ar%), 130.35 (Ar%),

134.23 (C_quat), 137.93 (CHN), 146.90 (C_quat), 148.98

(C_quat), 168.34 (CꢁO), 171.16 (OCO). EIMS; m/z (%):

383 ([M⁺], 81), 283 (17), 190 (48), 164 (72), 43 (100). IR

(KBr, cm⁻¹): w_max1742, 1698 (CꢁO), 1638 (CꢁN).

EIHRMS Found: 383.14879. Calc. for C₂₀H₂₁O₅N₃:

383.14757.

4.7.2. 1%-Benzyl-3%-acetoxy-4%-[5-(N,N-dimethylamino)-

1,3-benzodioxole]azetidin-2%-one (8b)

Complex 6b (0.010 g, 0.019 mmol) afforded b-lactam

1

8b as a colourless oil (0.006 g, 80%). H-NMR (CDCl₃,

4.8. (7R,1%S)-[p⁶-5-(N,N-Dimethylamino)-7-(N%-methyl-

benzylimino)-1,3-benzodixole]tricarbonylchromium (10I)

and (7S,1S%)-[p⁶-5-(N,N-dimethylamino)-7-(N%-methyl-

benzylimino)-1,3-benzodioxole]tricarbonylchromium

(10II)

300 MHz): l=1.81 (s, 3H, CH₃COO), 2.83 [s, 6H,

(NCH₃)₂], 3.98 (d, 1H, J=15.0 Hz, NCH₂), 4.79 (d,

1H, J=15.0 Hz, NCH₂), 4.83 (d, 1H, J=4.5 Hz, CH),

5.80 (d, 1H, J=4.5 Hz, CH), 5.84 (s, 2H, CH₂), 5.92

(d, 1H, J=2.4 Hz, ArH), 6.37 (d, 1H, J=2.4 Hz,

ArH), 7.25 (m, 5H, Ar%H). ¹³C-NMR (CDCl₃, 100

MHz): l=20.16 (CH₃), 41.66 [N(CH₃)₂], 44.73 (CH₂),

56.81 (CH), 76.89 (CH), 96.39 (Ar), 101.02 (CH₂),

104.48 (Ar), 113.51 (Ar, C_quat), 127.88 (Ar%), 128.45

(Ar%), 128.74 (Ar%), 134.47 (Ar, C_quat), 138.24 (Ar,

C_quat), 146.62 (Ar, C_quat), 148.28 (Ar%, C_quat), 164.64

(CꢁO), 169.16 (OCO). EIMS; m/z (%): 382 ([M⁺], 11),

282 (6), 207 (7), 162 (18), 120 (67), 91 (98), 43 (100). IR

(ﬁlm, cm⁻¹): w_max1752, 1677 (CꢁO). EIHRMS Found:

382.15212. Calc. for C₂₁H₂₂O₅N₂: 382.15232.

(S)-(−)-(a)-Methylbenzylamine (0.40 ml, 2.89

mmol) was added to an Et₂O (50 ml) solution of

,

complex 4 (0.95 g, 2.89 mmol) containing 4 A molecu-

lar sieves. The mixture was stirred for 4 h at r.t. and

ﬁltered through celite. TLC (Et₂O–n-hexane–Et₃N,

1

80:15:5 and Et₂O–n-hexane, 75:25) and H-NMR spec-

trum showed a mixture of two compounds in a 1:1

ratio. Separation of the two complexes was only possi-

ble by recrystallisation from CH₂Cl₂–Et₂O–n-hexane

and afforded complexes 10I and 10II. First, the com-

plex 10I was afforded (0.35 g, 30%) as red crystals.

With no more complex 10I in solution the complex 10II

recrystallised as an orange powder (0.15 g, 12%). Fol-

lowing the order of recrystallisation — complex 10I:

4.7.3. 1%-Phenyl-3%-acetoxy-4%-[5-(N,N-dimethylamino)-

1,3-benzodioxole]azetidin-2%-one (8c)

Complex 6c (0.022 g, 0.043 mmol) afforded b-lactam

1

8c as a colourless oil (0.016 g, 74%). H-NMR (CDCl₃,

1

m.p. (dec.) 138–140°C. H-NMR (CDCl₃, 300 MHz):

300 MHz): l=1.86 (s, 3H, CH₃COO), 2.81 [s, 6H,

(NCH₃)₂], 5.41 (d, 1H, J=4.8 Hz, CH), 5.81 (s, 1H,

CH₂), 5.90 (s, 1H, CH₂), 5.98 (d, 1H, J=4.8 Hz, CH),

6.04 (d, 1H, J=2.1 Hz, ArH), 6.37 (d, 1H, J=2.1 Hz,

ArH), 7.07–7.38 (m, 5H, Ar%H). ¹³C-NMR (CDCl₃, 75

MHz): l=19.77 (CH₃), 41.33 [N(CH₃)₂], 57.22 (CH),

75.98 (CH), 96.44 (Ar), 101.01 (CH₂), 104.44 (Ar),

113.85 (Ar, C_quat), 117.66 (2Ar%), 124.44 (Ar%), 128.89

(2Ar%), 137.20 (Ar, C_quat), 138.24 (Ar, C_quat), 147.10

l=1.61 (d, 3H, J=6.6 Hz, CH₃), 2.89 [s, 6H,

N(CH₃)₂], 4.67 (q, 1H, J=6.6 and 13.4 Hz, CH), 4.89

(d, 1H, J=2.1 Hz, ArH), 5.20 (d, 1H, J=2.1 Hz,

ArH), 5.77 (s, 1H, CH₂), 6.01 (s, 1H, CH₂), 7.38–7.40

(m, 5H, Ar%H), 8.35 (s, 1H, CHN). ¹³C-NMR (CDCl₃,

75 MHz): l=23.72 (CH₃), 40.55 [(NCH₃)₂], 62.38

(2Ar), 68.79 (CHAr%), 88.31 (Ar, C_quat), 100.44 (CH₂),

121.22 (Ar, C_quat), 126.89 (Ar%), 127.09 (Ar%), 128.44

M. Filomena Costa et al. / Journal of Organometallic Chemistry 632 (2001) 27–40

37

(Ar%), 129.64 (Ar, C_quat), 132.41 (Ar, C_quat), 143.40 (Ar%,

_quat), 152.83 (CHN), 234.44 (CꢂO). EIMS; m/z (%):

according to the general procedure for the preparation

of imine complexes. Recrystallisation from CH₂Cl₂–n-

hexane afforded 11a as a red powder (0.21 g, 70%),

m.p. (dec.) 145–147°C. [h]²_D⁵= −490 (c=0.10,

C

376 ([M⁺−2CO], 1), 348 (4), 296 (100). IR (KBr,

cm⁻¹): w_max1939, 1880, 1848 (CꢂO), 1641 (CꢁN). Anal.

Found: C, 58.39; H, 4.67; N, 6.34. Calc. for

C₁₂H₂₀O₅N₂Cr (MW 432.40): C, 58.33; H, 4.66; N,

6.48%. Complex 10II: m.p. (dec.) 122–125°C. ¹H-NMR

(CDCl₃, 300 MHz): l=1.61 (d, 3H, J=6.6 Hz, CH₃),

2.90 [s, 6H, N(CH₃)₂], 4.59 (q, 1H, J=6.6 and 13.1 Hz,

CH), 4.98 (d, 1H, J=1.8 Hz, ArH), 5.20 (d, 1H,

J=1.8 Hz, ArH), 5.77 (s, 1H, CH₂), 5.98 (s, 1H, CH₂),

7.23–7.43 (m, 5H, Ar%H), 8.40 (s, 1H, CHN). ¹³C-NMR

(CDCl₃, 75 MHz): l=24.96 (CH₃), 40.48 [(NCH₃)₂],

62.14 (Ar), 62.44 (Ar), 69.97 (CHAr%), 87.90 (Ar, C_quat),

100.54 (CH₂), 121.51 (Ar, C_quat), 126.65 (Ar%), 127.06

(Ar%), 128.47 (Ar%), 129.66 (Ar, C_quat), 132.53 (Ar,

C_quat), 144.24 (Ar%, C_quat), 152.20 (CHN), 234.61 (CꢂO).

EIMS; m/z (%): 376 ([M⁺−2CO], 1), 348 (4), 296

(100). IR (KBr, cm⁻¹): w_max1937, 1883, 1852 (CꢁO),

1646 (CꢁN). Anal. Found: C, 58.22; H, 4.59; N, 6.42.

Calc. for C₁₂H₂₀O₅N₂Cr (MW 432.40): C, 58.33; H,

4.66; N, 6.48%.

1

CHCl₃). H-NMR (CDCl₃, 300 MHz): l=2.94 [s, 6H,

N(CH₃)₂], 5.04 (d, 1H, J=1.2 Hz, ArH), 5.29 (d, 1H,

J=1.2 Hz, ArH), 5.82 (s, 1H, CH₂), 6.06 (s, 1H, CH₂),

7.05–7.24 (m, 4H, Ar%H), 8.47 (s, 1H, CHN). ¹³C-NMR

(CDCl₃, 75 MHz): l=40.57 [N(CH₃)₂], 61.81 (Ar),

62.56 (Ar), 87.08 (Ar, C_quat), 100.72 (CH₂), 115.99 (d,

2Ar%, J=23.3 Hz), 122.02 (Ar, C_quat), 122.53 (d, 2Ar%,

J=8.3 Hz), 129.76 (Ar, C_quat), 132.42 (Ar, C_quat),

147.12 (Ar%, C_quat), 153.52 (CHN), 161.61 (d, Ar%, J=

243.6 Hz, C_quat), 234.51 (CꢂO). EIMS; m/z (%): 422

([M⁺], 1), 366 (2), 338 (6), 286 (100). IR (KBr, cm⁻¹):

w_max1938, 1873, 1848 (CꢂO), 1629 (CꢁN). EIHRMS

Found: 422.03631. Calc. for C₁₉H₁₅O₅N₂CrF:

422.03646.

4.10.2. (7R)-[p⁶-5-(N,N-Dimethylamino)-7-(N%-

benzylimino)-1,3-benzodioxole]tricarbonylchromium

(11b)

Benzylamine (ﬁve equivalents, 0.18 ml, 1.66 mmol) in

CH₂Cl₂(20 ml) and complex 4I (0.11 g, 0.33 mmol)

afforded 11b, according to the general procedure for

the preparation of racemic imine complexes. Recrys-

tallisation from CH₂Cl₂–n-hexane afforded 11b as an

orange powder (0.12 g, 86%), m.p. (dec.) 128–130°C.

4.9. (7R)-[p⁶-5-(N,N-Dimethylamino)-7-formyl-1,3-

benzodioxole]tricarbonylchromium (4I)

Complex 10I (0.42 g, 0.97 mmol) was dissolved in

THF (15 ml) and a solution of concentrated HCl (six

drops) in H₂O (2 ml) was added. After stirring for 30

min, a saturated solution of NH₄Cl (20 ml) and Et₂O

(20 ml) was added. The organic phase was dried, con-

centrated and puriﬁed by column chromatography (n-

hexane–Et₂O, 50:50) to yield complex 4I. Recrystalli-

sation from CH₂Cl₂–n-hexane gave a red powder

(0.23g, 72%), m.p. (dec.) 119–121°C. [h]²_D⁵= −364

1

[h]²_D⁵= −835 (c=0.15, CHCl₃). H-NMR (CDCl₃, 300

MHz): l=2.89 [s, 6H, N(CH₃)₂], 4.70–4.92 (m, 3H,

CH₂and ArH), 5.22 (d, 1H, J=2.1 Hz, ArH), 5.78 (s,

1H, CH₂), 6.02 (s, 1H, CH₂), 7.26–7.40 (m, 5H, Ar%H),

8.40 (s, 1H, CHN). ¹³C-NMR (CDCl₃, 100 MHz):

l=40.52 [N(CH₃)₂], 61.92 (Ar), 62.23 (Ar), 64.99

(CH₂), 87.99 (Ar, C_quat), 100.47 (CH₂), 121.04 (Ar,

1

(c=0.23, CHCl₃). H-NMR (CDCl₃, 300 MHz): l=

C_quat), 127.39 (Ar%), 128.41 (Ar%), 128.66 (Ar%), 129.89

2.88 [s, 6H, N(CH₃)₂], 4.64 (d, 1H, J=2.4 Hz, ArH),

5.47 (d, 1H, J=2.4 Hz, ArH), 5.85 (s, 1H, CH₂), 6.11

(s, 1H, CH₂), 10.01 (s, 1H, CHO). ¹³C-NMR (CDCl₃,

75 MHz): l=40.56 [(NCH₃)₂], 61.46 (Ar), 64.40 (Ar),

82.99 (Ar, C_quat), 101.50 (CH₂), 124.83 (Ar, C_quat),

128.14 (Ar, C_quat), 131.08 (Ar, C_quat), 185.96 (CꢁO),

233.37 (CꢂO). EIMS; m/z (%): 329 ([M⁺], 9), 273 (7),

245 (18), 193 (100). IR (KBr, cm⁻¹): w_max1946, 1891,

1847 (CꢂO), 1688 (CꢁO). Anal. Found: C, 47.29; H, 39;

N, 4.06. Calc. for C₁₃H₁₁O₆NCr (MW 329.23): C,

47.43; H, 3.37; N, 4.25%.

(Ar, C_quat), 132.60 (Ar, C_quat), 138.04 (Ar%, C_quat),

155.29 (CHN), 234.82 (CꢂO). EIMS; m/z (%): 418

([M⁺], 1), 362 (9), 334 (34), 282 (87), 179 (41), 91 (99),

52 (100). IR (KBr, cm⁻¹): w_max1938, 1870, 1844 (CꢂO),

1646 (C=N). Anal. Found: C, 57.19; H, 4.28; N, 6.52.

Calc. for C₂₀H₁₈O₅N₂Cr (MW 418.37): C, 57.42; H,

4.34; N, 6.70%.

4.11. Synthesis of enantiomerically pure i-lactams 12

and 13

4.11.1. (7R,3%R,4%S)-{1%-(4¦-Fluorophenyl)-3%-acetoxy-

4%-[p⁶-5-(N,N-dimethylamino)-1,3-benzodioxole]-

azetidin-2%-one}tricarbonylchromium (12a) and the

corresponding decomplexed product (3%R,4%S)-

{1%-(4¦-ﬂuorophenyl)-3%-acetoxy-4%-[5-(N,N-dimethyl-

amino)-1,3-benzodioxole]azetidin-2%-one} (13a)

These complexes were prepared from imine 11a (0.15

g, 0.36 mmol), Et₃N (0.30 ml, 2.13 mmol) and acetoxy-

4.10. Synthesis of enantiomerically pure imine

complexes 11

4.10.1. (7R)-[p⁶-5-(N,N-Dimethylamino)-7-

(N%-4%-ﬂuoro-phenylimino)-1,3-benzodioxole]-

tricarbonylchromium (11a)

4-Fluoroaniline (0.33 ml, 3.50 mmol) in THF (20 ml)

and complex 4I (0.23 g, 0.70 mmol) afforded 11a,

38

M. Filomena Costa et al. / Journal of Organometallic Chemistry 632 (2001) 27–40

cm⁻¹): w_max1937, 1871, 1851 (CꢂO), 1782, 1762 (CꢁO).

acetyl chloride (0.24 ml, 2.14 mmol) after 3 days at r.t.,

according to the general method for preparation of

b-lactam complexes. The crude product was obtained

as an orange oil, which corresponded to a mixture of

b-lactam complex 12a and its decomplexed form 13a.

Column chromatography (n-hexane–Et₂O, 25:75) of

this mixture yielded product 13a as a colourless oil

(0.066 g, 48%) and complex 12a, which recrystallised

from Et₂O–n-hexane as yellow crystals (0.060 g, 32%).

Following the order of elution — b-lactam 13a:

Found: 518.07770. Calc. for C₂₄H₂₂O₈N₂Cr: 518.07758.

4.11.3. (3%R,4%S)-{1%-Benzyl-3%-acetoxy-4%-[5-(N,N-

dimethylamino)-1,3-benzodioxole]azetidin-2%-one} (13b)

Complex 12b (0.050 g, 0.096 mmol) afforded after

decomplexation procedure b-lactam 12b as a colourless

1

oil (0.025 g, 70%). [h]²_D⁵= +18 (c=0.30, CHCl₃). H-

NMR (CDCl₃, 300 MHz): l=1.81 (s, 3H, CH₃COO),

2.83 [s, 6H, (NCH₃)₂], 3.98 (d, 1H, J=15.0 Hz, NCH₂),

4.79 (d, 1H, J=15.0 Hz, NCH₂), 4.83 (d, 1H, J=4.5

Hz, CH), 5.80 (d, 1H, J=4.5 Hz, CH), 5.84 (s, 2H,

CH₂), 5.92 (d, 1H, J=2.4 Hz, ArH), 6.37 (d, 1H,

J=2.4 Hz, ArH), 7.25 (m, 5H, Ar%H). ¹³C-NMR

(CDCl₃, 100 MHz): l=20.16 (CH₃), 41.66 [N(CH₃)₂],

44.73 (CH₂), 56.81 (CH), 76.89 (CH), 96.39 (Ar), 101.02

(CH₂), 104.48 (Ar), 113.51 (Ar, C_quat), 127.88 (Ar%),

128.45 (Ar%), 128.74 (Ar%) 134.47 (Ar, C_quat), 138.24 (Ar,

C_quat), 146.62 (Ar, C_quat), 148.28 (Ar%, C_quat), 164.64

(CꢁO), 169.16 (OCO). EIMS; m/z (%): 382 ([M⁺], 100),

282 (52), 91 (98), 43 (84). IR (ﬁlm, cm⁻¹): w_max1752,

1677 (CꢁO). EIHRMS Found: 382.15358. Calc. for

C₂₁H₂₂O₅N₂: 382.15232.

1

[h]²_D⁵= −17 (c=0.14, CHCl₃). H-NMR (CDCl₃, 300

MHz): l=1.86 (s, 3H, CH₃COO), 2.82 [s, 6H,

(NCH₃)₂], 5.38 (d, 1H, J=4.8 Hz, CH), 5.80 (s, 1H,

CH₂), 5.90 (s, 1H, CH₂), 5.98 (d, 1H, J=4.8 Hz, CH),

6.01 (d, 1H, J=2.4 Hz, ArH), 6.37 (d, 1H, J=2.4 Hz,

ArH), 6.98 (t, 2H, J=8.4 Hz, Ar%H), 7.34 (m, 2H,

Ar%H). ¹³C-NMR (CDCl₃, 75 MHz): l=20.12 (CH₃),

41.56 [N(CH₃)₂], 57.48 (CH), 76.09 (CH), 96.51 (Ar),

101.21 (CH₂), 104.05 (Ar), 113.23 (Ar, C_quat), 115.97 (d,

2Ar%, J=22.6 Hz), 118.80 (d, 2Ar%, J=8.2 Hz), 133.25

(Ar%, C_quat), 138.13 (Ar, C_quat), 146.94 (Ar, C_quat),

148.56 (Ar, C_quat), 159.46 (d, Ar%, J=242.9, C_quat),

161.65 (CꢁO), 169.07 (OCO). EIMS; m/z (%): 386

([M⁺], 18), 286 (100). IR (ﬁlm, cm⁻¹): w_max1762, 1637

(CꢁO). EIHRMS Found: 386.12727. Calc. for

C₂₀H₁₉O₅N₂F: 386.12725. b-lactam complex 12a: m.p.

4.12. Crystal structure determination of complex 4I

4.12.1. Crystal data

C₁₃H₁₁CrNO₆, M_r=329.23. The crystals are mono-

clinic and belong to the space group P2₁, with cell

1

(dec.) 143–145°C. [h]²_D⁵= +10 (c=0.10, CHCl₃). H-

NMR (CDCl₃, 300 MHz): l=2.05 (s, 3H, CH₃COO),

2.72 [s, 6H, (NCH₃)₂], 4.37 (d, 1H, J=1.8 Hz, ArH),

5.11 (d, 1H, J=1.8 Hz, ArH), 5.46 (s, 1H, CH₂), 5.67

(d, 1H, J=5.4 Hz, CH), 5.88 (s, 1H, CH₂), 6.43 (d, 1H,

J=5.4 Hz, CH), 7.13 (t, 2H, J=9.0 Hz, Ar%H), 7.70

(m, 2H, Ar%H). EIMS; m/z (%): 438 ([M⁺−3CO], 1),

386 (66), 286 (100). IR (KBr, cm⁻¹): w_max1947, 1880,

1862 (CꢂO), 1773, 1753 (CꢁO). Found: 522.05253. Calc.

for C₂₃H₁₉O₈N₂CrF: 522.05251.

,

dimensions a=7.688(3) A, b=13.245(4) A, c=

3

,

13.463(5) A, i=97.16(4)°, V=1360.2(8) A , Z=2

(with two molecules in the asymmetric unit with the

same conﬁguration), D_calc=1.61 g cm⁻³, v=0.868

mm⁻¹, F(000)=672. Of the 8654 reﬂections measured,

4227 were independent (R_int=0.0415) and 3896 were

observed [I\2|(I)]. Full anisotropic reﬁnement for all

non-hydrogen atoms yielded the ﬁnal R-values: R₁[I\

2|(I)]=4.30%, wR₂[I\2|(I)]=11.00%, R₁(all

data)=4.95% and wR₂(all data)=12.65%.

4.11.2. (7R,3%R,4%S)-{1%-Benzyl-3%-acetoxy-4%-

[p⁶-5-(N,N-dimethylamino)-1,3-benzodioxole]-

4.13. Crystal structure determination of complex 12a

azetidin-2%-one}tricarbonylchromium (12b)

Imine 11b (0.10 g, 0.20 mmol), Et₃N (0.24 ml, 1.44

mmol) and acetoxyacetyl chloride (0.08 ml, 0.72 mmol)

after 4 h of reaction at r.t. afforded 12b. Recrystallisa-

tion from Et₂O–n-hexane yielded a yellow powder

(0.050g, 40%), m.p. (dec.) 112–114°C. [h]²_D⁵= +6 (c=

4.13.1. Crystal data

C₂₃H₁₉CrN₂O₈F, M_r=522.40. The crystals are mon-

oclinic and belong to the space group P2₁, with cell

,

dimensions a=18.122(10) A, b=7.277(2) A, c=

3

,

19.173(11) A, i=108.36(6)°, V=2400(2) A , Z=2

(with two molecules in the asymmetric unit with the

same conﬁguration), D_calc=1.45 g cm⁻³, v=0.535

mm⁻¹, F(000)=1072. Of the 15 669 reﬂections mea-

sured, 7196 were independent (R_int=0.0581) and 5713

were observed [I\2|(I)]. Full anisotropic reﬁnement

for all non-hydrogen atoms yielded the ﬁnal R-values:

R₁[I\2|(I)]=4.44%, wR₂[I\2|(I)]=11.25%, R₁

(all data)=5.57% and wR₂(all data)=13.14%.

1

0.10, Et₂O). H-NMR (CDCl₃, 300 MHz): l=1.94 (s,

3H, CH₃COO), 2.50 [s, 6H, (NCH₃)₂], 3.88 (d, 1H,

J=2.1 Hz, ArH), 4.44 (d, 1H, J=15.0 Hz, NCH₂),

4.86 (d, 1H, J=15.0 Hz, NCH₂), 4.94 (d, 1H, J=2.1

Hz, ArH), 5.26 (d, 1H, J=5.1 Hz, CH), 5.44 (s, 1H,

CH₂), 5.87 (s, 1H, CH₂), 6.15 (d, 1H, J=5.1 Hz, CH),

7.28–7.57 (m, 5H, Ar%H). EIMS; m/z (%): 434 ([M⁺−

3CO]), 2), 382 (100), 282 (52), 91 (85), 43 (61). IR (KBr,

M. Filomena Costa et al. / Journal of Organometallic Chemistry 632 (2001) 27–40

39

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5. Supplementary material

Full details of data collection and reﬁnement, tables

of ﬁnal atomic coordinates, anisotropic thermal

parameters for all non-hydrogen atoms, hydrogen

atomic coordinates, complete tables for bond lengths

and angles as well as torsion angles have been deposited

with the Cambridge Crystallographic Data Centre,

CCDC no. 157891 for complex 4I and no. 157871 for

complex 12a. Copies of this information may be ob-

tained free of charge from The Director, CCDC, 12

Union Road, Cambridge CB2 1EZ, UK (Fax: 44-1223-

336033; e-mail: deposit@ccdc.cam.ac.uk or www: http:/

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.

Article Doi

Synthesis of chiral (7R)-[η6-5-(N,N-dimethylamino)-7-formyl-1,3-benzodioxole]-chromium complex and its application in the synthesis of optically active cis-β-lactam

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