New axially chiral atropos and tropos secondary diamines as ligands for enantioselective intramolecular hydroamination

Available online at www.sciencedirect.com

Tetrahedron: Asymmetry 19 (2008) 82–92

New axially chiral atropos and tropos secondary diamines as ligands

for enantioselective intramolecular hydroamination

Isabelle Aillaud,^aKaren Wright,^bJacqueline Collin,^aEmmanuelle Schulz^a,*and

Jean-Paul Mazaleyrat^b,*

a

ˆ

Equipe de Catalyse Mole´culaire, ICMMO, UMR 8182, Universite´ Paris-Sud 11, Bat 420, 91405 Orsay Cedex, France

^bILV, UMR CNRS 8180, Universite´ de Versailles, 78035 Versailles Cedex, France

Received 29 October 2007; accepted 22 November 2007

Available online 4 January 2008

Abstract—The highly constrained, axially chiral atropos diamines (Rⁱ,S,S)-1, (Rⁱ,R,R)-1 and (Rⁱ,S,R)-1 and their tropos analogue (Rⁱ)-2

have been prepared via bis-N,N-dialkylation of (R)-2,2⁰-diamino-1,1⁰-binaphthyl, using either (R)- or (S)-2,2⁰-bis(bromomethyl)-1,1⁰-

binaphthyl and 2,2⁰-bis(bromomethyl)-1,1⁰-biphenyl as alkylating agents, followed by selective nickel chloride-catalysed bis(mono-

hydrogenolysis) of the tertiary amino groups of the so-obtained (Rⁱ,R,R)-4, (Rⁱ,S,S)-4, (Rⁱ,R,S)-4 and (Rⁱ)-6, respectively, by lithium alu-

minium hydride in reﬂuxing THF or THF/diglyme. The diamines (Rⁱ,S,S)-1, (Rⁱ,R,R)-1, (Rⁱ,S,R)-1 and (Rⁱ)-2 have been evaluated as

ligands for ytterbium-catalysed intramolecular hydroamination and compared to the ligand 1,1⁰-binaphthyl-2,2⁰-bis(benzylamine)

(Rⁱ)-3. They aﬀorded highly active catalysts for the cyclisation of aminopentenes and aminohexenes with up to 58% ee.

1. Introduction

ligands with chirality arising from a biphenylamine or

binaphthylamine moiety were also successfully used for

enantioselective rare-earth-catalysed hydroaminations.⁴

The use of biaryl amines with axial chirality for the prepa-

ration of rare earth amides was ﬁrst described by Scott

et al., although low enantioselectivities were obtained for

the cyclisation of an aminopentene.⁵

Enantioselective hydroamination reactions have been the

focus of increased interest in recent years as atom economic

ways for the formation of carbon–nitrogen bonds, and

especially for intramolecular reactions, which allow the

synthesis of scalemic nitrogen heterocycles.¹Since the pio-

neering work of Marks et al. showing the activity and

enantioselectivity of lanthanocenes for the catalysis of

intramolecular hydroamination,²a large variety of ligands

and diﬀerent metals have been evaluated. Up until now,

rare earths aﬀorded the most active catalysts. As for

numerous other catalytic reactions, ligands with chiral

binaphthyl or biphenyl moieties have allowed the prepara-

tion of eﬃcient enantioselective rare earth-catalysts for the

cyclisation of aminoalkenes. Bisphenolate and bisnaphtho-

lates have been studied by Hultzsch et al. and furnished the

highest enantiomeric excess to date (95%) for an intra-

molecular hydroamination reaction.³Phosphine oxide-

substituted bisnaphtholate and bisphenolate or bis thiolate

In previous studies, we synthesised a new family of lantha-

nide amide ate complexes from 1,1⁰-binaphthyl-2,2⁰-

bis(alkylamines), by metathetic reactions of the dilithium

salts of the ligands with anhydrous LnCl₃. These ate com-

plexes were eﬃciently used as enantioselective catalysts for

the intramolecular hydroamination of gem-substituted

aminopentene or aminohexene derivatives to the corre-

sponding chiral pyrrolidines or piperidines. Ytterbium cat-

alysts in particular combined a high reactivity (>90–100%

conversion within a few hours at 25 °C with a catalyst ratio

of 6 mol %) and moderate to high enantioselectivities (up

to 87% ee).⁶In the search for even more potent catalysts,

we considered the introduction of binaphthyl or biphenyl

units linked via a methylene spacer to the NH groups

instead of alkyl substituents, to enhance both steric and

chiral barriers. Herein we report the synthesis of highly

constrained polybinaphthyl diastereoisomeric diamines

*

Corresponding authors. Fax: +33 0 1 69 15 46 80 (E.S.); fax: +33 0 1 39

25 44 52 (J.-P.M.); e-mail addresses: emmaschulz@icmo.u-psud.fr; jean-

paul.mazaleyrat@chimie.uvsq.fr

doi:10.1016/j.tetasy.2007.11.029

I. Aillaud et al. / Tetrahedron: Asymmetry 19 (2008) 82–92

83

amine (DIEA) in toluene–acetonitrile 1:1 at 85 °C for 6

days, gave the bis-tertiary diamine (Rⁱ,R,R)-4 in 66% yield,

accompanied by the corresponding primary–tertiary dia-

mine (Rⁱ,R)-5 in 29% yield.^àIn the same manner, the treat-

ment of enantiomerically pure (R)-2,2⁰-diamino-1,1⁰-

binaphthyl with enantiomerically pure (S)-2,2⁰-bis(bromo-

methyl)-1,1⁰-binaphthyl^15–19and DIEA in toluene–aceto-

nitrile 1:1 at 85 °C for 7 days aﬀorded (Rⁱ,S,S)-4 in 87%

yield and (Rⁱ,S)-5 in 12% yield. The reaction of the

side products (Rⁱ,R)-5 and (Rⁱ,S)-5 with enantiomerically

pure (S)- and (R)-2,2⁰-bis(bromomethyl)-1,1⁰-binaphthyl,

respectively, under similar experimental conditions, gave

(Rⁱ,R,S)-4 in 49% and 47% yields. Finally, the reaction of

enantiomerically pure (R)-2,2⁰-diamino-1,1⁰-binaphthyl

with 2,2⁰-bis(bromomethyl)-1,1⁰-biphenyl under the same

conditions aﬀorded (Rⁱ)-6 in 87% yield after 6 days at

85 °C (Fig. 2).

NH

(Rⁱ

,

S,S)-1

(Rⁱ)-2

(Rⁱ)-3

[

(Rⁱ

R

,R)-1]

(Rⁱ

S,R)-1]

Figure 1. Chemical structures of the polybinaphthyl/biphenyl atropos and

tropos diamines (Rⁱ,S,S)-1 [or (Rⁱ,R,R)-1 or (Rⁱ,S,R)-1 (not shown)] and

(Rⁱ)-2 compared to the 1,1⁰-binaphthyl-2,2⁰-bis(benzylamine) model (Rⁱ)-3.

(Rⁱ,S,S)-1, (Rⁱ,R,R)-1, (Rⁱ,S,R)-1 and their conformationally

labile analogue (Rⁱ)-2, (Fig. 1). Their use as ytterbium li-

gands for the enantioselective catalysis of intramolecular

hydroamination is reported and compared to the results

obtained with 1,1⁰-binaphthyl-2,2⁰-bis(benzylamine) (Rⁱ)-3

as a ligand.^6b

The formation of the target bis-secondary diamines

(Rⁱ,S,S)-1, (Rⁱ,R,R)-1 and (Rⁱ,S,R)-1 from (Rⁱ,R,R)-4,

(Rⁱ,S,S)-4 and (Rⁱ,R,S)-4, respectively, was expected to

occur following our previously reported results: the

hydrogenolysis of related N-substituted 4,5-dihydro-3H-

dinaphtho[2,1-c:1⁰,2⁰-e]azepines and the corresponding

quaternary ammonium salts by lithium aluminium hydride,

provided easy access to the unsymmetrical binaphthyl

secondary or tertiary amines in high yields.¹³However,

when (Rⁱ,R,R)-4 was treated with a large excess of LiAlH₄

in reﬂuxing THF, no reaction occurred after 24 h. The

important steric constraint associated with the chemical

structure of (Rⁱ,R,R)-4 could explain its lack of reactivity.

The reaction was then attempted in the presence of

nickel(II) chloride, previously shown to be a highly eﬃcient

catalyst for the total hydrogenolysis of quaternary

ammonium salts of N-substituted 4,5-dihydro-3H-dinaph-

tho[2,1-c:1⁰,2⁰-e]azepines derived from l-ephedrine, to form

2,2⁰-dimethyl-1,1⁰-binaphthyl¹⁵(Fig. 3).

The chiral rigid atropos⁷ligands (Rⁱ,S,S)-1, (Rⁱ,R,R)-1 and

(Rⁱ,S,R)-1 belong to the class of 2,2⁰-substituted-

1,1⁰-binaphthyl derivatives, a very important family of

compounds, showing outstanding chiral discrimination

properties in a variety of reactions.⁸Multibinaphthyl oxy-

gen-, nitrogen- or phosphorous-based dimers, oligomers

and polymers have also been widely used as chiral auxilia-

ries to provide high levels of stereochemical control.⁹On

the other hand the use of chiral ﬂexible tropos⁷ligands,

such as (Rⁱ)-2 in which asymmetric activation by the inter-

nal (Rⁱ)-binaphthyl moiety through tropo-inversion of the

chiral axis of the biphenyl units may occur, has been shown

to allow remarkable ampliﬁcation of both catalytic activity

and enantioselectivity.¹⁰Herein we report an eﬃcient

method for the synthesis of these chiral diamines as single

enantiomers.

When (Rⁱ,R,R)-4 was treated with a large excess of LiAlH₄

and NiCl₂in reﬂuxing THF for only 7 h, the desired di-

amine (Rⁱ,S,S)-1 was indeed obtained as a single product,

in 83–88% yield after chromatography. Several duplicate

experiments at various scales (up to 0.43 mmol) and with

various reaction times (7 h and 16 h) gave a similar yield

(see Section 4).

2. Results and discussion

2.1. Synthesis

Similar treatment of (Rⁱ,S,S)-4 and (Rⁱ,R,S)-4 with LiAlH₄

and NiCl₂in reﬂuxing THF for 7–16 h aﬀorded the target

bis-secondary diamines (Rⁱ,R,R)-1 in 73–80% yield and

(Rⁱ,S,R)-1 in 62% yield, respectively. Remarkably, the

expected formation of 2,2⁰-dimethyl-1,1⁰-binaphthyl as a

side product did not occur.^13,15Nickel chloride had been

previously shown to catalyse the hydrogenolysis of both

aryl allyl ethers and aryl benzyl ethers by lithium

aluminium hydride,²⁰as well as the hydrogenolysis of

N-alkyl-N-allyl-arylamines, but surprisingly not of

N-alkyl-N-benzyl-arylamines.²¹In this case, and for the

The bis-secondary diamines (Rⁱ,S,S)-1, (Rⁱ,R,R)-1,

(Rⁱ,S,R)-1 and (Rⁱ)-2 were readily prepared in two steps

from (R)-2,2⁰-diamino-1,1⁰-binaphthyl. The gem-dialkyla-

tion with exclusive formation of a seven-membered

ring system in the reaction of primary or secondary amines

with either 2,2⁰-bis(bromomethyl)-1,1⁰-binaphthyl or 2,2⁰-

bis(bromomethyl)-1,1⁰-biphenyl was established in the

1950’s,¹¹and has very often been exploited in the synthesis

of a variety of catalysts.^{10c–e,12–17}The treatment of enantio-

merically pure (R)-2,2⁰-diamino-1,1⁰-binaphthyl with

resolved, enantiomerically pure (R)-2,2⁰-bis(bromomethyl)-

1,1⁰-binaphthyl,^15–19and an excess of diisopropylethyl-

^àProlonged reaction time (12 days) resulted in a decreased yield in both

(Rⁱ,R,R)-4 (51%) and (Rⁱ,R)-5 (6%), possibly because of product

decomposition.

For clarity, we have denoted (Rⁱ) as the absolute conﬁguration of the

internal 2,2⁰-diamino-1,1⁰-binaphthyl moiety of the diﬀerent compounds.

84

I. Aillaud et al. / Tetrahedron: Asymmetry 19 (2008) 82–92

(i)

NH₂

CH₂Br

N

+

NH₂

(i) (S)-dibromide

(i) (R)-dibromide

(Rⁱ

,

R

S

,

R)-4

S)-4]

(R ⁱ

,

R)-5

S)-5]

(R)

(S)

[

(Rⁱ,R,S)-4]

[

]

}

[

(i)

NH₂

CH₂Br

N

+

(R)

(Rⁱ)-6

Figure 2. Synthesis of the diamines (Rⁱ,R,R)-4, (Rⁱ,S,S)-4, (Rⁱ,R,S)-4 [and the side-products (Rⁱ,R)-5, (Rⁱ,S)-5] and (Rⁱ)-6 by the reaction of (R)-2,2⁰-

diamino-1,1⁰-binaphthyl with (R)- and/or (S)-2,2⁰-bis(bromomethyl)-1,1⁰-binaphthyl and 2,2⁰-bis(bromomethyl)-1,1⁰-biphenyl, respectively. Reagents and

conditions: (i) DIEA; toluene–acetonitrile 1:1; 85 °C.

Table 1. Chemical shifts d (ppm) of the ArCH₂N and ArCH₃signals in

the ¹H NMR spectra of the various diamines in CDCl₃solution

Diamine

ArCH₂N

ArCH₃

(Rⁱ,R,R)-4

(Rⁱ,S,S)-4

(Rⁱ,R,S)-4

3.88 (d) and 3.58 (d)

3.99 (d) and 3.57 (d)

3.93 (d) and 3.73 (d)

3.87 (d) and 3.55 (d)

4.10 (d) and 3.55 (d)

4.10 (d) and 3.64 (d)

4.01 (s)

(i)

N

NH

(Rⁱ,R)-5

(Rⁱ,S)-5

(Rⁱ,S,S)-1

(Rⁱ,R,R)-1

(Rⁱ,S,R)-1

(R

[

,

ⁱR

S

R

,

R)-4

S)-4]

(Rⁱ

[

,

S

,

S)-1

R)-1]

(Rⁱ

,R,

,S,

2.00 (s)

1.99 (s)

2.03 (s) and 1.97 (s)

4.03 (s)

4.02 (s) and 4.00 (s)

(ii)

N

NH

glet) of (Rⁱ,S,S)-1, (Rⁱ,R,R)-1 and (Rⁱ,S,R)-1, with no extra

signals arising from other stereoisomers.

(Rⁱ)-6

(Rⁱ)-2

For the tropos bis-tertiary diamine (Rⁱ)-6, hydrogenolysis

did not occur under the same experimental conditions as

for (Rⁱ,R,R)-4 (LiAlH₄and NiCl₂in reﬂuxing THF at

85 °C) even after prolonged reaction time (72 h). However,

when the reaction was performed in a mixture of diglyme

and THF (5:6) (but not in diglyme alone, in which only

decomposition occurred) at 155 °C for 1.5 h, the selective

bis(mono-hydrogenolysis) furnished the desired secondary

diamine (Rⁱ)-2 in 56% yield.

Figure 3. Synthesis of the target secondary diamines (Rⁱ,S,S)-1, (Rⁱ,R,R)-

1, (Rⁱ,S,R)-1 and (Rⁱ)-2 resulting from selective bis(mono-hydrogenolysis)

of (Rⁱ,R,R)-4, (Rⁱ,S,S)-4, (Rⁱ,R,S)-4 and (Rⁱ)-6, respectively. Reagents and

conditions: (i) LiAlH₄; NiCl₂; THF; 85 °C; (ii) LiAlH₄; NiCl₂; THF/

diglyme; 155 °C.

sterically constrained bis-tertiary diamines 4 with two 4,5-

dihydro-3H-dinaphtho[2,1-c:1⁰,2⁰-e]azepines linked to a

1,1⁰-binaphthyl unit at its 2,2⁰positions, catalysis by NiCl₂

is required. This allowed a very clean reaction selectively

providing two secondary amino groups by bis(mono-

hydrogenolysis). The expected²²absence of racemisation

of the binaphthyl units in both steps 1 and 2, is inferred

from the formation of a single stereoisomer for each reac-

NH

1

tion product, as shown by the H NMR spectra of all the

polybinaphthyl diamines (Table 1): as in previously re-

ported examples,¹³a single pattern was always observed

in CDCl₃at 300 MHz for the benzylic-like ArCH₂–NR₂

protons of (Rⁱ,R,R)-4, (Rⁱ,S,S)-4, (Rⁱ,R,S)-4 and (Rⁱ,R)-5,

(Rⁱ,S)-5 (AB quartet), as well as for either the benzylic-like

ArCH₂–NHR protons (singlet) or the ArCH₃protons (sin-

(Rⁱ)RR-2

(Rⁱ)RS-2

(Rⁱ)SS-2

Figure 4. Conformational equilibrium between the three diastereoisomeric

conformers (Rⁱ)RR-2, (Rⁱ)RS-2 and (Rⁱ)SS-2 of the diamine (Rⁱ)-2.

I. Aillaud et al. / Tetrahedron: Asymmetry 19 (2008) 82–92

85

Interestingly, the ¹H NMR spectrum of (Rⁱ)-2 at room tem-

perature in either CDCl₃or in benzene-d₆or toluene-d₈

shows the presence of the three expected conformers

(Rⁱ)RR-2, (Rⁱ)RS-2 and (Rⁱ)SS-2 (Fig. 4) exchanging slowly

on the NMR timescale, in a ca. 1:2:1 ratio as determined by

the integration of their respective ArCH₃singlets. The

ArCH₃singlet at lower ﬁeld is assigned to (Rⁱ)RS-2 (the

same compound as (Rⁱ)SR-2) on the basis of its double

intensity. The two ArCH₃singlets of equal half intensity

at higher ﬁeld are ambiguously assigned to either one of

the (Rⁱ)RR-2 and (Rⁱ)SS-2 conformers.

Evolution of the ¹H NMR spectrum (300 MHz) of (Rⁱ)-2 in

toluene-d₈with temperature (Fig. 5) shows that coalescence

of the ArCH₃singlets assigned to the (Rⁱ)RR-2 and (Rⁱ)SS-

2 pair of conformers (Dm₁= 3.3 Hz) occurs at T_Cꢀ 355 K,

1

while coalescence of the ArCH₃singlets assigned to the

(Rⁱ)RS-2 and (Rⁱ)RR or (Rⁱ)SS-2 pair of conformers

(average Dm₂ꢀ 13.2 Hz) occurs at T _Cꢀ 385 K, in agree-

2

ment with a calculated²³rotational energy barrier of ca.

20 kcal mol^ꢁ1

.

Altogether, the straightforward synthesis of four new

enantiopure ligands based on the binaphthyl diamine back-

bone was achieved in two steps, while ﬁne tuning of the

experimental parameters provided the desired compounds

in high yield with the retention of their enantiomeric

purity.

2.2. Evaluation of ligands (Rⁱ)-1 to (Rⁱ)-3 in the ytterbium-

catalysed intramolecular hydroamination of various

aminoalkenes

Figure 5. Temperature-dependent ¹H NMR (300 MHz) pattern of the

ArCH₃protons of the three diastereoisomeric conformers (Rⁱ)RS-2 (d

1.93 ppm at 295 K), (Rⁱ)RR-2 and (Rⁱ)SS-2 (d 1.89 ppm and/or 1.88 ppm

at 295 K) in toluene-d₈. Observed coalescence temperatures for the couple

In our previous studies on hydroamination reactions

catalysed by lanthanide ate complexes coordinated by

N-substituted binaphthylamine ligands, we found that

ytterbium-based catalysts aﬀorded the highest enantio-

meric excesses.⁶We thus focused on the evaluation of

our new ligands with this metal. The ate complexes were

(Rⁱ)RR-2 and (Rⁱ)SS-2: T_Cꢀ 355 K (Dm₁= 3.3 Hz at 295 K), and for the

1

couple (Rⁱ)RS-2 and (Rⁱ)RR or (Rⁱ)SS-2: T_Cꢀ 385 K (average

2

Dm₂ꢀ 13.2 Hz at 295 K).

Li (THF)₄

R¹

R²

R¹

R²

R¹

R²

nBuLi

NH

YbCl₃

THF

NLi

N

Hexane

or THF

Yb

+ 3 LiCl

R²

Complexes:

(Rⁱ,S,S)-7 R¹,R²

=

(Rⁱ,R,R)-7 R¹,R²

=

(Rⁱ,S,R)-7 R¹

=

(Rⁱ)-8 R¹,R²

=

(Rⁱ)-9 R¹,R²= Ph

R²

=

Figure 6. Synthesis of new chiral amido ate complexes of ytterbium.

86

I. Aillaud et al. / Tetrahedron: Asymmetry 19 (2008) 82–92

Table 2. Comparison of ligands for the ytterbium-catalysed enantioselec-

R'

R

Cat*

R

R'

n

tive cyclisation of aminoalkenes

n

NH

NH₂

C₆D₆or

C₇H₈

Entry Product Catalyst^a,bTime (h) Conversion (%) ee (%)

10 a-e

11 a-e

1

2

3

4

5

(Rⁱ,S,S)-7

(Rⁱ,R,R)-7

(Rⁱ,S,R)-7

(Rⁱ)-8

3.5

4.5

3

21

23

93

100

69

96

92

21

16

28

38

a, n= 1, R,R = -(CH₂)₅-, R' = H

b, n= 1, R,R = CH₃, R' = H

c, n= 1, R,R = Ph, R' = H

11a

11b

11c

11d

d, n= 2, R,R = -(CH₂)₅-, R' = H

e, n= 1, R,R = -(CH₂)₅-, R' = CH₃

(Rⁱ)-9

Figure 7. Intramolecular hydroamination reactions for the synthesis of

scalemic N-heterocycles.

6

7

8

9

10

(Rⁱ,S,S)-7

(Rⁱ,R,R)-7

(Rⁱ,S,R)-7

(Rⁱ)-8

24

8.5

27

45

96

97

100

99

>90

94

32

17

22

28

22

synthesised as previously reported in two steps, by the

metathesis reaction of 2 equiv of the bis lithium salt of

the ligand with anhydrous YbCl₃. Indeed, Li₂-{(Rⁱ)-

C₂₀H₁₂(NCH₂Ph)₂} was prepared by the reaction of ligand

(Rⁱ)-3 with n-BuLi in hexane and the subsequent metathesis

reaction was performed in THF at room temperature. This

complex was previously isolated and characterised.^6bAs

ligands (Rⁱ,S,S)-1, (Rⁱ,R,R)-1, (Rⁱ,S,R)-1 and (Rⁱ)-2 were

not soluble in hexane, the corresponding complexes,

[(Rⁱ,S,S)-7, (Rⁱ,R,R)-7, (Rⁱ,S,R)-7 and (Rⁱ)-8] were prepared

in THF at room temperature (Fig. 6). Complexes (Rⁱ,S,S)-

7, (Rⁱ,S,R)-7 and (Rⁱ)-8 were obtained as green powders

and complex (Rⁱ,R,R)-7 as a brown powder, after evapora-

tion of solvent. These complexes were not isolated but used

in situ immediately after their preparation for catalytic

intramolecular hydroamination tests (see Fig. 7).

(Rⁱ)-9

11

12

13

14

15

(Rⁱ,S,S)-7

(Rⁱ,R,R)-7

(Rⁱ,S,R)-7

(Rⁱ)-8

1.5

3

1.5

0.5

100

56

50

58

52

ꢁ23^c

(Rⁱ)-9

16

17

18

19

20

(Rⁱ,S,S)-7

(Rⁱ,R,R)-7

(Rⁱ,S,R)-7

(Rⁱ)-8

18

8.5

27

45

130

100

89

100

43^d

38

44^e

44

(Rⁱ)-9

39

21

22

23

24

25

26

(Rⁱ,S,S)-7^f

72

31

100

57

23

11

13

11

38

23

(Rⁱ,R,R)-7^f120

(Rⁱ,S,R)-7^f

(Rⁱ)-8^f

96

144

288

168

11e

All ytterbium catalysts were active for the hydroamination/

cyclisation of aminopentene derivatives and of C-(1-but-3-

enyl-cyclohexyl)-methylamine. Various results were ob-

tained according to the targeted substrates but as a general

trend, complexes 7 proved to be the most active species of

the series. For example, whereas C-(1-allyl-cyclohexyl)-

methylamine 10a was completely transformed in almost

one day with catalysts (Rⁱ)-8 and (Rⁱ)-9, only about 3.5 h

were necessary in the presence of catalysts 7 (Table 2,

entries 1–5). This was also observed with other substrates.

The three complexes 7 gave similar results in terms of activ-

ity with all the substrates tested. As already observed from

our previous results,^6bthese benzyl-type substituted cata-

lysts were less enantioselective but more active compared

to those bearing more sterically hindered substituents

directly bonded to the nitrogen atoms. 3-Methyl-2-aza-

spiro[4.5]decane 11a was obtained with up to 38% ee, this

highest value arising from the use of catalyst (Rⁱ)-9 (Table

2, entry 5). The cyclisation in the presence of a more

sterically demanding catalyst ((Rⁱ)-8) or with complexes

containing additional chirality elements [(Rⁱ,S,S)-7,

(Rⁱ,R,R)-7 or (Rⁱ,S,R)-7] did not provide the expected

product with improved enantioselectivity (Table 2, entries

1–4). 1,1-Dimethyl-but-3-enylamine 10b, known as the test

substrate for intramolecular asymmetric hydroamination,

was smoothly transformed at room temperature to provide

2,4,4-trimethyl-pyrrolidine 11b with up to 32% ee (Table 2,

entries 6–10). As already noted,^6c–eand due to an impor-

tant Thorpe–Ingold eﬀect, the gem-substituted aminopen-

tene 10c was rapidly cyclised in a few hours with up to

58% ee, the highest value obtained with this series of cata-

lysts. Interestingly, complex (Rⁱ)-9 aﬀorded the expected

product rapidly, with the major enantiomer bearing the

opposite conﬁguration to that obtained with the other cat-

(Rⁱ)-9^f

(Rⁱ)-9^g

82

^a6 mol % catalyst.

^bC₆D₆at 25 °C.

^cThe absolute conﬁguration of product 11c was opposite to that obtained

with catalysts 7 and (Rⁱ)-8.

^d75% conv. after 4.5 h.

^eReaction time not optimised.

^fC₇H₈at 110 °C.

^gC₇H₈at 120 °C.

alysts (Table 2, entries 11–15). Piperidine 11d was obtained

at room temperature with all catalysts, indicating a higher

activity than those furnished by other lanthanide ate com-

plexes.^6c–eComplete conversion in 18 h was observed by

using catalyst (Rⁱ,S,S)-7 and the product was isolated with

43% ee (Table 2, entries 16–20). C-(1-But-2-enyl-cyclo-

hexyl)-methylamine 10e, a more demanding substrate pos-

sessing an internal double bond, was next engaged in the

reaction, albeit at high temperature to promote cyclisation.

Complete conversion was obtained with catalysts (Rⁱ,R,R)-

7, (Rⁱ,S,R)-7 and (Rⁱ)-8; unfortunately product 11e was iso-

lated in only 13% ee. Complex (Rⁱ)-9 led to a slower reac-

tion but interestingly with a higher value of 38% for the

enantiomeric excess. Increasing the temperature to 120 °C

allowed a better conversion for this cyclisation but with a

decrease in the enantioselectivity (23% ee, Table 2, entries

21–26). The synthesis of this type of product has rarely

been described by intramolecular asymmetric hydroamina-

tion, and lower enantiomeric excesses were reported for

pyrrolidines resulting from aminoalkenes with internal

double bonds.^6e,24Also worth mentioning are the similar

enantiomeric values obtained in almost all cases with the

I. Aillaud et al. / Tetrahedron: Asymmetry 19 (2008) 82–92

87

diastereoisomeric complexes 7 although (Rⁱ,R,R)-7 fur-

nished slightly lower values. From these results it can be

concluded that the chirality arising from the binaphthyldi-

amine unit is of major importance for the enantiofacial dis-

crimination of the transformation. Additional stereogenic

centres do not alter the enantioselectivity in a signiﬁcant

manner.

sodium benzophenone ketyl and degassed immediately

prior to use. Hexane and toluene were distilled from

CaH₂and degassed immediately prior to use. Deuterated

benzene was dried with sodium benzophenone ketyl and

vacuum-transferred. Bruker AV 300 and AC 300 NMR

spectrometers (operating at 300 MHz) were used for

1

recording NMR spectra. Chemical shifts for H and ¹³C

spectra were referenced internally according to the residual

solvent resonances and reported relative to tetramethyl-

silane. Splitting patterns are abbreviated as follows: (s) sin-

glet, (d) doublet, (t) triplet, (q) quartet, (m) multiplet. Mass

spectra (electrospray mode) were recorded on a Hewlett–

Packard HP5989MS spectrometer. High resolution mass

spectra were performed on a Q-TOF Ultima Bruker mass

3. Conclusion

The straightforward synthesis of highly constrained,

enantiomerically pure, atropos polybinaphthyl diamines

(Rⁱ,R,R)-4, (Rⁱ,S,S)-4, (Rⁱ,R,S)-4 and (Rⁱ,S,S)-1, (Rⁱ,R,R)-

1, (Rⁱ,S,R)-1, as well as the corresponding tropos diamines

(Rⁱ)-6 and (Rⁱ)-2 opens the route to libraries of new chiral

binaphthyl-based derivatives. Both reaction steps can be

applied to a variety of linear or cyclic diamines or poly-

amines, either achiral or chiral, to obtain the corresponding

series of binaphthyl tertiary and/or secondary diamine cat-

alysts with potentially interesting chiral recognition proper-

ties. The ﬁrst step, gem-dialkylation of amines using as

alkylating agent either 2,2⁰-bis(bromomethyl)-1,1⁰-biphenyl

or the (R)- as well as the (S)-enantiomer of 2,2⁰-bis(bromo-

methyl)-1,1⁰-binaphthyl both easily accessible by several

procedures,^15–19has been widely used. It always occurs

with the exclusive formation of seven-membered ring alkyl

tertiary amines or diamines. We have now demonstrated

that the second step involving a selective bis(mono-hydro-

genolysis) of the biphenylic or binaphthylic tertiary amino

groups by lithium aluminium hydride in the presence of

nickel chloride, proceeds in high yield to aﬀord binaphthy-

lic bis(biphenyl) and bis(binaphthyl)-substituted secondary

diamines with steric and chiral constraints.

´

spectrometer (Universite d’Amiens, France). Elemental

analyses were performed by the C.N.R.S. Service of Micro-

analyses in Gif-sur-Yvette (France). Melting points were

determined with a temperature increase of 3 °C/min and

are uncorrected. The optical rotations were measured by

using a Perkin Elmer 241 polarimeter at room temperature

in a 1 dm thermostated cell (with an accuracy of 0.3%), and

rt

were reported as follows: ½aꢂ_k(c in g per 100 mL, solvent).

Analytical thin-layer chromatography (TLC), preparative

TLC and column chromatography were performed

on Silica Gel F 254 (Merck), Silica Gel G-25 (1 mm)

(Macherey-Nagel) and kieselgel gel 60 (0.040–0.063 mm)

(Merck), respectively. UV light (254 nm) allowed the visu-

alisation of the spots after TLC runs for all compounds,

even at low concentration. Enantiomeric excesses of the

products have been determined by GC or HPLC analyses

after derivatisation, and compared to racemic products

prepared with Y[N(TMS)₂]₃, using the methods previously

described.^6c,eGC analyses were performed on Fisons 800

apparatus with a DB1 column (30 m ꢃ 0.32 mm ꢃ 0.5 lm)

and HPLC analyses on Thermo Separation Product

Spectra Series tsp 100 P100/UV100 or Perkin Elmer Pump

Series 200/ DAD 20. Enantiomerically pure (+)-(R)-2,2⁰-

bis-(bromomethyl)-1,1⁰-binaphthyl,¹⁵and the substrates

4a–e for the hydroamination/cyclisation reactions^6c–ewere

prepared as previously described. Enantiomerically pure

(+)-(R)-2,2⁰-diamino-1,1⁰-binaphthyl and anhydrous YbCl₃

were purchased. All other commercially available chemi-

cals were used after the appropriate puriﬁcation.

The new atropos diamines (Rⁱ,S,S)-1, (Rⁱ,R,R)-1 and

(Rⁱ,S,R)-1 or the tropos one (Rⁱ)-2 have been used to pre-

pare ytterbium ate complexes, which catalyse the forma-

tion of scalemic pyrrolidines and a piperidine. Although

the introduction of additional chiral moieties on the ligand

did not increase the enantioselectivity of the transforma-

tion, the replacement of the phenyl substituent by a

binaphthyl backbone unexpectedly increased the rates of

the cyclisation reactions. Albeit the enantiomeric excesses

remain modest, these catalysts exhibited higher activities

than the other lanthanide ate complexes we have previously

studied. The formation of a six-membered nitrogen hetero-

cycle at room temperature is particularly interesting.^6d,e

Based on these results, we are currently studying more

active and enantioselective catalysts aimed at promoting

the intramolecular hydroamination of more demanding

substrates.

4.2. Alkylation of (+)-(R)-2,2⁰-diamino-1,1⁰-binaphthyl by

(+)-(R)- and (ꢁ)-(S)-2,2⁰-bis-(bromomethyl)-1,1⁰-binaphthyl,

and by 2,2⁰-bis-(bromomethyl)-1,1⁰-biphenyl

(a) To a solution of (+)-(R)-2,2⁰-diamino-1,1⁰-binaphthyl

(0.355 g; 1.25 mmol) and (+)-(R)-2,2⁰-bis-(bromo-

methyl)-1,1⁰-binaphthyl (1.100 g; 2.50 mmol) in tolu-

ene (15 mL) and acetonitrile (15 mL) was added

DIEA (1.09 mL; 6.25 mmol). The solution was stirred

under argon at 85 °C for 6 days, and then evaporated

in vacuo. The residue was dissolved in CH₂Cl₂

(150 mL); kieselgel Si 60 (15 g) was added and the

mixture was evaporated in vacuo at 50 °C. The result-

ing product-impregnated silica gel was poured onto

the top of a 3 ꢃ 57 cm column of kieselgel Si 60 made

up with cyclohexane–CH₂Cl₂7:3. Elution with cyclo-

hexane–CH₂Cl₂7:3–3:7 followed by preparative TLC

of the impure fractions on silica gel with eluent cyclo-

4. Experimental

4.1. General experimental

For the preparation of catalysts and the realisation of the

catalytic tests, manipulations were carried out under an

argon atmosphere using standard Schlenk or glove box

techniques. THF and diethyl ether were distilled from

88

I. Aillaud et al. / Tetrahedron: Asymmetry 19 (2008) 82–92

hexane–CH₂Cl₂7:3, aﬀorded 0.696 g (66%) of pure

7.91 [d, J = 8.1 Hz, 4H, ArH], 7.85 [d, J = 8.3 Hz, 4H,

ArH], 7.68 [d, J = 8.8 Hz, 2H, ArH], 7.48–7.39 [m, 6H,

ArH], 7.34 [d, J = 8.3 Hz, 4H, ArH], 7.26 [m, 4H, ArH],

7.19 [m (t-like), 4H, ArH], 6.84 [d, J = 8.3 Hz, 4H, ArH],

3.88 and 3.58 [d, J = 12.5 Hz, 4H and d, J = 12.5 Hz,

4H, Ar–CH₂N]. ¹³C NMR (CDCl₃): d 149.6 (C_Ar–NR₂),

134.8, 134.2, 134.1, 132.8, 131.4, 131.2, 131.0, 128.7,

diamine (Rⁱ,R,R)-4 (see Section 4.3), 0.206 g (29%)

of pure diamine (Rⁱ,R)-5 (see Section 4.4) and

0.071 g (6%) of recovered (R)-dibromide. In a second

run, a solution of (+)-(R)-2,2⁰-diamino-1,1⁰-binaph-

thyl (0.284 g; 1.00 mmol), (+)-(R)-2,2⁰-bis-(bromo-

methyl)-1,1⁰-binaphthyl (0.968 g; 2.20 mmol) and

DIEA (0.87 mL; 5.00 mmol) in toluene (10 mL) and

acetonitrile (10 mL), was stirred under argon at

85 °C for 12 days. Column chromatography of the

crude product followed by preparative TLC of the

impure fractions in the same conditions as above

aﬀorded 0.431 g (51%) of pure (Rⁱ,R,R)-4, 0.035 g

(6%) of pure (Rⁱ,R)-5 and 0.085 g (9%) of recovered

(R)-dibromide.

128.5, 128.1, 128.0, 127.43, 127.41, 126.3, 126.0, 125.5,

25

125.2, 124.9, 124.3 (C_Ar), 54.9 (Ar–CH₂N). ½aꢂ₅₈₉¼ ꢁ78;

25

½aꢂ₅₇₈¼ ꢁ83; ½aꢂ₅₄₆¼ ꢁ92; ½aꢂ₄₃₆¼ ꢁ238 (c 0.2, CHCl₃).

MS (ES⁺) m/z (relative intensity): 841.8 (100) [M+H]⁺,

864.1 (12) [M+Na]⁺. TOF-MS (ES⁺) m/z (relative inten-

sity): 841.4 (100) [M+H]⁺, 863.3 (10) [M+Na]⁺, 879.4 (3)

[M+K]⁺. TOF-HRMS (ES⁺), calcd for [M+H]⁺

(C₆₄H₄₅N₂): 841.3583. Found: 841.3638. Anal. Calcd for

C₆₄H₄₄N₂ꢄ2H₂O (877.040): C, 87.64; H, 5.52; N, 3.19.

Found: C, 87.71; H, 5.53; N, 3.14.

(b) A solution of (+)-(R)-2,2⁰-diamino-1,1⁰-binaphthyl

(0.355 g; 1.25 mmol), (ꢁ)-(S)-2,2⁰-bis-(bromomethyl)-

1,1⁰-binaphthyl (1.100 g; 2.50 mmol) and DIEA

(1.09 mL; 6.25 mmol) in toluene (15 mL) and aceto-

nitrile (15 mL), was stirred under argon at 85 °C for

7 days, and then evaporated in vacuo. Column

chromatography of the crude product followed by

preparative TLC of the impure fractions under the

same conditions as above aﬀorded 0.912 g (87%) of

pure (Rⁱ,S,S)-4 (see Section 4.5), 0.087 g (12%) of pure

(Rⁱ,S)-5 (see Section 4.6) and 0.014 g (1%) of recov-

ered (S)-dibromide.

4.4. Diamine (Rⁱ,R)-5

Yellow solid. Mp = 195–198 °C. R_f= 0.15 (cyclohexane–

CH₂Cl₂7:3); 0.34 (cyclohexane–CH₂Cl₂1:1); 0.65

1

(CH₂Cl₂). H NMR (CDCl₃): d 7.91–7.87 [m, 4H, ArH],

7.83 [d, J = 8.3 Hz, 2H, ArH], 7.71 [m (t-like), 2H, ArH],

7.47–7.28 [m, 8H, ArH], 7.26–7.18 [m, 6H, ArH], 7.09 [m

(t-like), 2H, ArH], 3.84 [m (br), 2H, NH₂], 4.10 and 3.55

[d, J = 12.2 Hz, 2H and d, J = 12.0 Hz, 2H, Ar–CH₂N].

(c)

A

solution of diamine (Rⁱ,R)-5 (0.226 g; 0.40

¹³C NMR (CDCl₃): d 149.0 (C_Ar–NR₂), 141.8 (C_Ar

–

mmol), (ꢁ)-(S)-2,2⁰-bis-(bromomethyl)-1,1⁰-binaphthyl

(0.193 g; 0.43 mmol) and DIEA (0.2 mL; 1.15 mmol)

in toluene (10 mL) and acetonitrile (10 mL), was

stirred under argon at 85 °C for 8 days, and then

evaporated in vacuo. Preparative TLC of the crude

product on silica gel with eluent cyclohexane–CH₂Cl₂

7:3 aﬀorded 0.166 g (49%) of pure (Rⁱ,R,S)-4 (see Sec-

tion 4.7). The remaining starting materials, (Rⁱ,R)-5

and (S)-dibromide, were not isolated.

NH₂), 134.5, 133.8, 133.2, 132.95, 132.89, 131.1, 130.1,

129.0, 128.9, 128.6, 128.3, 128.2, 128.1, 127.9, 127.6,

127.4, 126.7, 126.1, 125.6, 125.3, 124.9, 124.4, 123.9,

123.2, 122.1, 121.1, 118.0, 116.5 (C_Ar), 53.9 (Ar–CH₂N).

25

½aꢂ₅₈₉¼ þ535; ½aꢂ₅₇₈¼ þ572; ½aꢂ₅₄₆¼ þ701; ½aꢂ₄₃₆¼ þ1970

(c 0.2, CHCl₃). MS (ES⁺) m/z (relative intensity): 563.4

(100) [M+H]⁺, 585.4 (46) [M+Na]⁺, 601.3 (18) [M+K]⁺.

TOF-MS (ES⁺) m/z (relative intensity): 563.3 (100)

[M+H]⁺, 585.2 (22) [M+Na]⁺, 601.2 (5) [M+K]⁺. TOF-

HRMS (ES⁺), calcd for [M+H]⁺(C₄₂H₃₁N₂): 563.2487.

Found: 563.2509. Anal. Calcd for C₄₂H₃₀N₂ꢄ1.7H₂O

(593.303): C, 85.01; H, 5.67; N, 4.72. Found: C, 84.97; H,

5.61; N, 4.11.

(d)

A

solution of diamine (Rⁱ,S)-5 (0.075 g; 0.13

mmol), (+)-(R)-2,2⁰-bis-(bromomethyl)-1,1⁰-binaphthyl

(0.071 g; 0.16 mmol) and DIEA (0.06 mL; 0.03 mmol)

in toluene (10 mL) and acetonitrile (10 mL), was

stirred under argon at 85 °C for 7 days, and then

evaporated in vacuo. Preparative TLC of the crude

product on silica gel with eluent cyclohexane–CH₂Cl₂

7:3 aﬀorded 0.053 g (47%) of pure (Rⁱ,R,S)-4 (see

Section 4.7). The remaining starting materials,

(Rⁱ,S)-5 and (R)-dibromide, were not isolated.

4.5. Diamine (Rⁱ,S,S)-4

Pale yellow solid. Mp = 222–228 °C. R_f= 0.47 (cyclohex-

ane–CH₂Cl₂7:3); 0.69 (cyclohexane–CH₂Cl₂1:1). ¹H

NMR (CDCl₃): d 7.99 [d, J ꢀ 8.3 Hz, 4H, ArH], 7.97 [d

(br), J ꢀ 7.9 Hz, 4H, ArH], 7.82 [d, J = 7.7 Hz, 2H, ArH],

7.73 [d, J = 8.8 Hz, 2H, ArH], 7.57–7.23 [m, 22H, ArH],

3.99 and 3.57 [d, J = 12.1 Hz, 4H and d, J = 12.1 Hz, 4H,

Ar–CH₂N]. ¹³C NMR (CDCl₃): d 147.3 (C_Ar–NR₂),

135.0, 134.7, 134.0, 133.0, 131.2, 129.6, 128.5, 128.2,

(e) A solution of (+)-(R)-2,2⁰-diamino-1,1⁰-binaphthyl

(0.703 g; 2.47 mmol), 2,2⁰-bis-(bromomethyl)-1,1⁰-

biphenyl (1.851 g; 5.44 mmol) and DIEA (2.15 mL;

12.35 mmol) in toluene (25 mL) and acetonitrile

(25 mL), was stirred under argon at 85 °C for 6 days,

and then evaporated in vacuo. The residue was chro-

matographed on a 4 ꢃ 85 cm column of silica gel

eluted with cyclohexane–CH₂Cl₂7:3–3:7 to aﬀord

1.384 g (87%) of pure (Rⁱ)-6 (see Section 4.8).

128.1, 127.8, 127.4, 126.5, 126.1, 125.7, 125.4, 125.1,

25

123.4, 120.2 (C_Ar), 53.7 (Ar–CH₂N). ½aꢂ₅₈₉¼ ꢁ1164;

25

½aꢂ₅₇₈¼ ꢁ1235; ½aꢂ₅₄₆¼ ꢁ1505; ½aꢂ₄₃₆¼ ꢁ4526 (c 0.23,

CHCl₃). MS (ES⁺) m/z (relative intensity): 841.8 (100)

[M+H]⁺. TOF-MS (ES⁺) m/z (relative intensity): 841.4

(100) [M+H]⁺. TOF-HRMS (ES⁺), calcd for [M+H]⁺

(C₆₄H₄₅N₂): 841.3583. Found: 841.3550. Anal. Calcd for

C₆₄H₄₄N₂ꢄ0.5H₂O (850.016): C, 90.43; H, 5.34; N, 3.29.

Found: C, 90.61; H, 5.55; N, 3.14.

4.3. Diamine (Rⁱ,R,R)-4

Pale yellow solid. Mp = 204–207 °C. R_f= 0.54 (cyclohex-

ane–CH₂Cl₂7:3); 0.73 (cyclohexane–CH₂Cl₂1:1). ¹H

NMR (CDCl₃): d 8.02 [m (t-like), J ꢀ 8.7 Hz, 4H, ArH],

I. Aillaud et al. / Tetrahedron: Asymmetry 19 (2008) 82–92

89

4.6. Diamine (Rⁱ,S)-5

4.9. Hydrogenolysis of (Rⁱ,R,R)-4, (Rⁱ,S,S)-4, (Rⁱ,R,S)-4 and

(Rⁱ)-6

Yellow solid. Mp = 175–185 °C. R_f= 0.09 (cyclohexane–

CH₂Cl₂7:3); 0.25 (cyclohexane–CH₂Cl₂1:1). ¹H NMR

(CDCl₃): d 7.96–7.86 [m, 6H, ArH], 7.77 [d, J = 7.9 Hz,

1H, ArH], 7.71 [d, J = 8.7 Hz, 1H, ArH], 7.58–7.18 [m,

15H, ArH], 7.04 [d, J = 8.7 Hz, 1H, ArH], 3.80 [m (br),

2H, NH₂], 4.10 and 3.64 [d, J = 12.1 Hz, 2H and d,

J = 12.1 Hz, 2H, Ar–CH₂N]. ¹³C NMR (CDCl₃): d 148.0

(C_Ar–NR₂), 141.7 (C_Ar–NH₂), 134.7, 134.6, 134.0, 133.7,

133.0, 131.1, 129.9, 129.0, 128.75, 128.69, 128.2, 127.8,

127.4, 127.3, 126.7, 126.4, 125.9, 125.7, 125.6, 125.4,

124.7, 123.8, 122.9, 122.0, 120.0, 118.9, 116.3 (C_Ar), 54.1

(a) To a solution of (Rⁱ,R,R)-4 (0.118 g; 0.14 mmol) in

THF (15 mL) was added LiAlH₄(0.25 g; 6.5 mmol)

by portions, under an argon stream. The reaction

mixture was stirred under argon at 80 °C for 24 h,

cooled to room temperature, hydrolysed by the cau-

tious addition of H₂O (ca. 0.5 mL), then 15% aq

NaOH (ca. 0.5 mL), then H₂O (ca. 1 mL), and then

ﬁltered on sintered glass through Celite. The ﬁltrate

was diluted with CH₂Cl₂(ca. 150 mL), and the solu-

tion was washed with H₂O (3 ꢃ 100 mL), dried

(MgSO₄), ﬁltered and evaporated in vacuo. The crude

product (0.120 g) consisted of unreacted (Rⁱ,R,R)-4

25

(Ar–CH₂N). ½aꢂ₅₈₉¼ ꢁ507; ½aꢂ₅₇₈¼ ꢁ544; ½aꢂ₅₄₆¼ ꢁ656;

25

½aꢂ₄₃₆¼ ꢁ1779 (c 0.2, CHCl₃). MS (ES⁺) m/z (relative

intensity): 563.4 (100) [M+H]⁺. TOF-MS (ES⁺) m/z

(relative intensity): 563.3 (100) [M+H]⁺. TOF-HRMS

(ES⁺), calcd for [M+H]⁺(C₄₂H₃₁N₂): 563.2487. Found:

563.2479. Anal. Calcd for C₄₂H₃₀N₂ꢄ0.5H₂O (571.684):

C, 88.23; H, 5.47; N, 4.63. Found: C, 88.69; H, 5.55; N,

4.63.

with no trace of (Rⁱ,S,S)-1 by TLC, H/¹³C NMR

1

and MS (ES⁺).

(b) To a solution of (Rⁱ,R,R)-4 (0.360 g; 0.43 mmol) in

THF (100 mL) was added anhydrous NiCl₂(0.150 g;

1.1 mmol). The suspension was magnetically stirred

at room temperature and LiAlH₄(1.500 g; 39 mmol)

was added by portions, under argon stream. The

resulting black-greenish solution was stirred under

argon at 85 °C for 7.5 h, cooled to room temperature,

hydrolysed by the cautious addition of H₂O (ca.

2 mL), then 15% aq NaOH (ca. 3 mL), then H₂O

(ca. 8 mL). The mixture was ﬁltered on sintered glass

through Celite and the solid washed with CH₂Cl₂(ca.

400 mL). The whole ﬁltrate was repeatedly washed

with H₂O (3 ꢃ 400 mL), dried over MgSO₄, ﬁltered

and evaporated in vacuo. The crude product, which

presented a single spot on analytical TLC (with no

trace of the starting diamine), was chromatographed

on two preparative TLC plates of silica gel (1 mm)

eluted with cyclohexane–CH₂Cl₂7:3 to aﬀord

0.319 g (88%) of pure diamine (Rⁱ,S,S)-1 (see Section

4.10). Four other runs under similar experimental

conditions always gave (Rⁱ,S,S)-1 as single product

in high yield: (1) Treatment of (Rⁱ,R,R)-4 (0.331 g;

0.39 mmol) in THF (100 mL) with NiCl₂(0.150 g)

and LiAlH₄(1.500 g) at 85 °C for 7 h, aﬀorded

0.279 g (84%) of pure (Rⁱ,S,S)-1 after chromatogra-

phy. (2) Treatment of (Rⁱ,R,R)-4 (0.0507 g;

0.060 mmol) in THF (15 mL) with NiCl₂(0.025 g)

and LiAlH₄(0.25 g) at 85 °C for 16 h, aﬀorded

0.0425 g (84%) of pure (Rⁱ,S,S)-1. (3) Treatment of

(Rⁱ,R,R)-4 (0.0509 g; 0.060 mmol) in THF (15 mL)

with NiCl₂(0.025 g) and LiAlH₄(0.25 g) at 85 °C

for 6.5 h, aﬀorded 0.042 g (82%) of pure (Rⁱ,S,S)-1.

(4) Treatment of (Rⁱ,R,R)-4 (0.0664 g; 0.079 mmol)

in THF (15 mL) with NiCl₂(0.025 g) and LiAlH₄

(0.25 g) at 85 °C for 7 h, aﬀorded 0.0554 g (83%) of

pure (Rⁱ,S,S)-1.

4.7. Diamine (Rⁱ,R,S)-4

Pale yellow solid. Mp = 196–206 °C. R_f= 0.45 (cyclohex-

ane–CH₂Cl₂7:3). ¹H NMR (CDCl₃): d 7.97–7.75 [m,

10H, ArH], 7.72 [d, J = 8.3 Hz, 2H, ArH], 7.62–7.39 [m,

14H, ArH], 7.32–7.17 [m, 6H, ArH], 7.06 [d, J = 8.3 Hz,

2H, ArH], 6.89 [d, J = 8.3 Hz, 2H, ArH], 3.93 and 3.73

[d, J = 12.5 Hz, 2H and d, J = 12.5 Hz, 2H, Ar–CH₂N],

3.87 and 3.55 [d, J = 11.9 Hz, 2H and d, J = 11.9 Hz,

2H, Ar–CH₂N]. ¹³C NMR (CDCl₃): d 149.6, 147.7 (C_Ar

–

NR₂), 134.8, 134.7, 134.53, 134.47, 134.2, 133.7, 132.9,

131.34, 131.32, 131.1, 130.9, 129.6, 128.9, 128.6, 128.4,

128.2, 127.9, 127.6, 127.5, 127.3, 126.5, 126.4, 126.1,

125.7, 125.6, 125.5, 125.4, 125.3, 125.2, 124.9, 124.3,

25

123.4, 120.2 (C_Ar), 54.9, 53.8 (Ar–CH₂N). ½aꢂ₅₈₉¼ ꢁ533;

25

½aꢂ₅₇₈¼ ꢁ566; ½aꢂ₅₄₆¼ ꢁ685; ½aꢂ₄₃₆¼ ꢁ2070 (c 0.2, CHCl₃).

MS (ES⁺) m/z (relative intensity): 841.7 (100) [M+H]⁺.

TOF-MS (ES⁺) m/z (relative intensity): 841.4 (100)

[M+H]⁺. TOF-HRMS (ES⁺), calcd for [M+H]⁺

(C₆₄H₄₅N₂): 841.3583. Found: 841.3559. Anal. Calcd for

C₆₄H₄₄N₂ꢄ0.5H₂O (850.016): C, 90.42; H, 5.34; N, 3.30.

Found: C, 90.21; H, 5.95; N, 3.07.

4.8. Diamine (Rⁱ)-6

Pale yellow foam. R_f= 0.53 (cyclohexane–CH₂Cl₂7:3). ¹H

NMR (CDCl₃): d 7.90 [d, J = 8.6 Hz, 4H, ArH], 7.57 [d,

J = 8.8 Hz, 2H, ArH], 7.45–7.22 [m, 18H, ArH], 6.84 [d,

J = 7.3 Hz, 4H, ArH], 3.73 and 3.66 [d, J = 12.5 Hz, 4H

and d, J = 12.5 Hz, 4H, Ar–CH₂N]. ¹³C NMR (CDCl₃):

d 140.9 (C_Ar–NR₂), 135.6, 134.6, 130.4, 129.5, 128.5,

128.0, 127.8, 127.7, 127.4, 126.3, 126.1, 123.9, 122.5

(c) A solution of (Rⁱ,S,S)-4 (0.460 g; 0.55 mmol), anhy-

drous NiCl₂(0.150 g; 1.1 mmol) and LiAlH₄

(1.500 g; 39 mmol) in THF (100 mL) was stirred

under argon at 85 °C for 16 h, cooled to room temper-

ature, hydrolysed by the cautious addition of H₂O

and 15% aq NaOH as above in (b). The mixture

was ﬁltered on sintered glass over Celite, the solid

was washed with CH₂Cl₂(ca. 400 mL) and the whole

ﬁltrate was repeatedly washed with H₂O

25

(C_Ar), 54.5 (Ar–CH₂N). ½aꢂ₅₈₉¼ ꢁ279; ½aꢂ₅₇₈¼ ꢁ293;

25

½aꢂ₅₄₆¼ ꢁ357; ½aꢂ₄₃₆¼ ꢁ1096 (c 0.5, CH₂Cl₂). CI-MS

(NH₃) m/z (relative intensity): 641 (100) [M+H]⁺. Anal.

Calcd for C₄₈H₃₆N₂ꢄ0.5H₂O (649.792): C, 88.72; H, 5.74;

N, 4.31. Found: C, 88.69; H, 5.91; N, 4.07.

90

I. Aillaud et al. / Tetrahedron: Asymmetry 19 (2008) 82–92

(3 ꢃ 400 mL), dried over MgSO₄, ﬁltered and evapo-

for [M+Na]⁺(C₆₄H₄₈N₂Na): 867.3715. Found: 867.3757.

Anal. Calcd for C₆₄H₄₈N₂ꢄ4H₂O (917.104): C, 83.81; H,

6.15; N, 3.05. Found: C, 83.78; H, 5.63; N, 2.87.

rated in vacuo. The crude product was chromato-

graphed on two preparative TLC plates of silica gel

(1 mm) eluted with cyclohexane–CH₂Cl₂7:3 to aﬀord

0.368 g (80%) of pure diamine (Rⁱ,R,R)-1 (see Section

4.11). In a second run under similar experimental con-

ditions, treatment of (Rⁱ,S,S)-4 (0.447 g; 0.53 mmol)

in THF (100 mL) with NiCl₂(0.150 g) and LiAlH₄

(1.500 g) at 85 °C for 7 h, aﬀorded 0.327 g (73%) of

pure (Rⁱ,R,R)-1 after chromatography.

4.11. Diamine (Rⁱ,R,R)-1

Pale yellow solid. Mp = 152–160 °C. R_f= 0.41 (cyclohex-

1

ane–CH₂Cl₂7:3). H NMR (CDCl₃): d 7.94–7.82 [m, 6H,

ArH], 7.76–7.57 [m, 8H, ArH], 7.47–7.42 [m, 6H, ArH],

7.28–7.00 [m, 14H, ArH], 6.90 [d, J = 8.8 Hz, 2H, ArH],

4.24 [s (br), 2H, NH], 4.03 [s, 4H, Ar–CH₂N], 1.99 [s,

6H, Ar–CH₃]. ¹³C NMR (CDCl₃): d 144.0 (C_Ar–NHR),

135.6, 134.5, 134.4, 133.8, 133.5, 132.8, 132.5, 132.2,

129.4, 128.8, 128.4, 128.1, 128.03, 127.99, 127.9, 127.8,

127.6, 127.0, 126.7, 126.3, 126.2, 125.9, 125.6, 125.5,

125.4, 125.1, 124.5, 123.8, 121.9, 113.9, 111.6 (C_Ar), 45.4

(d) A solution of (Rⁱ,R,S)-4 (0.191 g; 0.23 mmol), anhy-

drous NiCl₂(0.075 g; 0.55 mmol) and LiAlH₄

(0.750 g; 19.5 mmol) in THF (50 mL) was stirred

under argon at 85 °C for 7.5 h, cooled to room tem-

perature, hydrolysed by cautious addition of H₂O

and 15% aq NaOH as above in paragraph (b). The

mixture was ﬁltered on a sintered glass over Celite,

the solid was washed with CH₂Cl₂(ca. 400 mL) and

the whole ﬁltrate was repeatedly washed with H₂O

(3 ꢃ 400 mL), dried over MgSO₄, ﬁltered and evapo-

rated in vacuo. The crude product was chromato-

graphed on two preparative TLC plates of silica gel

(1 mm) eluted with cyclohexane–CH₂Cl₂7:3 to aﬀord

0.119 g (62%) of pure diamine (Rⁱ,S,R)-1 (see Section

4.12).

25

(Ar–CH₂NHR), 20.0 (Ar–CH₃). ½aꢂ₅₈₉¼ ꢁ23; ½aꢂ₅₇₈

¼

25

ꢁ24; ½aꢂ₅₄₆¼ ꢁ26; ½aꢂ₄₃₆¼ ꢁ124 (c 0.2, CHCl₃). MS

(ES⁺) m/z (relative intensity): 845.5 (100) [M+H]⁺. TOF-

MS (ES⁺) m/z (relative intensity): 867.0 (100) [M+Na]⁺.

TOF-HRMS (ES⁺), calcd for [M+Na]⁺(C₆₄H₄₈N₂Na):

867.3715. Found: 867.3741. Anal. Calcd for C₆₄H₄₈N₂

(845.040): C, 90.96; H, 5.73; N, 3.31. Found: C, 90.81; H,

5.93; N, 3.11.

(e) To a solution of (Rⁱ)-6 (0.490 g; 0.76 mmol) in THF

(12 mL) and diglyme (10 mL) was added anhydrous

NiCl₂(0.2 g; 1.5 mmol). The suspension was magnet-

ically stirred at room temperature and LiAlH₄(0.87 g;

22 mmol) was added by portions, under argon stream.

The resulting black-greenish solution was stirred

under argon at 155 °C for 1.5 h, cooled to room tem-

perature, hydrolysed by the cautious addition of H₂O

(ca. 5 mL), then 15% aq NaOH (ca. 5 mL), and then

H₂O (ca. 10 mL), and then ﬁltered on a sintered glass

through Celite. The ﬁltrate was diluted with CH₂Cl₂

(ca. 300 mL), and the solution was washed with

H₂O (3 ꢃ 100 mL), dried over MgSO₄, ﬁltered and

evaporated in vacuo. The crude product was dissolved

in a minimum of hot CH₂Cl₂and the same volume of

cyclohexane was added. The solution was kept at

4 °C, resulting in the crystallisation of (Rⁱ)-2

(0.276 g; 56%) (see Section 4.13).

4.12. Diamine (Rⁱ,S,R)-1

Pale yellow solid. Mp = 120–128 °C. R_f= 0.37 (cyclohex-

1

ane–CH₂Cl₂7:3). H NMR (CDCl₃): d 7.92–7.82 [m, 6H,

ArH], 7.75–7.51 [m, 8H, ArH], 7.48–7.39 [m, 6H, ArH],

7.27–7.00 [m, 14H, ArH], 6.92 [d, J = 8.8 Hz, 1H, ArH],

6.88 [d, J = 8.8 Hz, 1H, ArH], 4.22 [s (br), 2H, NH], 4.02

[s, 2H, Ar–CH₂N], 4.00 [s, 2H, Ar–CH₂N], 2.03 [s, 3H,

Ar–CH₃], 1.97 [s, 3H, Ar–CH₃]. ¹³C NMR (CDCl₃): d

144.02, 143.95 (C_Ar–NHR), 135.6, 135.5, 134.45, 134.42,

134.39, 133.2, 133.8, 133.7, 133.6, 133.5, 132.8, 132.7,

132.6, 132.5, 132.2, 129.44, 129.40, 128.7, 128.1, 128.04,

127.98, 127.92, 127.89, 127.83, 127.79, 127.59, 127.57, 12

6.7, 126.32, 126.26, 125.62, 125.56, 125.5,125.44, 125.39,

125.3, 125.1, 124.6, 124.3, 123.8, 121.9, 113.94, 113.87,

111.62, 111.56 (C_Ar), 45.5, 45.3 (Ar–CH₂NHR), 20.1,

25

20.0 (Ar–CH₃). ½aꢂ₅₈₉¼ ꢁ27; ½aꢂ₅₇₈¼ ꢁ28; ½aꢂ₅₄₆¼ ꢁ31;

25

½aꢂ₄₃₆¼ ꢁ128 (c 0.18, CHCl₃). MS (ES⁺) m/z (relative

intensity): 845.5 (100) [M+H]⁺. TOF-MS (ES⁺) m/z (rela-

tive intensity): 867.4 (100) [M+Na]⁺. TOF-HRMS (ES⁺),

calcd for [M+Na]⁺(C₆₄H₄₈N₂Na): 867.3715. Found:

867.3709. Anal. Calcd for C₆₄H₄₈N₂(845.040): C, 90.96;

H, 5.73; N, 3.31. Found: C, 90.43; H, 6.05; N, 3.05.

4.10. Diamine (Rⁱ,S,S)-1

Pale yellow solid. Mp = 123–127 °C. R_f= 0.50 (cyclohex-

1

ane–CH₂Cl₂7:3). H NMR (CDCl₃): d 7.93–7.86 [m, 6H,

ArH], 7.76–7.68 [m, 6H, ArH], 7.54 [d, J = 8.7 Hz, 2H,

ArH], 7.48–7.40 [m, 6H, ArH], 7.28–7.17 [m, 8H, ArH],

7.13–7.05 [m, 6H, ArH], 6.91 [d, J = 8.8 Hz, 2H, ArH],

4.22 [s (br), 2H, NH], 4.01 [s, 4H, Ar–CH₂N], 2.00 [s,

6H, Ar–CH₃]. ¹³C NMR (CDCl₃): d 144.0 (C_Ar–NHR),

135.6, 134.5, 134.3, 133.8, 133.6, 132.8, 132.5, 132.2,

129.4, 128.7, 128.1, 128.04, 127.98, 127.88, 127.82, 127.6,

126.7, 126.3, 126.2, 125.6, 125.5, 125.4, 125.2, 124.4,

123.8, 121.9, 114.0, 111.6 (C_Ar), 45.3 (Ar–CH₂NHR),

4.13. Diamine (Rⁱ)-2

White solid. Mp = 133–135 °C. R_f= 0.38 (EtOAc–CH₂Cl₂

1

3:97). H NMR (C₆D₆): d 7.67–7.63 [m, 4H, ArH], 7.39–

7.36 [m, 2H, ArH], 7.29–7.21 [m, 2H, ArH], 7.15–6.96

[m, 20H, ArH], 4.20–4.14 [m, 2H, NH], 3.87–3.78 and

3.73–3.62 [2m, 4H, Ar–CH₂N], 1.93 [s, 3H, Ar–CH₃],

1.88, 1.87 [2s, 3H, Ar–CH₃]. ¹H NMR (toluene-d₈): d

7.64–7.61 [m, 4H, ArH], 7.31 [m, 2H, ArH], 7.21–6.98

[m, 22H, ArH], 4.10 [m, 2H, NH], 3.73–3.64 [m, 4H, Ar–

CH₂N], 1.93 [s, 3H, Ar–CH₃], 1.89, 1.88 [2s, 3H, Ar–

CH₃].¹³C NMR (C₆D₆): d 144.5 (C_Ar–NHR), 140.8,

140.7, 137.6, 135.9, 134.7, 134.6, 130.4, 130.0 129.9,

25

20.1 (Ar–CH₃). ½aꢂ₅₈₉¼ ꢁ41; ½aꢂ₅₇₈¼ ꢁ42; ½aꢂ₅₄₆¼ ꢁ50;

25

½aꢂ₄₃₆¼ ꢁ177 (c 0.2, CHCl₃). MS (ES⁺) m/z (relative inten-

sity): 845.7 (18) [M+H]⁺, 867.8 (100) [M+Na]⁺. TOF-MS

(ES⁺) m/z (relative intensity): 845.4 (14) [M+H]⁺, 867.4

(100) [M+Na]⁺, 883.4 (3) [M+K]⁺. HRMS (ES⁺), calcd

I. Aillaud et al. / Tetrahedron: Asymmetry 19 (2008) 82–92

91

129.7, 129.5, 129.4, 128.6, 128.5, 128.3, 128.0, 127.7, 127.5,

127.2, 127.1, 127.0, 126.9, 126.8, 126.0, 124.5, 124.4, 122.4,

122.3, 114.3, 112.4 (C_Ar), 45.5, 45.4 (Ar–CH₂N), 20.0, 19.9

ﬂask equipped with a magnetic stirring bar. n-BuLi

(1.6 M in hexanes, 0.15 mL, 0.24 mmol) was added

dropwise and the reaction mixture was stirred for 10 min

to give a yellowish suspension. The solvent was evaporated

in vacuo. YbCl₃(16.5 mg, 0.06 mmol) was added to the

solution of the bis lithium salt of the ligand in THF

(2 mL). The reaction mixture was stirred at room tempera-

ture for 45 min and THF was evaporated in vacuo. The

crude product was dissolved in C₆D₆or toluene and the

solution was immediately used for the catalytic tests.

25

(Ar–CH₃). ½aꢂ₅₈₉¼ þ13; ½aꢂ₅₇₈¼ þ15; ½aꢂ₅₄₆¼ þ21;

25

½aꢂ₄₃₆¼ þ81 (c 0.5, CH₂Cl₂). ES-MS m/z (relative inten-

sity): 667.3 (100) [M+Na]⁺, 645 (7) [M+H]⁺. Anal. Calcd

for C₄₈H₄₀N₂ꢄ1.5H₂O (671.84): C, 85.81; H, 6.45; N,

4.17. Found: C, 86.07; H, 6.71; N, 3.66.

4.14. Preparation of (+)-(R)-2,2⁰-bis(benzylamino)-1,1⁰-

binaphthyl (Rⁱ)-3

4.15.3. General procedures for NMR-scale asymmetric

hydroamination–cyclisation of aminoalkenes. For the

cyclisation of aminoalkenes performed at room tempera-

ture the appropriate aminoalkene (0.20 mmol) was dis-

solved in C₆D₆(0.1 mL) in the glove box and dried on

To a solution of (+)-(R)-2,2⁰-diamino-1,1⁰-binaphthyl

(1.22 g, 4.30 mmol) in THF (30 mL) was added triethyl-

amine (2.20 mL, 15.50 mmol) by syringe. Benzoyl chloride

(1.00 mL, 8.50 mmol) was then added dropwise under ar-

gon. A suspension appeared immediately and the reaction

mixture was heated at 60 °C for 2 h and stirred at room tem-

perature overnight. The solid was separated from the mix-

ture by ﬁltration. The solvent was concentrated in vacuo

and the crude product was used in the following step with-

out puriﬁcation. THF (30 mL) was added, and the solution

was added dropwise under argon to a suspension of LiAlH₄

(1.63 g, 43.00 mmol) in THF (50 mL) at 0 °C. The reaction

mixture was allowed to warm up to room temperature over-

night, and then heated at 60 °C for 4 h. The mixture was

hydrolysed with water until the formation of white hydrox-

ide aluminium salts. The solid was separated from the mix-

ture by ﬁltration. The organic layer was dried over MgSO₄,

ﬁltered and concentrated in vacuo. The crude product was

puriﬁed by ﬂash chromatography on silica gel (heptanes–

ethyl acetate = 99.5:0.5) to give a pale yellow solid (1.32 g,

65% yield). Mp = 134 °C. R_f= 0.3 (heptanes–ethyl acetate

˚

4 A molecular sieves for 2 h at room temperature. A solu-

tion of the ytterbium catalyst in C₆D₆(0.7 mL) was intro-

duced into a J. Young NMR tube equipped with a teﬂon

valve, and the aminoalkene solution was then added. The

1

hydroamination reaction was monitored by H NMR by

the observation of the decrease of the oleﬁnic protons

signals. After the appropriate time, the reaction was

quenched with CH₂Cl₂.

For the cyclisation of aminoalkenes performed at 110 °C

and 120 °C, the appropriate aminoalkene (0.20 mmol)

was dissolved in toluene (0.1 mL) in the glove box and

˚

dried on 4 A molecular sieves for 2 h at room temperature.

A solution of the ytterbium catalyst in toluene (0.7 mL)

was introduced into a sealed tube and the aminoalkene

solution was then added. The sealed tube was heated out

of the glove box during the appropriate time. The reaction

was quenched with CH₂Cl₂. The reaction products were

derivatised and the enantiomeric excesses were measured

as previously described.^6c,e

1

99.5:0.5). H NMR (CDCl₃): d 7.89–7.81 [m, 4H, ArH],

7.27–7.11 [m, 18H, ArH], 4.47–4.45 [m, 4H, CH₂–Ph] and

4.39 [br s, 2H, NH]. ¹³C NMR (CDCl₃): d 144.2, 139.8,

133.8 (C_Ar), 129.6, 128.4, 128.1 (CH_Ar), 127.7 (C_Ar),

126.8, 126.7 (CH_Ar), 123.9, 122.0, 114.1 (CH_Ar), 111.9

25

(C_Ar), 47.5 (CH₂–Ph). ½aꢂ₅₈₉¼ þ84; ½aꢂ₅₇₈¼ þ91; ½aꢂ₅₄₆

¼

Acknowledgements

25

þ114; ½aꢂ₄₃₆¼ þ353 (c 1.4, CHCl₃). Anal. Calcd for

C₃₄H₂₈N₂(464.60): C, 87.90; H, 6.07; N, 6.03. Found: C,

87.46; H, 6.12; N, 5.92.

We thank CNRS and MENESR for ﬁnancial support and

´ ´

Conseil General de l’Essonne for PhD grant for I.A.

4.15. Intramolecular hydroamination reactions

References

4.15.1. In situ preparation of ytterbium ate complexes

(Rⁱ,S,S)-7, (Rⁱ,R,R)-7, (Rⁱ,S,R)-7 and (Rⁱ)-8. In an

argon-ﬁlled glove box, the ligand (0.12 mmol) was solubi-

lised in THF (2 mL) in a Schlenk ﬂask equipped with a

magnetic stirring bar. n-BuLi (1.6 M in hexanes, 0.15 mL,

0.24 mmol) was added dropwise and the reaction mixture

was stirred for 10 min. YbCl₃(16.5 mg, 0.06 mmol) was

then added to the solution of the bis lithium salt of the

ligand in THF. The reaction mixture was stirred at room

temperature for 45 min and THF was evaporated in

vacuo. The crude product was dissolved in C₆D₆or toluene

and the solution was immediately used for the catalytic

tests.

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Article Doi

New axially chiral atropos and tropos secondary diamines as ligands for enantioselective intramolecular hydroamination

DOI: 10.1016/j.tetasy.2007.11.029

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