Synthesis, resolution, and application of 2,2′-bis(diphenylphosphino) -3,3′-binaphtho[b]furan (BINAPFu)

145

Synthesis, resolution, and application of 2,2′-

bis(diphenylphosphino)-3,3′-binaphtho[b]furan

(BINAPFu)¹

Neil G. Andersen, Masood Parvez, Robert McDonald, and Brian A. Keay

Abstract: ( )-2,2′-Bis(diphenylphosphino)-3,3′-binaphtho[2,1-b]furan (BINAPFu) was synthesized from 2-naphthoxy-

acetic acid in a five-step sequence in 62% overall yield. A variety of reported resolution procedures for biaryl bisphos-

phines did not work with ( )-BINAPFu; thus, a new resolution method was developed, involving the Staudinger reaction

of the aforementioned racemate of BINAPFu with an enantiopure camphor sulfonyl azide derivative. The resulting

diastereomeric phosphinimines were separated by flash chromatography. Subsequent hydrolysis to the corresponding

bis-phosphine oxide and trichlorosilane reduction provided enantiopure BINAPFu. The absolute stereochemical configu-

ration of BINAPFu was established by X-ray crystallography. BINAPFu was compared with commercially available

2,2′-bis(diphenylphosphino)-1,1′-binaphthalene (BINAP) in Pd(0)-catalyzed intermolecular Heck reactions. Investigation

of the Heck arylation of 2,3-dihydrofuran showed BINAPFu to be more efficacious than BINAP in dioxane at 30 °C.

1

A variety of phosphorus selenides were prepared, and the J_P-Secoupling constants measured, to obtain a comparative

scale of parent phosphine basicity. The phosphorus atoms in BINAPFu were found to be electron deficient when com-

pared with BINAP but slightly more electron rich than trifurylphosphine.

Key words: naphthofurans, atropisomers, electron-deficient phosphines, asymmetric Heck reactions, Staudinger reaction.

Résumé : Utilisant l’acide 2-naphtoxyacétique comme produit de départ, on a réalisé la synthèse en cinq étapes du

( )-2,2′-bis(diphénylphosphino)-3,3′-binaphto[2,1-b]furane (BINAPFu), avec un rendement global de 62 %. Plusieurs

méthodes connues de résolutions ont été tentées sans succès sur le ( )-BINAPFu; on a donc développé une nouvelle

méthode de résolution impliquant la réaction du ( )-BINAPFu avec un dérivé énantiopur de l’azoture de camphresulfo-

nyle. On a séparé les phosphinimines diastéréomères résultantes par chromatographie éclair. L’hydrolyse subséquente de

l’oxyde de bis-phosphine correspondante et une réduction à l’aide de trichlorosilane ont conduit au BINAPFu énantio-

pur. La configuration stéréochimique absolue du BINAPFu a été établie par diffraction des rayons X. On a comparé le

BINAPFu au 2,2′-bis(diphénylphosphino)-1,1′-binaphtalène (BINAP) dans les réactions intermoléculaires de Heck cata-

lysées par le Pd(0). Une étude de l’arylation de Heck du 2,3-dihydrofurane a montré que le BINAPFu est plus efficace

que le BINAP, dans le dioxane, à 30 °C. On a préparé une variété de séléniures de phosphore et on a mesuré les cons-

1

tantes de couplage J_P-Seafin d’obtenir une échelle comparative de la basicité de la phosphine de base. On a trouvé

que les atomes de phosphore du BINAPFu sont déficients en électron par comparaison avec le BINAP, mais qu’ils sont

plus riches en électrons que la trifurylphosphine.

Mots clés : naphtofuranes, atropisomères, phosphine déficiente en électron, réaction de Heck asymétriques, réaction de

Staudinger.

[Traduit par la Rédaction] Andersen et al. 161

Introduction

the superior results often realized using BINAP in asymmet-

ric transformations, coupled with the recent interest in 2-

furyl phosphine ligands (3), a project was undertaken to

develop an axially stereogenic diphosphine ligand that incor-

porates the 2-furyl group. At the onset of this endeavor, a

literature search revealed that no such structure had ever

been reported. Moreover, it was clear that very little was

known about how phosphine σ-donor ability affected the

Since Noyori and co-workers’ (1) introduction of 2,2′-

bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) as a chiral

ligand for asymmetric catalysis, numerous workers have

shown that remarkably high degrees of enantioselectivity

can be obtained using this phosphine in a wide variety of

transition-metal-mediated organic reactions (2). Based on

Received 19 June 2003. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 9 January 2004.

Dedicated to Dr. E. Piers for his outstanding chemistry contributions and to him as an invaluable mentor over the years.

N.G. Andersen, M. Parvez, and B.A. Keay.²Department of Chemistry, University of Calgary, Calgary, AB T2N 1N4, Canada.

R. McDonald. Department of Chemistry, University of Alberta, Edmonton, AB T6G 2G2, Canada.

¹This article is part of a Special Issue dedicated to Professor Ed Piers.

²Corresponding author (e-mail: keay@ucalgary.ca).

Can. J. Chem. 82: 145–161 (2004)

doi: 10.1139/V03-173

146

Can. J. Chem. Vol. 82, 2004

Scheme 1.

course of enantioselective reactions. However, many work-

ers have now sought to develop chiral 2-furyl phosphine

ligands for asymmetric synthesis, and several reports of

asymmetric reactions using these ligands have recently been

disclosed (4, 5). These investigations have been prompted,

in part, by recent evidence that suggests that less electron-

rich ligands are or should be advantageous in some metal-

mediated organic processes. For example, Shibasaki and co-

workers (6) have recently developed 2,2′-bis(diphenyl-

arsino)-1,1′-binaphthyl (1, BINAs) and have shown this

poorly donating ligand to be more effective than BINAP 2

for an intramolecular asymmetric Heck reaction (Scheme 1)

(7). In addition, Amatore and co-workers (8) have studied

the oxidative addition of phenyl iodide with in situ gener-

ated palladium(0) complexes of triphenylphosphine and

TFP, showing that in DMF, {Pd(dba)₂+ n(trifurylphosphine)}

is always more reactive than {Pd(dba)₂+ nPPh₃}, for n ≥ 2

(7). These reports, in conjunction with our interests in the

asymmetric polyene cyclization (9), led to the development

of a novel 3,3′-bifuryl-derived diphosphine analogue of

BINAP (Scheme 1), namely, BINAPFu 3 (10).

Scheme 2.

To develop a C₂-symmetric furyl phosphine analogue of

BINAP, it was conceived that a prudent design would retain

the bis(diphenylphosphino) moieties and incorporate the

furyl functionality into the biaryl framework. In this way, it

was felt that the electronic properties of the phosphine

ligand could be altered with minimal perturbation of the

chiral pocket structure. Since Benincori and co-workers (5i,

11) have concluded that the BIBENFu 4 ligand is not config-

urationally stable at room temperature, it was decided to pre-

pare the more sterically bulky bisnaphtho[b]furan skeleton,

as PM3 semi-empirical calculations on 3 indicated that the

rotational energy of the bifuryl bond in 3 would be quite

high. This paper describes the design aspects, synthesis, res-

olution, and application of the BINAPFu 3 ligand.

Scheme 3. (a) 1–5 equiv SO₂Cl₂, DCM, reflux, 4.5–12 h, <5%;

(b) 2 equiv hexachloro-2,4-cyclohexadienone, EtOH, reflux, 18 h,

30%; (c) 1.1 equiv TBSCl, Et₃N, DCM, rt, 18 h, 89%; (d) 1.0 equiv

TMSOTf, Et₃N, DCM, rt, 2 h; (e) 1 equiv Br₂, CCl₄; (f) 1 equiv

TBAF, THF, rt, 0.5 h, 72% (2 steps); (g) excess P₂O₅, MsOH, rt,

18 h, 68%; (h) 2 equiv SOCl₂, benzene, catalytic (cat) Py, re-

flux, 2 h; (i) 1.5 equiv AlCl₃, benzene, rt, 12 h, 95% (2 steps).

Synthesis of ( )-BINAPFu 3

Two initial routes to the synthesis of 3 were unsuccessful

(12) and led to a design in which the key reaction involved a

McMurry coupling. The low-valent titanium homocoupling

of aldehydes and ketones, developed independently by

Mukaiyama et al. (13), Tyrlik et al. (14), and McMurry et al.

(15), has been applied in a wide variety of contexts to pre-

pare symmetrical olefins (16). It was thought that the

BINAPFu bifuryl bond could be constructed via a McMurry

coupling of ketone 7 followed by DDQ oxidation of the

resultant olefin 6 (Scheme 2). Finally, introduction of the

diphenylphosphino groups into 5 would give ( )-BINAPFu

3.

Although ketone 7 has been previously reported (17), the

syntheses were characterized by low product yields (<35%)

and difficult isolation procedures. It was therefore decided

that a new, efficient synthesis of the required ketone 7

should be developed. Since 1-acetyl-2-hydroxynaphthalene

(8) was readily available, it was reasoned that α-chlorination

of the ketone function to give 9, followed by 5-exo-trig ring

closure, would provide an expedient route to the desired

ketone 7 (Scheme 3). Unfortunately, several chlorination re-

agents, including sulfuryl chloride (18) and hexachloro-2,4-

cyclohexadienone (19), failed to provide α-chloroketone 9 in

good yields. Recourse was sought in the three-step α-bro-

mination of ketone 10 via TMS enol ether 11 (Scheme 3).

Treatment of hydroxy-ketone 8 with 1.1 equiv of tert-

butyldimethylsilyl chloride in CH₂Cl₂and Et₃N furnished

TBS ether 10 in 89% yield. Although the TMS enol ether 11

could be formed using LHMDS and TMSCl in an ethereal

solvent, much more consistent results were obtained when

ketone 10 was treated with TMSOTf in a mixture of CH₂Cl₂

and triethylamine. Bromination of enol silyl ether 11 with

Andersen et al.

147

Scheme 4. 8.2 equiv Zn dust, 2.0 equiv TiCl₄, DME, reflux,

1 equiv of Br₂in CCl₄proceeded with loss of TMSBr to fur-

nish α-bromo ketone 12 in modest yield. Cleavage of the

TBS ether under standard conditions occurred with concom-

itant ring closure, to provide the desired naphthoketone 7 in

61% overall yield. Although this four-step synthetic se-

quence provided the desired ketone 7 in moderate yield,

without the need for costly purification routines, the use of

expensive protecting groups and reagents rendered this

method somewhat infeasible for large-scale preparation.

To address these concerns, an alternative synthesis of

compound 7 was conceived whereby readily available 2-

naphthoxyacetic acid (13) could be subjected to Friedel–

Crafts acylation conditions to provide the desired compound

directly (Scheme 3). Treatment of acid 13 with Eaton’s re-

agent (20) at ambient temperature for 18 h afforded the de-

sired ketone 7 in 68% yield. Alternatively, preparation of the

corresponding acyl chloride, under standard conditions, and

subsequent reaction with AlCl₃gave naphthoketone 7 in

95% yield. Interestingly, in both cases, acylation occurred

regiospecifically in the 1-position to give the desired product

7 with remarkable purity. This procedure, which does not re-

quire any purification steps, can easily be performed on a

50 g scale to provide ketone 7 in excellent yield.

18 h; (b) 1.0 equiv DDQ, benzene, reflux, 4 h, 78% (2 steps);

(c) 2.5 equiv t-BuLi, Et₂O, rt, 2 h; (d) 2.0 equiv PPh₂(O)Cl, rt,

12 h, 88%; (e) 20 equiv SiCl₃H, 24 equiv Et₃N, xylenes, 150 °C,

3 h, >95%; (f) 2.0 equiv PPh₂Cl, rt, 12 h, 91%; (g) 1.0 equiv

(CH₃CN)₂PdCl₂, DCM, rt, 28 h, 93%.

Reductive coupling of compound 7 with TiCl₄and zinc–

copper couple (21) in refluxing DME smoothly provided

olefin 6 in good yield (Scheme 4). Activated zinc dust (22)

worked equally as well for this purpose, giving biaryl 5 in

1

78% isolated yield after DDQ oxidation (23). H NMR anal-

ysis of compound 6 showed that the product had been

formed essentially as a single isomer (>95%), which was as-

signed the E configuration on the basis of steric arguments.

Owing to facile carbon-carbon double bond migration, olefin

6 could not be fully characterized. Upon oxidation with

DDQ, the broad singlet (δ: 5.25 ppm) that integrated as four

Et₂O into an acetone-saturated solution of the complex un-

der an argon atmosphere.

Comparing the projections of [( )-BINAPFu]PdCl₂(15)

with Hayashi’s [(R)-BINAP]PdCl₂structure 16 (24), a few

structural differences are immediately apparent. Whereas two

of the phenyl rings (A and B) in the [(R)-BINAP]PdCl₂

complex 16 π-stack with the binaphthalene framework, the

corresponding phenyl groups in compound 15 (A and B)

do not show perpendicular relationships with the binaph-

tho[b]furan system. Also noteworthy in the [( )-

BINAPFu]PdCl₂structure 15 is that the square planar geom-

etry about the palladium atom seems to be less distorted

than in the corresponding (R)-BINAP complex 16. These ob-

servations suggest that the chiral pocket formed in the

[BINAPFu]PdCl₂complex 15 is somewhat less rigid than

that obtained with the BINAP ligand 16. However, several

1

protons in the H NMR spectrum of 6 was replaced by a

sharp singlet (δ: 7.87 ppm) that represented the two furan α-

protons in biaryl 5.

Installation of the bis(diphenylphosphino) moieties was

accomplished by lithiation of the biaryl scaffold 5 with 2.5

equiv of t-BuLi and subsequent treatment of the resulting

dianion with freshly distilled diphenylphosphinic chloride.

This provided phosphine oxide 14 in 88% yield (Scheme 4).

Reduction of the oxide 14 with trichlorosilane in a mixture

of xylenes and triethylamine furnished ( )-BINAPFu (3) in

>95% yield. Alternatively, lithiation of biaryl 5 followed by

treatment of the resultant dianion with 2.0 equiv of

chlorodiphenylphosphine gave ( )-BINAPFu 3 directly in

91% yield.

similarities

are

also

observed

upon

comparing

[BINAP]PdCl₂16 and [BINAPFu]PdCl₂15. In both struc-

tures, two of the phenyl rings (C and D) project outward to-

ward the coordination sites occupied by the chloride ligands.

The [BINAP]PdCl₂16 bite angle (25), defined by the P1-Pd-

P2 vertex, of 92.7° compares well with that measured for the

[BINAPFu]PdCl₂15 (93.4°). Values for the Pd—P (16:

2.245 Å; 15: 2.264 Å) and Pd—Cl (16: 2.350 Å; 15:

2.333 Å) bond lengths compare quite favorably, although

slight differences can be seen because of the reduced elec-

tron-donor ability of the BINAPFu ligand. As expected, the

mean Pd—P bond length is slightly longer in the

[BINAPFu]PdCl₂complex, owing to the reduced σ-donor

ability of the phosphorus atoms relative to BINAP. As a re-

sult, the Pd—Cl bond lengths are slightly shorter in com-

pound 15. Given the structural changes that had to be made

to incorporate the 2-furyl moieties, it was felt that the struc-

Structural characterization of ( )-BINAPFu 3

As stated previously, a fundamental aspect of the ligand

design required that the 2-furyl groups be incorporated in

such a way that the electronic properties of the phosphorus

atoms may be altered with as little perturbation of the chiral

pocket structure as possible. To investigate the success of the

ligand design with respect to this requirement, the palla-

dium(II) chloride complex of BINAPFu 15 was prepared (5i)

and analyzed by single crystal X-ray diffraction (Fig. 1).

Crystals of compound 15 were obtained by slow diffusion of

148

Can. J. Chem. Vol. 82, 2004

Fig. 1. X-ray crystal structure of [( )-BINAPFu]PdCl₂(15) vs. Hayashi’s (24) [( )-BINAP]PdCl₂(16) structure (hydrogen atoms omit-

ted for clarity).

tural homology between the two organometallic complexes

was great enough to warrant further investigation with the

BINAPFu ligand.

ing similar chiral stationary phases are commercially avail-

able (26), optical resolution of the BINAPFu ligand in large

quantities using this method was deemed to be infeasible.

Although several methods for achieving optical resolution

of stereogenic organophosphorus compounds are known (27),

efforts were initially focused on procedures that have been

applied to BINAP and related C₂-symmetric diphosphines.

Unfortunately, the following reported procedures did not

afford a suitable resolution method for ( )-BINAPFu 3:

(a) co-crystallization of phosphine oxide 14 with (–)-DBTA

or (1S)-(+)-10-camphorsulfonic acid (28); (b) using

enantiopure palladium(II) complexes with (S)-N,N-dimethyl-

α-phenylethylamine or (S)-N,N-dimethyl-α-(2-naphthyl)ethyl-

amine (29–31); (c) via formation of phosphonium salts with

enantiopure organohalides like (S)-(+)-citronellyl bromide,

(S)-(+)-citronellyl iodide (32), or (S)-(+)-1-iodo-2-methyl-

butane; and (d) attempts to resolve the bis-phosphonium salt

Resolution of ( )-BINAPFu 3

Subsequent to developing a simple, highly efficient syn-

thesis of ( )-BINAPFu 3, attention focused on finding a

method for obtaining the two pure optical antipodes. To

achieve this goal, it was first necessary to find a convenient

method for determining the enantiopurity of diphosphine 3.

Fortunately, ( )-BINAPFu 3 could be readily separated by

analytical HPLC using a Chiralcel® OJ column (25 °C; 95:5

MeOH:EtOH; 0.5 mL min^–1; 270 nm UV detection), indicat-

ing that the rotational barrier of the biaryl axis was of suffi-

cient magnitude to impart optical activity at room

temperature. Although preparative HPLC columns employ-

Andersen et al.

149

Scheme 5. (a) 2.1 equiv ethyl chloroacetate, 4.6 equiv NaOH,

H₂O, 0 °C, 2 h, 82%; (b) 8.5 equiv LiAlH₄, THF, rt, 1 h, 92%;

(c) 1.0 equiv PCl₃, 2 equiv NEt₃, Et₂O, –40 °C, 72%; (d) 0.5

equiv compound 16, Et₂O, rt, 1.5 h; (e) 2 equiv BH₃·DMS, rt,

24 h, 74% (2 steps).

of 3 (generated with 2 equiv of iodomethane) by reaction

with silver hydrogen dibenzoyl-^L-tartrate (Ag-DBHT) (33)

or silver (1S)-(+)-10-camphorsulfonate (34).

Although the synthesis developed for the BINAPFu ligand

(vide supra) is short and efficient, failure to identify a suit-

able method for obtaining the optically pure material via

known resolution methods led to the consideration of alter-

native synthetic routes. It was postulated that an enantiopure

electrophile of type 17 could potentially be reacted with

lithiated biaryl 16 to give bis-phosphonamide 18 as a 1:1

mixture of diastereomers (35) (Scheme 5). Such an approach

would thus install the required 2,2′-phosphorus atoms while

appending a chiral auxiliary for optical resolution. Separa-

tion of the resulting diastereomer mixture and subsequent

synthetic manipulation of each pure isomer, 18a and 18b,

would then provide routes to the optically pure BINAPFu

antipodes. Following this general scheme, commercially

available trans-1,2-cyclohexane diamine was resolved (36),

and the (R,R)-isomer (37) 20 was converted to the corre-

sponding N,N′-dimethyl derivative 21 according to a litera-

ture procedure (38) (Scheme 5). Diamine 21, thus obtained,

was treated with

1 molar equivalent of phosphorus

trichloride, according to a standard procedure (39), to fur-

nish chlorophosphine 22 in 72% isolated yield. This highly

moisture- and oxygen-sensitive (39) compound was prepared

using Schlenk techniques under an atmosphere of argon and

was used without purification. Trapping dianion 16, pre-

pared as previously described, with 1,3-diazaphopholidine

derivative 22 and subsequent reaction with BH₃·DMS pro-

vided a 1:1 mixture of diastereomers 23a and 23b, respec-

tively (Scheme 5). Bis-borane complex 23 was prepared in

situ to prevent potential complications due to air oxidation

of the phosphine precursor (39). Although separation of

compounds 23a and 23b could not be achieved using stan-

dard recrystallization or flash chromatographic techniques, a

small sample (~3 mg) of each pure diastereomer was ob-

tained by preparative HPLC, using a reversed-phase C₁₈col-

umn. While this labor-intensive and costly separation

technique clearly did not provide large quantities of resolved

material, the obtainment of diastereomerically pure borane

adducts 23a and 23b was highly encouraging. Moreover, it

was postulated that by simply changing the diamine used to

prepare phosphoramidous chloride 17 (Scheme 5), it may be

possible to prepare a more readily separable mixture of axial

diastereomers.

Scheme 6. (a) 1.5 equiv Mg, 1.5 equiv TiCl₄, 4 mol% HgCl₂,

THF, 0 °C, 12 h, 61%; (b) optical resolution with ^L-(+)-tartaric

acid; (c) 1.0 equiv PCl₃, 2 equiv NEt₃, Et₂O, –40 °C, 81%;

(d) 0.5 equiv compound 16, Et₂O, rt, 1.5 h; (e) 2 equiv

BH₃·DMS, rt, 24 h, 71% (2 steps); (f) 8 equiv anhyd HCl, Et₂O.

Diamine 25 was prepared from 24 (40) and resolved (41)

according to standard literature procedures (Scheme 6).

Diazaphospholidine 26 (42) was subsequently prepared upon

treatment of (S,S)-(–)-diamine 25 with 1 equiv of phospho-

rus trichloride in Et₃N–Et₂O solution. Further reaction with

2,2′-dilithiated binaphthofuran 16 and BH₃·DMS furnished a

1:1 mixture of axially isomeric borane adducts 27a and 27b

in 71% yield. Fortunately, separation of stereoisomers 27a

and 27b was facile by fractional crystallization from a

CHCl₃–hexanes solvent system. Under these conditions,

compound 27a selectively crystallized, leaving highly en-

riched (>95%) isomer 27b in the mother liquor. The latter

compound could be further purified by flash chromatogra-

phy. With pure borane adducts 27a and 27b in hand, atten-

tion was focused on removing the diamine moiety and

installing the required phenyl substituents.

Supported by literature precedent (35, 43), it was envi-

sioned that the diamine chiral auxiliary could be cleaved

from borane adduct 27a upon treatment with anhyd HCl,

providing enantiopure chloride 28 (Scheme 6). Subsequent

150

Can. J. Chem. Vol. 82, 2004

Scheme 7. (a) 2 equiv enantiopure azide (*RN₃); (b) separate

axial stereoisomers; (c) H^–reduction, Et₂O.

reaction of 28 with 4 equiv of phenyllithium or phenyl Grig-

nard and removal of the BH₃protecting group would then

furnish the desired BINAPFu 3 in optically pure form. Fol-

lowing this approach, isomerically pure compound 27a was

treated with 8 molar equivalents of HCl (1.0 mol L^–1solu-

tion in Et₂O) at 0 °C for 1 h. The mixture thus obtained was

filtered under argon to remove (1S,2S)-N,N′-dimethyl-1,2-

diphenylethylenediamine dihydrochloride, and the filtrate

was treated with 5 equiv of phenyllithium at –40 °C. Under

these conditions, a complex mixture of products was

obtained, as evidenced by ³¹P NMR analysis. Lowering the

reaction temperature to –40 °C for the acid addition or using

phenyl Grignard in place of phenyllithium failed to improve

this result. Employing anhyd HCl(g) instead of the 1.0 mol L^–1

ethereal solution also afforded a complex mixture of prod-

ucts. In all cases, isolation of the unwanted amine hydro-

chloride salt confirmed that cleavage of the P—N bonds was

occurring under the reaction conditions. Low temperature

³¹P NMR analysis indicated that complex mixture formation

was occurring previous to the addition of the organometallic

reagent. Other Brönsted acids, including MsOH and TFA in

methanolic solution, afforded similar results. The failure to

identify suitable conditions for cleaving the diamine chiral

auxiliary from borane adduct 27a led to the development of

a new resolution procedure for phosphines.

As several of the known methods for phosphine resolution

were unsuccessful, we decided to develop a new resolution

to obtain enantiopure BINAPFu 3. Consideration of the reso-

lution methods already attempted (vide supra) suggested that

a newly developed procedure should ideally act directly on

BINAPFu 3 or the corresponding bis-phosphine oxide 14

to minimize the number of synthetic steps. Moreover, owing

to the difficulties experienced in the CSA and DBTA resolu-

tion techniques, it was concluded that a successful route

would likely involve appending the resolving agent via a co-

valent linkage, thus providing two discrete diastereomeric

compounds. Based on unsuccessful attempts with the ortho-

palladated resolving agents (29–31), the diastereomeric com-

pounds obtained by appending a resolving agent to the phos-

phine ligand should be neutral intermediates, to allow for

possible chromatographic separation. Finally, considering

the impasse reached with diazaphospholidine compound 27a,

cleavage of the chiral auxiliary to furnish the desired opti-

cally pure phosphine 3 or phosphine oxide 14 should not

require strongly acidic reaction conditions. With these pa-

rameters in mind, it was conceived that a Staudinger reaction

(44) between ( )-BINAPFu 3 and 2 equiv of an enantiopure

organoazide could potentially give a 1:1 mixture of

diastereomeric phosinimines 29a and 29b (Scheme 7) if the

P=N bond rotational barrier was low enough to prevent geo-

metrical isomerism. A literature survey revealed that the

P=N rotational barrier for simple phosphinimines has been

calculated to be ca. 2.54 kcal mol^–1(45). Hence it was ratio-

nalized that P=N geometrical isomerism would likely not

complicate the proposed resolution technique. Separation of

the phosphinimine mixture and subsequent reductive cleav-

age of the resolving agent from each pure isomer with

LiAlH₄would then furnish the desired, enantiomerically

pure antipodes.

cally pure organoazide needed to be identified (46). (1S)-10-

camphorsulfonyl azide was chosen as a possible resolving

agent; it can be prepared in a single step from commercially

available (1S)-(+)-10-camphorsulfonyl chloride (47). Treat-

ment of ( )-BINAPFu 3 with 2 molar equivalent of

enantiopure sulfonyl azide 30 smoothly provided a 1:1 mix-

ture of diastereomeric phosphinimines 31a and 32b in near

quantitative yield (Scheme 8). Fortunately, phosphinimines

31a and 31b could be readily separated by flash chromatog-

raphy on silica gel using a 9:1 CHCl₃–CH₃CN eluent mix-

ture. With isomerically pure phosphinimines 31a and 32b in

hand, attention was now focused on identifying a method for

removing the chiral auxiliary to give optically pure

BINAPFu 3 or the corresponding phosphine oxide 14.

It was postulated that treatment of isomerically pure phos-

phinimine 31a with excess LiAlH₄would provide optically

pure BINAPFu 3 along with isobornyl-10-sulfonamide 32

(Scheme 8) (48). Interestingly, heating compound 31a with

10 equiv of LAH in THF resulted in the unexpected forma-

tion of 3,3′-binaphtho[b]furan (5) and monophosphine 33.

Although a small amount of the desired product was ob-

tained and shown to be optically pure by HPLC analysis

(Chiralcel® OJ column; 25 °C; 95:5 MeOH:EtOH;

0.5 mL min^–1; 270 nm UV detection), conditions to attenu-

ate the formation of byproducts 5 and 33 could not be found.

Performing this reaction at ambient temperature resulted in a

similar product mixture, while employing weaker reducing

agents, such as DIBAL or NaBH₄, failed to cleave the P=N

bond.

Faced with the failure to prepare optically pure BINAPFu

3 in good yield via direct reduction of phosphinimine 31a, it

was postulated that the P=N bond could be cleaved using an

aza-Wittig process (49). Hence, reaction of either compound

31a or 31b with CO₂would afford optically pure phosphine

To develop a resolution procedure for ( )-BINAPFu based

on phosphinimine formation, a readily available and opti-

Andersen et al.

151

Scheme 8.

oxide 14 along with (1S)-10-camphorsulfonamide 34

(Scheme 8). Subsequent trichlorosilane reduction of phos-

phine oxide 14 thus obtained would then furnish the desired

enantiopure BINAPFu ligand 3. Surprisingly, bubbling CO₂

gas through a solution of isomerically pure phosphinimine

31a in THF for a period of 4 h failed to cause any detectable

cleavage of the P=N bond. Changing the solvent to acetone

and lengthening the exposure time did not improve this re-

sult. Moreover, no reaction was observed upon refluxing

compound 31a in carbon disulfide for 24 h, suggesting that

an aza-Wittig approach toward cleaving the phosphinimine

moiety was not going to be feasible.

Since phosphinimine 31a was inert towards aza-Wittig

conditions, recourse was sought in the hydrolytic cleavage of

the P=N bond using mineral acids (50). Stirring a solution of

compound 31a in THF and 1.5 mol L^–1H₂SO₄at ambient

temperature for 24 h failed to give any reaction, as evi-

denced by ³¹P NMR analysis. Although this experiment did

not result in the cleavage of the P=N bond, it is noteworthy

that the binaphtho[b]furan system withstood the reaction

conditions and was therefore more stable to acid than previ-

ously anticipated. Performing the reaction in refluxing THF,

under otherwise identical conditions, cleanly provided the

desired phosphine oxide, albeit in poor conversion (~15%).

Subsequent experimentation revealed phosphine oxide 14

could be obtained in near quantitative yield by refluxing

compound 31a in a 3:2 mixture of 1,4-dioxane and 3 mol L^–1

H₂SO₄for 24 h (Scheme 9). Subsequent chromatographic re-

moval of sulfonamide 32 and trichlorosilane reduction of the

resulting phosphine oxide 14 provided BINAPFu 3 in excel-

lent yield. HPLC analysis (vide supra) of the bisphosphine

thus obtained showed a single peak at R_T= 23.7 min.

Finally, optical rotation data revealed that phosphinimine

31a yielded (–)-BINAPFu ([α]¹_D⁹–203.0 (c 1.09, CHCl₃)).

Performing the same hydrolysis–reduction sequence on

phosphinimine 31b provided (+)-BINAPFu 3 in near quanti-

tative yield ([α]²_D⁰+201.8 (c 1.28, CHCl₃)). Heating the

enantiopure (–)-BINAPFu ligand in p-xylenes at 150 °C for

7 days did not result in any racemization of the chiral axis,

as evidenced by optical rotation and HPLC analysis.

Physical characterization of the BINAPFu

ligand: Investigation of the ␴-donor ability

and absolute configuration assignment

1

Allen and Taylor (51) have reported that the J(³¹P-⁷⁷Se)

coupling constant of phosphorus selenides may be used as a

measure of parent phosphine basicity. A large coupling con-

stant indicates high s-character of the phosphorus lone-pair

orbital. In other words, poorly donating phosphine ligands

1

exhibit large J(³¹P-⁷⁷Se) coupling constants. To gauge the

donor ability of the BINAPFu ligand, a solution of optically

pure (–)-3 in CHCl₃was heated with 10 molar equivalent of

selenium powder for

5 h to afford bis-selenide 35

(Scheme 8). ³¹P NMR analysis of selenide 35 clearly

showed a strong singlet at +19.4 ppm with a satellite doublet

(¹J_P-Se= 762 Hz) due to ³¹P-⁷⁷Se coupling. Performing the

same reaction and ³¹P NMR analysis on a variety of other

1

commonly used phosphine ligands yielded the J_P-Secou-

pling constants shown in Fig. 2. As the data clearly indi-

152

Can. J. Chem. Vol. 82, 2004

1

Scheme 9. (a) 3 mol L^–1H₂SO₄, 1,4-dioxane, 100 °C, 24 h,

>95%; (b) 20 equiv SiCl₃H, 24 equiv Et₃N, xylenes, 150 °C,

3 h, >95%; (c) 10 equiv Se powder (100 mesh), CHCl₃, 60 °C,

5 h, 97%.

Fig. 2. J_P-Secoupling constants for selected phosphine selenides.

cates, the BINAPFu ligand 3 is far less basic than both

triphenylphosphine (47) and BINAP (1). Moreover,

BINAPFu 3 is significantly less basic that Benincori’s

benzothiophene-derived ligand BITIANP (38) (5i). Phos-

phinoaryl oxazoline ligand 40, which has gained much atten-

tion in enantioselective allylic alkylation reactions (52), is

also less basic than triphenylphosphine but significantly

more basic than either BINAPFu or BITIANP. The small

difference observed between the coupling constants for bis-

selenides 42 and 46 suggest that this measure of σ-donor

ability can be quite a sensitive technique. The latter selenide,

derived from 7,7′-dimethoxy-2,2′-bis(diphenylphosphino)-

1,1′-binaphthalene (45) (53), is slightly more basic than

BINAP, owing to the electron-donating capacity of the re-

mote 7,7′-methoxy substituents.

Having demonstrated that the electronic properties of

BINAPFu 3 and BINAP 1 are dissimilar, with the former

ligand resembling those of tri-2-furylphosphine (36), atten-

tion was focused on the final task of characterization. The

absolute configuration of the biaryl axis needed to be eluci-

dated. With phosphine selenide 35 in hand, prepared from

optically pure (–)-BINAPFu (vide supra), it was rationalized

that X-ray diffraction using the Bijvoet method (54) could

determine the stereochemical assignment. Single crystal

analysis of compound 35 furnished the structure depicted in

Fig. 3. By refining the inverted structure and evaluating the

Flack parameter, it was shown that the S-configuration was

present in the crystal. Hence, phosphinimine 31a corre-

sponds to (S)-(–)-BINAPFu, while phosphinimine 31b corre-

sponds to (R)-(+)-BINAPFu. This relationship was verified

via single crystal X-ray diffraction analysis of phosphini-

mine 31a (Fig. 3). In this case, Bijvoet analysis was not re-

quired since the absolute stereochemistry of the biaryl axis

could be ascertained by simple comparison with the known

configurations of the camphor residues. Since (1S)-(+)-10-

camphorsulfonyl chloride was used to prepare resolving

agent 30, it follows from Fig. 3 that phosphinimine 31a is

the S-axial diastereomer.

Having attained the goal of preparing and optically resolv-

ing a C₂-symmetric bifuran analogue of BINAP, the task of

Andersen et al.

153

Scheme 10. (a) 3.0 equiv DIPEA, 3 mol% Pd(OAc)₂, 6 mol%

Fig. 3. X-ray crystal structures of phosphine selenide 35 (one

solvent molecule of crystallization (CH₃CN) omitted for clarity)

and phosphinimine 31a (unit cell contains two identical mole-

cules of compound 31a and five molecules of CH₃CN (not

shown)); hydrogen atoms omitted for clarity.

(R)-BINAP, C₆H₆, 30 °C, 66 h.

(5.1 mmol) were carefully added by microlitre-syringe. The

argon-purged vessels were subsequently sealed and placed

in a thermostatically controlled oil bath for a specified pe-

riod. In light of our inability to repeat Hayashi’s experimen-

tal results, coupled with the fact that the reported ee values

were ascertained using the chiral shift NMR analysis

method, it was deemed prudent to perform control experi-

ments using commercially supplied (R)-BINAP. To this end,

all experiments were performed in parallel, using both the

(R)-BINAP and (R)-BINAPFu catalyst systems, and were

analyzed using chiral GC analysis conditions.

Employing Hayashi’s original Heck arylation conditions

with the (R)-BINAP ligand afforded 2,3-dihydrofuran prod-

uct 51 in 27% yield and 86% ee (entry 1b). However, the re-

action was only 30% complete after a 9 day period at 30 °C.

In our hands, neither Hayashi’s reported yield (78%) (55a)

nor the enantiomeric excess of the 2,3-dihydrofuran product

51 (93%) (55a) were attainable under these reaction condi-

tions. Utilizing (R)-BINAPFu under otherwise identical con-

ditions afforded a 21% yield of product 51, favoring the R-

configuration in >97% ee. Extraordinarily, the enantiomeric

purity of the minor isomer 52 was also greater than when

(R)-BINAP was employed, and the sense of enantioselection

was reversed. In other words, both products 51 and 52 were

enriched in the R-configuration, suggesting that the reaction

with BINAPFu may not follow Hayashi’s proposed kinetic

resolution mechanism. Repeating this experiment using Pro-

ton Sponge^®(3.0 equiv) as the base provided much lower

product conversion factors (entries 2a and 2b). Since the

conditions reported in the literature for this reaction failed to

give useful product conversions, alternative palladium

sources, solvents, bases, and reaction temperatures were in-

vestigated.

evaluating the performance of this ligand in metal-mediated

asymmetric transformations remained.

Application of BINAPFu in the Heck

arylation of 2,3-dihydrofuran using (R)-

BINAP and (R)-BINAPFu

A significant increase in product conversion was observed

upon using a polar solvent such as 1,4-dioxane with DIPEA

as the base (entry 3). The effect was more pronounced for

the (R)-BINAPFu catalyst, giving a 61% yield of the 2,3-

dihydrofuran product 51 (97% ee, entry 3a). Under identical

conditions, the (R)-BINAP catalyst afforded only 43% yield

of 51 (73% ee, entry 3b), albeit with higher regioselectivity.

Again, the 2,5-dihydrofuran product 52 was formed with S-

configuration selectivity using the (R)-BINAP catalyst, while

the R-configuration was preferred with the (R)-BINAPFu

catalyst. Since NMP has been used successfully in the Stille

reaction with trifurylphosphine-derived catalysts (56), it was

conceived that this polar solvent may also work well in the

present case. Employing NMP as the solvent also afforded

The asymmetric Heck arylation of 2,3-dihydrofuran (49),

first reported by Hayashi and co-workers (24, 55), has been

studied extensively and was therefore chosen as a suitable

reaction to study using the BINAPFu ligand (Scheme 10).

The Heck arylation of 2,3-dihydrofuran (49) was performed

under a variety of reaction conditions (Table 1) on a

1.0 mmol scale (based on PhOTf) in sealed, screw-cap sam-

ple vials. In all cases, the Pd-catalysts (3 mol%) were

formed in situ at 60 °C in the presence of an amine base un-

der argon for 30 min. In general, catalysts formed using (R)-

BINAP were bright orange in color, while catalysts derived

from (R)-BINAPFu were bright yellow in color. After for-

mation of the catalyst, PhOTf and 2,3-dihydrofuran

154

Can. J. Chem. Vol. 82, 2004

Table 1. Asymmetric Heck results with BINAPFu (3) and BINAP (1).

Yield (% (% ee))

Entry

1a

Ligand

Solvent

T (°C)

30^b

Conversion (%)

(R)-51

53

1

(R)-52

a

33

30

17

1

(R)-3

(R)-1

(R)-3

(R)-1

C₆H₆

21 (>97)

27 (86)

1 (—)

11 (75)

3 (51)^c

13 (93)

—

1b

C₆H₆

30^b

0

a

2a

C₆H₆

30^d

3

a

2b

C₆H₆

30^d

1 (—)

—

a

3a

3b

4a

4b

5a

5b

6a

(R)-3

(R)-1

(R)-3

(R)-1

(R)-3

(R)-1

(R)-3

Dioxane^a

NMP^a

30^b

50^b

70^b

71

46

41

69

30

56

31

61 (>97)

43 (73)

32 (>79)

67 (72)

25 (76)

53 (66)

26 (74)

1

0

1

9 (57)

2 (46)^c

8 (22)

1 (38)^c

5 (37)

2 (15)

4 (61)

NMP^a

Dioxane^e

e

C₆H₆

6b

(R)-1

C₆H₆

70^b

99

77 (54)

3

19 (35)

e

7a

7b

8a

8b

9a

(R)-3

(R)-1

(R)-3

(R)-1

(R)-3

(R)-1

(R)-3

(R)-1

(R)-3

(R)-1

(R)-3

(R)-1

(R)-3

(R)-1

THF^e

70^b

83

100

77 (75)

74 (53)

95 (73)

55 (48)

90 (77)

73 (41)

94 (71)

55 (35)

83 (80)

62 (50)

66 (79)

93 (54)

94 (74)

90 (57)

1

4

1

13

1

9

3

5

3

5

5 (61)

22 (71)

4 (64)

32 (72)

10 (40)

17 (26)

3 (39)

41 (47)

14 (40)

33 (11)

33 (44)

3 (23)

THF^e

70^b

DME^e

85^b

DME^e

85^b

Dioxane^e

DMF^e

100^b

90^b

9b

10a

10b

11a

11b

12a

12b

13a

13b

DMF^e

90^b

Dioxane^e

Dioxane^a

100^f

100^d

100^b

1

4

1

2

7 (64)

12 (79)

^a3 mol% Pd(OAc)₂for 9 days.

^b(i-Pr)₂NEt used as base.

^cS-configuration was favoured.

^dProton sponge used as base.

^e1.5 mol% Pd₂dba₃for 7 days.

^fPMP used as base.

higher conversion factors (entries 4a and 4b) than those ob-

served using benzene (entries 1a and 1b), but the ee of the

major product 51 was diminished (79%) relative to the result

obtained with dioxane (97%). The same general trend in

enantioselection was observed, wherein the absolute config-

uration of the 2,5-dihydrofuran product 52 differed between

the two catalyst systems studied. The use of Pd(OAc)₂as the

pre-catalyst was not required to achieve good enantioselecti-

vity. Utilizing the Pd₂(dba)₃–(R)-BINAPFu catalyst system

in dioxane at 50 °C with DIPEA as the base afforded a 25%

yield of compound 51 in 76% ee (entry 5a). The same con-

ditions in conjunction with a Pd₂(dba)₃–(R)-BINAP catalyst

system furnished compounds 51 and 52 in higher conversion

and isomeric selectivity but with reduced enantioselectivity

(entry 5b). Using these conditions, both catalysts provided

2,5-dihydrofuran product 52, favoring the R-configuration.

Virtually the same product conversion, regioselectivity, and

ee were obtained using the (R)-BINAPFu ligand in benzene

at 70 °C (entry 6a). However, a significant increase in con-

version and decrease in isomer selectivity was observed us-

ing (R)-BINAP in benzene at 70 °C (entry 6b). Although the

conversion was certainly poorer with the (R)-BINAPFu cata-

lyst, it was encouraging to note that respectable enantio-

selectivities could also be achieved at higher temperatures.

In other words, this result suggested that it may be possible

to get this reaction to go to completion while still obtaining

reasonable levels of enantioselection.

A study of various ethereal solvents at elevated tempera-

ture (entries 7–9) revealed that full conversion was attain-

able, without a significant loss in enantioselectivity, using

1,4-dioxane as the solvent at 100 °C (entries 9a and 9b).

Moreover, at high temperatures, the (R)-BINAPFu catalyst

Andersen et al.

155

afforded less of the unwanted conjugated isomer 53 and af-

forded higher selectivity in favor of the 2,3-dihydrofuran

product 51. In all cases, utilization of high-temperature con-

ditions (>50 °C) provided the 2,5-dihydrofuran product 52

enriched in the R-isomer, regardless of whether (R)-BINAP

or (R)-BINAPFu was used as the ligand. Conducting the re-

action in DMF at 90 °C with DIPEA as the base and an (R)-

BINAPFu-derived catalyst afforded excellent isomer selec-

tivity with a slight reduction in enantioselectivity (entry 10a).

At elevated temperatures, the conditions that employed di-

oxane as the solvent and PMP as the tertiary amine base

yielded the 2,3-dihydrofuran product 51 in 80% ee with only

modest regioselectivity (entry 11a). Ozawa, Kubo, and

Hayashi have reported (55b) higher degrees of enantioselec-

tion, at the expense of regioselectivity, using Proton Sponge^®

as the base. Using this base in dioxane at 100 °C with the

(R)-BINAPFu catalyst did not result in increased enantio-

selectivity (entry 12a). However, in accordance with

Hayashi’s findings, a significant decrease in isomer selectiv-

ity was observed. Finally, changing back to the Pd(OAc)₂

catalyst and using dioxane as the solvent at 100 °C with

DIPEA as the base gave a slight increase in product regio-

selectivity (entry 13a, cf. entry 9a).

Examining the results listed in Table 1 as a whole, a few

general trends immediately emerge. Firstly, the enantiomeric

purity of the 2,3-dihydrofuran isomer 51 was always higher

when the (R)-BINAPFu-derived catalyst system was used.

At low temperatures (<50 °C), employing dioxane as the

solvent with DIPEA as the base afforded the best balance

between conversion (71%) and enantioselectivity of the 2,3-

dihydrofuran product 51 (97%). However, in this tempera-

ture domain, the (R)-BINAP catalyst generally affords a

much higher isomer selectivity. The (R)-BINAPFu catalyst

consistently provides products 51 and 52, both enriched in

the R-configuration. In contrast, the (R)-BINAP catalyst

gives compounds 51 and 52 of opposite configuration only

at low temperature (30 °C). At higher temperatures (>70 °C),

full conversion of the phenyl triflate can be realized with ei-

ther catalyst system. Under such conditions, the (R)-

BINAPFu catalyst typically gives the major product in 71%–

80% ee, while the (R)-BINAP catalyst produces product 51

in 35%–57% ee. High-temperature conditions, in conjunc-

tion with the (R)-BINAPFu catalyst system, give rise to

higher isomeric ratios in favor of the 2,3-dihydrofuran prod-

uct 51 and attenuated formation of the conjugated isomer 53,

relative to the corresponding reactions employing the (R)-

BINAP-derived catalyst. Perhaps of greatest significance is

the observation that high enantioselectivity for the 2,3-

dihydrofuran isomer 51 does not seem to correlate with poor

isomeric selectivity. Recall that Hayashi, Ozawa, and co-

workers used this argument as strong evidence supporting a

kinetic resolution mechanism (24). Notwithstanding our in-

ability to repeat these workers’ findings (vide supra), the ex-

perimental results obtained using the BINAPFu ligand

suggest that this assertion may indeed be incorrect.

Conclusions

We have designed, synthesized, and resolved a new

binaphthofuran ligand (BINAPFu) for use in asymmetric

metal-catalyzed reactions. The ligand is easily prepared in 5

steps from readily available starting material. A new resolu-

tion procedure was designed for phosphines, involving the

Staudinger reaction with a camphor sulfonyl azide deriva-

tive. BINAPFu outperformed BINAP in the Heck reaction

between phenyl triflate and 2,3-dihydrofuran. Further struc-

tural modifications of BINAPFu are currently underway to

improve the enantioselectivity of high-temperature Heck

arylation reactions.

Experimental section

General comments

Melting points were determined using either an

Electrothermal^®melting point apparatus in sealed capillary

tubes or an A.H. Thomas hot-stage and are uncorrected.

Boiling points are uncorrected and refer to measured air-bath

temperatures using a Kugelrohr short-path distillation appa-

ratus. Optical rotation data was obtained on a Rudolph

Autopol III polarimeter using a quartz cell with a 10 cm path

length. Infrared spectra were recorded on a Mattson Galaxy

Series 4030 FT-IR spectrometer. H and ¹³C NMR spectra

1

were obtained on a Bruker ACE 200 (¹H, 200 MHz; ¹³C,

50 MHz), a Bruker AM 400 (¹H, 400 MHz; ¹³C, 100 MHz),

or a Bruker DRX 400 (¹H, 400 MHz; ¹³C, 100 MHz) spec-

trometer. Unless otherwise noted, deuteriochloroform was

used as the NMR solvent. ³¹P NMR spectra were obtained

on a Varian XL 200 (³¹P, 81 MHz), a Bruker AMX 300 (³¹P,

121.5 MHz), or a Bruker DRX 400 (³¹P, 162 MHz) spec-

trometer using an external reference of 30% H₃PO₄in D₂O

set to 0 ppm. Unless specified otherwise, ³¹P NMR samples

were prepared using deuteriochloroform as the solvent. GC–

MS analysis was performed on a Hewlett-Packard 5890 Se-

ries II gas chromatograph equipped with a Hewlett-Packard

OV 101, low polarity, 12 m × 0.2 mm column, in conjunc-

tion with a Hewlett-Packard 5971A mass selective detector.

Low-resolution mass spectra on nonvolatile samples were

obtained on a VG 7070 or a Kratos MS80 mass spectrometer

using 70 eV ionization with direct probe sample introduc-

tion. HR-MS and FAB-MS analyses were obtained using a

Kratos MS80 spectrometer. Elemental analyses were ob-

tained from the University of Calgary’s Control Equipment

Corporation 440 Elemental Analyzer. X-ray structure deter-

mination³was performed by Dr. M. Parvez (University of

Calgary), using a Rigaku AFC6S diffractometer with graph-

ite monochromated Mo Kα radiation, or by Dr. R. McDon-

ald (University of Alberta), using a Bruker P4 diffractometer

equipped with a SMART 1000 CCD area detector and

18 kW rotating anode X-ray generator. Column chromatog-

raphy was performed using silica gel 60 (E. Merck, 0.04–

0.063 mm, 230–400 mesh), using the flash method (57). Sol-

³Supplementary data may be purchased from the Depository of Unpublished Data, Document Delivery, CISTI, National Research Council

Canada, Ottawa, ON K1A 0S2, Canada (http://www.nrc.ca/cisti/irm/unpub_e.shtml for information on ordering electronically). CCDC

221199, 221200, and 147246 contain the supplementary data for this paper. These data can be obtained, free of charge, via

www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, U.K.; fax

+44 1223 336033; or deposit@ccdc.cam.ac.uk).

156

Can. J. Chem. Vol. 82, 2004

vent systems refer to mixtures, by volume, of hexanes and

ethyl acetate unless specified otherwise. Analytical HPLC

analyses were performed on an ICI LC 1440 instrument

equipped with an ICI LC 1150 HPLC Pump (C₁₈column or

Chiralcel OJ column with an ICI LC 12010 UV–vis detec-

tor) or a Waters 4886 instrument (Nova-Pak C₁₈reverse-

phase column or Chiralcel OB column with a Waters 486

UV detector). Preparative HPLC was done on the latter in-

strument equipped with a 25 mm × 100 mm Water Nova-

Pak C₁₈reversed-phase column. Chiral gas chromatography

CH₂Cl₂(600 mL) and Et₃N (73 mL, 0.52 mol) at 0 °C was

added TMSOTf (24 mL, 0.13 mol). The mixture was

warmed to rt and stirring was continued for 1 h under an N₂

atmosphere. The mixture was diluted with CHCl₃(100 mL),

washed with brine (2 × 300 mL), dried (Na₂SO₄), and evap-

orated to dryness under reduced pressure to give crude enol

1

ether 11 in quantitative yield. H NMR (200 MHz) δ: 0.18

(s, 9H), 0.27 (s, 6H), 1.09 (s, 9H), 4.39 (s, 1H), 4.74 (s, 1H),

7.07 (d, J = 11 Hz, 1H), 7.45 (m, 2H), 7.71 (m, 2H), 8.08 (d,

J = 11 Hz, 1H). Trimethylsilyl enol ether 11 was used di-

rectly in the subsequent step.

was performed on either

a

Shimadzu GC-9A gas

chromatograph (25 m × 0.33 mm (i.d.) Cydex-B fused silica

column with a flame ionization detector) or a Varian Star

3400 CX instrument (30 m × 0.32 mm (i.d.) Cyclodex-B

fused silica column with a flame ionization detector).

1-(2-Bromoacetyl)-2-[(tert-butyldimethylsilyl)oxy]naph-

thalene (12)

In a flask equipped with a dropping funnel, TMS enol

ether 11 (38.9 g, 0.105 mol) was dissolved in CCl₄(450 mL)

and cooled to 0 °C. A solution of bromine (5.66 mL, 0.119

mol) in CCl₄(100 mL) was placed in the dropping funnel,

and 20 mL of this solution was added to the reaction mix-

ture; after warming to rt, the remaining 80 mL of the bro-

mine solution was added over a 30 min period. The mixture

was stirred for a further 30 min and diluted with H₂O

(200 mL), and the layers were separated. The aqueous layer

was extracted with CHCl₃(2 × 100 mL), and the combined

organic layers were washed with an Na₂S₂O₃solution

(200 mL) and H₂O (2 × 200 mL). The organic fraction was

dried (Na₂SO₄) and concentrated in vacuo to furnish 39.5 g

Chlorination of 1-acetyl-2-hydroxynaphthalene (8)

Method 1

To

a

solution of 1-acetyl-2-hydroxynaphthalene

8

(100 mg, 0.537 mmol) in CH₂Cl₂(2 mL), H₂O (11 µL,

0.59 mmol), and MeOH (23 µL, 0.59 mmol), was added

SO₂Cl₂(53 µL, 0.65 mmol). The mixture was refluxed under

an N₂atmosphere for 1 h and subsequently quenched with

H₂O (20 mL). The solution was extracted with ether

(20 mL), washed with H₂O (2 × 20 mL), and dried

(MgSO₄). Concentration of the organic phase afforded a

greenish yellow oil. Only a trace amount of the desired

1

of compound 12 as a light orange oil. H NMR (200 MHz)

1

product 9 was evident in the crude H NMR spectrum.

δ: 0.29 (s, 6H), 1.05 (s, 9H), 4.58 (s, 2H), 7.08 (d, J = 11 Hz,

1H), 7.50 (m, 2H), 7.78 (m, 2H), 7.85 (d, J = 11 Hz, 1H).

Method 2

Hexachloro-2,4-cyclohexadienone (19) (111 mg, 0.371 mmol)

was added to a solution of 1-acetyl-2-hydroxynaphthalene

(69 mg, 0.37 mmol) in absolute ethanol (3 mL), and the

mixture was refluxed under a nitrogen atmosphere for 15 h.

The solvent was removed in vacuo to give a brown residue.

¹H NMR analysis showed that the major component of the

mixture was unreacted starting material 8, as well as a minor

amount (<30%) of the desired α-chloroketone 9, as evi-

denced by a singlet at 4.8 ppm corresponding to H-12. The

product was not stable to column chromatography.

Naphtho[2,1-b]furan-3(2H)-one (7) from bromide 12

To a solution of compound 12 (39.7 g, 0.105 mol) in THF

(400 mL) at 0 °C was slowly added TBAF (1.0 mol L^–1so-

lution in THF, 110 mL, 0.110 mol) under an N₂atmosphere.

The mixture was allowed to stir at 0 °C for 10 min and at rt

for 15 min. The dark purple solution was then quenched

with NH₄Cl solution (100 mL), and the THF was removed in

vacuo. The remaining residue was extracted with ether (3 ×

100 mL), and the combined ether layers were washed with

brine (100 mL) and H₂O (3 × 150 mL), dried (MgSO₄), and

evaporated under reduced pressure. The crude product was

purified by column chromatography (20:1, hexanes – ethyl

acetate) to give 15.1 g (72% from compound 11) of cyclized

ketone 7 as a light yellow solid: mp 133 °C (lit (58) 133 °C).

1-Acetyl-2-[(tert-butyldimethylsilyl)oxy]naphthalene (10)

To

a solution of 1-acetyl-2-hydroxynaphthalene (8)

(21.9 g, 0.117 mol) in Et₃N (75 mL, 0.538 mol) and CH₂Cl₂

(500 mL) was added TBSCl (19.4 g, 0.129 mmol). The mix-

ture was stirred at room temperature (rt) for 18 h before it

was quenched with H₂O (500 mL). The mixture was then

stirred for 1 h and extracted with ether (3 × 500 mL), and

the pooled organic extracts were washed with a 10% HCl so-

lution (2 × 500 mL) and H₂O (2 × 500 mL). The organic

layer was dried (MgSO₄) and concentrated under reduced

pressure to give 31.4 g (89%) of the TBS ether 10 as a light

yellow oil. ¹H NMR (200 MHz) δ: 0.28 (s, 6H), 1.02 (s, 9H),

2.68 (s, 3H), 7.10 (d, J = 12 Hz, 1H), 7.47 (m, 2H), 7.76 (m,

2H), 7.78 (d, J = 12 Hz, 1H). This material was used in the

next step without further purification.

1

IR (KBr) (cm^–1): 1688. H NMR (200 MHz, CDCl₃) δ: 8.75

(d, J = 8.2 Hz, 1H), 8.05 (d, J = 9.0 Hz, 1H), 7.82 (d, J =

8.0 Hz, 1H), 7.66 (dt, J = 7.6, 0.9 Hz, 1H), 7.47 (dt, J = 7.6,

1.0 Hz, 1H), 7.24 (dd, J = 7.8, 2.4 Hz, 1H), 4.77 (s, 2H). ¹³

C

NMR (50 MHz, CDCl₃) δ: 199.9 (C), 176.6 (C), 139.7 (CH),

129.8 (CH), 129.2 (C), 129.1 (C), 126.4 (CH), 125.4 (CH),

123.1 (CH), 113.9 (CH), 113.5 (C), 75.5 (CH₂). MS, m/z

(relative intensity, %): 184 ([M]⁺, 74), 155 (87), 126 (100).

Exact mass calcd for C₁₂H₈O: 184.0524; found: 184.0520.

Naphtho[2,1-b]furan-3(2H)-one (7) from 2-naphthoxy-

acetic acid (13)

2-Naphthoxyacetic acid (20.1 g, 99.3 mmol) in dry ben-

zene (1000 mL) was treated with a catalytic amount of

pyridine and 2 equiv SOCl₂(14.4 mL, 198.6 mmol) at reflux

under an N₂atmosphere for 2 h. The cooled solution was

1-[(1-Trimethylsilyl)oxy]ethenyl-2-[(tert-butyldimethyl-

silyl)oxy]naphthalene (11)

To a solution of silyl ether 10 (31.4 g, 0.105 mol) in

Andersen et al.

157

then concentrated in vacuo, and the resulting residue was

taken up into C₆H₆(500 mL) and cooled to 0 °C. To the so-

lution was then added AlCl₃(19.8 g, 148.9 mmol), and the

resulting solution was stirred for 12 h at ambient tempera-

ture. The mixture was then quenched with brine and ex-

tracted with benzene (2 × 100 mL). The combined organic

extracts were then washed with water (2 × 100 mL) and fil-

tered through neutral alumina. The filtrate was then concen-

trated under reduced pressure to afford the desired product 7

fied by column chromatography (3:1 CH₂Cl₂–EtOAc → 19:1

CH₂Cl₂–MeOH) to afford the title compound (1.150 g,

88%). mp 289–290 °C. IR (KBr) (cm^–1): 2924, 1437, 1120.

¹H NMR (400 MHz, CDCl₃) δ: 7.87 (d, J = 8.1 Hz, 1H),

7.83 (d, J = 9.1 Hz, 1H), 7.72 (m, 2H), 7.64 (d, J = 9.0 Hz,

1H), 7.56 (d, J = 7.3 Hz, 1H), 7.53 (d, J = 7.3 Hz, 1H), 7.46

(d, J = 8.3 Hz, 1H), 7.36 (m, 2H), 7.23 (m, 3H), 7.06 (t, J =

7.6 Hz, 1H), 6.96 (dt, J = 7.7, 3.1 Hz, 2H). ¹³C NMR

(50 MHz, CDCl₃) δ: 155.5 (d, J = 8 Hz, C), 145.8 (d, J =

128 Hz, C), 132.1 (CH), 132.1 (d, J = 35 Hz, C), 132.0

(CH), 131.9 (d, J = 3 Hz, CH), 130.8 (C), 129.9 (d, J =

31 Hz, C), 128.7 (CH), 128.1 (d, J = 13 Hz, CH), 127.6 (d,

J = 13 Hz, CH), 126.9 (CH), 124.8 (CH), 124.6 (C), 122.7

(CH), 121.5 (d, J = 8 Hz, C), 112.6 (CH). ³¹P NMR

(81 MHz, CDCl₃) δ: 16.5. MS, m/z (relative intensity, %):

533 ([M⁺– P(O)Ph₂], 100), 201 (54). Exact mass calcd for

C₄₈H₃₂P₂O₄: 734.1778; found: 734.1731.

1

(17.2 g, 95%), which was found to be clean by H NMR

analysis. Spectra were identical to compound 7 made from

bromide 12.

3,3′-Binaphtho[2,1-b]furan (5)

Into a 1 L, 3-neck round-bottom flask equipped with an

addition funnel was weighed activated zinc dust (29.3 g,

0.448 mol) and DME (300 mL). The mixture was cooled to

–78 °C, and to it was carefully added TiCl₄dropwise via sy-

ringe over a 30 min period. The resulting blue mixture was

warmed to reflux, and the starting naphthoketone 7 (10.0 g,

54.4 mmol in 100 mL DME) was added dropwise over a

20 min period. The resulting mixture was heated to reflux

under an N₂atmosphere for 18 h. The cooled mixture was

then filtered through a coarse sintered glass funnel, and the

filtrate was concentrated under reduced pressure to give 6 as

an orange, gummy residue. This residue was immediately

dissolved in C₆H₆(300 mL) and treated with DDQ (6.17 g,

27.2 mmol) at reflux under an N₂atmosphere for 4 h. The

cooled mixture was then quenched with saturated Na₂S₂O₃

and extracted with ether (3 × 100 mL). The combined or-

ganic extracts were dried (MgSO₄) and concentrated to af-

ford the crude title compound. The product 5 was readily

purified by flash chromatography (100:1 hexanes – ethyl ac-

etate) to afford the analytically pure biaryl (7.13 g, 78%).

( )-2,2′-Bis(diphenylphosphino)-3,3′-binaphtho[2,1-

b]furan (3)

3,3′-Binaphtho[2,1-b]furan 5 (3.4 g, 10.2 mmol) in dry

Et₂O (130 mL) was lithiated with t-BuLi (11.2 mL,

22.4 mmol, 2.0 mol L^–1solution in hexanes) at 0 °C. After

1 h at 0 °C, the vessel was warmed to rt and stirred for a fur-

ther 2 h under an N₂atmosphere. To the mixture was then

added freshly distilled chlorodiphenylphosphine (4.0 mL,

22.4 mmol), and the resulting white slurry was stirred over-

night at room temperature. The reaction mixture was quenched

with water and extracted with CHCl₃(3 × 125 mL). The

combined organic extracts were washed with 10% NaHCO₃,

water, and brine. The organic phase was dried (MgSO₄) and

concentrated in vacuo to afford a light brown solid residue.

The crude material ( )-3 was purified by crystallization

(CHCl₃–MeOH) to afford the title compound (6.49 g, 91%).

1

mp 292–294 °C. IR (KBr) (cm^–1): 2850, 1436. H NMR

mp 228–229 °C. IR (KBr) (cm^–1): 3052, 1433. H NMR

(200 MHz, CDCl₃) δ: 7.94 (d, J = 8.2 Hz, 1H), 7.86 (s, 1 H),

7.84 (m, 2H), 7.75 (d, J = 8.5 Hz, 1H), 7.35 (dt, J = 7.5,

1.0 Hz, 1H), 7.09 (dt, J = 7.7, 1.3 Hz, 1H). ¹³C NMR

(50 MHz, CDCl₃) δ: 153.5 (C), 142.8 (CH), 130.8 (C), 128.6

(CH), 128.4 (C), 126.4 (CH), 126.3 (CH), 124.5 (CH), 123.3

(CH), 112.1 (C), 113.9 (C), 112.6 (CH). MS, m/z (relative

intensity, %): 334 ([M]⁺, 100), 305 (31), 276 (32), 138 (18).

Exact mass calcd for C₂₄H₁₄O₂: 334.0994; found: 334.0970.

Anal calcd for C₂₄H₁₄O₂: C 86.20, H 4.22; found: C 85.96,

H 4.04.

(400 MHz, CDCl₃) δ: 7.90 (d, J = 8.1 Hz, 1H), 7.84 (d, J =

9.0 Hz, 1H), 7.76 (d, J = 9.1 Hz, 1H), 7.62 (d, J = 8.3 Hz,

1H), 7.37 (m, 2H), 7.35–7.30 (m, 4H), 7.24–7.14 (m, 5H),

7.04 (td, J = 7.4, 1.0 Hz, 1H). ¹³C NMR (100 MHz, CDCl₃)

δ: 156.3 (C), 152.9 (d, J = 34 Hz, C), 135.4 (d, J = 71 Hz,

C), 133.7 (CH), 133.6 (CH), 133.5 (CH), 130.7 (C), 128.6

(d, J = 4 Hz, CH), 128.5 (CH), 128.3 (C), 128.1 (d, J =

2 Hz, CH), 127.4 (CH), 126.5 (d, J = 35 Hz, C), 126.7 (CH),

124.5 (CH), 123.0 (CH), 122.5 (C), 112.9 (CH). ³¹P NMR

(81 MHz, CDCl₃) δ: –32.3. MS, m/z (relative intensity, %):

625 ([M⁺– Ph], 1), 517 (37), 408 (79), 183 (100). Exact

mass calcd for C₄₈H₃₂P₂O₂: 702.1878; found: 702.1841.

2,2′-Bis(diphenylphosphonyl)-3,3′-binaphtho[2,1-b]furan

(14)

*

3,3′-Binaphtho[2,1-b]furan 5 (0.593 g, 1.776 mmol) in dry

Et₂O (30 mL) was lithiated with t-BuLi (2.61 mL,

4.440 mmol, 1.7 mol L^–1solution in hexanes) at 0 °C. After

1 h at 0 °C, the vessel was warmed to rt and stirred for a fur-

ther 2 h under an N₂atmosphere. To the mixture was then

added freshly distilled diphenylphosphinic chloride

(0.85 mL, 4.440 mmol), and the resulting white slurry was

stirred overnight at room temperature. The reaction mixture

was then quenched with water and extracted with CHCl₃

(3 × 50 mL). The combined organic extracts were washed

with 10% NaHCO₃, water, and brine. The organic phase was

then dried (MgSO₄) and concentrated in vacuo to afford a

light yellow solid residue. The crude material 14 was puri-

Preparation of bis-P-borane-(R_ax)-2,2′-bis[(8R,9R)-N,N′-

dimethyl-1,3-diazahexahydro-2-phosphinoindan-2-yl]-

3,3′-binaphtho[2,1-b]furan complex (23a) and bis-P-bor-

*

ane-(S_ax)-2,2′-bis[(8R,9R)-N,N′-dimethyl-1,3-diazahexahy-

dro-2-phosphinoindan-2-yl]-3,3′-binaphtho[2,1-b]furan

complex (23b)

To a solution of naphtho[b]furan 5 (0.173 g, 0.518 mmol)

in Et₂O (5.0 mL) at –78 °C was added 2.05 equiv of t-BuLi

(1.7 mol L^–1in hexanes, 0.62 mL, 1.1 mmol). The resulting

mixture was warmed to 0 °C and stirred under an atmo-

sphere of nitrogen for 1.5 h. To the vessel was then added

enantiopure 2-chloro-2,2′-bis[8R,9R]-N,N′-dimethyl-1,3-di-

azahexahydro-2-phosphinoindane (22) (38, 39) (0.219 g,

158

Can. J. Chem. Vol. 82, 2004

1.06 mmol). The reaction contents were allowed to warm to

rt over a 1 h period and subsequently left to stir for 24 h. To

the vessel was then added borane – dimethyl sulfide com-

plex (2.0 mol L^–1solution in THF, 0.531 mL, 1.06 mmol),

and the resulting mixture was left to react for a further 24 h.

The reaction contents were then quenched with brine

(50 mL) and extracted with CHCl₃(3 × 50 mL). The com-

bined organic extracts were dried (MgSO₄) and concentrated

under reduced pressure to afford a light yellow oil. The

crude material was purified by column chromatography

(15:1) to afford a 1:1 mixture of the title compounds

(0.270 g, 74%). A small sample (~3 mg) of each pure

diastereomer was obtained by exhaustive preparative high

performance liquid phase chromatography (Nova-Pak C₁₈,

93:7 CH₃CN:H₂O, 1.0 mL min^–1, 320 nm detection). The

first isomer to elute, compound 23a, was obtained as a col-

orless film exhibiting the following analytical data: IR (KBr)

atmosphere of argon, and the filtrate was concentrated under

reduced pressure in an inert atmosphere to give a bright yel-

low solid residue. Crude phosphoramidous chloride 26: H

NMR (200 MHz) δ: 2.55 (d, J = 19.5 Hz, 3H), 4.28 (d, J =

7.4 Hz, 1H), 7.11–7.40 (m, 5H). ¹³C NMR (50 MHz) (ppm):

31.8 (d, J = 21 Hz, CH₃), 78.1 (d, J = 11 Hz, CH), 128.2

(CH), 128.7 (CH), 128.8 (CH), 137.1 (d, J = 2 Hz, C). ³¹P

NMR (62 MHz) (ppm): +173.6. Compound 26 was used in

the subsequent step without further purification.

1

*

Bis-P-borane-(R_ax)-2,2′-bis[(4R,5R)-1,3-dimethyl-4,5-

diphenyl-1,3,2-diazaphospholidin-2-yl]-3,3′-binaphtho-

*

[2,1-b]furan complex (27a) and bis-P-borane-(S_ax)-2,2′-

bis[(4R,5R)-1,3-dimethyl-4,5-diphenyl-1,3,2-diazaphos-

pholidin-2-yl]-3,3′-binaphtho[2,1-b]furan complex (27b)

To

a

solution of naphtho[b]furan (5) (0.245 g,

0.734 mmol) in Et₂O (8.0 mL) at –78 °C was added

2.2 equiv of t-BuLi (1.7 mol L^–1in hexanes, 0.949 mL,

1.61 mmol). The resulting mixture was warmed to 0 °C and

stirred under an atmosphere of nitrogen for 1.5 h. To the

vessel was then added enantiopure diazaphospholidine re-

agent 26 (0.491 g, 1.61 mmol). The reaction contents were

allowed to warm to rt over a 1 h period and subsequently left

to stir for 3 h. To the vessel was then added borane –

dimethyl sulfide complex (2.0 mol L^–1solution in THF,

1.10 mL, 2.20 mmol), and the resulting mixture was left to

react for a further 4 h. The reaction contents were then

quenched with brine (50 mL) and extracted with CHCl₃(3 ×

75 mL). The combined organic extracts were dried (MgSO₄)

and concentrated in vacuo to afford a light yellow solid resi-

due. The crude material was purified by column chromatog-

raphy (15:1) to afford a 1:1 mixture of the title compounds.

Separation of the mixture was achieved by recrystallization

from a binary mixture of CHCl₃and hexanes. Under these

conditions, compound 27a crystallized, diastereomerically

pure, as long white needles (0.304 g, 46%) characterized by

the following analytical data: mp 123–124 °C. IR (KBr)

1

(cm^–1): 2937, 2387 (BH₃), 1462, 1025. H NMR (400 MHz)

δ: –0.50 to 0.63 (bq, 3H), 1.10–1.62 (m, 4H), 1.89 (t, J =

12.9 Hz, 2H), 2.00–2.13 (m, 2H), 2.19 (d, J = 14.5 Hz, 3H),

2.48 (td, J = 10.4, 3.0 Hz, 1H), 2.74 (d, J = 12.8 Hz, 3H),

3.18 (t, J = 9.6 Hz, 1H), 7.02 (t, J = 7.0 Hz, 1H), 7.32 (t, J =

7.0 Hz, 1H), 7.58 (d, J = 7.8 Hz, 1H), 7.82 (d, J = 9.1 Hz,

1H), 7.90 (d, J = 9.1 Hz, 1H), 7.91 (d, J = 7.8 Hz, 1H). ¹³C

NMR (100 MHz) (ppm): 24.7 (CH₂), 24.8 (CH₂), 29.0 (d,

J = 8 Hz, CH₂), 29.3 (d, J = 5 Hz, CH₂), 30.4 (d, J = 3 Hz,

CH₃), 32.6 (d, J = 10 Hz, CH₃), 65.8 (d, J = 3 Hz, CH), 68.4

(CH), 113.4 (CH), 122.8 (C), 122.9 (C), 123.5 (CH), 125.1

(CH), 126.4 (d, J = 19 Hz, C), 126.8 (CH), 128.9 (CH),

129.3 (CH), 131.3 (C), 150.4 (d, J = 30 Hz, C), 155.5 (d, J =

4 Hz, C). ³¹P NMR (162 MHz) (ppm): +94.1 (q, J = 71 Hz).

FAB-MS, m/z (relative intensity, %): 725 (48, [M + Na]⁺).

Compound 23b, also obtained as a colorless film, had the

following properties: IR (KBr) (cm^–1): 2935, 2390 (BH₃),

1

1461, 1003. H NMR (400 MHz) δ: –0.48 (qd, J = 12.3,

3.6 Hz, 1H), 0.08 (m, 1H), 0.20–1.20 (bq, 3H), 0.78–0.97

(m, 2H), 1.28 (d, J = 8.6 Hz, 1H), 1.39 (d, J = 9.8 Hz, 2H),

1.65 (d, J = 8.9 Hz, 1H), 2.10 (td, J = 12.0, 3.2 Hz, 1H),

2.26 (m, 1H), 2.36 (d, J = 13.1 Hz, 3H), 2.62 (d, J =

14.2 Hz, 3H), 7.13 (t, J = 8.0 Hz, 1H), 7.36 (t, J = 7.1 Hz,

1H), 7.55 (d, J = 8.3 Hz, 1H), 7.88 (ABq, J = 9.2 Hz, 2H),

7.94 (d, J = 8.1 Hz, 1H). ¹³C NMR (100 MHz) (ppm): 23.7

(CH₂), 24.1 (CH₂), 27.3 (d, J = 5 Hz, CH₂), 28.2 (d, J =

8 Hz, CH₂), 30.3 (d, J = 2 Hz, CH₃), 32.8 (d, J = 10 Hz,

CH₃), 64.1 (d, J = 3 Hz, CH), 68.2 (CH), 113.5 (CH), 123.1

(d, J = 5 Hz, C), 123.2 (d, J = 9 Hz, C), 123.7 (CH), 125.3

(CH), 127.1 (CH), 128.7 (CH), 129.0 (C), 129.5 (CH), 131.5

(C), 150.3 (d, J = 40 Hz, C), 155.5 (d, J = 6 Hz, C). ³¹P

NMR (162 MHz) (ppm): +98.7 (q, J = 74 Hz). FAB-MS,

m/z (relative intensity, %): 725 (7, [M + Na]⁺).

1

(cm^–1): 2869, 2392 (BH₃), 1455, 1147. H NMR (300 MHz)

δ: –0.32 to 0.84 (bs, 3H), 2.02 (d, J = 11.3 Hz, 3H), 2.71 (d,

J = 13.3 Hz, 3H), 4.00 (d, J = 8.7 Hz, 1H), 4.80 (d, J =

8.7 Hz, 1H), 7.02–7.45 (m, 12H), 7.74 (d, J = 7.9 Hz, 1H),

7.84–8.10 (m, 3H). ¹³C NMR (75 MHz) (ppm): 31.8 (d, J =

3 Hz, CH₃), 32.7 (d, J = 11 Hz, CH₃), 75.1 (d, J = 3 Hz,

CH), 76.3 (CH), 112.7 (CH), 122.4 (C), 122.5 (C), 122.8

(CH), 124.8 (CH), 126.2 (C), 126.9 (CH), 127.7 (CH), 128.0

(CH), 128.5 (CH), 128.6 (CH), 128.8 (CH), 129.1 (CH),

131.1 (C), 137.6 (d, J = 9 Hz, C), 138.5 (d, J = 4 Hz, C),

151.6 (d, J = 26 Hz, C), 155.0 (d, J = 3 Hz, C). ³¹P NMR

(81 MHz) (ppm): +98.7 (bs). FAB-MS, m/z (relative inten-

sity, %): 899 (1, [M + H]⁺). Borane adduct 27b was obtained

isomerically pure after flash chromatographic (15:1) purifi-

cation of the mother liquor. The following analytical data

were recorded for this compound: mp 138–140 °C (CHCl₃–

hexanes). IR (KBr) (cm^–1): 2869, 2390 (BH₃), 1455, 1146.

¹H NMR (400 MHz) δ: –0.32–1.00 (bs, 3H), 2.11 (d, J =

13.7 Hz, 3H), 2.86 (d, J = 11.1 Hz, 3H), 4.15 (d, J = 8.7 Hz,

1H), 4.61 (d, J = 8.7 Hz, 1H), 6.99 (t, J = 7.2 Hz, 1H), 7.12–

7.23 (m, 2H), 7.25–7.34 (m, 4H), 7.35–7.50 (m, 5H), 7.70

(d, J = 8.2 Hz, 1H), 7.91–8.03 (m, 3H). ¹³C NMR

(100 MHz) (ppm): 31.8 (d, J = 5 Hz, CH₃), 33.4 (d, J =

11 Hz, CH₃), 75.1 (d, J = 2 Hz, CH), 76.4 (CH), 113.3

2-Chloro-1,3-dimethyl-4,5-diphenyl-1,3,2-diazaphos-

pholidine (26)

Under an argon atmosphere, (1S,2S)-N,N-dimethyl-1,2-

diphenylethylenediamine (25) (40, 41) (1.59 g, 6.63 mmol)

was dissolved in freshly distilled Et₂O (40 mL) and Et₃N

(1.85 mL, 13.3 mmol). The reaction mixture was then

cooled to –40 °C; phosphorus trichloride (0.578 mL,

6.63 mmol) was added; and the resultant thick white slurry

was stirred for 30 min at –40 °C, for 1 h at 0 °C, and for

24 h at room temperature. The slurry was filtered under an

Andersen et al.

159

(CH), 122.9 (C), 123.0 (C), 123.5 (CH), 125.2 (CH), 126.7

(C), 126.9 (CH), 128.5 (CH), 128.6 (CH), 128.7 (CH), 128.8

(CH), 128.9 (CH), 129.3 (CH), 129.4 (CH), 131.5 (C), 137.6

(d, J = 9 Hz, C), 138.6 (d, J = 4 Hz, C), 151.3 (d, J = 26 Hz,

C), 155.6 (d, J = 3 Hz, C). ³¹P NMR (81 MHz) (ppm): +91.3

(bs). FAB-MS, m/z (relative intensity, %): 899 (4, [M +

H]⁺).

a = 16.248(2) Å; b = 11.0208(16) Å; c = 35.643(5) Å; V =

6372.8(15) Å³; Z = 4; R = 0.0696; Rw = 0.2355.

(–)-2,2′-Bis(diphenylphosphonyl)-3,3′-binaphtho[2,1-

b]furan (14)

Phosphinimine 31a (1.44 g, 1.24 mmol) in dioxane

(50 mL) was treated with 3 mol L^–1aqueous H₂SO₄

(35 mL), and the resulting mixture was heated to reflux for

12 h. The cooled mixture was then quenched with 10%

NaOH and extracted with CHCl₃(3 × 100 mL). The com-

bined organic extracts were dried (MgSO₄) and concentrated

in vacuo to afford the crude phosphine oxide. The product

was purified by flash chromatography on basic alumina (1:1

hexanes – ethyl acetate → 9:1 CHCl₃–MeOH) to afford the

desired phosphine oxide (–)-14 in quantitative yield. [α]¹_D⁹

Phosphinimine 31a and 31b

BINAPFu ( )-3 (2.65 g, 3.78 mmol) in THF (60 mL) was

treated with (1S)-camphor-10-sulfonyl azide (59) (1.95 g,

7.55 mmol) at reflux under an N₂atmosphere for 12 h. The

cooled mixture was then concentrated under reduced pres-

sure to afford a 1:1 mixture of 31a and 31b in quantitative

yield. The diastereomeric products were separated by flash

chromatography (9:1 CHCl₃–CH₃CN). The first spot off the

column, 31a, was determined to be the S axial isomer by

single crystal X-ray analysis and afforded the following ana-

lytical data: mp 175–177 °C. [α]²_D¹–72.1 (c 4.13, CHCl₃). IR

1

–166.6 (c 1.01, CHCl₃). H and ¹³C spectra were indentical

to those of ( )-14.

(–)-2,2′-Bis(diphenylphosphino)-3,3′-binaphtho[2,1-

b]furan (3)

1

(KBr) (cm^–1): 1745. H NMR (200 MHz, CDCl₃) δ: 7.97–

Phosphine oxide (–)-14 (821 mg, 1.12 mmol) was dis-

solved in a mixture of xylenes (25 mL) and Et₃N (3.75 mL,

26.8 mmol). To the solution was added SiCl₃H (2.26 mL,

22.4 mmol), and the resulting mixture was heated to 100 °C

under argon for 1 h. The mixture was then heated to 150 °C

for 3 h and subsequently cooled to 65 °C. To the vessel was

then added dropwise 30% NaOH (60 mL). The resulting

mixture was vigorously stirred for 1 h at 65 °C. The cooled

reaction mixture was extracted with CHCl₃(3 × 100 mL),

and the combined organic phases were dried (MgSO₄) and

concentrated in vacuo. The product (–)-3 was purified by

flash chromatography (20:1 hexanes – ethyl acetate) to af-

ford the optically pure (S)-BINAPFu (785 mg, 100%). [α]¹_D⁹

–203.0 (c 1.09, CHCl₃). Heating the enantiopure ligand in p-

xylenes at 150 °C for 7 days did not result in any

racemization of the chiral axis, as evidenced by optical rota-

tion and HPLC analysis (Chiralcel^®OJ, 95:5 MeOH:EtOH,

7.52 (m, 11H), 7.44 (t, J = 8.0 Hz, 1H), 7.38 (d, J = 8.4 Hz,

1H), 7.17 (t, J = 6.6 Hz, 1H), 6.88 (m, 2H), 2.51–2.26 (m,

2H), 2.18 (dt, J = 16.0, 3.0 Hz, 1H), 1.94–1.54 (m, 4H),

1.50–1.07 (m, 2H), 0.90 (s, 3H), 0.53 (s, 3H). ¹³C NMR

(50 MHz, CDCl₃) δ: 214.8 (C), 156.3 (d, J = 10 Hz, C),

140.1 (d, J = 154 Hz, C), 134.1 (CH), 134.0 (CH), 133.9

(CH), 133.8 (CH), 133.6 (CH), 133.0 (d, J = 1 Hz, CH),

131.2 (C), 129.9 (CH), 129.5 (CH), 129.4 (CH), 129.3 (CH),

129.0 (C), 128.5 (CH), 128.4 (CH), 128.0 (CH), 127.9 (d,

J = 15 Hz, C), 127.4 (d, J = 81 Hz, C), 126.3 (d, J = 84 Hz,

C), 125.9 (CH) 123.7 (CH), 122.5 (d, J = 8 Hz, C), 112.5

(CH), 78.0 (CH₂), 58.7 (C), 51.7 (d, J = 4 Hz, CH₂), 47.8

(C), 42.9 (CH), 27.3 (CH₂), 24.6 (CH₂), 20.4 (CH₃), 20.2

(CH₃). ³¹P NMR (81 MHz, CDCl₃) δ: 5.7. MS, m/z (relative

intensity, %): 531 ([M⁺– C₃₂H₄₀NO₆PS₂], 1). FAB-MS, m/z

(relative intensity, %): 1161 ([M]⁺, 31), 531 (68). Compound

31b gave the following analytical data: mp 229 °C

(decomposition (dec.)). [α]²_D¹+66.5 (c 1.55, CHCl₃). IR (KBr)

(cm^–1): 1743. ¹H NMR (200 MHz, CDCl₃) δ: 7.93 (t, J = 9.6,

2H), 7.78 (t, J = 8.5, 4H), 7.70–7.29 (m, 7H), 7.11 (t, J =

8.0, 1H), 6.89–6.71 (m, 2H), 2.59–2.32 (m, 2H), 2.21 (dt,

J = 16.0, 3.0, 1H), 1.93–1.60 (m, 4H), 1.49–1.08 (m, 2H),

0.71 (s, 3H), 0.45 (s, 3H). ¹³C NMR (50 MHz, CDCl₃) δ:

215.0 (C), 156.5 (d, J = 9 Hz, C), 140.0 (d, J = 151 Hz, C),

134.1 (CH), 134.0 (CH), 133.7 (CH), 133.6 (CH), 133.5

(CH), 132.9 (d, J = 1 Hz, CH), 130.5 (CH), 129.6 (CH),

129.3 (CH), 129.2 (CH), 128.9 (C), 128.3 (CH), 128.2 (CH),

127.8 (d, J = 15 Hz, C), 127.8 (CH), 127.2 (C), 126.5 (C),

125.7 (CH), 125.5 (C), 123.7 (CH), 122.2 (d, J = 8 Hz, C),

112.6 (CH), 58.3 (C), 51.7 (d, J = 3 Hz, CH₂), 47.6 (C), 42.6

(CH₂), 42.5 (CH), 27.2 (CH₂), 24.8 (CH₂), 20.4 (CH₃), 20.2

(CH₃). ³¹P NMR (81 MHz, CDCl₃) δ: 4.9. MS, m/z (relative

intensity, %): 531 ([M⁺– C₃₂H₄₀NO₆PS₂], 1). FAB MS, m/z

(relative intensity, %): 1161 ([M]⁺, 38), 531 (72). Anal calcd

for C₆₈H₆₂P₂S₂O₈N₂+ CHCl₃: C 64.61, H 5.11, N 2.18;

found: C 64.75, H 4.98, N 2.37.

1

0.5 mL min^–1, 270 nm detection). H and ¹³C spectra were

identical to those of ( )-3.

( )-Dichloro[2,2′-bis(diphenylphosphino)-3,3′-

binaphtho[2,1-b]furan]-palladium (II) (15)

( )-2,2′-Bis(diphenylphosphino)-3,3′-binaphtho[2,1-b]furan

(3) (300 mg, 0.427 mmol) and bis(acetonitrile)dichloro-

palladium(II) (111 mg, 0.427 mmol) were stirred in CH₂Cl₂

(20 mL) at rt for 15 h. The solution was concentrated in

vacuo, and the residue was purified by recrystallization from

acetone–ether to give 349 mg (93%) of palladium adduct 15

as orange crystals: mp 312–314 °C. IR (KBr) (cm^–1): 3056,

1

1095, 999, 690. H NMR (400 MHz) δ: 6.59 (m, J = 6.9 Hz,

2H), 6.82 (t, J = 7.3 Hz, 1H), 7.08 (t, J = 7.6 Hz, 1H), 7.27–

7.52 (m, 6H), 7.65 (d, J = 7.5 Hz, 1H), 7.67 (d, J = 8.4 Hz,

1H), 7.77 (d, J = 9.1 Hz, 1H), 7.91 (d, J = 8.1 Hz, 1H), 8.11

(d, J = 7.6 Hz, 1H), 8.15 (d, J = 7.6 Hz, 1H). ¹³C NMR

(100 MHz) (ppm): 112.6 (CH), 122.0 (d, J = 2 Hz, C), 123.8

(dd, J = 7, 6 Hz, C), 124.3 (dd, J = 62, 4 Hz, C), 125.8

(CH), 126.8 (dd, J = 68, 5 Hz, C), 127.8 (CH), 128.1 (C),

128.3 (t, J = 6 Hz, CH), 128.5 (t, J = 6 Hz, CH), 128.9

(CH), 129.2 (CH), 131.2 (d, J = 2 Hz, C), 131.6 (CH), 132.0

(CH), 134.3 (t, J = 5 Hz, CH), 136.3 (t, J = 7 Hz, CH),

147.4 (d, J = 73 Hz, C), 158.1 (dd, J = 4, 3 Hz, C). ³¹P

X-ray crystallographic analysis on 31a was performed at

the University of Alberta on a Bruker P4 diffractometer

equipped with a SMART 1000 CCD area detector, using

graphite-monochromated Mo Kα radiation. The following

crystal parameters were obtained: monoclinic, P2₁(No. 4);

160

Can. J. Chem. Vol. 82, 2004

NMR (162 MHz) (ppm): +11.3. FAB-MS, m/z (relative in-

tensity, %): 901 (9, [M(³⁵Cl₂) + Na]⁺), 878 (9, [M⁺(³⁵Cl₂)]).

X-ray crystallographic analysis on 15 was performed at

the University of Calgary on an Enraf-Nonius CAD-4

diffractometer with graphite monochromated Cu Kα radia-

tion. The following crystal parameters were obtained: mono-

clinic, P2₁/n (No. 14); a = 16.673(5) Å, b = 18.478(7) Å, c =

13.702(3) Å; V = 4134(2) Å³; Z = 4; R = 0.053; Rw = 0.041.

to 60 °C under an argon atmosphere for 30 min. To the ves-

sel was then added 2,3-dihydrofuran (189 µL, 2.50 mmol)

and phenyl triflate (79 µL, 0.488 mmol). The mixture was

thermostatically heated to 100 °C for a 7 day period. The

crude mixture was filtered through a pad of celite and ana-

lyzed by chiral GC (Cyclodex B column, 80 °C start temper-

ature, 2 min initial hold time, 1 °C min^–1ramp rate, 220 °C

final temperature). The reaction products eluted in the fol-

lowing order: (S)-2-phenyl-2,3-dihydrofuran T_r= 26.1 min;

(R)-5-phenyl-2,3-dihydrofuran T_r= 26.7 min; 2-phenyl-4,5-

dihydrofuran T_r= 28.9 min; (R)-2-phenyl-2,5-dihydrofuran

T_r= 31.2 min; (S)-2-phenyl-2,5-dihydrofuran T_r= 31.6 min.

(–)-(S_ax)-2,2′-Bis(selenodiphenylphosphinyl)-3,3′-

binaphtho[2,1-b]furan (35)

The following procedure is based on a method reported by

Allen and Taylor (51). To a 0.02 mol L^–1solution of the

BINAPFu (–)-3 (0.119 g, 0.170 mmol) in CHCl₃was added

10 molar equivalents of Se dust (100 mesh). The resulting

mixture was heated to reflux under an atmosphere of argon

gas for a 5 h period. The cooled mixture was filtered through

a pad of Celite^®, and the filterings were washed with a small

volume of CHCl₃. Concentration of the filtrate under re-

duced pressure furnished the crude phosphine selenide (–)-

35. The crude product was recrystallized from CH₃CN to

furnish the analytically pure product (0.142 g, 97%). X-ray

diffraction analysis of a single crystal thus obtained, using

the Bijvoet method, showed the S-configuration for the

biaryl axis. Phosphine selenide (–)-35 gave the following an-

alytical data: mp 176–178 °C (CH₃CN). IR (KBr) (cm^–1):

Acknowledgments

We thank the Natural Sciences and Engineering Research

Council of Canada (NSERC) for financial support. N.G.A.

gratefully acknowledges receipt of an NSERC scholarship, a

Ralph Steinhauer Award of Distinction from the Alberta

Heritage Foundation, and an Honorary Killam Fellowship.

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2923, 1435, 1095, 1003. H NMR (400 MHz) δ: 7.04–7.15

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Article Doi

Synthesis, resolution, and application of 2,2′-bis(diphenylphosphino) -3,3′-binaphtho[b]furan (BINAPFu)

DOI: 10.1139/v03-173

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