Intramolecularly Sulfur-Stabilized Silicon Cations with Chiral Binaphthyl Backbones: Synthesis of Three Different Motifs and Their Application in Enantioselective Diels-Alder Reactions

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Intramolecularly Sulfur-Stabilized Silicon Cations with Chiral

Binaphthyl Backbones: Synthesis of Three Diﬀerent Motifs and Their

Application in Enantioselective Diels−Alder Reactions

Volker H. G. Rohde,^†Maria F. Muller,^†and Martin Oestreich*

̈

Institut fur Chemie, Technische Universitat Berlin, Straße des 17. Juni 115, 10623 Berlin, Germany

̈

S

* Supporting Information

ABSTRACT: The formation and ²⁹Si NMR spectroscopic

characterization of silicon cations that are intramolecularly

stabilized by a dialkyl thioether are described. The chemical

stability of the silicon−sulfur Lewis pair and, hence, the viability

of the approach, were probed with a 2-[(alkylthio)methyl]phenyl-

substituted hydrosilane as a proxy before three diﬀerent motifs

with chiral binaphthyl backbones were prepared in multistep

sequences. The degree of shielding of the silicon atom in these

cations was found to depend on the substitution pattern at the silicon atom and the ring size generated by the silicon−sulfur

interaction. These sulfur-stabilized silicon cations are suﬃciently reactive to promote Diels−Alder reactions of cyclohexa-1,3-

diene with various dienophiles; the same set of reactions with cyclopentadiene is also reported. One of the three chiral Lewis

acids induces low, but promising, enantioselectivity, and 24% ee is the highest value so far obtained with a cationic

tetracoordinate silicon catalyst.

diﬃcult Diels−Alder reaction of cyclohexa-1,3-diene and

chalcone, but no asymmetric induction was seen.

INTRODUCTION

■

Lewis acids, including those based on silicon,¹are widely used

as catalysts in synthetic chemistry.²However, the number of

structurally deﬁned, chiral silicon Lewis acid catalysts is small

(Figure 1). The seminal work in this ﬁeld was done by Ghosez

and co-workers, who accomplished an enantioselective Diels−

Alder reaction with terpene-derived triﬂimide 1 as catalyst.³

The methoxymethyl group in 1 in the proximity of the silicon

atom was shown to be vital for achieving enantioinduction.

Hatanaka and co-workers recently obtained a similar result with

binaphthyl-derived triﬂimide 3,⁴whereas related iodide 2 did

not induce any enantioselectivity.⁵Leighton and co-workers

further advanced the ﬁeld by introducing fully heteroatom-

substituted 4 with strain-release Lewis acidity.⁶It catalyzes

Diels−Alder reactions of cyclopentadiene and selected α,β-

unsaturated aldehydes with excellent enantioselectivities. These

neutral tetracoordinate silicon compounds are suﬃciently Lewis

acidic to promote Diels−Alder reactions of reactive 1,3-dienes

such as cyclopentadiene. To make, for example, less reactive

cyclohexa-1,3-diene amenable to catalysis with silicon Lewis

acids, the development of cationic catalysts is the logical next

step, but there is little precedence for this. Jørgensen,

Helmchen, and co-worker disclosed an enantioselective

Diels−Alder reaction catalyzed by the acetonitrile-stabilized

silicon cation or silylnitrilium ion 5.⁷The enantiomeric excess

obtained is low but still the only one reported for a cationic

tetracoordinate silicon Lewis acid.^8,9

Since the silicon−sulfur interaction tames this and related

silicon cations 7a−7d (see Figure 2, right) while preserving

their reactivity,¹⁰we envisioned chiral backbones other than

ferrocene. Axially chiral binaphthyl groups seemed viable

alternatives as there is ample precedence for highly

enantioselective Diels−Alder reactions catalyzed by binaphthol-

and binaphthyl-derived Lewis acids based on aluminum and

boron.¹¹⁻¹³Consequently, we opted for motifs (S)-8 and (R)-9

with the hydrosilane unit and the pending sulfur donor attached

to either the 2- and 2′- or the 2- and 3-positions of the

binaphthyl backbone (Figure 3, top). Inspired by cation 5

(Figure 1, bottom right), we also targeted the axially chiral

dihydrosilepine (S)-10 with a 2-[(alkylthio)methyl]phenyl

group installed at the silicon atom (Figure 3, bottom).

Diﬀerent from our previous work,¹⁰we aimed to accomplish

stabilization by acyclic rather than cyclic dialkyl thioethers (cf.

1,3-dithiolan-2-yl and 1,3-dithian-2-yl substituents in 6 and 7a−

7d, respectively, Figure 2). Even though Olah and co-workers

had not been able to generate the intermolecular Lewis pair of

the trimethyl silicon cation and dimethylsulﬁde,¹⁴we hoped

that the corresponding intramolecular adducts would be

chemically stable due to the formation of seven- (as in (S)-8)

or ﬁve-membered rings (as in (R)-9 and (S)-10). This

assumption was supported by a recent study of the beneﬁcial

eﬀect of the formation of common-sized rings to stabilize

silicon cations.¹⁵In this article, we report the preparation and

As part of our ongoing research, we recently reported the

synthesis of intramolecularly sulfur-stabilized silicon cation 6

with a planar chiral ferrocenyl substituent (Figure 2, left).¹⁰Its

ability to act as a Lewis acid catalyst was demonstrated in the

Received: April 27, 2015

Published: June 12, 2015

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new silicon Lewis acids are assessed in diﬃcult Diels−Alder

reactions of cyclohexa-1,3-diene¹⁶and cycloadditions of more

reactive cyclopentadiene.

RESULTS AND DISCUSSION

■

Achiral Sulfur-Stabilized Silicon Cations as Model

Compounds. Before preparing the precursors for silicon

cations (S)-8, (R)-9, and (S)-10 in multistep sequences, we

synthesized hydrosilanes 13 and 14 with the 2-[(ethylthio)-

methyl]phenyl group (Scheme 1). With the thioether unit

Scheme 1. Preparation of Precursors with a Benzene

Platform and Silicon Cation Generation

Figure 1. Reported neutral (top and bottom left) and cationic

(bottom right) chiral tetracoordinate silicon Lewis acid catalysts.

Enantiomeric excesses refer to the highest enantioselectivity achieved

in a Diels−Alder reaction.

installed ortho to the silicon atom, we would be able to ﬁnd out

whether this motif lends suﬃcient stabilization to the electron-

deﬁcient tricoordinate silicon atom. Dimethyl-substituted 13

and diisopropyl-substituted 14 were prepared starting from 1-

bromo-2-(bromomethyl)benzene (11). After base-mediated

thioether formation (11 → 12), 13 and 14 were accessed in

good yields by bromine−lithium exchange followed by trapping

with R₂Si(H)Cl (12 → 13 for R = Me and 12 → 14 for R =

iPr). These substitution patterns at the silicon atom were

chosen to evaluate the inﬂuence of steric bulk around the

silicon atom on Lewis pair formation.

Figure 2. Intramolecularly sulfur-stabilized silicon cations based on a

planar chiral ferrocene platform (left) or a benzene platform (right).

The generation of sulfur-stabilized silicon cations 15 and 16

was achieved by hydride abstraction from 13 and 14 with trityl

tetrakis(pentaﬂuorophenyl)borate, [Ph₃C]⁺[B(C₆F₅)₄]⁻

(Scheme 1). Both were stable in 1,2-Cl₂C₆D₄for weeks with

little decomposition. The ²⁹Si NMR spectra showed resonance

signals at δ 56.4 ppm for 15 and δ 57.6 ppm for 16, and these

are signiﬁcantly shifted to higher frequencies compared to the

respective hydrosilane, δ −21.6 ppm for 13 and δ −1.1 ppm for

14.¹⁷The substituents at the silicon atom had no eﬀect on the

degree of deshielding of the silicon atom in 15 and 16.¹⁸

However, the resonance signals of the diastereotopic protons at

each of the methylene groups attached to the sulfur atom show

1

signiﬁcant line broadening in the H NMR spectra of 15 and

16. This is more pronounced for 15 with the Me₂Si group than

for 16 with the iPr₂Si group, indicating that increased steric

bulk retards solvent-induced equilibration of the enantiomeric

silicon−sulfur Lewis pairs with either of the lone pairs at the

sulfur atom.

Figure 3. Sulfur-stabilized silicon cations with chiral binaphthyl

backbones.

Synthesis of Thioether-Containing Hydrosilanes with

Chiral Binaphthyl Backbones. The above model system

proves that Lewis pairs composed of a silicon cation and a

tethered dialkyl thioether are chemically robust. Moreover, the

NMR-spectroscopic characterization of chiral silicon cations

that are intramolecularly stabilized by a tethered thioether

donor. The catalytic activity and asymmetric induction of these

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Scheme 2. Preparation of the Precursor with the 2,2′-Disubstituted Binaphthyl Backbone

Scheme 3. Preparation of the Precursor with the 2,3-Disubstituted Binaphthyl Backbone and Its Molecular Structure (ORTEP

Plot Rendered with POV-Ray)

solvent rapidly scrambles the stereogenicity established at the

sulfur atom with the sterically accessible Me₂Si group. Hence,

we continued with the synthesis of Me₂Si-based systems with

chiral binaphthyl backbones where solvent-promoted epimeri-

zation at the sulfur atom would be feasible. For this, new

synthetic routes to the hydrosilanes that serve as precursors for

(S)-8, (R)-9, and (S)-10 depicted in Figure 3 had to be

designed (Schemes 2−4).

The preparation of hydrosilane (S)-28 with a 2,2′-

disubstituted binaphthyl backbone commenced with ﬁve

routine functional-group manipulations at (S)-BINOL [(S)-

17, Scheme 2]: monoprotection with TBDPSCl [(S)-17 →

(S)-18], triﬂation of the remaining phenol [(S)-18 → (S)-19],

nickel(0)-catalyzed methylation of that triﬂate [(S)-19 → (R)-

20], deprotection of the TBDPS ether [(R)-20 → (R)-21], and

triﬂation of the liberated hydroxy group [(R)-21 → (R)-22].

Intermediate (R)-22 was obtained in 52% overall yield.¹⁹

The triﬂate group in (R)-22 was then converted into iodide

(R)-25 by a three-step sequence. Buchwald−Hartwig amination

with benzylamine furnished (R)-23, and reductive debenzyla-

tion aﬀorded the free amine (R)-24 [(R)-22 → (R)-23 → (R)-

24]. Iodide (R)-25 was subsequently obtained by a Sandmeyer-

type reaction of amine (R)-24 [(R)-24 → (R)-25]. Radical

bromination of the benzylic position in (R)-25 yielded (S)-26

that was transformed into thioether (S)-27 [(R)-25 → (S)-26

→ (S)-27]. (S)-27 was then subjected to the usual iodine−

lithium exchange, followed by the addition of Me₂Si(H)Cl as

the electrophile [(S)-27 → (S)-28], aﬀording hydrosilane (S)-

28 in 11 steps from (S)-17 in 1.6% overall yield. The

enantiomeric purity of (S)-28 was 98% ee by comparison with a

racemic sample.

Hydrosilane (R)-38 with a 2,3-disubstituted binaphthyl

backbone was prepared starting from the known MOM-

protected alcohol (R)-29²⁰(Scheme 3). Directed ortho

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metalation of (R)-29 and trapping with methyl iodide gave (R)-

30 [(R)-29 → (R)-30]. Acid-mediated cleavage of the MOM

group was followed by triﬂation of the unprotected phenol

[(R)-30 → (R)-31 → (R)-32]. Advanced intermediate (R)-32

was then subjected to the same sequence elaborated for the

synthesis of 2,2′-disubstituted (S)-28 from (R)-22 (see Scheme

2). By this, hydrosilane (R)-38 was obtained in nine steps from

(R)-29 in 15% overall yield (9.6% yield starting from (S)-

BINOL (S)-17), and its enantiomeric purity was 96% ee by

comparison with a racemic sample. The molecular structure of

(R)-38 was secured by X-ray diﬀraction and is included in

Scheme 3. It is worthy of note that especially the late-stage

transformations were substantially higher yielding for 2,3-

disubstituted (R)-38 (19% for (R)-32 → (R)-38) compared to

2,2′-disubstituted (S)-28 (3.0% for (R)-22 → (S)-28).

subsequent steps appears unlikely. The molecular structure of

(S)-42 was also assigned by X-ray diﬀraction and is included in

Scheme 4.

Generation of Sulfur-Stabilized Silicon Cations with

Chiral Binaphthyl Backbones. Silicon cations (S)-8, (R)-9,

and (S)-10 were again successfully generated by conventional

hydride abstraction with the trityl salt [Ph₃C]⁺[B(C₆F₅)₄]⁻.

Their ²⁹Si NMR shifts together with those of benzene-based 15

and 16 are collected in Figure 4.

We next focused on the synthesis of dihydrosilepine (S)-42

that was made from literature-known 2,2′-dimethyl-substituted

(S)-39²¹(Scheme 4). From this, diethoxy-substituted (S)-40

Scheme 4. Preparation of the Dihydrosilepine Precursor

with a 2-[(Ethylthio)methyl]phenyl Group Installed at the

Silicon Atom and Its Molecular Structure (ORTEP Plot

Rendered with POV-Ray)

Figure 4. Sulfur-stabilized silicon cations prepared by hydride

abstraction (cf. Scheme 1, bottom) and their ²⁹Si NMR shifts.

As previously observed for benzene-based silicon cations 15

and 16 (Scheme 1), line broadening in the ¹H NMR spectrum

of 2,2′-disubstituted (S)-8 is evidence of a dynamic equilibrium

between silicon−sulfur Lewis pairs. Coordination of either of

the sulfur lone pairs to the electron-deﬁcient silicon atom

produces diastereomers that cannot be resolved by NMR

spectroscopy. As a result of the fast epimerization, the ²⁹Si

NMR shift of δ 32.0 ppm could not be detected by a ²⁹Si DEPT

experiment and had to be determined by a more sensitive

¹H,²⁹Si HMQC NMR measurement. For 2,3-disubstituted (R)-

9, the equilibration was slower, allowing for the detection of

1

both diastereomers in the H NMR spectrum (dr = 67:33).

However, only one resonance signal at δ 50.7 ppm was seen in

1

the ²⁹Si NMR spectrum. H,²⁹Si HMQC NMR spectroscopy

then showed that the methyl groups of both diastereomers

correlate to that signal. Attempts to determine the relative

conﬁguration by NOE experiments were unsuccessful. Like-

wise, the dihydrosilepine-derived silicon cation (S)-10 showed

was accessed by double lithiation followed by trapping of the

dianionic intermediate with (EtO)₂SiCl₂[(S)-39 → (S)-40].

Reductive silicon−oxygen bond cleavage with DIBAL-H

aﬀorded the dihydrosilepine with two silicon−hydrogen

bonds [(S)-40 → (S)-41]. Treatment of (S)-41 with the

metalated thioether 12 (see Scheme 1) yielded desired (S)-42

with the 2-[(ethylthio)methyl]phenyl group bound to the

silicon atom [(S)-41 → (S)-42]. Reversing the order of the last

two steps resulted in lower yield of (S)-42 due to disubstitution

of diethoxy-substituted (S)-40 with metalated 12 (not shown).

The enantiomeric purity of (S)-42 was not determined by

comparison with a racemic sample. However, the enantiomeric

excess of (S)-39 was 99%, and racemization during any of the

1

two distinct diastereomers in the H NMR spectrum (dr =

75:25). As for (R)-9, the ²⁹Si NMR spectrum of (S)-10 only

showed one signal at δ 46.0 ppm.

Except for 2,2′-disubstituted (S)-8 (δ 32.0 ppm), the ²⁹Si

NMR resonances are in the same order of those found for 1,3-

dithiolan-2-yl- and 1,3-dithian-2-yl-substituted silicon cations (δ

42.3−57.8 ppm, Figure 2).¹⁰That diﬀerence is likely the result

of the larger ring size of (S)-8, i.e., seven vs ﬁve. These ﬁndings

are in good agreement with a recent study by Muller and co-

̈

workers, where it was shown that the silicon nucleus of silicon

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a b

,

Table 1. Model Diels−Alder Reaction Catalyzed by Sulfur-Stabilized Silicon Cations

c

d

e

entry

silicon cation

²⁹Si NMR (δ/ppm)

conv. (%)

yield (%)

ee (%)

1

2

3

4

5

15

16

56.4

57.6

32.0

50.7

46.0

79

77

94

81

87

63

52

70

67

(S)-8

(R)-9

(S)-10

0

67

11

a

b

All reactions were performed according to General Procedure 2 at a concentration of 0.5 M of the dienophile. Diastereomeric (trans:cis) and

c

endo:exo ratios determined by GLC analysis of the reaction mixture prior to puriﬁcation. Determined by GLC analysis using triphenylmethane as an

internal standard. Analytically pure cycloadduct after ﬂash column chromatography on silica gel. Determined by HPLC analysis using chiral

d

e

stationary phases.

cations stabilized in six-membered rings is considerably more

shielded than in its ﬁve-membered counterparts.¹⁵

The commonly used dienophile methyl acrylate (49) reacted

smoothly, and adduct 54 was formed in high yield and with

14% ee (Table 2, entry 5). The highest enantioselectivity was

achieved with α,β-unsaturated oxazolidinone imide 50 (Table

2, entry 6). Cycloadduct 55 was isolated in 52% yield at full

conversion with 24% ee. This enantiomeric excess is higher

than that obtained in the same reaction with the related

acetonitrile-stabilized silicon cation 5 introduced by Jørgensen,

Helmchen, and co-worker (10% ee, Figure 1, bottom right).⁷

We then examined the catalyses of the same set of

dienophiles with more reactive cyclopentadiene (56, Table

3). All reactions were completed within 1 h due to the higher

reactivity of 56. The observed trends (conversion, yield, and

enantioinduction) were largely similar to those seen with

cyclohexa-1,3-diene (43), but the endo/exo selectivities were

markedly lower in the majority of the examples (Table 3,

entries 2−5). The enantiomeric excess in this series was again

highest for dienophile 50 (Table 3, entry 6). However, the

value of 20% ee is still signiﬁcantly lower than that reported by

Hatanaka and co-workers for the same Diels−Alder reaction;

the related triﬂimide 3 induced 56% ee (Figure 1, upper right).⁴

Diels−Alder Reactions Catalyzed by Sulfur-Stabilized

Silicon Cations. Both achiral 15 and 16 and chiral (S)-8, (R)-

9, and (S)-10 were tested as catalysts in the challenging Diels−

Alder reaction of cyclohexa-1,3-diene (43) and chalcone (44)

to allow for comparison with known Lewis acids (Table

1).^{3,4,6,7,10,16,22}All reactions were performed at room temper-

ature and stopped after 3 h. The new sulfur-stabilized silicon

cations catalyzed this cycloaddition without exception, reaching

high conversion within the set time frame. Cycloadduct 45 was

isolated in good yields.

Silicon cation (S)-8 with the 2,2′-disubstituted binaphthyl

backbone again stood out (δ 32.0 ppm), being more reactive

than any of the other catalysts with less shielded silicon atoms

(δ 46.0−57.6 ppm). These results emphasize once again^16cthat

²⁹Si NMR shifts are not suitable for predicting the catalytic

performance of a silicon Lewis acid. It is, at best, a qualitative

measure to estimate the Lewis acidity of the silicon atom.¹⁷The

catalytic activity will also depend on the stability, i.e., strain, of

the cyclic Lewis pair. Moreover, the ring size determines

whether the silicon−sulfur interaction is optimal or not, and

this becomes immediately visible from the ²⁹Si NMR shifts.¹⁵

The interplay of the Lewis acidity and the ability of the sulfur

donor to form the cyclic Lewis pair explains the diﬀerence

between the seven-membered-ring cation (S)-8 and the ﬁve-

membered-ring cations (R)-9, (S)-10, 15, and 16.

Neither (S)-8 nor (R)-9 induced any enantioselectivity

(Table 1, entries 3 and 4). Conversely, little, but promising,

11% ee was obtained with (S)-10 where the silicon atom is part

of a more rigid silepine ring (Table 1, entry 5). Repeating this

experiment at −40 °C in toluene did not improve the

enantiomeric excess but dramatically slowed down the reaction

(14% conversion after 1 day).

Encouraged by these results, we explored the substrate scope

using Lewis acid (S)-10. Diﬃcult diene/dienophile combina-

tions, such as 43 and α,β-unsaturated carbonyls 44 and 46 as

well as particularly unreactive cyclic 47 and 48,^{16a,b,22−25}were

subjected to the standard setup in 1,2-Cl₂C₆H₄at room

temperature (Table 2, entries 1−4). The endo/exo selectivities

of cycloadducts 45 and 51−53 were excellent and conversions

were good, but the level of enantioselection was poor.

Unexpectedly,^16a,bthe yields obtained with cyclic dienophiles

47 and 48 were low, likely due to competing oligomerization.

CONCLUSION

■

In summary, a new class of sulfur-stabilized silicon cations is

introduced. A simple dialkyl thioether tether was shown to

suﬃciently stabilize silicon cations, and this motif was

combined with chiral binaphthyl backbones having diﬀerent

substitution patterns. The generated silicon Lewis acids were

fully characterized by NMR spectroscopy, showing distinct

diﬀerences in the shielding of the cationic silicon atom in the

²⁹Si NMR spectra. As supported by Muller and co-workers’

̈

recent ﬁndings,¹⁵the ²⁹Si NMR shifts correlate with the ring

size formed by intramolecular coordination of the sulfur atom

to the silicon atom. All sulfur-stabilized silicon cations were

shown to be potent Lewis acid catalysts for diﬃcult Diels−

Alder reactions. However, it was only the rigid dihydrosilepine-

derived silicon cation (S)-10 that induced low, but promising,

levels of enantioselection. The enantiomeric excess achieved in

the cycloaddition of cyclohexa-1,3-diene (43) and oxazolidi-

none imide 50 is higher than that obtained with the famous

Jørgensen−Helmchen catalyst 5 (24% ee, Table 2, entry 6 vs

10% ee, Figure 1, bottom right). We consider these results a

promising starting point for the development of a highly

reactive and more selective silicon Lewis acid catalyst. Hence,

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Table 2. Cyclohexa-1,3-diene (43) in Diels−Alder Reactions

Table 3. Cyclopentadiene (56) in Diels−Alder Reactions

a

Catalyzed by Sulfur-Stabilized Silicon Cation (S)-10

a

All reactions were performed according to General Procedure 2 at a

a

b

All reactions were performed according to General Procedure 2 at a

concentration of 0.5 M of the dienophile. Determined by GLC

b

c

concentration of 0.5 M of the dienophile. Determined by GLC

analysis of the reaction mixture prior to puriﬁcation. trans:cis ratio.

c

d

analysis of the reaction mixture prior to puriﬁcation. trans:cis ratio.

Determined by GLC analysis using triphenylmethane as an internal

d

e

Determined by GLC analysis using triphenylmethane as an internal

standard. Analytically pure endo-product after ﬂash column

chromatography on silica gel. Determined by HPLC or GLC analysis

using chiral stationary phases. Not determined as the starting material

could not be detected by GLC analysis.

e

f

standard. Analytically pure endo-product after ﬂash column

chromatography on silica gel. Determined by HPLC or GLC analysis

using chiral stationary phases. Not determined as the starting material

could not be detected by GLC analysis.

f

g

solids) prior to use. 1-Bromo-2-(bromomethyl)benzene (11) was

prepared according to a reported procedure.²⁶Trityl tetrakis(penta-

ﬂuorophenyl)borate ([Ph₃C]⁺[B(C₆F₅)₄]⁻) was prepared following a

reported procedure,²⁷recrystallized from CH₂Cl₂/n-pentane, and

stored in a glovebox. Analytical thin-layer chromatography (TLC) was

performed on silica gel 60 F254 glass plates by Merck. Flash column

chromatography was performed on silica gel LC60A (40−63 μm) by

new sulfur-stabilized silicon cations on this basis are currently

under investigation in our laboratory.

EXPERIMENTAL SECTION

■

General Remarks. All reactions were performed in ﬂame-dried

glassware using an MBraun glovebox (O₂< 2.0 ppm, H₂O < 2.0 ppm)

or conventional Schlenk techniques under a static pressure of argon or

nitrogen. Liquids and solutions were transferred with syringes.

Solvents were dried and puriﬁed following standard procedures.

Technical grade solvents for extraction or chromatography were

distilled prior to use. C₆D₆and CDCl₃were dried over 4 Å molecular

sieves, and 1,2-Cl₂C₆D₄was dried over CaH₂, distilled, and stored

under argon. Cyclohexa-1,3-diene (43) was distilled from NaBH₄, and

cyclopentadiene (56) was obtained by cracking of its dimer at 180 °C

prior to use. Dienophiles were distilled (for liquids) or recrystallized

from ethanol and dried by azeotropic distillation with benzene (for

1

Grace using the indicated solvents. H, ¹¹B, ¹³C, ¹⁹F, and ²⁹Si NMR

spectra were recorded in CDCl₃, C₆D₆, or 1,2-Cl₂C₆D₄on Bruker

AV500 or Bruker AV400 instruments. Chemical shifts are reported in

parts per million (ppm) and are referenced to the residual solvent

1

resonance as the internal standard (CHCl₃: δ 7.26 ppm for H NMR

1

and CDCl₃: δ 77.16 ppm for ¹³C NMR, C₆D₅H: δ 7.16 ppm for H

NMR and C₆D₆: δ 128.06 ppm for ¹³C NMR, 1,2-Cl₂C₆D₃H: δ 6.94

and 7.20 ppm for ¹H and 1,2-Cl₂C₆D₄: δ 127.1, 130.1, and 132.5 ppm

for ¹³C NMR). Data are reported as follows: chemical shift,

multiplicity (br s = broad singlet, s = singlet, br d = broad doublet,

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d = doublet, t = triplet, q = quartet, m = multiplet, m_c

=

(m), 1234 (m), 1157 (w), 1109 (w), 1022 (s), 970 (w), 871 (w), 817

(w), 732 (s), 693 (m) cm⁻¹. HRMS (ESI) calculated for C₉H₁₁BrS

centrosymmetric multiplet), coupling constants (Hz), and integration.

1

[M]⁺: 229.9765; found: 229.9760. H NMR (500 MHz, CDCl₃): δ

¹H,²⁹Si HMQC NMR spectra were measured with a coupling constant

3

1

of 7.0 Hz for the J_H,Sicoupling. The peak intensities in the H,²⁹Si

HMQC NMR spectra cannot be correlated to the amount of

compound. Infrared (IR) spectra were recorded on an Agilent

Technologies Cary 630 FTIR spectrophotometer equipped with an

ATR unit and are reported as wavenumbers [cm⁻¹] (w = weak, m =

medium, s = strong, vs = very strong). Gas liquid chromatography

(GLC) was performed on an Agilent Technologies 7820A gas

chromatograph equipped with a HP-5 capillary column (30 m × 0.32

mm, 0.25 μm ﬁlm thickness) using the following program: N₂carrier

gas, column ﬂow: 1.74 mL min⁻¹, injection temperature: 250 °C,

detector temperature: 300 °C; temperature program: start temperature

40 °C, heating rate 10 °C min⁻¹, end temperature 280 °C for 10 min.

Melting points (m.p.) were determined with a Stuart Scientiﬁc SMP20

melting point apparatus and are not corrected. Enantiomeric excesses

were determined by analytical high performance liquid chromatog-

raphy (HPLC) analysis on an Agilent Technologies 1200 Inﬁnity

instrument with a chiral stationary phase using a Daicel Chiralcel OD-

H or AD-H column (n-heptane/i-PrOH mixtures as solvents), and an

Agilent Technologies 1290 Inﬁnity instrument with a chiral stationary

phase using a Daicel Chiralcel OJ-RH column (acetonitrile/H₂O

mixtures as solvents), or by analytical gas liquid chromatography

(GLC) on an Agilent Technologies 7820A gas chromatograph

equipped with an IVAdex-1 capillary column (25 m × 0.25 mm,

0.25 μm ﬁlm thickness) using the program indicated in the respective

experiments. High-resolution mass spectrometry (HRMS) and

elemental analysis were performed at the Analytical Facility of the

1.27 (t, J = 7.4 Hz, 3H), 2.52 (q, J = 7.5 Hz, 2H), 3.85 (s, 2H), 7.10

(m_c, 1H), 7.27 (m_c, 1H), 7.37 (dd, J = 7.6 Hz, J = 1.5 Hz, 1H), 7.56

(dd, J = 8.0 Hz, J = 1.1 Hz, 1H). ¹³C NMR (126 MHz, CDCl₃): δ

14.7, 25.8, 36.3, 124.6, 127.5, 128.6, 130.8, 133.2, 138.2. Anal. Calcd

for C₉H₁₁BrS: C, 46.77; H, 4.80; S, 13.87. Found: C, 46.65; H, 4.94; S,

14.10. The analytical and spectroscopic data are in accordance with

those reported.²⁸

(2-((Ethylthio)methyl)phenyl)dimethylsilane (13). To a sol-

ution of thioether 12 (0.10 g, 0.43 mmol, 1.0 equiv) in THF (5 mL)

cooled to −78 °C was added nBuLi (3.9 M in hexane fractions, 0.15

mL, 0.56 mmol, 1.3 equiv) dropwise, and the resulting mixture was

stirred for 1 h at −78 °C. Me₂Si(H)Cl (63 μL, 53 mg, 0.56 mmol, 1.3

equiv) was added, and then the mixture was allowed to slowly warm to

room temperature, followed by stirring overnight. The reaction was

quenched by the addition of water (5 mL), and the phases were

separated. The aqueous phase was extracted with CH₂Cl₂(3 × 5 mL),

the combined organic phases were washed with saturated aqueous

NaCl (20 mL) and dried over Na₂SO₄, and the solvent was removed

under reduced pressure. The residue was puriﬁed by ﬂash column

chromatography on silica gel using cyclohexane/CH₂Cl₂(20/1) as

eluent, aﬀording hydrosilane 13 (60 mg, 0.29 mmol, 66%) as a

colorless oil. R_f= 0.20 (cyclohexane). GLC (HP-5): t_R= 13.0 min. IR

(ATR): nu(tilde) = 3055 (w), 2959 (m), 2924 (m), 2319 (w), 2120

(m), 1924 (w), 1578 (w), 1435 (m), 1248 (m), 1194 (w), 1119 (m),

1069 (w), 972 (w), 878 (vs), 835 (s), 722 (s) cm⁻¹. HRMS (ESI)

1

calculated for C₁₁H₁₉SSi [M + H]⁺: 211.0997; found: 211.0991. H

NMR (500 MHz, CDCl₃): δ 0.40 (d, J = 3.8 Hz, 6H), 1.26 (t, J = 7.6

Hz, 3H), 2.51 (q, J = 7.4 Hz, 2H), 3.88 (s, 2H), 4.63 (sept, J = 3.8 Hz,

1H), 7.24 (m_c, 1H), 7.31−7.36 (m, 2H), 7.50 (m_c, 1H). ¹³C NMR

(126 MHz, CDCl₃): δ −2.6 (2C), 14.7, 26.0, 36.5, 126.5, 129.4, 129.5,

135.1, 137.0, 144.1. ²⁹Si DEPT (99 MHz, CDCl₃): δ −21.6.

Institut fur Chemie, Technische Universitat Berlin.

̈

General Procedure for the Generation of Intramolecularly

Sulfur-Stabilized Silicon Cations (S)-8, (R)-9, and (S)-10, 15, and

16 (GP1). In a glovebox, a solution of the indicated hydrosilane (1.00

equiv) in 1,2-Cl₂C₆D₄(0.4 mL) was added to a suspension of

[Ph₃C]⁺[B(C₆F₅)₄]⁻(1.00 equiv) in 1,2-Cl₂C₆D₄(0.2 mL) in an 8 mL

vial. The resulting mixture is stirred for 5 min, transferred to an NMR

tube, and directly subjected to NMR spectroscopic analysis.

(2-((Ethylthio)methyl)phenyl)diisopropylsilane (14). To a

solution of thioether 12 (0.20 g, 0.87 mmol, 1.0 equiv) in THF (8.7

mL) cooled to −78 °C was added nBuLi (1.8 M in hexane fractions,

0.64 mL, 1.1 mmol, 1.3 equiv) dropwise, and the resulting mixture was

stirred for 2 h at −78 °C. iPr₂Si(H)Cl (0.19 mL, 0.17 g, 1.1 mmol, 1.3

equiv) was added, and then the mixture was allowed to slowly warm to

room temperature, followed by stirring overnight. The reaction was

quenched by the addition of water (10 mL), and the phases were

separated. The aqueous phase was extracted with tert-butyl methyl

ether (3 × 10 mL), the combined organic phases were washed with

saturated aqueous NaCl (20 mL) and dried over Na₂SO₄, and the

solvent was removed under reduced pressure. The residue was puriﬁed

by ﬂash column chromatography on silica gel using cyclohexane as

eluent, aﬀording hydrosilane 14 (186 mg, 0.698 mmol, 81%) as a

colorless oil. R_f= 0.31 (cyclohexane). GLC (HP-5): t_R= 16.4 min. IR

(ATR): nu(tilde) = 3055 (w), 2937 (m), 2861 (m), 2113 (m), 1923

(w), 1811 (w), 1587 (w), 1460 (m), 1381 (w), 1261 (m), 1117 (m),

1069 (m), 1002 (s), 918 (w), 878 (m), 786 (vs), 734 (s). HRMS

General Procedure for Diels−Alder Reactions Catalyzed by

Sulfur-Stabilized Silicon Cations (GP2). In a glovebox, a ﬂame-

dried Schlenk tube equipped with a magnetic stir bar was charged with

[Ph₃C]⁺[B(C₆F₅)₄]⁻(5.00 mol %). The Schlenk tube was transferred

to a fume hood and connected to a nitrogen-vacuum manifold. After

addition of 1,2-Cl₂C₆H₄(0.2 mL), a solution of the corresponding

silane (5.50 mol %) in 1,2-Cl₂C₆H₄(0.4 mL) was added, and the

resulting mixture was maintained for 30 min at room temperature. To

the thus-obtained catalyst, a solution of diene (2.10 equiv) and

dienophile (1.00 equiv) in 1,2-Cl₂C₆H₄(0.4 mL) was added dropwise.

The reaction mixture was stirred at room temperature for 1−3 h,

followed by addition of saturated aqueous NaHCO₃solution. The

phases were separated, and the aqueous phase was extracted with tert-

butyl methyl ether (3×). The combined organic phases were washed

with saturated aqueous NaCl solution, dried over Na₂SO₄, and

concentrated under reduced pressure. The residue was puriﬁed by

ﬂash column chromatography on silica gel using cyclohexane/ethyl

acetate as eluent, aﬀording analytically pure Diels−Alder adduct.

(2-Bromobenzyl)(ethyl)sulfane (12). 1-Bromo-2-(bromo-

methyl)benzene (11, 1.0 g, 4.0 mmol, 1.0 equiv) was dissolved in

ethanol (8 mL). K₂CO₃(1.1 g, 8.0 mmol, 2.0 equiv) and ethanethiol

(0.59 mL, 0.50 g, 8.0 mmol, 2.0 equiv) were added, and the resulting

mixture was stirred at 45 °C for 15 h. After cooling to room

temperature, the reaction was quenched by the addition of water (15

mL). The phases were separated, and the aqueous phase was extracted

with CH₂Cl₂(2 × 10 mL). The combined organic phases were washed

with aqueous NaOH (2 M, 10 mL) and saturated aqueous NaCl (10

mL), dried over Na₂SO₄, and concentrated under reduced pressure.

The residue was puriﬁed by ﬂash column chromatography on silica gel

using cyclohexane as eluent, aﬀording thioether 12 (0.690 g, 2.99

mmol, 75%) as a colorless oil. R_f= 0.21 (cyclohexane). GLC (HP-5):

t_R= 13.3 min. IR (ATR): nu(tilde) = 3056 (w), 2965 (m), 2922 (m),

2868 (w), 1918 (w), 1798 (w), 1565 (m), 1437 (s), 1374 (m), 1264

1

(ESI) calculated for C₁₅H₂₆SSi [M]⁺: 266.1524; found: 266.1526. H

NMR (500 MHz, CDCl₃): δ 0.99 (d, J = 7.2 Hz, 6H), 1.10 (d, J = 7.2

Hz, 6H), 1.23−1.30 (m, 5H), 2.50 (q, J = 7.4 Hz, 2H), 3.86 (s, 2H),

4.19 (t, J = 3.5 Hz, 1H), 7.21 (m_c, 1H), 7.31 (m_c, 1H), 7.35−7.39 (m,

1H), 7.43 (m_c, 1H). ¹³C NMR (126 MHz, CDCl₃): δ 11.5 (2C), 14.9,

19.1 (4C), 26.0, 36.9, 126.1, 129.2, 129.6, 134.3, 135.9, 144.8. ²⁹Si

DEPT (99 MHz, CDCl₃): δ −1.1.

(2-((Ethylthio)methyl)phenyl)dimethylsilylium Tetrakis-

(pentaﬂuorophenyl)borate (15). Prepared from (2-((ethylthio)-

methyl)phenyl)dimethylsilane (13, 11 mg, 50 μmol, 1.0 equiv) and

[Ph₃C]⁺[B(C₆F₅)₄]⁻(46 mg, 50 μmol, 1.0 equiv) according to GP1.

1

NMR spectroscopic data for 15 are as follows. H NMR (500 MHz,

1,2-Cl₂C₆D₄): δ 0.66 (s, 6H), 1.14 (t, J = 7.4 Hz, 3H), 2.41−2.68 (br s,

2H), 3.97−4.41 (br s, 2H), 7.09−7.11 (m, 1H), 7.20−7.23 (m, 1H),

7.28 (m_c, 1H), 7.35 (m_c, 1H). ¹³C NMR (126 MHz, 1,2-Cl₂C₆D₄): δ

11.5 (br s, 2C), 23.0, 31.1, 42.0, 124.8 (br m), 130.4, 133.2, 136.8 (d, J

= 236 Hz), 138.3, 138.7 (d, J = 236 Hz), 139.6, 142.4, 143.3, 148.9 (d,

J = 240 Hz). ¹¹B NMR (160 MHz, 1,2-Cl₂C₆D₄): δ −16.0. ¹⁹F NMR

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(471 MHz, 1,2-Cl₂C₆D₄): δ −165.8, −161.9, −131.5. ²⁹Si DEPT NMR

(99 MHz, 1,2-Cl₂C₆D₄): δ 56.4 ppm.

(R)-tert-Butyl((2′-methyl-[1,1′-binaphthalen]-2-yl)oxy)-

diphenylsilane [(R)-20]. 1,3-Bis(diphenylphosphino)propane nickel-

(II) chloride (27 mg, 0.053 mmol, 7.0 mol %) was placed in a ﬂame-

dried Schlenk ﬂask, and a solution of triﬂate (S)-19 (0.50 g, 0.76

mmol, 1.0 equiv) in THF (6 mL) was added. The suspension was

cooled to 0 °C, and methylmagnesium bromide (3.0 M in Et₂O, 0.38

mL, 0.11 mmol, 1.5 equiv) was added dropwise. The cooling bath was

replaced by an oil bath, and the mixture heated at reﬂux for 4 h. The

mixture was diluted with THF (3 mL), cooled to 0 °C, and carefully

quenched by the addition of water (5 mL) and hydrochloric acid (2 M,

5 mL). The phases were separated, and the aqueous phase extracted

with tert-butyl methyl ether (2 × 5 mL). The combined organic phases

were washed with water (5 mL), and saturated aqueous NaCl (5 mL),

dried over Na₂SO₄, and concentrated under reduced pressure. The

residue was puriﬁed by ﬂash column chromatography on silica gel

using cyclohexane/ethyl acetate (10/1) as eluent, aﬀording (R)-20

(0.39 g, 0.75 mmol, 99%) as a yellow solid. m.p.: 122 °C (CH₂Cl₂). R_f

= 0.73 (cyclohexane/ethyl acetate 5/1). IR (ATR): nu(tilde) = 3048

(w), 2925 (m), 2852 (m), 2220 (w), 1950 (w), 1891 (w), 1619 (w),

1589 (m), 1502 (m), 1461 (m), 1425 (m), 1334 (m), 1247 (m), 1145

(w), 1107 (s), 996 (s), 950 (w), 863 (w), 806 (vs), 741 (s), 696 (vs)

cm⁻¹. HRMS (ESI) calculated for C₃₇H₃₄OSi [M]⁺: 522.2373; found:

(2-((Ethylthio)methyl)phenyl)diisopropylsilylium Tetrakis-

(pentaﬂuorophenyl)borate (16). Prepared from (2-((ethylthio)-

methyl)phenyl)diisopropylsilane (14, 21 mg, 80 μmol, 1.0 equiv) and

[Ph₃C]⁺[B(C₆F₅)₄]⁻(74 mg, 80 μmol, 1.0 equiv) according to GP1.

1

NMR spectroscopic data for 16 are as follows. H NMR (500 MHz,

1,2-Cl₂C₆D₄): δ 0.82−0.91 (m, 6H), 0.96−1.08 (m, 6H), 1.24 (t, J =

7.3 Hz, 3H), 1.38 (sept, J = 7.5 Hz, 2H), 2.53−2.66 (m, 1H), 2.71−

2.83 (m, 1H), 4.03−4.16 (m, 1H), 4.26−4.37 (m, 1H), 7.10−7.12 (m,

1H), 7.24−7.29 (m, 1H), 7.31−7.35 (m, 1H), 7.36−7.40 (m, 1H). ¹³C

NMR (126 MHz, 1,2-Cl₂C₆D₄): δ 11.9, 13.2, 13.4, 16.9, 17.0 (br s,

2C), 17.4, 31.3, 42.8, 124.8 (br m), 126.1, 133.3, 134.0, 136.8 (d, J =

236 Hz), 138.7 (d, J = 236 Hz), 139.5, 148.9 (d, J = 240 Hz). ¹¹B

NMR (160 MHz, 1,2-Cl₂C₆D₄): δ −16.0. ¹⁹F NMR (471 MHz, 1,2-

Cl₂C₆D₄): δ −165.9, −162.0, −131.5. ²⁹Si DEPT NMR (99 MHz, 1,2-

Cl₂C₆D₄): δ 57.6 ppm.

(S)-2′-((tert-Butyldiphenylsilyl)oxy)-[1,1′-binaphthalen]-2-ol

[(S)-18]. (S)-BINOL [(S)-17, 5.01 g, 17.5 mmol, 1.00 equiv] and

imidazole (2.38 g, 34.9 mmol, 2.00 equiv) were dissolved in dry DMF

(35 mL). TBDPSCl (5.14 g, 18.7 mmol, 1.07 equiv) was added, and

the resulting mixture was stirred at 50 °C for 16 h. After cooling to

room temperature, saturated aqueous NH₄Cl (5 mL) was added. This

mixture was extracted with Et₂O (3 × 20 mL). The combined organic

phases were washed with saturated aqueous NaCl (50 mL), dried over

Na₂SO₄, and concentrated under reduced pressure. Puriﬁcation by

ﬂash column chromatography on silica gel using cyclohexane/ethyl

acetate (10/1) aﬀorded (S)-18 (6.87 g, 13.1 mmol, 75%) as a white

solid. m.p.: 142 °C (CH₂Cl₂). R_f= 0.53 (cyclohexane/ethyl acetate 5/

1). GLC (HP-5): t_R= 30.7 min. IR (ATR): nu(tilde) = 3528 (m),

3062 (w), 2922 (w), 2849 (w), 2041 (w), 1980 (w), 1902 (w), 1620

(m), 1588 (m), 1505 (m), 1459 (m), 1425 (m), 1360 (m), 1266 (m),

1208 (m), 1174 (m), 1108 (m), 1003 (m), 935 (w), 861 (w), 811 (s),

741 (s), 699 (s) cm⁻¹. HRMS (ESI) calculated for C₃₆H₃₂O₂Si [M]⁺:

1

522.2359. H NMR (500 MHz, C₆D₆): δ 0.60 (s, 9H), 2.25 (s, 3H),

7.03 (m_c, 1H), 7.08 (m_c, 1H), 7.10 (m_c, 2H), 7.12−7.15 (m, 3H),

7.18−7.21 (m, 3H), 7.23 (m_c, 1H), 7.30 (m_c, 1H), 7.34 (m_c, 1H), 7.44

(m_c, 1H), 7.49 (m_c, 1H), 7.53 (m_c, 1H), 7.69 (m_c, 2H), 7.77 (m_c, 2H),

7.79 (m_c, 2H). ¹³C NMR (126 MHz, C₆D₆): δ 19.2, 20.6, 25.8 (3C),

120.8, 124.1, 124.4, 125.2, 125.6, 126.2, 126.6, 127.0, 127.9, 128.1,

128.2, 128.3, 128.4, 128.6, 129.0, 129.1, 129.8, 130.2, 133.0, 133.1,

133.6, 133.7, 134.1, 134.6, 135.3, 135.7, 135.8, 150.7. Anal. Calcd for

C₃₇H₃₁F₃O₄SSi: C, 85.01; H, 6.56. Found: C, 84.63; H, 6.60.

(R)-2′-Methyl-[1,1′-binaphthalen]-2-ol [(R)-21]. To a solution

of (R)-20 (0.39 g, 0.75 mmol, 1.0 equiv) in THF (5 mL) was added

TBAF (0.22 g, 0.83 mmol, 1.1 equiv). The resulting mixture was

stirred at room temperature for 3.5 h and quenched by the addition of

water (5 mL). The phases were separated, and the aqueous phase was

extracted with tert-butyl methyl ether (3 × 5 mL). The combined

organic phases were washed with saturated aqueous NaCl (5 mL) and

dried over Na₂SO₄, and the solvent was removed under reduced

pressure. The free alcohol (R)-21 (0.16 g, 0.55 mmol, 73%) was

obtained as a mixture with the corresponding ﬂuorosilane. The yield

was determined by ¹H NMR spectroscopy by integration of the

baseline-separated resonances of the methyl group of (R)-21 and the

tert-butyl group of the silane. The mixture of (R)-21 with the

ﬂuorosilane was used without further puriﬁcation. An aliquot for

characterization was puriﬁed by repeated ﬂash column chromatog-

raphy on silica gel using cyclohexane as eluent. m.p.: 127 °C

(CH₂Cl₂). R_f= 0.44 (cyclohexane/ethyl acetate 5/1). GLC (HP-5): t_R

= 22.6 min. IR (ATR): nu(tilde) = 3489 (m), 3413 (w), 3039 (w),

2920 (w), 2104 (w), 1896 (w), 1751 (w), 1591 (m), 1505 (m), 1462

(m), 1377 (m), 1299 (m), 1268 (m), 1200 (m), 1172 (s), 1143 (s),

1025 (s), 955 (m), 860 (m), 804 (vs), 739 (vs), 663 (s) cm⁻¹. HRMS

1

524.2167; found: 524.2148. H NMR (500 MHz, CDCl₃): δ 0.50 (s,

9H), 5.00 (s, 1H), 6.90 (m_c, 1H), 7.21 (m_c, 1H), 7.27−7.44 (m, 12H),

7.53 (m_c, 2H), 7.61 (m_c, 1H), 7.64 (m_c, 2H), 7.78 (m_c, 1H), 7.89 (m_c,

1H), 7.93 (m_c, 1H). ¹³C NMR (126 MHz, CDCl₃): δ 19.1, 25.7 (3C),

115.7, 117.5, 117.6, 120.8, 123.3, 124.3, 125.1, 125.2, 126.5, 127.3,

127.8, 128.01, 128.02, 128.20, 128.23, 129.5, 129.6, 129.9, 130.0,

130.1, 130.3, 132.4, 132.8, 134.1, 134.3, 135.5, 135.6, 151.6, 152.2. The

analytical and spectroscopic data are in accordance with those

reported.²⁹

(S)-2′-((tert-Butyldiphenylsilyl)oxy)-[1,1′-binaphthalen]-2-yl

Triﬂuoromethanesulfonate [(S)-19]. To a solution of (S)-18 (5.00

g, 9.53 mmol, 1.00 equiv) in CH₂Cl₂(20 mL) cooled to 0 °C were

added N,N-diisopropylethylamine (2.2 mL, 1.6 g, 12 mmol, 1.3 equiv)

and subsequently triﬂuoromethanesulfonic anhydride (1.8 mL, 3.0 g,

11 mmol, 1.1 equiv). The cooling bath was removed, and the mixture

was stirred at room temperature for 12 h. The mixture was washed

with hydrochloric acid (2 M, 15 mL), saturated aqueous NaHCO₃(15

mL), and saturated aqueous NaCl (15 mL). The organic phase was

dried over Na₂SO₄, and the solvent was removed under reduced

pressure. Triﬂate (S)-19 (6.2 g, 9.4 mmol, 99%) was obtained as a

white solid and used without further puriﬁcation. m.p.: 109 °C

(CH₂Cl₂). R_f= 0.55 (cyclohexane/ethyl acetate 5/1). GLC (HP-5): t_R

= 31.3 min. IR (ATR): nu(tilde) = 3054 (w), 2931 (w), 2856 (w),

2199 (w), 1897 (w), 1590 (m), 1505 (m), 1470 (m), 1419 (m), 1338

(m), 1278 (m), 1209 (s), 1139 (s), 1111 (m), 1000 (m), 863 (w), 812

(s), 743 (m), 689 (s) cm⁻¹. HRMS (ESI) calculated for

C₃₇H₃₁F₃O₄SSi [M]⁺: 656.1659; found: 656.1653. ¹H NMR (500

MHz, C₆D₆): δ 0.64 (s, 9H), 7.00−7.08 (m, 4H), 7.10−7.15 (m, 3H),

7.16−7.18 (m, 1H), 7.21−7.25 (m, 2H), 7.29 (m_c, 3H), 7.44 (m_c, 1H),

7.50 (m_c, 1H), 7.53−7.55 (m, 1H), 7.57−7.59 (m, 1H), 7.60 (m_c, 2H),

7.66 (m_c, 2H), 7.93 (m_c, 2H). ¹³C NMR (126 MHz, C₆D₆): δ 19.1,

25.9 (3C), 117.7, 118.9 (q, J = 320.1 Hz), 120.0, 120.5, 124.2, 125.5,

127.0, 127.2, 127.4, 127.7, 128.2, 128.3, 128.38, 128.41, 128.46,

128.48, 129.5, 130.2, 130.47, 130.49, 130.7, 132.8, 133.0, 134.4, 134.5,

135.7, 135.8, 146.3, 151.6.

1

(ESI) calculated for C₂₁H₁₆O [M]⁺: 284.1201; found: 284.1188. H

NMR (500 MHz, CDCl₃): δ 2.16 (s, 3H), 4.49 (br s, 1H), 6.98 (d, J =

8.7 Hz, 1H), 7.21−7.25 (m, 2H), 7.29 (m_c, 1H), 7.31−7.38 (m, 2H),

7.45 (m_c, 1H), 7.56 (d, J = 8.7 Hz, 1H), 7.88 (d, J = 8.2 Hz, 1H), 7.92

(d, J = 8.7 Hz, 2H), 7.95 (d, J = 8.2 Hz, 1H). ¹³C NMR (126 MHz,

CDCl₃): δ 20.3, 117.5, 117.7, 123.6, 124.7, 125.6, 125.7, 126.8, 127.0,

128.27, 128.31, 128.8, 129.15, 129.18, 129.3, 129.9, 132.7, 133.4,

133.5, 137.3, 150.9. The analytical and spectroscopic data are in

accordance with those reported.³⁰

(R)-2′-Methyl-[1,1′-binaphthalen]-2-yl Triﬂuoromethane-

sulfonate [(R)-22]. To a solution of alcohol (R)-21 (51 wt %, 446

mg, 0.546 mmol, 1.00 equiv) in CH₂Cl₂(4 mL) cooled to 0 °C were

added N,N-diisopropylethylamine (0.24 mL, 0.18 g, 1.4 mmol, 2.5

equiv) and subsequently triﬂuoromethanesulfonic anhydride (0.19 mL,

0.33 g, 1.2 mmol, 2.1 equiv). The cooling bath was removed, and the

mixture was stirred at room temperature for 12 h. The mixture was

washed with hydrochloric acid (2 M, 5 mL), saturated aqueous

NaHCO₃(5 mL), and saturated aqueous NaCl (5 mL). The organic

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phase was dried over Na₂SO₄, and the solvent was removed under

reduced pressure. The residue was puriﬁed by ﬂash column

chromatography on silica gel using cyclohexane/ethyl acetate (10/1)

as eluent, aﬀording triﬂate (R)-22 (226 mg, 0.525 mmol, 96%) as a

yellow solid. m.p.: 87 °C (CH₂Cl₂). R_f= 0.50 (cyclohexane/ethyl

acetate 5/1). GLC (HP-5): t_R= 22.2 min. IR (ATR): nu(tilde) = 3042

(w), 2924 (w), 2429 (w), 1908 (w), 1760 (w), 1505 (w), 1408 (m),

1204 (s), 1129 (s), 939 (m), 865 (m), 807 (m), 778 (m), 760 (m),

707 (m), 675 (m) cm⁻¹. HRMS (ESI) calculated for C₂₂H₁₅F₃O₃S

[M]⁺: 416.0694; found: 416.0680. ¹H NMR (500 MHz, C₆D₆): δ 2.04

(s, 3H), 6.92 (m_c, 1H), 7.02 (m_c, 1H), 7.11−7.14 (m, 1H), 7.17−7.20

(m, 2H), 7.22 (m_c, 1H), 7.27 (m_c, 1H), 7.38 (m_c, 1H), 7.48 (m_c, 1H),

7.54 (m_c, 1H), 7.68 (m_c, 1H), 7.71 (m_c, 1H). ¹³C NMR (126 MHz,

C₆D₆): δ 20.3, 118.7 (q, J = 320.0 Hz), 120.0, 125.6, 125.8, 126.91,

126.94, 127.2, 128.0, 128.4, 128.5, 128.6, 128.8, 128.9, 129.4, 130.4,

130.6, 132.6, 133.0, 133.3, 133.7, 145.4.

C₂₁H₁₅I [M]⁺: 394.0218; found: 394.0200. ¹H NMR (500 MHz,

C₆D₆): δ 2.00 (s, 3H), 6.87 (m_c, 1H), 7.02 (m_c, 1H), 7.13 (m_c, 1H),

7.17−7.20 (m, 2H), 7.26 (m_c, 1H), 7.31 (m_c, 1H), 7.56 (m_c, 1H),

7.71−7.77 (m, 3H), 7.92 (m_c, 1H). ¹³C NMR (126 MHz, C₆D₆): δ

20.1, 100.2, 125.5, 126.6, 126.9, 127.0, 127.5, 128.3, 128.4, 128.5,

128.6, 129.1, 129.4, 132.8, 132.9, 133.5, 134.0, 134.4, 136.1, 139.1,

142.7.

(S)-2-(Bromomethyl)-2′-iodo-1,1′-binaphthalene [(S)-26]. Io-

dide (R)-25 (80 mg, 0.20 mmol, 1.0 equiv), NBS (43 mg, 0.24 mmol,

1.2 equiv), and benzoyl peroxide (49 mg, 0.20 mmol, 1.0 equiv) were

dissolved in benzene (4 mL). The resulting mixture was heated at

reﬂux for 4 h, cooled to room temperature, and stirred for further 21 h.

The solvent was removed under reduced pressure. The residue was

puriﬁed by ﬂash column chromatography on silica gel using

cyclohexane/CH₂Cl₂(20/1) as eluent, aﬀording benzyl bromide

(S)-26 (44 mg, 92 μmol, 45%) as a white solid. m.p.: 191 °C

(benzene). R_f= 0.12 (cyclohexane). GLC (HP-5): t_R= 27.1 min. IR

(ATR): nu(tilde) = 3044 (w), 1753 (w), 1614 (w), 1575 (w), 1497

(m), 1433 (w), 1304 (w), 1210 (m), 1102 (m), 1053 (w), 957 (m),

871 (w), 808 (s), 784 (m), 750 (s), 690 (m) cm⁻¹. HRMS (ESI)

(R)-2′-Methyl-[1,1′-binaphthalen]-2-amine [(R)-24]. Triﬂate

(R)-22 (1.84 g, 4.41 mmol, 1.00 equiv), Pd(OAc)₂(0.247 g, 1.10

mmol, 0.250 equiv), rac-BINAP (0.822 g, 1.32 mmol, 0.300 equiv),

and Cs₂CO₃(4.01 g, 12.3 mmol, 2.80 equiv) were dissolved in dry 1,4-

dioxane (18 mL). To this suspension was added benzylamine (4.09

mL, 4.01 g, 37.4 mmol, 8.49 equiv), and the resulting mixture was

degassed (three freeze−pump−thaw cycles). The mixture was stirred

at 80 °C for 90 h. After cooling to room temperature, the mixture was

ﬁltered through Celite, and the solvent was removed under reduce

pressure. Crude (R)-23 was directly used in the next step without

puriﬁcation. A solution of crude (R)-23 in ethyl acetate (10 mL) was

added to palladium on activated charcoal (10 wt %, 0.486 g, 0.439

mmol, 10.0 mol % based on (R)-22). The atmosphere was changed to

dihydrogen (1 atm), and the mixture was stirred at 40 °C. The

1

calculated for C₂₁H₁₄BrI [M]⁺: 471.9324; found: 471.9315. H NMR

(500 MHz, C₆D₆): δ 4.04 (d, J = 10.4 Hz, 1H), 4.11 (d, J = 10.4 Hz,

1H), 6.88 (m_c, 1H), 6.94 (m_c, 1H), 7.10−7.15 (m, 3H), 7.17−7.19 (m,

1H), 7.24 (m_c, 1H), 7.53 (m_c, 2H), 7.62 (m_c, 1H), 7.70 (m_c, 1H), 7.86

(m_c, 1H). ¹³C NMR (126 MHz, C₆D₆): δ 31.9, 100.5, 126.5, 126.8,

126.9, 127.3, 127.5, 127.7, 128.34, 128.36, 128.4, 129.6, 130.0, 132.4,

133.3, 133.8, 133.9, 134.1, 136.0, 140.0, 140.7.

(S)-Ethyl((2′-iodo-[1,1′-binaphthalen]-2-yl)methyl)sulfane

[(S)-27]. Benzyl bromide (S)-26 (72 mg, 0.15 mmol, 1.0 equiv) was

dissolved in ethanol (1 mL). K₂CO₃(42 mg, 0.30 mmol, 2.0 equiv)

and ethanethiol (22 μL, 19 mg, 0.30 mmol, 2.0 equiv) were added, and

the resulting mixture was stirred overnight at 45 °C. After cooling to

room temperature, the reaction was quenched by the addition of water

(3 mL). The phases were separated, and the aqueous phase was

extracted with CH₂Cl₂(2 × 2 mL). The combined organic phases

were washed with aqueous NaOH (2 M, 2 mL) and saturated aqueous

NaCl (2 mL), dried over Na₂SO₄, and concentrated under reduced

pressure. Ethyl thioether (S)-27 (58 mg, 0.13 mmol, 85%) was

obtained as a colorless sticky oil and used without further puriﬁcation.

GLC (HP-5): t_R= 28.2 min. IR (ATR): nu(tilde) = 3053 (m), 2980

(m), 2921 (m), 2866 (w), 2354 (w), 2199 (w), 1914 (w), 1813 (w),

1689 (w), 1616 (w), 1577 (m), 1499 (m), 1449 (m), 1305 (w), 1260

(m), 1133 (w), 1104 (m), 1025 (w), 955 (w), 810 (s), 746 (s), 682

(w) cm⁻¹. HRMS (ESI) calculated for C₂₃H₂₀IS [M + H]⁺: 455.0330;

found: 455.0319. ¹H NMR (500 MHz, CDCl₃): δ 0.93 (t, J = 7.0 Hz,

3H), 2.29 (m_c, 2H), 3.41 (d, J = 14.9 Hz, 1H), 3.56 (d, J = 14.9 Hz,

1H), 7.02 (m_c, 1H), 7.13 (m_c, 1H), 7.24 (m_c, 1H), 7.26−7.29 (m, 1H),

7.45 (m_c, 1H), 7.49 (m_c, 1H), 7.69 (m_c, 1H), 7.88 (m_c, 1H), 7.92 (m_c,

2H), 8.01 (m_c, 1H), 8.06 (m_c, 1H). ¹³C NMR (126 MHz, CDCl₃): δ

14.5, 26.6, 34.1, 100.7, 125.9, 126.0, 126.68, 126.72, 127.1, 127.2,

127.3, 128.21, 128.23, 128.8, 129.6, 132.1, 132.9, 133.0, 134.0, 134.9,

135.8, 139.0, 141.0.

(S)-(2′-((Ethylthio)methyl)-[1,1′-binaphthalen]-2-yl)-

dimethylsilane [(S)-28]. To a solution of thioether (S)-27 (43 mg,

96 μmol, 1.0 equiv) in THF (1.2 mL) cooled to −78 °C was added

nBuLi (2.2 M in hexane fractions, 57 μL, 0.12 mmol, 1.3 equiv)

dropwise, and the resulting mixture was stirred for 1 h at −78 °C.

Me₂Si(H)Cl (13 μL, 11 mg, 0.12 mmol, 1.3 equiv) was added, and

then the mixture was allowed to slowly warm to room temperature,

followed by stirring overnight. The reaction was quenched by the

addition of water (3 mL), and the phases were separated. The aqueous

phase was extracted with tert-butyl methyl ether (3 × 3 mL), and the

combined organic phases were washed with saturated aqueous NaCl

(3 mL), dried over Na₂SO₄, and concentrated under reduced pressure.

The residue was puriﬁed by ﬂash column chromatography on silica gel

using cyclohexane/CH₂Cl₂(10/1) as eluent, aﬀording hydrosilane

(S)-28 (16 mg, 41 μmol, 43%, 98% ee) as a colorless sticky oil. R_f=

0.18 (cyclohexane/CH₂Cl₂10/1). GLC (HP-5): t_R= 25.7 min. IR

(ATR): nu(tilde) = 3047 (m), 2957 (m), 2921 (m), 2287 (w), 2111

(m), 1911 (w), 1813 (w), 1772 (w), 1590 (w), 1548 (w), 1499 (m),

1

reaction was monitored by H NMR spectroscopy, and another batch

of palladium on activated charcoal (10 wt %, 0.486 g, 0.439 mmol, 10.0

mol % based on (R)-22) was added after 18 h. The suspension was

stirred for further 66 h. After cooling to room temperature, the mixture

was ﬁltered through Celite, and the solvent was removed under

reduced pressure. The residue was puriﬁed by ﬂash column

chromatography on silica gel using cyclohexane/ethyl acetate (20/1)

as eluent, aﬀording amine (R)-24 (0.542 g, 1.91 mmol, 43% over two

steps) as a white solid. m.p.: 111 °C (CH₂Cl₂). R_f= 0.43

(cyclohexane/ethyl acetate 5/1). GLC (HP-5): t_R= 23.5 min. IR

(ATR): nu(tilde) = 3481 (w), 3387 (w), 3195 (w), 3045 (w), 1916

(w), 1826 (w), 1613 (s), 1505 (m), 1471 (m), 1430 (m), 1377 (w),

1352 (m), 1258 (w), 1145 (w), 1024 (w), 903 (w), 811 (s), 751 (s)

cm⁻¹. HRMS (ESI) calculated for C₂₁H₁₇N [M]⁺: 283.1361; found:

1

283.1352. H NMR (500 MHz, CDCl₃): δ 2.15 (s, 3H), 3.51 (br s,

2H), 6.89 (m_c, 1H), 7.13 (m_c, 1H), 7.16 (m_c, 1H), 7.22 (m_c, 1H),

7.24−7.26 (m, 2H), 7.42 (m_c, 1H), 7.55 (m_c, 1H), 7.80 (m_c, 2H), 7.90

(m_c, 2H). ¹³C NMR (126 MHz, CDCl₃): δ 20.1, 116.4, 118.2, 122.4,

124.1, 125.3, 125.7, 126.5, 126.7, 128.1, 128.16, 128.18, 128.3, 129.1,

129.2, 132.2, 132.8, 132.9, 133.9, 136.2, 141.7.

(R)-2-Iodo-2′-methyl-1,1′-binaphthalene [(R)-25]. To a sus-

pension of amine (R)-24 (0.30 g, 1.1 mmol, 1.0 equiv) in concentrated

hydrochloric acid (37%, 1 mL) cooled to 0 °C was slowly added a

solution of NaNO₂(0.16 g, 2.3 mmol, 2.2 equiv) in water (3 mL). The

mixture was warmed to room temperature, stirred for 2.5 h, and

cooled back to 0 °C. To this mixture was added a solution of KI (1.8 g,

11 mmol, 10 equiv) in water (9 mL) dropwise. The resulting mixture

was allowed to warm to room temperature and stirred overnight. The

reaction was quenched by the addition of saturated aqueous Na₂SO₃

(5 mL), and the aqueous phase was extracted with CH₂Cl₂(3 × 5

mL). The combined organic phases were washed with saturated

aqueous NaCl (5 mL), dried over Na₂SO₄, and concentrated under

reduced pressure. The residue was puriﬁed by ﬂash column

chromatography on silica gel using cyclohexane/CH₂Cl₂(100/1) as

eluent, aﬀording iodide (R)-25 (0.18 g, 0.46 mmol, 43%) as a yellow

solid. m.p.: 133 °C (CH₂Cl₂). R_f= 0.24 (cyclohexane). GLC (HP-5):

t_R= 23.9 min. IR (ATR): nu(tilde) = 3039 (m), 2913 (w), 2846 (w),

2047 (w), 1996 (w), 1753 (w), 1573 (w), 1497 (m), 1408 (m), 1304

(w), 1255 (w), 1201 (m), 1129 (m), 1061 (w), 942 (m), 866 (w), 806

(s), 773 (m), 742 (s), 675 (m) cm⁻¹. HRMS (ESI) calculated for

3366

DOI: 10.1021/acs.organomet.5b00351

Organometallics 2015, 34, 3358−3373

Organometallics

Article

1449 (m), 1312 (m), 1245 (m), 1166 (w), 1110 (w), 1023 (m), 959

(w), 885 (s), 814 (s), 746 (s), 684 (m) cm⁻¹. HRMS (ESI) calculated

for C₂₅H₂₆SSi [M]⁺: 386.1524; found: 386.1508. ¹H NMR (500 MHz,

C₆D₆): δ −0.22 (d, J = 4.0 Hz, 3H), 0.05 (d, J = 4.0 Hz, 3H), 0.72 (t, J

= 7.3 Hz, 3H), 2.00 (m, 2H), 3.51 (d, J = 13.3 Hz, 1H), 3.56 (d, J =

13.3 Hz, 1H), 4.12 (sept, J = 3.8 Hz, 1H), 6.95 (m_c, 1H), 6.98 (m_c,

1H), 7.16−7.19 (m, 2H), 7.22 (m_c, 1H), 7.35 (m_c, 1H), 7.68 (m_c, 1H),

7.72 (m_c, 1H), 7.76 (m_c, 2H), 7.82 (m_c, 1H), 7.86 (m_c, 1H). ¹³C NMR

(126 MHz, C₆D₆): δ −3.3, −3.0, 14.4, 26.6, 34.9, 125.9, 126.5, 126.6,

126.9, 127.3, 127.4, 127.5, 127.7, 128.2, 128.3, 128.6, 131.1, 133.0,

133.3, 134.3, 134.6, 135.8, 136.3, 137.3, 143.8. ²⁹Si DEPT (99 MHz,

C₆D₆): δ −19.1. HPLC (Daicel Chiralcel OJ-RH, 20 °C, acetonitrile/

H₂O 60/40, ﬂow rate: 0.50 mL/min, λ = 254 nm): t_R= 41.9 min [(R)-

(2′-((ethylthio)methyl)-[1,1′-binaphthalen]-2-yl)dimethylsilane], t_R=

45.3 min [(S)-(2′-((ethylthio)methyl)-[1,1′-binaphthalen]-2-yl)-

dimethylsilane].

(S)-2′-Hydroxy-[1,1′-binaphthalen]-2-yl Triﬂuoromethane-

sulfonate. To a solution of (S)-BINOL [(S)-17, 5.00 g, 17.5

mmol, 1.00 equiv] in CH₂Cl₂(100 mL) cooled to 0 °C were added a

solution of N,N-diisopropylethylamine (3.05 mL, 2.26 g, 17.5 mmol,

1.00 equiv) in CH₂Cl₂(30 mL) and, at the same time, a solution of

triﬂuoromethanesulfonic anhydride (2.93 mL, 4.93 g, 17.5 mmol, 1.00

equiv) in CH₂Cl₂(30 mL) over a period of 30 min. The cooling bath

was removed, and the mixture was stirred at room temperature for 12

h. The mixture was washed with hydrochloric acid (2 M, 100 mL),

saturated aqueous NaHCO₃(100 mL), and saturated aqueous NaCl

(100 mL). The organic phase was dried over Na₂SO₄, and the solvent

was removed under reduced pressure. The residue was puriﬁed by

ﬂash column chromatography on silica gel using cyclohexane/CH₂Cl₂

(1/1) as eluent, aﬀording (S)-2′-hydroxy-[1,1′-binaphthalen]-2-yl

triﬂuoromethanesulfonate (6.79 g, 16.2 mmol, 93%) as a colorless

(R)-2-(Methoxymethoxy)-1,1′-binaphthalene [(R)-29]. To a

solution of (R)-[1,1′-binaphthalen]-2-ol (2.02 g, 7.47 mmol, 1.00

equiv) in THF (35 mL) cooled to 0 °C was added NaH (60 wt %,

0.448 g, 11.2 mmol, 1.50 equiv) portionwise. The resulting mixture

was stirred for 30 min at 0 °C. MOMBr (0.82 mL, 1.3 g, 9.0 mmol, 1.2

equiv) was added, and then the mixture was allowed to warm to room

temperature, followed by stirring for 12 h. The reaction was quenched

by the addition of water (25 mL), the phases were separated, and the

aqueous phase was extracted with tert-butyl methyl ether (3 × 35 mL).

The combined organic phases were washed with saturated aqueous

NaCl (30 mL), dried over MgSO₄, and concentrated under reduced

pressure. MOM-protected alcohol (R)-29 (2.32 g, 7.39 mmol, 99%)

was obtained as a pale yellow solid and used without further

puriﬁcation. m.p.: 157 °C (benzene). GLC (HP-5): t_R= 23.6 min. IR

(ATR): nu(tilde) = 3410 (w), 3037 (w), 2917 (s), 2848 (s), 2122 (w),

2050 (w), 1998 (w), 1826 (w), 1736 (w), 1685 (w), 1587 (m), 1502

(m), 1457 (m), 1367 (m), 1330 (m), 1240 (s), 1144 (s), 1028 (s),

1005 (vs), 894 (s), 781 (s), 690 (s) cm⁻¹. HRMS (ESI) calculated for

1

C₂₂H₁₈O₂[M]⁺: 314.1307; found: 314.1297. H NMR (500 MHz,

C₆D₆): δ 2.87 (s, 3H), 4.68 (s, 2H), 7.00−7.08 (m, 2H), 7.16−7.19

(m, 1H), 7.24 (m_c, 1H), 7.36−7.48 (m, 3H), 7.52 (m_c, 1H), 7.56 (m_c,

1H), 7.70 (m_c, 1H), 7.72−7.77 (m, 3H). ¹³C NMR (126 MHz, C₆D₆):

δ 55.6, 94.9, 117.1, 124.4, 125.3, 125.9, 126.0, 126.26, 126.27, 126.8,

126.9, 127.8, 128.0, 128.6, 128.9, 129.7, 130.3, 133.8, 134.4, 135.0,

135.4, 153.0.

(R)-2-(Methoxymethoxy)-3-methyl-1,1′-binaphthalene [(R)-

30]. To a solution of MOM-protected alcohol (R)-29 (1.11 g, 3.53

mmol, 1.00 equiv) in THF (39 mL) cooled to −78 °C was added

nBuLi (1.41 M in hexane fractions, 3.00 mL, 4.24 mmol, 1.20 equiv)

dropwise, and the resulting mixture was stirred for 1 h at 0 °C. Methyl

iodide (0.26 mL, 0.60 g, 4.2 mmol, 1.2 equiv) was added, and then the

mixture was allowed to warm to room temperature, followed by

stirring overnight. The reaction was quenched by the addition of

saturated aqueous NH₄Cl (15 mL) and water (15 mL). The phases

were separated, and the aqueous phase was extracted with tert-butyl

methyl ether (2 × 15 mL). The combined organic phases were washed

with saturated aqueous NaCl (15 mL), dried over Na₂SO₄, and

concentrated under reduced pressure. The title compound (R)-30

(1.12g, 3.41 mmol, 97%) was obtained as a pale yellow solid and used

without further puriﬁcation. m.p.: 89 °C (benzene). GLC (HP-5): t_R=

24.0 min. IR (ATR): nu(tilde) = 3043 (w), 2918 (s), 2851 (m), 2182

(w), 2070 (w), 1944 (w), 1588 (w), 1499 (w), 1441 (m), 1368 (m),

1331 (w), 1240 (m), 1200 (s), 1158 (s), 1094 (s), 1037 (m), 959 (vs),

926 (s), 890 (s), 796 (s), 777 (s) cm⁻¹. HRMS (ESI) calculated for

sticky oil. R_f= 0.22 (cyclohexane/CH₂Cl₂1/1). GLC (HP-5): t_R

=

23.3 min. IR (ATR): nu(tilde) = 3531 (w), 3060 (w), 2923 (w), 2850

(w), 2109 (w), 1908 (w), 1818 (w), 1760 (w), 1620 (m), 1595 (m),

1506 (m), 1473 (w), 1415 (s), 1345 (m), 1204 (vs), 1132 (vs), 1066

(m), 945 (s), 810 (s), 747 (s), 675 (s) cm⁻¹. HRMS (ESI) calculated

1

for C₂₁H₁₃F₃O₄S [M]⁺: 418.0487; found: 418.0477. H NMR (500

MHz, C₆D₆): δ 4.40 (s, 1H), 6.94 (m_c, 1H), 6.99 (m_c, 1H), 7.02 (m_c,

1H), 7.06−7.11 (m, 2H), 7.13 (m_c, 1H), 7.33 (m_c, 1H), 7.38 (m_c, 1H),

7.46 (m_c, 1H), 7.51 (m_c, 1H), 7.60 (m_c, 2H). ¹³C NMR (126 MHz,

C₆D₆): δ 112.5, 118.2, 118.8 (q, J = 320.8 Hz), 120.1, 124.0, 124.6,

126.0, 127.0, 127.4, 127.5, 128.3, 128.4, 128.6, 129.6, 131.4, 131.6,

133.2, 133.8, 133.9, 146.5, 152.4. The analytical and spectroscopic data

are in accordance with those reported.^20a

1

(R)-[1,1′-Binaphthalen]-2-ol. To a suspension of palladium on

activated charcoal (10 wt %, 1.27 g, 1.19 mmol, 10.0 mol %) in MeOH

(20 mL) were added N,N-diisopropylethylamine (4.15 mL, 3.08 g,

23.8 mmol, 2.00 equiv) and a solution of (S)-2′-hydroxy-[1,1′-

binaphthalen]-2-yl triﬂuoromethanesulfonate (4.99 g, 11.9 mmol, 1.00

equiv) in MeOH (30 mL). The atmosphere was changed to

dihydrogen (1 atm), and the mixture was stirred at room temperature

for 60 h. The mixture was ﬁltered through Celite, the residue was

rinsed with ethyl acetate (20 mL), and the solvent was removed under

reduced pressure. The residue was puriﬁed by ﬂash column

chromatography on silica gel using cyclohexane/ethyl acetate (20/1)

as eluent, aﬀording (R)-[1,1′-binaphthalen]-2-ol (2.22 g, 8.20 mmol,

69%) as a white solid. m.p.: 170 °C (CH₂Cl₂). R_f= 0.50 (cyclohexane/

ethyl acetate 5/1). GLC (HP-5): t_R= 22.7 min. IR (ATR): nu(tilde) =

3522 (w), 3049 (w), 2918 (w), 1929 (w), 1813 (w), 1616 (w), 1587

(w), 1500 (w), 1465 (w), 1434 (w), 1380 (m), 1344 (w), 1267 (m),

1186 (m), 1141 (m), 1071 (w), 1012 (w), 968 (m), 935 (m), 864 (w),

777 (s), 750 (s), 677 (m) cm⁻¹. HRMS (ESI) calculated for C₂₀H₁₄O

C₂₃H₂₀O₂[M]⁺: 328.1463; found: 328.1452. H NMR (500 MHz,

C₆D₆): δ 2.50 (s, 3H), 2.70 (s, 3H), 4.45 (d, J = 5.7 Hz, 1H), 4.50 (d, J

= 5.7 Hz, 1H), 6.98 (m_c, 1H), 7.04 (m_c, 1H), 7.21 (m_c, 2H), 7.30−7.35

(m, 2H), 7.39 (m_c, 1H), 7.52 (m_c, 1H), 7.61 (s, 1H), 7.67−7.73 (m,

3H). ¹³C NMR (126 MHz, C₆D₆): δ 18.0, 56.3, 99.3, 125.2, 125.7,

125.8, 126.1, 126.5, 127.1, 127.5, 128.2, 128.3, 128.4, 129.50, 129.51,

130.0, 131.6, 132.0, 133.7 (2C), 134.2, 135.3, 153.5.

(R)-3-Methyl-[1,1′-binaphthalen]-2-ol [(R)-31]. To a solution of

(R)-30 (2.0 g, 6.1 mmol, 1.0 equiv) in 1,4-dioxane (15 mL) was added

concentrated hydrochloric acid (37%, 0.27 mL), and the resulting

mixture was stirred for 72 h at 50 °C. After cooling to room

temperature, the reaction was poured into water (30 mL). The phases

were separated, and the aqueous phase was extracted with ethyl acetate

(3 × 25 mL). The combined organic phases were washed with

saturated aqueous NaCl (15 mL) and dried over Na₂SO₄, and the

solvent was removed under reduced pressure. Alcohol (R)-31 (1.7 g,

6.0 mmol, 98%) was obtained as a white solid and used without further

puriﬁcation. m.p.: 145 °C (CH₂Cl₂). GLC (HP-5): t_R= 23.3 min. IR

(ATR): nu(tilde) = 3537 (vs), 3054 (w), 2915 (w), 2847 (w), 2732

(w), 2064 (w), 1939 (w), 1825 (w), 1621 (w), 1587 (w), 1501 (w),

1423 (w), 1383 (m), 1188 (s), 1137 (m), 1099 (m), 1061 (w), 938

(w), 853 (w), 800 (s), 749 (s), 686 (m) cm⁻¹. HRMS (ESI) calculated

1

[M]⁺: 270.1039; found: 270.1042. H NMR (500 MHz, CDCl₃): δ

4.89 (s, 1H), 7.11 (m_c, 1H), 7.24 (m_c, 1H), 7.31−7.37 (m, 3H), 7.38−

7.42 (m, 1H), 7.51−7.57 (m, 2H), 7.67 (m_c, 1H), 7.87 (m_c, 1H), 7.91

(m_c, 1H), 7.99 (m_c, 1H), 8.04 (m_c, 1H). ¹³C NMR (126 MHz,

CDCl₃): δ 117.6, 118.9, 123.5, 125.1, 125.9, 126.2, 126.69, 126.71,

127.0, 128.2, 128.6, 129.1, 129.4, 129.8, 130.0, 131.6, 133.0, 134.0,

134.4, 151.1. The analytical and spectroscopic data are in accordance

with those reported.³¹

1

for C₂₁H₁₆O [M]⁺: 284.1201; found: 284.1193. H NMR (500 MHz,

C₆D₆): δ 2.48 (s, 3H), 4.85 (s, 1H), 7.00 (m_c, 2H), 7.14 (m_c, 1H),

7.17−7.27 (m, 4H), 7.49 (m_c, 1H), 7.57 (s, 1H), 7.86 (m_c, 3H). ¹³C

NMR (126 MHz, C₆D₆): δ 17.2, 118.7, 123.7, 125.3, 126.1, 126.3,

3367

DOI: 10.1021/acs.organomet.5b00351

Organometallics 2015, 34, 3358−3373

Organometallics

Article

126.4, 126.8, 126.9, 127.2, 127.7, 128.3, 129.3, 129.6, 129.9 (2C),

132.5, 133.5 (2C), 134.7, 150.8. Anal. Calcd for C₂₁H₁₆O: C, 88.70; H,

5.67. Found: C, 88.74; H, 5.68.

(5 mL), and the aqueous phase was extracted with CH₂Cl₂(3 × 5

mL). The combined organic phases were washed with saturated

aqueous NaCl (15 mL), dried over Na₂SO₄, and concentrated under

reduced pressure. The residue was puriﬁed by ﬂash column

chromatography on silica gel using cyclohexane/CH₂Cl₂(100/1) as

eluent, aﬀording iodide (R)-35 (0.28 g, 0.72 mmol, 68%) as a yellow

solid. m.p.: 160 °C (chloroform). R_f= 0.25 (cyclohexane). GLC (HP-

5): t_R= 25.0 min. IR (ATR): nu(tilde) = 3054 (w), 2940 (w), 2915

(w), 2849 (w), 2121 (w), 2070 (w), 2024 (w), 1931 (w), 1815 (w),

1578 (m), 1502 (m), 1430 (m), 1360 (m), 1314 (m), 1254 (s), 1189

(m), 982 (m), 883 (m), 777 (s), 750 (s) cm⁻¹. HRMS (ESI)

(R)-3-Methyl-[1,1′-binaphthalen]-2-yl Triﬂuoromethane-

sulfonate [(R)-32]. To solution of alcohol (R)-31 (1.5 g, 5.3 mmol,

1.0 equiv) in CH₂Cl₂(12 mL) cooled to 0 °C were added N,N-

diisopropylethylamine (1.2 mL, 0.89 g, 6.9 mmol, 1.3 equiv) and

subsequently triﬂuoromethanesulfonic anhydride (1.0 mL, 1.7 g, 5.8

mmol, 1.1 equiv). The cooling bath was removed, and then the

mixture was stirred at room temperature for 12 h. The mixture was

washed with hydrochloric acid (2 M, 15 mL), saturated aqueous

NaHCO₃(15 mL), and saturated aqueous NaCl (15 mL). The organic

phase was dried over Na₂SO₄, and the solvent was removed under

reduced pressure. The residue was puriﬁed by ﬂash column

chromatography on silica gel using cyclohexane/ethyl acetate (20/1)

as eluent, aﬀording triﬂate (R)-32 (1.8 g, 4.4 mmol, 82%) as a white

solid. m.p.: 75 °C (benzene). R_f= 0.55 (cyclohexane/ethyl acetate 5/

1). GLC (HP-5): t_R= 23.1 min. IR (ATR): nu(tilde) = 3059 (w),

2219 (w), 2061 (w), 1591 (w), 1501 (w), 1326 (w), 1199 (vs), 1128

(s), 1079 (m), 936 (s), 885 (s), 818 (s), 777 (s), 749 (s), 666 (m)

cm⁻¹. HRMS (ESI) calculated for C₂₂H₁₅F₃O₃S [M]⁺: 416.0694;

1

calculated for C₂₁H₁₅I [M]⁺: 394.0218; found: 394.0209. H NMR

(500 MHz, CDCl₃): δ 2.74 (s, 3H), 7.11 (m_c, 1H), 7.16−7.21 (m,

2H), 7.30 (m_c, 1H), 7.36 (m_c, 1H), 7.44−7.51 (m, 2H), 7.64 (m_c, 1H),

7.83 (m_c, 1H), 7.86 (m_c, 1H), 7.98 (m_c, 1H), 8.01 (m_c, 1H). ¹³C NMR

(126 MHz, CDCl₃): δ 30.2, 108.1, 125.8, 125.9, 126.1, 126.2, 126.4,

126.6, 127.3, 127.45, 127.51, 128.1, 128.3, 128.5, 132.0, 132.3, 133.2,

133.9, 138.5, 142.2, 143.8.

(R)-3-(Bromomethyl)-2-iodo-1,1′-binaphthalene [(R)-36]. Io-

dide (R)-35 (0.11 g, 0.28 mmol, 1.0 equiv), NBS (60 mg, 0.34 mmol,

1.2 equiv), and benzoyl peroxide (68 mg, 0.28 mmol, 1.0 equiv) were

dissolved in benzene (5 mL). The resulting mixture was heated to

reﬂux for 3 h. After cooling to room temperature, the solvent was

removed under reduced pressure. The residue was puriﬁed by ﬂash

column chromatography on silica gel using cyclohexane/CH₂Cl₂(10/

1) as eluent, aﬀording benzyl bromide (R)-36 (94 mg, 0.20 mmol,

71%) as a white solid. m.p.: 183 °C (CH₂Cl₂). R_f= 0.33 (cyclohexane/

CH₂Cl₂10/1). GLC (HP-5): t_R= 29.0 min. IR (ATR): nu(tilde) =

3054 (m), 2920 (m), 2848 (m), 2123 (w), 2021 (w), 1954 (w), 1804

(w), 1610 (w), 1572 (m), 1486 (m), 1430 (m), 1358 (m), 1281 (m),

1210 (s), 1131 (w), 1072 (w), 988 (m), 859 (w), 772 (s), 752 (s)

cm⁻¹. HRMS (ESI) calculated for C₂₁H₁₄BrI [M]⁺: 471.9324; found:

1

found: 416.0676. H NMR (500 MHz, C₆D₆): δ 2.47 (s, 3H), 6.90

(m_c, 1H), 7.04 (m_c, 1H), 7.17−7.18 (m, 1H), 7.20 (m_c, 1H), 7.28 (m_c,

1H), 7.31 (m_c, 1H), 7.36 (m_c, 3H), 7.52 (m_c, 1H), 7.68 (m_c, 1H), 7.73

(m_c, 1H). ¹³C NMR (126 MHz, C₆D₆): δ 18.3, 117.3, 118.6 (q, J =

320.1 Hz), 125.5, 126.1, 126.3, 126.8, 127.2, 127.4, 127.6, 128.6, 129.5,

129.6, 129.9, 131.2, 131.4, 131.8, 133.1, 133.16, 133.18, 134.2, 145.5.

(R)-3-Methyl-[1,1′-binaphthalen]-2-amine [(R)-34]. Triﬂate

(R)-32 (1.5 g, 3.6 mmol, 1.0 equiv), Pd(OAc)₂(0.20 g, 0.90 mmol,

0.25 equiv), rac-BINAP (0.67 g, 1.1 mmol, 0.30 equiv), and Cs₂CO₃

(3.3 g, 10 mmol, 2.8 equiv) were dissolved in dry 1,4-dioxane (15 mL).

To that suspension was added benzylamine (1.94 mL, 1.90 g, 18.0

mmol, 5.00 equiv), and the resulting mixture was degassed (three

freeze−pump−thaw cycles). The mixture was stirred at 80 °C for 90 h.

After cooling to room temperature, the mixture was ﬁltered through

Celite, and the solvent was removed under reduce pressure. The crude

benzylamine (R)-33 was directly used in the next step without

puriﬁcation. A solution of crude (R)-33 in ethyl acetate (60 mL) was

added to palladium on activated charcoal (10 wt %, 0.40 g, 0.38 mmol,

10 mol % based on (R)-32). The atmosphere was changed to

dihydrogen (1 atm), and the mixture was stirred at 40 °C. The

1

471.9310. H NMR (500 MHz, C₆D₆): δ 4.56 (d, J = 10.2 Hz, 1H),

4.59 (d, J = 10.2 Hz, 1H), 6.84 (m_c, 1H), 7.00 (m_c, 1H), 7.08 (m_c,

1H), 7.11−7.15 (m, 2H), 7.18−7.24 (m, 2H), 7.33 (m_c, 1H), 7.50 (m_c,

1H), 7.61 (s, 1H), 7.71 (m_c, 1H), 7.75 (m_c, 1H). ¹³C NMR (126 MHz,

C₆D₆): δ 41.0, 105.5, 125.96, 126.03, 126.4, 126.9, 127.1, 127.8, 127.9,

128.2, 128.3, 128.7 (2C), 129.7, 132.4, 133.3, 133.8, 134.3, 137.6,

142.1, 145.7.

(R)-Ethyl((2-iodo-[1,1′-binaphthalen]-3-yl)methyl)sulfane

[(R)-37]. Benzyl bromide (R)-36 (94 mg, 0.20 mmol, 1.0 equiv) was

dissolved in ethanol (1.4 mL). K₂CO₃(55 mg, 0.40 mmol, 2.0 equiv)

and ethanethiol (29 μL, 25 mg, 0.40 mmol, 2.0 equiv) were added, and

the resulting mixture was stirred overnight at 45 °C. After cooling to

room temperature, the reaction was quenched by the addition of water

(3 mL). The phases were separated, and the aqueous phase was

extracted with CH₂Cl₂(2 × 2 mL). The combined organic phases

were washed with aqueous NaOH (2 M, 2 mL) and saturated aqueous

NaCl (2 mL), dried over Na₂SO₄, and concentrated under reduced

pressure. Ethyl thioether (R)-37 (82 mg, 0.18 mmol, 91%) was

obtained as a colorless sticky oil and used without further puriﬁcation.

GLC (HP-5): t_R= 30.8 min. IR (ATR): nu(tilde) = 3053 (m), 2964

(m), 2920 (m), 2867 (w), 2244 (w), 2049 (w), 1929 (w), 1812 (w),

1703 (w), 1577 (m), 1490 (m), 1448 (m), 1362 (m), 1317 (w), 1256

(m), 1131 (w), 1024 (m), 987 (m), 905 (s), 774 (s), 728 (s) cm⁻¹.

HRMS (ESI) calculated for C₂₃H₁₉IS [M]⁺: 454.0252; found:

1

reaction was monitored by H NMR spectroscopy, and another batch

of palladium on activated charcoal (10 wt %, 0.40 g, 0.39 mmol, 10

mol % based on (R)-32) was added after 16 h. The suspension was

stirred for a further 24 h. After cooling to room temperature, the

mixture was ﬁltered through Celite, and the solvent was removed

under reduced pressure. The residue was puriﬁed by ﬂash column

chromatography on silica gel using cyclohexane/ethyl acetate (20/1)

as eluent, aﬀording amine (R)-34 (0.75 g, 2.7 mmol, 71% over two

steps) as a white solid. m.p.: 228 °C (chloroform). R_f= 0.44

(cyclohexane/ethyl acetate 5/1). GLC (HP-5): t_R= 24.3 min. IR

(ATR): nu(tilde) = 3375 (w), 3055 (w), 2853 (w), 1936 (w), 1625

(m), 1499 (m), 1430 (m), 1383 (m), 1275 (m), 1214 (m), 1154 (w),

1011 (m), 887 (m), 852 (w), 783 (s), 748 (s) cm⁻¹. HRMS (ESI)

1

calculated for C₂₁H₁₇N [M]⁺: 283.1361; found: 283.1353. H NMR

(500 MHz, CDCl₃): δ 2.45 (s, 3H), 3.58 (s, 2H), 6.95 (m_c, 1H), 7.12

1

(m_c, 1H), 7.21 (m_c, 1H), 7.31 (m_c, 1H), 7.39 (m_c, 1H), 7.47−7.52 (m,

454.0238. H NMR (500 MHz, CDCl₃): δ 1.35 (t, J = 7.6 Hz, 3H),

2H), 7.65 (m_c, 1H), 7.69 (m_c, 1H), 7.74 (m_c, 1H), 7.98 (m_c, 2H). ¹³

C

2.65 (q, J = 7.6 Hz, 2H), 4.13 (d, J = 13.8 Hz, 1H), 4.16 (d, J = 13.8

Hz, 1H), 7.11 (m_c, 1H), 7.17 (m_c, 1H), 7.21 (m_c, 1H), 7.30 (m_c, 1H),

7.37 (m_c, 1H), 7.48 (m_c, 2H), 7.64 (m_c, 1H), 7.88 (m_c, 1H), 7.95 (s,

1H), 7.97 (m_c, 1H), 8.01 (m_c, 1H). ¹³C NMR (126 MHz, CDCl₃): δ

14.8, 26.2, 43.2, 106.9, 125.7, 125.9, 126.2, 126.5, 126.8, 126.9, 127.6,

127.7, 128.0, 128.1, 128.4, 128.5, 132.0, 132.8, 132.9, 133.8, 137.6,

142.1, 144.8.

(R)-(3-((Ethylthio)methyl)-[1,1′-binaphthalen]-2-yl)dimethyl-

silane [(R)-38]. To a solution of ethyl thioether (R)-37 (60 mg, 0.13

mmol, 1.0 equiv) in THF (1.6 mL) cooled to −78 °C was added

nBuLi (2.2 M in hexane fractions, 80 μL, 0.17 mmol, 1.3 equiv)

dropwise, and the resulting mixture was stirred for 1 h at −78 °C.

Me₂Si(H)Cl (19 μL, 16 mg, 0.17 mmol, 1.3 equiv) was added, and

NMR (126 MHz, CDCl₃): δ 18.6, 117.5, 122.3, 124.5, 125.1, 125.5,

126.1, 126.3, 126.4, 126.5, 127.3, 128.0, 128.3, 128.5, 128.7, 129.2,

132.7, 133.4, 134.4, 135.3, 141.4.

(R)-2-Iodo-3-methyl-1,1′-binaphthalene [(R)-35]. To a suspen-

sion of amine (R)-34 (0.30 g, 1.1 mmol, 1.0 equiv) in concentrated

hydrochloric acid (37%, 1 mL) cooled to 0 °C was slowly added a

solution of NaNO₂(0.16 g, 2.3 mmol, 2.2 equiv) in water (3 mL). The

mixture was warmed to room temperature, stirred for 2.5 h, and

cooled to 0 °C. To this mixture, a solution of KI (1.8 g, 11 mmol, 10

equiv) in water (9 mL) was added dropwise. The resulting mixture was

allowed to warm to room temperature and stirred overnight. The

reaction was quenched by the addition of saturated aqueous Na₂SO₃

3368

DOI: 10.1021/acs.organomet.5b00351

Organometallics 2015, 34, 3358−3373