Electrophilicities of symmetrically substituted 1,3-diarylallyl cations

ARTICLE

pubs.acs.org/joc

Electrophilicities of Symmetrically Substituted 1,3-Diarylallyl Cations

Konstantin Troshin, Claus Schindele, and Herbert Mayr*

Department Chemie, Ludwig-Maximilians-Universit€at M€unchen, Butenandtstrasse 5-13 (Haus F), 81377 M€unchen, Germany

S Supporting Information

b

ABSTRACT: Kinetics of the reactions of nine symmetrically

substituted 1,3-diarylallyl cations with diﬀerent nucleophiles

were studied photometrically in dichloromethane, acetonitrile,

and DMSO solutions. The second-order rate constants k₂were

found to follow the correlation log k₂= s_N(N + E). The

electrophilicity parameters E of the title cations were derived, using the known values of s_Nand N of the nucleophilic reaction

partners, and compared with the electrophilicities of analogously substituted benzhydrylium ions. Good linear correlations were

found between the electrophilicities E and the quantum chemically calculated gas-phase methyl anion aﬃnities of the allyl cations

and the σ⁺constants of the substituents X.

’ INTRODUCTION

We have now studied the reactions of nine symmetrically

substituted 1,3-diarylallyl cations 1(aꢀi) with nucleophiles

2(aꢀu) in order to derive the electrophilicity parameters E of

these carbocations, which we will employ in subsequent work for

elucidating solvolysis mechanisms⁴of allyl derivatives and for

investigating the eﬀect of palladium coordination in the inter-

mediates of TsujiꢀTrost reactions.¹¹The resulting E parameters

can also be used for designing new synthetic procedures as well as

for better understanding of known reactions via intermediate

1,3-diarylallyl cations, e.g., catalytic S_N1-type reactions of alco-

hols, which are relevant for designing environmentally benign

processes.¹²

Nucleophilic substitutions of allyl derivatives not only give

products where the nucleofuge is directly displaced by the

nucleophile but also may proceed with allylic rearrangement.¹

While concerted S_N2⁰reactions are rare or do not exist,²allylic

rearrangements via additionꢀelimination reactions are well-

established.³Of particular interest are allylic rearrangements

via intermediate allyl cations, i.e., S_N1 reactions. Because of the

possibility of internal return at both termini of the allylic system,

allyl solvolyses provide detailed information on the nature of ion

pairs, which cannot be derived from solvolyses of other S_N1

substrates.

Goering’s pioneering studies on the solvolyses of optically

active allyl derivatives using titrimetric, polarimetric, and isotope

exchange methods made it possible to diﬀerentiate various steps

of the multistep solvolytic processes.⁴However, a comprehensive

model, which explains the mechanistic changes caused by

structural modiﬁcations of the substrates and the solvent, re-

mained elusive.

In recent work, we have demonstrated that knowledge of the

absolute rate constants for the reactions of carbocations with

leaving groups (ion recombination) and other nucleophiles (e.g.,

solvents) allows one not only to predict whether solvolyses will

proceed with or without common ion return⁵but also to deﬁne

the border between S_N1 and S_N2 mechanisms.⁶Key to these

analyses was the linear free energy relationship (eq 1), where E is

an electrophilicity parameter, N is a nucleophilicity parameter,

and s_Nis a nucleophile-speciﬁc sensitivity parameter (previously

termed s).⁷

’ RESULTS AND DISCUSSION

Synthesis of 1,3-Diarylallyl Cations 1(aꢀi). Cations 1(aꢀf)

cannot be stored as stable salts; they were generated in solution

either by treatment of the corresponding chlorides 1-Cl or

trimethylsilyl ethers 1-OTMS with Lewis acids or by laser-

flash photolysis of the corresponding phosphonium salts 1-

+

ꢀ

+

PPh₃BF₄or 1-PPh₃TfO^ꢀas illustrated in Scheme 1.¹³

The diarylallyl tetrafluoroborates 1(gꢀi)-BF₄were obtained

as stable salts by treatment of the corresponding alcohols

1(gꢀi)-OH with HBF₄OEt₂or AcOH/NaBF₄as described

3

in the Experimental Section. All allyl cations 1(aꢀi) were

characterized by UVꢀvis spectroscopy (Table 1).

As shown in Supplementary Figure SX1 of the Supporting

Information, the UVꢀvis spectrum of cation 1e, generated

photolytically from (E)-(1,3-diphenylallyl)triphenylphosphonium

triﬂate in dichloromethane, was identical to that of 1e, generated

from (E)-((1,3-diphenylallyl)oxy)trimethylsilane and trimethylsilyl

triﬂate in the same solvent.

log k₂ð20 °CÞ ¼ s_NðN þ EÞ

ð1Þ

By deﬁning diarylmethyl (benzhydryl) cations and a set of

C-nucleophiles as reference compounds, we have succeeded in

arranging a large variety of electrophiles and nucleophiles in

electrophilicity and nucleophilicity scales.^8ꢀ10

Received: August 17, 2011

Published: September 22, 2011

r

2011 American Chemical Society

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Scheme 1. Generation of Allyl Cations 1(aꢀi)^a

^aFor deﬁnition of X see Table 1.

Table 1. Cations 1(aꢀi) and Their UVꢀvis Maxima in

Diﬀerent Solvents

Figure 1. ¹H NMR spectra of 1h-BF₄taken at diﬀerent temperatures.

Scheme 2

X

conditions

λ_max/nm

log ε

1a

1b

1c

m,m-F₂

m-F

1a-OH/conc H₂SO₄

1b-OH/conc H₂SO₄

1c-Cl/GaCl₃/CH₂Cl₂

1c-OH/conc H₂SO₄

1d-OH/AcOH

496

500

551

527

530

503

488

532

578

693

704

730

740

p-Br

∼5.16

1d

1e

p-Cl

H

1e-OTMS/TMSOTf/CH₂Cl₂

1e-OH/AcOH

5.16

1f

p-Me

1f-OTMS/TMSOTf/CH₂Cl₂

1g-BF₄/CH₂Cl₂

5.25

5.26

5.31

1g

1h

p-OMe

p-NMe₂

1h-BF₄/CH₃CN

1h-BF₄/CH₂Cl₂

The zinc chloride catalyzed reaction of 2,3-dimethylbut-2-ene

(2a) with 1e-Cl provided a complex product mixture, which was

not identiﬁed. When the reaction was carried out in the presence

of tetrabutylammonium chloride, a mixture of only two products,

(E)-(5-chloro-4,4,5-trimethylhex-1-ene-1,3-diyl)dibenzene (3a)

and (E)-(4,4,5-trimethylhexa-1,5-diene-1,3-diyl)dibenzene (3a⁰),

was formed (Scheme 2). Pure 3a⁰(35% yield) was obtained by

column chromatography of the crude product; as the isolated yield

of 3a⁰was higher than its content in the crude mixture, one can

conclude that 3a eliminates HCl on silica.

Under the same conditions, the reaction of 1e-Cl with 2,3-

dimethylbut-1-ene (2b) gave (E)-(5-chloro-5,6-dimethylhept-1-

ene-1,3-diyl)dibenzene as a mixture of two diastereomers (dr ca.

1.4: 1, ¹H NMR) contaminated by small amounts of byproducts.

In the case of 2-methylpent-1-ene (2c), the addition of

Bu₄NCl is not necessary, and the major product of the reaction

with 1e-Cl can be unambiguously identiﬁed as (E)-(5-chloro-5-

methyloct-1-ene-1,3-diyl)dibenzene (3c, 1.4:1 mixture of two

1i

jul^a

1i-BF₄/CH₃CN

5.34

1i-BF₄/CH₂Cl₂

^aFor structure, see heading of this table.

In addition, the stable cations 1(gꢀi) were identiﬁed by NMR

spectroscopy and HRMS (see Experimental Section). ¹H NMR

spectra of 1h-BF₄taken at diﬀerent temperatures allow determi-

nation of the barrier of rotation around the C2ꢀC3 bond in the

allyl cation 1h (Figure 1). From the coalescence temperature¹⁴of

a

b

0

H and H ⁰at ꢀ10 °C and for H and H at ꢀ20 °C, one derives

rotational barriers of 50.5 ( 2 and 52 ( 2 kJmol^ꢀ1, respectively.

The structure of 1h-BF₄was also conﬁrmed by X-ray analysis.¹⁵

Product Studies. As the nature of the reaction products can be

expected not to depend on the substituents X of the aryl groups

of 1(aꢀi), product studies were performed with only one repre-

sentative electrophile for each nucleophile.

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Scheme 3

Scheme 6

Scheme 7

Scheme 4

Scheme 8

Scheme 5

diastereomers, ¹H NMR). Additional signals between δ 4.5 and

1

6.0 ppm in the H NMR spectrum indicate the formation of

dienes, which may be produced via proton elimination from the

intermediate carbocation.

The combinations of allylsilanes 2(dꢀf) and of allyltriphenyl-

stannane (2g) with 1e or 1g aﬀorded the S_E2⁰products 3(dꢀf)

with moderate to good yields (Scheme 3). Similar results were

previously reported for the reaction of 1e-OH with 2e under

polymer-supported Brønsted acid catalysis.¹⁶

Silyl enol ethers and ketene acetals 2(hꢀk) react with the

allylium tetraﬂuoroborates 1g-BF₄and 1h-BF₄to form the corres-

ponding carbonyl compounds 3(hꢀk) (Scheme 4). The low yield

of the reaction of 1g-BF₄with 2h is probably due to decomposi-

tion of 3h on the silica column, as the same phenomenon

was also observed for the structurally analogous compound 3n⁰

(see below). The substituted cyclic ketones 3h and 3i were formed

as mixtures of diastereomers with dr of 1.3:1 and 1.9:1, respectively

(based on the ¹H NMR spectra of the crude products).

Dimethylphenylsilane (2l) reduces 1g-BF₄to yield 82% of (E)-

4,4⁰-(prop-1-ene-1,3-diyl)bis(methoxybenzene) (3l, Scheme 5).

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Scheme 9

Slow addition of a suspension of 1g-BF₄in CH₂Cl₂to 10 equiv

of 1-methyl-1H-pyrrole (2m) leads to a 9:1 mixture of (E)-

2-(1,3-bis(4-methoxyphenyl)allyl)-1-methyl-1H-pyrrole (3m)

and 2,5-bis((E)-1,3-bis(4-methoxyphenyl)allyl)-1-methyl-1H-

pyrrole (3m⁰) (Scheme 6). The formation of the disubstituted

product 3m⁰even in the presence of a high excess of 2m can be

explained by mixing control,¹⁷i.e., the diﬀusional separation of

3m from the sparsely soluble crystals of 1g-BF₄is slow compared

with the reaction of 1g-BF₄with 3m (k₂> 10⁵M^ꢀ1s^ꢀ1).

The enamines 2n and 2o react with the allylium tetraﬂuoro-

borate 1h-BF₄to form the iminium salts 3(n,o)-BF₄

(characterized by NMR and HRMS) as mixtures of diastereo-

1

mers (dr ca. 1.2:1, H NMR); their hydrolysis with aqueous

Figure 2. (a) Exponential decay of the absorbance A_t(λ = 500 nm) and

(b) correlation between the pseudo-ﬁrst-order rate constants k_obsand

the concentration of 2f for the reaction between (2-methylallyl)tri-

methylsilane (2f) and the cation 1b generated by laser-ﬂash photolysis

acetic acid aﬀords (E)-2-(1,3-bis(4-(dimethylamino)phenyl)allyl)-

cyclohexanone (3n⁰, 23%) and (E)-2-(1,3-bis(4-(dimethylamino)-

phenyl)allyl)cyclopentanone (3o⁰, 54%) (Scheme 7). The low

yield of 3n⁰must be due to its partial decomposition on silica, as

its precursor 3n is formed almost quantitatively (¹H NMR).

Amines 2(pꢀt) react with 1h-BF₄and 1i-BF₄to form (E)-1,3-

diarylallylamines 3(pꢀt) in good yields (Scheme 8).

+

from 1b-PPh₃BF₄^ꢀ(dichloromethane, 20 °C).

All kinetics were performed under pseudo-ﬁrst-order condi-

tions using the nucleophiles in high excess, resulting in the

monoexponential decays of the electrophiles' absorbances.

The pseudo-ﬁrst-order rate constants (k_obs) were obtained by

least-squares ﬁtting of the time-dependent absorbances (A_t) to

The combination of 1h-BF₄with 5 equiv of the potassium

salt of Meldrum’s acid (K-2u) aﬀords (E)-5-(1,3-bis(4-

(dimethylamino)phenyl)allyl)-2,2-dimethyl-1,3-dioxane-4,6-dione

(3u) and 5,5-bis((E)-1,3-bis(4-(dimethylamino)phenyl)allyl)-2,

2-dimethyl-1,3-dioxane-4,6-dione (3u⁰) in 24% and 39% yield,

respectively (Scheme 9). Obviously, 3u is deprotonated under

the reaction conditions and then reacts with a second equivalent

of 1h to yield 3u⁰. The formation of the double-alkylation

product 3u⁰indicates that the anion formed by deprotonation

of 3u is more reactive than 2u. The bisadduct 3u⁰is formed

exclusively (85% yield of isolated 3u⁰) when Meldrum’s acid is

combined with 2 equiv of 1h-BF₄in the presence of 2 equiv of

potassium tert-butoxide.

_obst

the monoexponential function A_t= A₀e^ꢀk+ C (Figure 2a).

The plots of the k_obsvalues versus the nucleophile concentrations

were linear (Figure 2b), and their slopes yielded the second-

order rate constants (k₂), which are summarized in Table 2.

In order to examine whether the rate constants depend on the

nature of the counterions, the reaction of 1e with the cyclohex-

anone-deri_ꢀved silyl enol ether 2h was studied with 1e-

PPh₃BF₄and 1e-PPh₃TfO^ꢀas precursors. The very small

diﬀerence between the resulting rate constants k₂(BF₄^ꢀ) = 6.41 ꢁ

10⁷M^ꢀ1s^ꢀ1and k₂(TfO^ꢀ) = 6.57 ꢁ 10⁷M^ꢀ1s^ꢀ1conﬁrms the

independence of k₂of the counterion, as previously found for

analogous reactions with benzhydrylium ions.¹⁸

+

Kinetic Experiments. For the investigations of the reactiv-

ities of the carbenium ions 1(gꢀi), stock solutions of the

isolated tetrafluoroborate salts were used; cations 1(aꢀf)

were generated in solution as described above. Most of the

reactions were studied at 20 °C; in some cases the k₂values for

20 °C were obtained from the Eyring activation parameters

derived from a series of low-temperature measurements. All

reactions were studied in those solvents to which the N and s_N

parameters of the nucleophiles refer: π-nucleophiles in di-

chloromethane, amines in acetonitrile, and the carbanion 2u

in DMSO.

The rates were determined by monitoring the decays of the

absorbances of the corresponding carbocations in the UVꢀvis

spectra. In case of slow reactions (τ_1/2> 3 s), conventional UVꢀvis

spectrophotometry was used, fast reactions (20 ms < τ_1/2< 3 s)

were followed with stopped-ﬂow devices, and very fast reactions

(τ_1/2< 1 ms) were investigated by generating the cations by

laser-ﬂash irradiation.¹³

Determination of the Electrophilicity Parameters E. Figure 3

shows plots of (log k₂)/s_Nversus N for the reactions of the

allyl cations 1(aꢀi) with the nucleophiles 2(aꢀu). Slopes of 1

were enforced in the drawn correlation lines, as required by eq 1.

The electrophilicity parameters E (Table 2) of the cations

1(aꢀi) were calculated by minimizing the sum of the squared

deviations Δ²= Σ(log k₂ꢀ s_N(N + E))²using the nonlinear

solver “What’s Best!”.¹⁹The good correlations shown in

Figure 3, which include rate constants determined in different

solvents, confirm that in 1,3-diarylallyl cations, as in benzhydrylium

ions, differential solvation of the carbocations is negligible, which

allows us to use the same electrophilicity parameters E in different

solvents. As explicitly explained in ref 7, the solvent effects on the

rate constants are fully incorporated in the nucleophile-specific

parameters N and s_N.

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Table 2. Second-Order Rate Constants for the Reactions of 1,3-Diarylallylium Ions 1(aꢀi) and Nucleophiles 2(aꢀu) at 20 °C

a

1,3-diarylallylium ion

generation of 1(aꢀi)

E^a

nucleophile/solvent

N, s_N

k₂/M^ꢀ1s^ꢀ1

k_calc^a/M^ꢀ1s^ꢀ1

k₂/k_calc

1a (X = m,m-F₂)

b

e

6.11

2a/CH₂Cl₂

2b/CH₂Cl₂

2c/CH₂Cl₂

2e/CH₂Cl₂

2f/CH₂Cl₂

2h/CH₂Cl₂

2e/CH₂Cl₂

2f/CH₂Cl₂

2d/CH₂Cl₂

2f/CH₂Cl₂

2h/CH₂Cl₂

2f/CH₂Cl₂

2c/CH₂Cl₂

2d/CH₂Cl₂

2f/CH₂Cl₂

2h/CH₂Cl₂

ꢀ1.00, 1.40

0.54, 1.00

0.96, 1.00

1.79, 0.94

4.41, 0.96

5.21, 1.00

1.79, 0.94

4.41, 0.96

ꢀ0.13, 1.21

4.41, 0.96

5.21, 1.00

4.41, 0.96

0.96, 1.00

ꢀ0.13, 1.21

4.41, 0.96

5.21, 1.00

3.56 ꢁ 10⁷

1.98 ꢁ 10⁶

9.11 ꢁ 10⁶

2.03 ꢁ 10⁷

5.88 ꢁ 10^8c

1.06 ꢁ 10^9c

6.99 ꢁ 10⁵

9.31 ꢁ 10⁷

2.93 ꢁ 10^3f

8.65 ꢁ 10⁶

7.86 ꢁ 10⁷

6.57 ꢁ 10⁶

2.88 ꢁ 10^3f

2.53 ꢁ 10^3f

5.94 ꢁ 10⁶

6.41 ꢁ 10^7b

6.54 ꢁ 10^7g

1.41 ꢁ 10⁷

4.43 ꢁ 10⁶

1.16 ꢁ 10⁷

2.64 ꢁ 10⁷

d

2.52

0.45

0.78

0.77

d

1b (X = m-F)

1c (X = p-Br)

4.15

2.85

3.86 ꢁ 10⁵

1.66 ꢁ 10⁸

1.98 ꢁ 10³

9.43 ꢁ 10⁶

1.16 ꢁ 10⁸

1.81

0.56

1.48

0.92

0.68

g

1d (X = p-Cl)

1e (X = H)

b

h

g

2.69

2.70

4.59 ꢁ 10³

1.29 ꢁ 10³

6.71 ꢁ 10⁶

8.15 ꢁ 10⁷

0.63

1.96

0.88

0.79

0.80

b

g

1f (X = p-Me)

h

b

i

1.23

2c/CH₂Cl₂

2d/CH₂Cl₂

2e/CH₂Cl₂

2f/CH₂Cl₂

2h/CH₂Cl₂

2e/CH₂Cl₂

2f/CH₂Cl₂

2g/CH₂Cl₂

2h/CH₂Cl₂

2i/CH₂Cl₂

2l/CH₂Cl₂

2m/CH₂Cl₂

2i/CH₂Cl₂

2j/CH₂Cl₂

2k/CH₂Cl₂

2n/CH₂Cl₂

2p/CH₃CN

2r/CH₃CN

2s/CH₃CN

2o/CH₂Cl₂

2q/CH₃CN

2s/CH₃CN

2t/CH₃CN

2u/DMSO

0.96, 1.00

ꢀ0.13, 1.21

1.79, 0.94

4.41, 0.96

5.21, 1.00

1.79, 0.94

4.41, 0.96

3.09, 0.90

5.21, 1.00

6.57, 0.93

3.27, 0.73

5.85, 1.03

6.57, 0.93

8.23, 0.81

9.00, 0.98

11.40, 0.83

10.13, 0.75

14.29, 0.67

15.65, 0.74

15.06, 0.82

13.77, 0.70

15.65, 0.74

17.35, 0.68

13.91, 0.86

5.01 ꢁ 10¹

4.98 ꢁ 10¹

5.03 ꢁ 10^2f

2.24 ꢁ 10⁵

4.56 ꢁ 10⁶

6.68 ꢁ 10^ꢀ1

5.53 ꢁ 10²

3.69 ꢁ 10¹

6.15 ꢁ 10³

1.13 ꢁ 10⁵

4.94^c

1.54 ꢁ 10²

2.12 ꢁ 10¹

6.85 ꢁ 10²

2.58 ꢁ 10⁵

2.73 ꢁ 10⁶

2.08

6.90 ꢁ 10²

2.98 ꢁ 10¹

5.72 ꢁ 10³

5.74 ꢁ 10⁴

2.12 ꢁ 10¹

3.38 ꢁ 10⁴

1.37 ꢁ 10^ꢀ1

3.90

2.95 ꢁ 10¹

1.73 ꢁ 10³

9.39 ꢁ 10¹

3.54 ꢁ 10⁴

1.07 ꢁ 10⁶

2.14 ꢁ 10⁴

6.22 ꢁ 10²

2.21 ꢁ 10⁴

1.41 ꢁ 10⁵

3.57 ꢁ 10³

0.33

2.35

0.73

0.87

1.67

0.32

0.80

1.24

1.08

1.97

0.23

1.45

0.57

0.48

3.73

4.93

1.37

0.63

0.87

3.88

0.75

1.29

1.09

0.95

1g (X = p-OMe)

ꢀ1.45

i

j

4.91 ꢁ 10⁴

7.82 ꢁ 10^ꢀ2

1.88

1h (X = p-NMe₂)

i

ꢀ7.50

ꢀ9.78

i

1.10 ꢁ 10²

8.51 ꢁ 10^3c

1.29 ꢁ 10²

2.22 ꢁ 10⁴

9.34 ꢁ 10⁵

8.30 ꢁ 10^4c

4.67 ꢁ 10²

2.85 ꢁ 10⁴

1.54 ꢁ 10⁵

3.38 ꢁ 10³

i

1i (X = jul) ^k

i

^aThe E parameters for 1(aꢀi) result from the least-squares minimization of Δ²= Σ(log k₂ꢀ s_N(N + E))², which uses the second-order rate constants k₂

(this table) and the N and s_Nparameters of the nucleophiles 2(aꢀu) given in ref 10 and listed in this table. E values with more decimals than given in this

table were used for the calculation of k_calcby eq 1 and for the correlations in Figures 5, 7, and 9. The use of E parameters given in this table leads to slightly

deviating results. ^bLaser-ﬂash photolysis of 1-PPh₃BF₄^ꢀ. ^cValues were not used for determination of E. ^dDiﬀusion limit approached. ^eFrom 1-Cl and

+

GaCl₃. ^fExtrapolated from rate constants at lower temperature by using the Eyring equation (for details see the Supporting Information). ^gLaser-ﬂash

+

photolysis of 1-PPh₃TfO^ꢀ. ^hFrom 1-OTMS and TMSOTf, BCl₃, or GaCl₃. ⁱIsolated tetraﬂuoroborate salt (1-BF₄). ^jFrom 1g-OMe and TMSOTf.

^kSee Table 1 for deﬁnition.

Though the three-parameter eq 1, which can be employed to

predict absolute rate constants in a reactivity range of 40 orders of

magnitude can only be expected to be reliable within a factor of

10ꢀ100,^8asome systematic deviations within this range shown in

Figure 3 prompt us also to comment on their possible origin.

In the combinations of 1a with 2f and 2h the diﬀusion limit is

approached; therefore the k₂values of these reactions were not

used for the determination of E.

Dimethylphenylsilane (2l) reacts with the (E)-1,3-bis(4-

methoxyphenyl)allyl cation (1g) 4.3 times more slowly than

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Figure 3. Plot of (log k₂)/s_Nversus N for the reactions of the 1,3-diarylallyl cations 1(aꢀi) with the nucleophiles 2(aꢀu) (solvents are speciﬁed in

Table 2). The data points shown with open symbols were not used for the determination of E (see text). The data for cations 1(cꢀd) are omitted for

clarity.

Figure 4. Weak transition state stabilization in reactions between

enamines and 1,3-diarylallyl cations.

Figure 5. Correlation of the electrophilicity parameters E of the

calculated by eq 1 from the E parameter of 1g (derived from its

carbocations 1(aꢀi) with the sum of the σ⁺parameters²⁵of the

reactions with carbon nucleophiles) and the N and s_Nparameters

corresponding aryl substituents. Open symbol: 1i is not included in

of 2l, which were derived from its reactions with benzhydrylium

the correlation, as σ⁺for the julolidyl moiety of 1i was estimated from

ions. Similar trends were observed for the reactions of hydride

donors with tropylium²⁰and 1,1,3-triarylallylium ions.²¹Ob-

viously, hydride donors react generally faster with benzhydrylium

ions than with more highly delocalized carbocations.

The amino-substituted allyl cations 1h and 1i react with the

enamines 2n and 2o about 4.5 times faster than expected from

their E parameters. Possibly, interaction of the nitrogen lone-pair

with the other allyl terminus, comparable to the transition state of

the aza-Claisen rearrangement,²²accounts for the slightly in-

creased reactivity of the enamines (Figure 4).

These deviations are quite moderate, however, so that the

inclusion of the rate constants in the least-squares minimization

mentioned above would not signiﬁcantly change the E para-

meters derived for the 1,3-diarylallyl cations.

Because of the low thermodynamic driving force of the

reaction of 1h with 2,2,2-triﬂuoroethylamine (2p), the nucleo-

phile had to be used in very high excess (over 5000 equiv). Under

such conditions, the kinetics may be aﬀected by traces of

impurities present in the reagent. However, the good ﬁt of this

rate constant to the correlation line indicates the reliability of the

value determined in this way.

the electrophilicities of benzhydrylium ions.^8a

The relevance of the electrophilicity parameters listed in

Table 2 for predicting reaction rates can be examined by

comparison with independently determined rate constants.

Miranda, Scaiano, and co-workers²³reported rate constants of

the reactions of cation 1e with a series of nucleophiles, two of

which have been characterized by N and s_N. Substitution of

E(1e) = 2.70 (Table 2) and N = 1.23, s_N= 0.92 for 2,2,2-

triﬂuoroethanol²⁴and N = 10.3, s_N= 0.60 for Cl^ꢀin

triﬂuoroethanol^5ain eq 1 yield k_calc(triﬂuoroethanol) = 4.1 ꢁ 10³

s^ꢀ1and k_calc(Cl^ꢀin triﬂuoroethanol) = 6.3 ꢁ 10⁷M^ꢀ1s^ꢀ1

,

respectively. As these numbers agree within factors 1.9 and 3.5 with

the experimental data reported in Table 1 of ref 23 (8.0 ꢁ 10³s^ꢀ1

and 2.2 ꢁ 10⁸M^ꢀ1s^ꢀ1, respectively), the applicability of electro-

philicity parameters E derived in this work has been demonstrated.

Figure 5 shows the correlation between the E parameters of

1(aꢀi) and Hammett-Brown’s σ⁺(σ_min case of F) parameters²⁵

of the corresponding substituents. The quality of this correlation

is comparable to that for benzhydrylium ions.^8a

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Table 3. Characteristic Bond Lengths Between Aromatic and

Allylic Carbons in the 1,3-Diarylallyl Cations 1(aꢀi) Opti-

mized at the B3LYP/6-31G(d,p) Level of Theory and Σσ⁺

(Σσ_m) of the Corresponding Substituents

cation

X

Σσ^+a

r_C2ꢀC3^b/Å

r_C1ꢀC2^b/Å

1a

1b

1c

1d

1e

1f

m,m-F₂

m-F

1.36^c

0.68^c

1.428

1.427

1.424

1.425

1.423

1.419

1.415

1.414

1.39022

1.39037

1.39087

1.39090

1.39067

1.39089

1.39134

1.39192

1.39219

p-Br

0.30

p-Cl

0.22

H

0.00

p-Me

p-OMe

p-NMe₂

jul

ꢀ0.62

ꢀ1.56

ꢀ3.40

ꢀ4.06^d

1g

1h

1i

^aFrom ref 25. ^bValues of r with more decimals than given in the table

were used for the correlations in Figure 6 and Figure SX2 in Supporting

Information. The use of the bond lengths given in this table leads to

slightly deviating results. ^cσ_m. ^dEstimated value from ref 8a.

Quantum Chemical Calculations. It has been shown^9athat

the electrophilicities E of differently substituted benzhydryl

cations correlate well with their methyl anion affinities calculated

at the B3LYP/6-31G(d,p) level of theory. Thus, it was of interest

to examine the analogous correlation for 1,3-diarylallyl cations.

As recent work has shown the higher reliability of the MP2

method for such comparisons,²⁶the methyl anion affinities

(eq 2) of the cations 1(aꢀi) have now been calculated at the

MP2(FC)/6-31+G(2d,p)//B3LYP/6-31G(d,p) level of theory.²⁷

Figure 6. Correlation of the bond lengths (a) r_C2ꢀC3and (b) r_C1ꢀC2in

cations 1(aꢀi) with the sum of the σ⁺parameters of the corresponding

substituents.^8a,25

Details of the determinations of the gas-phase methyl anion

aﬃnities (ΔH₂₉₈, ΔG₂₉₈, Table 4) deﬁned by eq 2 are given on

pages S21ꢀS29 of the Supporting Information. Single point

calculations were performed at the MP2(FC)/6-31+G(2d,p)

level of theory for all allyl cations 1(aꢀi) and the corresponding

methyl anion adducts 1(aꢀi)-Me using the geometries optimized

at the B3LYP/6-31G(d,p) level. The resulting MP2 energies were

converted to H₂₉₈and G₂₉₈using the thermochemical corrections

calculated with B3LYP/6-31G(d,p). As cations 1b, 1g, and 1i as

well as all (E)-1,3-diarylbut-1-enes 1(aꢀi)-Mehave several minima

in the conformational space, the Boltzmann distribution was used

to calculate their averaged energies.

As expected, the absolute values of ΔH₂₉₈and ΔG₂₉₈decrease

with increasing electron donating ability of the substituents. Both

ΔH₂₉₈and ΔG₂₉₈correlate linearly with the sum of the σ⁺

parameters of the corresponding substituents^8a,25(Figure SX3 in

the Supporting Information).

The geometrical parameters listed in Table 3 refer to the most

stable conformers of diarylallyl cations 1(aꢀi). In contrast to

benzhydryl^9aand trityl cations,²⁷the calculated structures for

1(aꢀi) are completely planar (all dihedral angles between ring

and allyl carbons and hydrogens deviate by less than 1.5° from 0°

or 180°), in line with the X-ray analysis of 1h-BF₄.¹⁵

Table 3 shows that the C2ꢀC3 bond lengths (r_C2ꢀC3

=

0

r_{C2 ꢀC3}) of the cations 1(aꢀi) decrease, while the C1ꢀC2 bond

0

lengths (r_C1ꢀC2= r_C1ꢀC2) increase with higher electron-donat-

ing ability of the substituents. Figure 6 depicts linear correlations

of the bond lengths r_C2ꢀC3and r_C1ꢀC2with Hammett-Brown’s

σ⁺parameters of the corresponding substituents (σ_min case of F).^8a,25

From the signiﬁcantly higher absolute value of the slope in

Figure 6a compared with that in Figure 6b one can derive that

substituent variation aﬀects the bonds of the allylic termini to

the aryl rings much more than the bond lengths in the allylic

fragment. The strong double-bond character of the C2ꢀC3

bond in the 1,3-diarylallyl cations 1 is also reﬂected by the high

rotational barrier (51 ( 2 kJ mol^ꢀ1) for 1h derived by dynamic

NMR spectroscopy (see above).

The correlation between the electrophilicity parameters E of

the allyl cations 1(aꢀi) and their ΔH₂₉₈values (Figure 7) shows

that quantum chemically calculated methyl anion aﬃnities can be

used for deriving E parameters of further 1,3-diarylallyl cations.

The correlation in eq 3

δE ¼ ꢀ 0:0769δΔH₂₉₈

ð3Þ

(δ describes the eﬀect of a substituent), which is derived from

Figure 7, can be transformed into the relationship (eq 4)

15

The bond lengths in the crystal structure of 1h-BF₄are

slightly smaller than those calculated for the gas phase (Figure

SX2 in the Supporting Information).

δΔG^q¼ 0:432s_NδΔH₂₉₈

ð4Þ

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Table 4. Gas-Phase Methyl Anion Aﬃnities (ΔH₂₉₈, ΔG₂₉₈

of eq 2) in kJ mol^ꢀ1Calculated at MP2(FC)/6-31+G(2d,p)//

B3LYP/6-31G(d,p)^a

b

cation

X

ΔH₂₉₈

ΔG₂₉₈

1a

1b

1c

1d

1e

1f

m,m-F₂

m-F

ꢀ962.44

ꢀ931.19

ꢀ912.92

ꢀ916.12

ꢀ901.07

ꢀ877.42

ꢀ847.22

ꢀ782.87

ꢀ753.03

ꢀ976.53

ꢀ945.91

ꢀ927.61

ꢀ930.84

ꢀ915.29

ꢀ891.91

ꢀ861.40

ꢀ797.04

ꢀ767.30

p-Br

p-Cl

H

p-Me

p-OMe

p-NMe₂

jul

1g

1h

1i

^aTotal energies and thermochemical corrections for the reactants and

products can be found in the Supporting Information. ^bThe values of

ΔH₂₉₈and ΔG₂₉₈with more decimals than given in the table were used

for the correlations in Figure 7 and Supplementary Figure SX3. The use

of ΔH₂₉₈given in this table leads to slightly deviating results.

Figure 8. Electrophilicities E of the 1,3-diarylallyl cations (n = 1, from

Table 2) compared with those of the corresponding benzhydrylium ions

(n = 0).⁸

Figure 7. Correlation of the electrophilicities E of the cations 1(aꢀi)

with their gas-phase methyl anion aﬃnities ΔH₂₉₈(calculated at MP2-

(FC)/6-31+G(2d,p)//B3LYP/6-31G(d,p)).

by using eq 1 and the Eyring equation. If one assumes that the

substituent eﬀects on the diarylallyl cations in the gas phase

(δΔH₂₉₈) are attenuated to 62% in dichloromethane solution, as

previously shown for the analogous benzhydrylium ions,^9aone

can derive a Brønsted coeﬃcient expressed in eq 5 by dividing the

slope of eq 4 by 0.62.

Figure 9. Linear correlation between the E parameters of analogously

substituted 1,3-diarylallyl and benzhydryl cations (formula see Figure 8).

benzhydrylium ions (Figure 9). The slope of this correlation

(0.82) reﬂects that the stabilization of 1,3-diarylallyl cations is

less aﬀected by the substituents at the aryl rings, which may be

explained by the charge delocalization between C1 and C3 in

diarylallyl cations, which reduces the electron demand of the

carbenium centers.

α ¼ 0:70s_N

ð5Þ

Details of this procedure have been described in ref 9a.

Comparison with Benzhydryl Cations. The reactivity range

covered by 1,3-diarylallyl cations 1(aꢀi) (16 orders of magni-

tude) is slightly smaller than that for analogously substituted

diarylmethyl cations⁸(Figure 8). While amino-substituted 1,3-

diarylallyl and diarylmethyl cations show almost identical electro-

philicities, 1,3-diarylallyl cations substituted with weaker electron

donors are increasingly less electrophilic than analogously sub-

stituted diarylmethyl cations.

’ CONCLUSIONS

The rate constants of the reactions of 1,3-diarylallyl cations

1(aꢀi) with nucleophiles of a large structural variety can be

described by the linear free-energy relationship log k₂(20 °C) =

s_N(N + E) (eq 1) using N and s_Nparameters that have previously

been derived from the reactions of the corresponding

As illustrated in Figure 9, the E parameters of 1,3-diarylallyl

cations correlate linearly with those of analogously substituted

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ARTICLE

nucleophiles with benzhydrylium ions.^8,10The fact that the

correlations used for the determination of the electrophilicity

parameters E of 1(aꢀi) include rate constants determined in

diﬀerent solvents (CH₂Cl₂, CH₃CN, DMSO) shows that the E

parameters listed in Table 2 can be treated as solvent-indepen-

dent. As pointed out previously,⁷this does not mean that all allyl

cations 1(aꢀi) are solvated to the same extent but that the

solvent eﬀects on these rate constants are fully taken account of

in the solvent-dependent nucleophile-speciﬁc parameters N and

s_Nof their reaction partners. As the electrophilicity parameters

E of 1(aꢀi) correlate linearly with the quantum chemically

calculated gas-phase methyl anion aﬃnities of these cations

and Hammett-Brown’s substituent constants σ⁺, these corre-

lations may be employed to estimate reactivities of further 1,3-

diarylallyl cations.

conversion of 1-bromo-3-fluorobenzene was reached (GCꢀMS mon-

itoring analogous to the method described in ref 28b), then cooled to

room temperature, and added to a suspension of ZnCl₂(4.67 g, 34.3

mmol) in THF (15 mL). After stirring for 3 h, the resulting solution was

added dropwise to a solution of acetyl chloride (5.38 g, 68.5 mmol) and

[Pd(PPh₃)₄] (50 mg, 0.042 mmol, 0.06 mol %) in diethyl ether

(500 mL). Stirring was continued for 12 h before saturated aqueous

NH₄Cl solution (250 mL) was added. The organic layer was separated,

washed with water and brine, and dried (MgSO₄). Evaporation of

solvents followed by distillation (75 mbar) afforded 3-fluoroacetophe-

1

none (4.18 g, 30.2 mmol, 44%) as a colorless liquid. The H NMR

spectrum agreed with literature data³⁰but showed some impurities

(probably owing to the product of ZnCl₂-catalyzed attack of acetyl

chloride on THF).

3,5-Difluoroacetophenone. Synthesized analogously to 3-fluoro-

acetophenone from 1-bromo-3,5-difluorobenzene (24.6 g, 128 mmol), a

solution of s-BuMgCl LiCl in THF (1.07 M, 120 mL, 128 mmol), zinc

3

chloride (8.70 g, 63.8 mmol), and acetyl chloride (9.2 mL, 10 g, 0.13 mol) to

give 3,5-difluoroacetophenone (13.2 g, 84.2 mmol, 66%).

’ EXPERIMENTAL SECTION

Materials for Synthesis. Substituted acetophenones and benzal-

dehydes with the exception of fluorinated ones (synthesis described

below) were purchased. The substituted chalcones (1(aꢀg)-O) and

chalcols (1(aꢀf)-OH) were synthesized using the general procedures

described below. Synthetic procedures have not been optimized for high

yields.

Materials for Kinetic Measurements. Dichloromethane (p.a.

grade) was subsequently treated with concentrated sulfuric acid, water,

10% NaHCO₃solution, and again water. After predrying with anhydrous

CaCl₂, it was freshly distilled over CaH₂. Acetonitrile (HPLC grade) and

DMSO (99.7% purity) were used as received.

General Method for the Synthesis of (E)-1,3-Diarylprop-2-

en-1-ones (1-O). According to Manolov’s procedure,³¹substituted

acetophenones (1 equiv) and benzaldehydes (1 equiv) were dissolved in

ethanol (ca. 200 mL ethanol per mole substrate) before an 11% (w/w)

aqueous NaOH solution was added (333 mL per mole acetophenone).

The resulting mixtures were stirred until precipitates formed (usually

after 2 h, otherwise the reaction mixtures were cooled with an ice bath for

further 3 h), which were filtered and washed with water until the washing

water reacted neutral. Recrystallization of crude products from ethanol

gave (E)-1,3-diarylprop-2-en-1-ones in 64ꢀ88% yields.

(E)-1,3-Bis(3,5-difluorophenyl)prop-2-en-1-one (1a-O).

From 3,5-difluoroacetophenone (7.18 g, 46.0 mmol) and 3,5-difluoro-

benzaldehyde (6.53 g, 46.0 mmol) in ethanol (10 mL) and 11% (w/w)

aqueous NaOH solution (15 mL): 8.26 g (29.5 mmol, 64%), yellow

needles (mp 159.0ꢀ160.1 °C). ¹H NMR (CDCl₃, 300 MHz): δ 6.89 (tt,

²J_HF= 8.7, ⁴J_HH= 2.3 Hz, 1 H, H_Ar), 7.06 (tt, ²J_HF₃= 8.4, ⁴J_HH= 2.4 Hz, 1

H, H_Ar), 7.11ꢀ7.20 (m, 2 H, H_Ar), 7.38 (d, J_HH= 15.7 Hz, 1 H,

ArCHCHCOAr), 7.46ꢀ7.57 (m, 2 H, H_Ar), 7.72 (d, ³J_HH= 15.7 Hz, 1

Gallium chloride was sublimed in a vacuum and stored under glove-

box conditions (dry Ar atmosphere). Trimethylsilyl triﬂate was used as

received.

1

NMR Spectroscopy. In the H and ¹³C NMR spectra chemical

shifts are expressed in δ (ppm) and refer to CDCl₃(δ_H7.26, δ_C77.0),

CD₂Cl₂(δ_H5.32, δ_C54.0), CD₃CN (δ_H1.94, δ_C1.39), nitrobenzene

(δ_H7.50, δ_C148.1), or TMS (δ_H0.00, δ_C0.0) as internal standards.

The coupling constants are given in Hz. Abbreviations used are s

(singlet), d (doublet), t (triplet), q (quartet), m (multiplet). In the case

of ¹³C NMR spectra, these abbreviations refer to the multiplicity in

proton-decoupled spectra, and hydrogen multiplicity (based on DEPT

or HSQC experiments) is shown as CH₃, CH₂, CH, or C to avoid

ambiguity.

H, ArCHCHCOAr). ¹³C NMR (CDCl₃, 75.5 MHz): δ 106.1 (t, J_CF

=

25.4 Hz, CH), 108.5 (t, J_CF= 25.4 Hz, CH), 110.9ꢀ111.7 (m, 2 ꢁ CH),

123.1 (CH), 137.6 (t, J_CF= 9.5 Hz, C), 140.6 (t, J_CF= 7.6 Hz, C), 143.4

(t, J_CF= 3.0 Hz, CH), 163.1 (dd, J_CF= 252, J_CF= 11.0 Hz, C), 163.3 (dd,

J_CF= 250, J_CF= 12.7 Hz, C), 187.1 ppm (t, J_CF= 2.5 Hz, C). ¹⁹F NMR

(CDCl₃, 282 MHz): δ ꢀ108.7 to ꢀ108.6 (m), ꢀ107.7 to ꢀ107.6

ppm (m). HRMS (EI; positive): calcd 280.0506 (C₁₅H₈F₄O), found

280.0505.

3,5-Difluorobenzaldehyde. Prepared according to Olah’s pro-

cedure:²⁸To 1-bromo-3,5-difluorobenzene (28.9 g, 150 mmol) was

slowly added a solution of s-BuMgCl LiCl in THF (1.07 M, 140 mL, 150

(E)-1,3-Bis(3-fluorophenyl)prop-2-en-1-one (1b-O). From

3-fluoroacetophenone (3.00 g, 21.7 mmol) and 3-fluorobenzaldehyde

(2.70 g, 21.7 mmol) in ethanol (5 mL) and 11% (w/w) aqueous NaOH

solution (7.5 mL): 3.85 g (15.7 mmol, 65% yield with correction for 10%

3

mmol) to keep the temperature of the reaction mixture below 30 °C.

The resulting reaction mixture was further stirred at room temperature.

GCꢀMS analysis^28bindicated full conversion after 3 h. The reaction

mixture was then cooled to ꢀ40 °C before DMF (12.7 mL, 12.1 g, 165

mmol) was added dropwise. After the mixture stirred overnight at

ꢀ40 °C, diethyl ether was added. The resulting mixture was successively

washed with saturated ammonium chloride solution, water, and brine

before it was dried (MgSO₄). Evaporation of solvents followed by

distillation under vacuum (75 mbar, 90ꢀ110 °C) afforded 3,5-difluoro-

benzaldehyde (11.2 g, 78.8 mmol, 53%). The ¹H NMR spectrum of the

product agreed with previously published data.²⁹

3-Fluoroacetophenone. A small portion of 1-bromo-3-fluoro-

benzene was added to Mg turnings (1.67 g, 68.5 mmol) and LiCl (2.91 g,

68.5 mmol) in dry THF (35 mL). To initiate the reaction, DIBAL-H

(1 M solution in hexane, 2.1 mL, 2.1 mmol) was added. After the

exothermic process had started, the remaining portion of 1-bromo-3-

fluorobenzene (12.0 g, 68.6 mmol in total) was added dropwise keeping

the THF gently boiling. The reaction mixture was kept refluxing until full

1

impurities), yellow solid. H NMR (CDCl₃, 300 MHz): δ 7.09ꢀ7.17

(m, 1 H, H_ar), 7.26ꢀ7.53 (m, 5 H, H_ar) superimposed with 7.46 (d,

³J_HH= 15.7 Hz, 1 H, ArCHCHCOAr), 7.68ꢀ7.72 (m, 1 H, H_ar), 7.78 (d,

³J_HH= 15.7 Hz, 1 H, ArCHCHCOAr) superimposed with 7.78ꢀ7.82

ppm (m, 1 H, H_ar); unknown impurities, which might be the products of

the reaction between impurities in 3-fluoroacetophenone and some

reagents used for the condensation reaction (NaOH etc.), caused

additional resonances in the range of 2ꢀ6 ppm. ¹³C NMR (CDCl₃,

75.5 MHz): δ 114.5 (d, J_CF= 21.9 Hz, CH), 115.3 (d, J_CF= 22.4 Hz,

CH), 117.6 (d, J_CF= 21.5 Hz, CH), 120.0 (d, J_CF= 21.5 Hz, CH), 122.6

(CH), 124.2 (d, J_CF= 3.0 Hz, CH), 124.6 (d, J_CF= 2.9 Hz, CH), 130.3

(d, J_CF= 7.7 Hz, CH), 130.5 (d, J_CF= 8.3 Hz, CH), 136.9 (d, J_CF= 7.7

Hz, C), 140.0 (d, J_CF= 6.3 Hz, C), 144.0 (d, J_CF= 2.8 Hz, CH), 162.9 (d,

J_CF= 248 Hz, C), 163.0 (d, J_CF= 247 Hz, C), 188.7 ppm (d, J_CF

=

2.2 Hz, C). ¹⁹F NMR (CDCl₃, 282 MHz): δ ꢀ112.34 to ꢀ112.26 (m),

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ꢀ111.64 to ꢀ111.56 ppm (m). HRMS (EI, positive): calcd 244.0694

(C₁₅H₁₀F₂O), found 244.0694.

¹H NMR (CDCl₃, 400 MHz): δ 0.16 (m, 9 H, OTMS), 2.34, 2.36 (2 s, 6

H, 2 ꢁ CH₃), 5.33 (d, ³J_HH= 6.5 Hz, 1 H, ArCHCHCH(OTMS)Ar),

6.27 (dd, ³J_HH= 15.8, 6.6 Hz, 1 H, ArCHCHCH(OTMS)Ar), 6.58 (d,

³J_HH= 15.8, 1 H, ArCHCHCH(OTMS)Ar), 7.12 (d, ³J_HH= 8.0 Hz, 2 H,

H_Ar), 7.16 (d, ³J_HH= 8.2 Hz, 2 H, H_Ar), 7.27ꢀ7.32 ppm (m, 4 H, H_Ar).

¹³C NMR (CDCl₃, 101 MHz): δ 0.3 (CH₃), 21.09 (CH₃), 21.14 (CH₃),

75.5 (CH), 126.2 (CH), 126.4 (CH), 128.95 (CH), 129.03 (CH), 129.2

(CH), 132.0 (CH), 134.2 (C), 136.7 (C), 137.2 (C), 140.8 ppm (C).

HRMS (EI, positive): calcd 310.1747 (C₂₀H₂₆OSi), found 310.1747.

(E)-(1,3-Bis(4-bromophenyl)allyl)oxy)trimethylsilane (1c-

OTMS). Prepared analogously to 1e-OTMS and used for further

synthesis without purification and characterization.

General Method for the Synthesis of (E)-1,3-Diarylprop-2-

en-1-ols (1-OH). Similarly to the procedure by Dickinson et al.,³²(E)-

1,3-diarylprop-2-enones (1-O) were dissolved in methanol (ca. 80 mM

solutions, in some cases heating or refluxing of the reaction mixture was

needed to achieve a homogeneous solution). Subsequently, sodium

borohydride (0.5ꢀ2 equiv) was added in small portions until the TLC

spots of (E)-1,3-diarylprop-2-enone disappeared. After evaporation

of the methanol the residue was dissolved in EtOAc, washed with water

(2 ꢁ ), and dried (MgSO₄). Drying in a vacuum afforded (E)-1,3-

diarylprop-2-en-1-ols in yields of 89ꢀ98%. The resulting alcohols were

used without further purification for subsequent syntheses because the

excellent crystallization ability of phosphonium salts allows for purifica-

tion of the cation precursors at the final stage of the synthesis.

(E)-1,3-Bis(3,5-difluorophenyl)prop-2-en-1-ol (1a-OH). From

1a-O (4.99 g, 17.8 mmol): 4.62 g (16.4 mmol, 92%), colorless oil. ¹H NMR

(CDCl₃, 200 MHz): δ 2.20 (br. s, 1 H, OH), 5.36 (d, ³J_HH= 6.4 Hz, 1 H,

ArCHCHCH(OH)Ar), 6.29 (dd, ³J_HH= 15.8, 6.4 Hz, 1 H, ArCHCHCH-

(OH)Ar), 6.54ꢀ6.81 (m, 3 H, ArCHCHCH(OH)Ar, H_Ar), 6.82ꢀ7.06

ppm (m, 4 H, H_Ar).

General Procedure for the Synthesis of (E)-(1,3-Diarylal-

+

lyl)triphenylphosphonium Tetrafluoroborates (1-PPh₃BF₄^ꢀ).

Analogously to ref 13, triphenylphosphine was dissolved in dichloro-

methane (5 mL), and 50% w/w tetrafluoroboric acid solution in diethyl

ether was added (1 equiv). After 5 min of stirring at rt, the corresponding

diarylallyl alcohol (1 equiv) was added, and the reaction mixture was stirred

for a further 30 min. Evaporation of the solvents followed by recrystalliza-

tion from a CH₂Cl₂/Et₂O mixture afforded the desired products.

(E)-(1,3-Bis(3,5-difluorophenyl)allyl)triphenylphosphonium

+

Tetrafluoroborate (1a-PPh₃BF₄^ꢀ). From 1a-OH (97.0 mg, 0.343

(E)-1,3-Bis(3-fluorophenyl)prop-2-en-1-ol (1b-OH). From

1b-O (1.00 g, 4.09 mmol): 893 mg (3.62 mmol, 89%), colorless oil.

mmol): 117 mg (0.205 mmol, 60%), colorless crystals (mp 225.2ꢀ

¹H NMR (CDCl₃, 200 MHz): δ 2.07 (br. s, 1 H, OH), 5.37 (d, ³J_HH

=

1

2

226.3 °C). H NMR (CD₂Cl₂, 400 MHz): δ 6.11 (dd, J_HP= 15.9,

³J_HH= 9.2 Hz, 1 H, ArCHCHCH(P⁺Ph₃)Ar), 6.15ꢀ6.27 (m, 1 H,

ArCHCHCH(P⁺Ph₃)Ar), 6.59ꢀ6.72 (m, 2 H, H_Ar), 6.71ꢀ6.78 (m, 1 H,

H_Ar), 6.79ꢀ6.91 (m, 3 H, H_Ar), 6.98 ppm (dd, ³J_HH= 15.4, ⁴J_HP= 4.6 Hz, 1

H, ArCHCHCH(P⁺Ph₃)Ar), 7.61ꢀ7.68(m, 6H, H_Ar), 7.68ꢀ7.75 (m, 6 H,

H_Ar), 7.82ꢀ7.95 ppm (m, 3 H, H_Ar). ¹³C NMR (CD₂Cl₂, 101 MHz): δ

45.8 (dt, J_CP= 45.7, J_CF= ca. 2 Hz, CH), 104.7 (t, J_CF= 25.7 Hz, CH), 105.6

(td, J_CF= 25.0, J_CP= 2.5 Hz, CH), 110.0ꢀ110.4 (m, CH), 113.8ꢀ114.2 (m,

CH), 116.8 (d, J_CP= 83.1 Hz, C), 121.4 (d, J_CP= 6.4 Hz, CH), 131.1 (d,

J_CP=12.5Hz,CH),135.1(d,J_CP= 9.1 Hz, CH), 135.7ꢀ136.0 (m, C), 136.3 (d,

J_CP= 3.1 Hz, CH), 138.4 (dt, J_CP= 12.9, J_CF= 3.0 Hz, CH), 139.0ꢀ139.3

(m, C), 162.4ꢀ162.6 (m, C), 164.9ꢀ165.1 ppm (m, C). ¹⁹F NMR

(CD₂Cl₂, 282 MHz): δ ꢀ151.10 to ꢀ151.05 (m, 3 F, BF₄^ꢀ), ꢀ151.03

to ꢀ151.00 (m, 1 F, BF₄^ꢀ), ꢀ113.6 to ꢀ113.5, ꢀ110.7 to ꢀ110.6 ppm

(2 m, 4 F, F_Ar). ³¹P NMR (CD₂Cl₂, 162 MHz): δ 23.5 ppm. HRMS (ESI,

positive): calcd 527.1546 (C₃₃H₂₄F₄P⁺), found 527.1543.

6.4 Hz, 1 H, ArCHCHCH(OH)Ar), 6.33 (dd, ³J_HH= 15.9, 6.4 Hz, 1 H,

3

ArCHCHCH(OH)Ar), 6.66 (d, J_HH= 15.9 Hz, 1 H, ArCHCHCH-

(OH)Ar), 6.88ꢀ7.39 ppm (m, 8 H, H_ar).

(E)-1,3-Bis(4-bromophenyl)prop-2-en-1-ol (1c-OH). From

1c-O (5.00 g, 13.7 mmol): 3.76 g (10.2 mmol, 75%), colorless solid.

¹H NMR (CDCl₃, 200 MHz): δ 2.13 (br. s, 1 H, OH), 5.33 (d, ³J_HH

=

6.3 Hz, 1 H, ArCHCHCH(OH)Ar), 6.31 (dd, ³J_HH= 15.8, 6.3 Hz, 1 H,

3

ArCHCHCH(OH)Ar), 6.61 (d, J_HH= 15.8 Hz, 1 H, ArCHCHCH-

(OH)Ar), 7.19ꢀ7.32 (m, 4 H, H_ar), 7.37ꢀ7.53 ppm (m, 4 H, H_ar).

(E)-4,4⁰-(3-Chloroprop-1-ene-1,3-diyl)bis(bromobenzene)

(1c-Cl). Synthesized from 1c-OH (1.00 g, 2.70 mmol) and concen-

trated HCl by using a procedure described in ref 33: 0.732 g (1.89 mmol,

70%), colorless solid. ¹H NMR (CDCl₃, 300 MHz): δ 5.61 (d, ³J_HH

=

7.2 Hz, 1 H, ArCHCHCH(Cl)Ar), 6.47 (dd, ³J_HH= 15.6, 7.2 Hz, 1 H,

3

ArCHCHCH(Cl)Ar), 6.58 (d, J_HH= 15.6 Hz, 1 H, ArCHCHCH-

(Cl)Ar), 7.25ꢀ7.29 (m, 2 H, H_Ar), 7.35ꢀ7.38 (m, 2 H, H_Ar), 7.43ꢀ7.50

(m, 2 H, H_Ar), 7.50ꢀ7.60 (m, 2 H, H_Ar). ¹³C NMR (CDCl₃, 75.5 MHz):

δ 62.6 (CH), 122.3 (C), 122.5 (C), 128.3 (CH), 129.0 (CH), 129.2

(CH), 131.3 (CH), 131.8 (CH), 131.9 (CH), 134.5 (C), 139.0 ppm (C).

(E)-(1,3-Bis(3-fluorophenyl)allyl)triphenylphosphonium

Tetrafluoroborate (1b-PPh₃⁺BF₄^ꢀ). From 1b-OH (298 mg, 1.21

mmol): 520 mg (0.899 mmol, 74%), colorless crystals (mp

176.3ꢀ177.3 °C). ¹H NMR (CD₂Cl₂, 400 MHz): δ 5.94 (dd, ²J_HP

=

1

Some impurities gave rise to additional resonances in the H and ¹³C

16.3, ³J_HH= 8.9 Hz, 1 H, ArCHCHCH(P⁺Ph₃)Ar), 6.24ꢀ6.31 (m, 1

H, ArCHCHCH(P⁺Ph₃)Ar), 6.76 (ddd, ³J_HF= 9.7, ³J_HH= 2.0, 2.0 Hz,

1 H, H_Ar), 6.90ꢀ6.98 (m, 4 H, ArCHCHCH(P⁺Ph₃)Ar, H_Ar),

7.06ꢀ7.09 (m, 1 H, H_Ar), 7.09ꢀ7.13 (m, 1 H, H_Ar), 7.23ꢀ7.33 (m,

2 H, 6-H, H_Ar), 7.57ꢀ7.62 (m, 6 H, H_Ar), 7.66ꢀ7.71 (m, 6 H, H_Ar),

7.83ꢀ7.87 ppm (m, 3 H, H_Ar). ¹³C NMR (CD₂Cl₂, 101 MHz): δ: 46.6

(dd, J_CP= 45.0, J_CF= 1.9 Hz, CH), 113.6 (dd, J_CF= 22.0, J_CP= 1.8 Hz,

CH), 116.3 (dd, J_CF= 21.4, J_CP= 1.1 Hz, CH), 117.05 (d, J_CP= 82.8

NMR spectra of 1c-Cl and could not be removed by distillation or

recrystallization. However, these impurities cannot influence the deter-

mination of the second-order rate constants (k₂) because in each kinetic

run the same cation precursor concentration was used, so that possible

side reactions with these impurities should cause the positive intercept of

the k_obsvs [Nu] plot and do not affect the slope.

(E)-((1,3-Diphenylallyl)oxy)trimethylsilane (1e-OTMS). Pre-

pared using a procedure analogous to that described in ref 34: Triethylamine

(0.83 g, 8.2 mmol) and chlorotrimethylsilane (0.96 mL, 0.82 g, 7.6 mmol)

were successively added to a solution of 1e-OH (1.33 g, 6.32 mmol) in

dichloromethane (25 mL) under N₂atmosphere. The reaction mixture was

stirred for a further 10 h at ambient temperature. The precipitate formed after

addition of diethyl ether (45 mL) was filtered off, and the filtrate was dried in

the vacuum providing 1e-OTMS (1.45 g, 5.12 mmol, 81%) as a yellow oil.

The ¹H and ¹³C NMR spectra of 1e-OTMS were in agreement with those

described in ref 35.

Hz, C), 117.06 (dd, J_CF= 20.9, J_CP= 3.0 Hz, CH), 117.6 (dd, J_CF

23.0, J_CP= 5.9 Hz, CH), 120.6 (d, J_CP= 6.3 Hz, CH), 123.5 (dd, J_CF

=

2.8, J_CP= 1.9 Hz, CH), 126.7 (dd, J_CP= 6.1, J_CF= 3.1 Hz, CH), 130.95

(d, J_CP= 12.4 Hz, CH), 130.99 (dd, J_CF= ca. 8, J_CP= 1.0 Hz, CH),

131.9 (dd, J_CF= 8.2, J_CP= 2.5 Hz, CH), 134.4 (dd, J_CF= 7.4, J_CP= 5.3

Hz, C), 135.2 (d, J_CP= 9.0 Hz, CH), 136.1 (d, J_CP= 3.1 Hz, CH), 138.1

(dd, J_CF= 7.7, J_CP= 3.0 Hz, C), 138.8 (dd, J_CP= 13.0, J_CF= 2.6 Hz,

CH), 163.4 (dd, J_CF= 249, J_CP= 2.5 Hz, C), 163.5 ppm (dd, J_CF= 246,

J_CP= 1.1 Hz, C). ¹⁹F NMR (CD₂Cl₂, 282 MHz): δ ꢀ150.93

to ꢀ150.90 (m, 3 F, BF₄^ꢀ), ꢀ150.87 to ꢀ150.85 (m, 1 F, BF₄^ꢀ),

ꢀ113.6 to ꢀ113.5, ꢀ110.7 to ꢀ110.6 ppm (2 m, 2 F, F_Ar). ³¹P NMR

(CD₂Cl₂, 162 MHz): δ 23.1 ppm. HRMS (ESI, positive): calcd

491.1735 (C₃₃H₂₆F₂P⁺), found 491.1732.

(E)-((1,3-Bis(4-methylphenyl)allyl)oxy)trimethylsilane (1f-

OTMS). Analogously to 1e-OTMS. From 1f-OH (5.89 g, 24.7 mmol),

chlorotrimethylsilane (3.22 g, 29.6 mmol), and triethylamine (3.25 g,

32.1 mmol): 5.89 g (19.0 mmol, 77%), colorless solid (mp 36.5ꢀ38 °C).

9400

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ARTICLE

(E)-(1,3-Bis(4-chlorophenyl)allyl)triphenylphosphonium

Tetrafluoroborate (1d-PPh₃⁺BF₄^ꢀ). From 1d-OH (600 mg, 2.15

mmol): 721 mg (1.18 mmol, 55%), colorless crystals (149.6ꢀ150.4 °C).

¹H NMR (CD₂Cl₂, 400 MHz): δ 5.96 (dd, ²J_HP= 16.3, ³J_HH= 9.0 Hz, 1

H, ArCHCHCH(P⁺Ph₃)Ar), 6.24ꢀ6.32 (m, 1 H, ArCHCHCH-

(P⁺Ph₃)Ar), 6.92 (dd, ³J_HH= 15.4, ⁴J_HP= 4.5 Hz, 1 H, ArCHCHCH-

(P⁺Ph₃)Ar), 6.99ꢀ7.09 (m, 2 H, H_Ar), 7.21ꢀ7.27 (m, 6 H, H_Ar),

7.59ꢀ7.64 (m, 6 H, H_Ar), 7.66ꢀ7.71 (m, 6 H, H_Ar), 7.83ꢀ7.88 ppm (m,

3 H, H_Ar). ¹³C NMR (CD₂Cl₂, 101 MHz): δ 46.4 (d, J_CP= 44.6 Hz,

CH), 117.1 (d, J_CP= 82.6 Hz, C), 119.9 (d, J_CP= 6.1 Hz, CH), 128.6 (d,

J_CP= 1.8 Hz, CH), 129.4 (d, J_CP= 0.9 Hz, CH), 130.1 (d, J_CP= 2.4 Hz,

CH), 130.7 (d, J_CP= 5.3 Hz, C), 130.9 (d, J_CP= 12.3 Hz, CH), 132.1 (d,

J_CP= 5.9 Hz, CH), 134.5 (d, J_CP= 2.9 Hz, C), 135.1 (d, J_CP= 9.0 Hz, CH

superimposed with signal for C (can be seen in HMBC spectrum)),

135.9 (d, J_CP= 3.7 Hz, C), 136.0 (d, J_CP= 3.0 Hz, CH), 138.6 ppm (d,

J_CP= 13.1 Hz, CH). ³¹P NMR (CD₂Cl₂, 162 MHz): δ 22.8 ppm. HRMS

(ESI, positive): calcd 523.1144 (C₃₃H₂₆³⁵Cl₂P), found 523.1142; calcd

525.1114 (C₃₃H₂₆³⁵Cl³⁷ClP), found 525.1115; calcd 527.1084 (C₃₃H₂₆³⁷Cl₂P),

found 527.1089.

730 mg (0.957 mmol, 68%), colorless crystals (mp 228.8ꢀ229.9 °C). ¹H

NMR (CD₂Cl₂, 400 MHz): δ 6.19ꢀ6.28 (m, 2 H, ArCHCHCH-

(P⁺Ph₃)Ar, ArCHCHCH(P⁺Ph₃)Ar), 6.91ꢀ7.00 (m, 3 H, ArCHCHCH

(P⁺Ph₃)Ar, H_Ar), 7.16 (d, ³J_HH= 8.4 Hz, 2 H, H_Ar), 7.42 (d, ³J_HH= 8.4

Hz, 4 H, H_Ar), 7.61ꢀ7.69 (m, 12 H, H_Ar), 7.82ꢀ7.87 ppm (m, 3 H,

H_Ar). ¹³C NMR (CD₂Cl₂, 101 MHz): δ 45.9 (d, J_CP= 44.4 Hz, CH),

117.3 (d, J_CP= 82.6 Hz, C), 120.0 (d, J_CP= 6.2 Hz, CH), 121.6 (q, J_CF

=

321.0 Hz, CF₃SO₃^ꢀ), 123.4 (d, J_CP= 1.6 Hz, C), 124.2 (d, J_CP= 3.9 Hz,

C), 128.9 (d, J_CP= 1.8 Hz, CH), 130.9 (d, J_CP= 12.3 Hz, CH), 131.3 (d,

J_CP= 5.3 Hz, C), 132.4 (d, J_CP= 1.8 Hz, CH), 132.5 (d, J_CP= 3.2 Hz,

CH), 133.1 (d, J_CP= 2.4 Hz, CH), 135.0 (d, J_CP= 2.9 Hz, C), 135.2 (d,

J_CP= 9.0 Hz, CH), 136.0 (d, J_CP= 3.1 Hz, CH), 138.9 ppm (d, J_CP= 13.1

Hz, CH). ³¹P NMR (CD₂Cl₂, 162 MHz): δ 22.6 ppm. HRMS (ESI,

positive): calcd 611.0133 (C₃₃H₂₆⁷⁹Br₂P⁺), found 611.0136; calcd 613.0113

(C₃₃H₂₆⁷⁹Br⁸¹BrP⁺), found 613.0113; calcd 615.0092 (C₃₃H₂₆⁸¹Br₂P⁺),

found 615.0098.

(E)-(1,3-Diphenylallyl)triphenylphosphonium Triflate (1e-

PPh₃⁺TfO^ꢀ). From 1e-OTMS (603 mg, 2.14 mmol): 1.01 g (1.66

mmol, 78%), colorless solid (mp 201.8ꢀ202.9 °C). ¹H NMR (CD₂Cl₂,

400 MHz): δ 5.98 (dd, ²J_HP= 16.4, ³J_HH= 8.7 Hz, 1 H, ArCHCHCH-

(P⁺Ph₃)Ar), 6.30ꢀ6.38 (m, 1 H, ArCHCHCH(P⁺Ph₃)Ar), 6.91 (dd,

³J_HH= 15.7, ⁴J_HP= 4.8 Hz, 1 H, ArCHCHCH(P⁺Ph₃)Ar), 7.07ꢀ7.11

(m, 2 H, H_Ar), 7.24ꢀ7.31 (m, 7 H, H_Ar), 7.38ꢀ7.42 (m, 1 H, H_Ar),

7.56ꢀ7.61 (m, 6 H, H_Ar), 7.64ꢀ7.68 (m, 6 H, H_Ar), 7.82ꢀ7.87 ppm (m,

3 H, H_Ar). ¹³C NMR (CD₂Cl₂, 101 MHz): δ 47.2 (d, J_CP= 43.9 Hz,

CH), 117.5 (d, J_CP= 82.5 Hz, C), 119.7 (d, J_CP= 6.4 Hz, CH), 121.6 (q,

(E)-(1,3-Diphenylallyl)triphenylphosphonium Tetrafluoro-

borate (1e-PPh₃⁺BF₄^ꢀ). From 1e-OH (310 mg, 1.26 mmol): 671

1

mg (1.24 mmol, 98%), colorless crystals (mp 202.6ꢀ203.5 °C). H

NMR (CD₂Cl₂, 400 MHz): δ 5.77 (dd, ²J_HP= 16.3 Hz, ³J_HH= 8.7 Hz, 1

H, ArCHCHCH(P⁺Ph₃)Ar), 6.31ꢀ6.39 (m, 1 H, ArCHCHCH-

(P⁺Ph₃)Ar), 6.88 (dd, ³J_HH= 15.7, ⁴J_HP= 3.9 Hz, 1 H, ArCHCHCH-

(P⁺Ph₃)Ar), 7.06ꢀ7.08 (m, 2 H, H_Ar), 7.24ꢀ7.33 (m, 7 H, H_Ar),

7.39ꢀ7.49 (m, 1 H, H_Ar), 7.53ꢀ7.59 (m, 6 H, H_Ar), 7.65ꢀ7.70 (m, 6 H,

H_Ar), 7.83ꢀ7.88 ppm (m, 3 H, H_Ar). ¹³C NMR (CD₂Cl₂, 101 MHz): δ

47.6 (d, J_CP= 44.2 Hz, CH), 117.3 (d, J_CP= 82.5 Hz, C), 119.7 (d,

J_CP= 6.4 Hz, CH), 127.2 (d, J_CP= 1.9 Hz, CH), 129.3 (d, J_CP= 1.0 Hz, CH),

129.5 (d, J_CP= 1.2 Hz, CH), 130.07 (d, J_CP= 3.1 Hz, CH), 130.10 (d,

J_CP= 2.3 Hz, CH), 130.7 (d, J_CP= 6.1 Hz, CH), 130.8 (d, J_CP= 12.3 Hz,

CH), 131.9 (d, J_CP= 5.4 Hz, C), 135.2 (d, J_CP= 8.9 Hz, CH), 135.9 (d,

J_CP= 3.1 Hz, CH), 136.0 (d, J_CP= 3.1 Hz, C), 139.5 ppm (d, J_CP= 13.0

Hz, CH). HRMS (ESI, positive): calcd 455.1923 (C₃₃H₂₈P⁺), found

455.1924.

J_CF= 321.0 Hz, CF₃SO₃^ꢀ), 127.2 (d, J_CP= 1.9 Hz, CH), 129.3 (d, J_CP

0.9 Hz, CH), 129.5 (d, J_CP= 1.2 Hz, CH), 130.0 (d, J_CP= 3.3 Hz, CH),

130.1 (d, J_CP= 2.3 Hz, CH), 130.7 (d, J_CP= 6.0 Hz, CH), 130.8 (d, J_CP

=

12.2 Hz, CH), 132.1 (d, J_CP= 5.4 Hz, C), 135.2 (d, J_CP= 8.9 Hz, CH),

135.9 (d, J_CP= 3.0 Hz, CH), 136.0 (d, J_CP= 3.0 Hz, C), 139.5 ppm (d,

J_CP= 13.0 Hz, CH). ³¹P NMR (162 MHz, CD₂Cl₂): δ 22.7 ppm. HRMS

(ESI, positive): calcd 455.1923 (C₃₃H₂₈P⁺), found 455.1921

(E)-1,3-Bis(4-methoxyphenyl)allylium Tetrafluoroborate

(1g-BF₄). (E)-1,3-Bis(4-methoxyphenyl)prop-2-enone 1g-O (5.00 g,

18.6 mmol) was dissolved in MeOH (250 mL). Sodium borohydride

(ca. 1.5 g, ca. 40 mmol) was added in small portions to the resulting

solution until complete disappearance of the (E)-1,3-bis(4-methoxy-

phenyl)prop-2-enone spot (TLC). Methanol was evaporated from the

reaction solution, and the remaining solid was dissolved in diethyl ether

and slowly added to a 50% w/w HBF₄solution in diethyl ether (40 mL,

250 mmol). The resulting suspension was stirred for 1 h at rt, and then

the precipitate was filtered and washed with diethyl ether. Recrystalliza-

tion from a dichloromethane/pentane mixture gave 1g-BF₄(3.42 g, 10.1

mmol, 54%) as violet crystals. The product is water- and air-sensitive, but

it can be stored for several months under glovebox conditions (dry Ar

atmosphere). ¹H NMR (CD₃CN, 400 MHz): δ 4.07 (s, 6 H, OMe), 7.24

(E)-(1,3-Di-p-tolylallyl)triphenylphosphonium Tetrafluor-

oborate (1f-PPh₃⁺BF₄^ꢀ). From 1f-OH (1.00 g, 4.24 mmol): 1.68 g

(2.95 mmol, 69%), colorless crystals (mp 188.9ꢀ189.9 °C). ¹H NMR

(CD₂Cl₂, 400 MHz): δ 2.30 (s, 3 H, CH₃), 2.35 (d, ⁷J_HP= 2.0 Hz, 3 H,

2

3

CH₃), 5.68 (dd, J_HP= 16.2, J_HH= 8.6 Hz, 1 H, ArCHCHCH-

(P⁺Ph₃)Ar), 6.24ꢀ6.31 (m, 1 H, ArCHCHCH(P⁺Ph₃)Ar), 6.79 (dd,

³J_HH= 15.7, ⁴J_HP= 4.8 Hz, 1 H, ArCHCHCH(P⁺Ph₃)Ar), 6.91ꢀ6.95

(m, 2 H, H_Ar), 7.07ꢀ7.15 (m, 4 H, H_Ar), 7.15ꢀ7.19 (m, 2 H, H_Ar),

7.52ꢀ7.58 (m, 6 H, H_Ar), 7.65ꢀ7.70 (m, 6 H, H_Ar), 7.83ꢀ7.88 ppm (m,

3 H, H_Ar). ¹³C NMR (CD₂Cl₂, 101 MHz): δ 21.4 (d, J_CP= 1.1 Hz,

CH₃), 21.5 (s, CH₃), 47.4 (d, J_CP= 43.9 Hz, CH), 117.5 (d, J_CP= 82.3

Hz, C), 118.6 (d, J_CP= 6.2 Hz, CH), 127.1 (d, J_CP= 1.9 Hz, CH), 128.7 (d,

J_CP= 5.4 Hz, C), 129.9 (d, J_CP= 1.0 Hz, CH), 130.5 (d, J_CP= 6.0 Hz, CH),

130.7 (d, J_CP= ca. 1.9 Hz, CH) superimposed with 130.8 (d, J_CP= 12.2 Hz,

3

(d, J_HH= 8.7 Hz, 4 H, H_Ar), 8.18ꢀ8.29 (m, 5 H, H_Ar,ArCH-

3

CHCH⁺Ar), 8.54 ppm (d, J_HH= 13.5 Hz, 2 H, ArCHCHCH⁺Ar).

¹³C NMR (CD₃CN, 101 MHz): δ 58.3 (CH₃), 114.5 (CH), 127.0

CH), 133.1 (d, J_CP= 3.0 Hz, C), 135.2 (d, J_CP= 8.8 Hz, CH), 135.9 (d, J_CP

=

(CH), 130.7 (C), 141.4 (CH), 172.9 (C), 176.3 ppm (CH). HRMS

(FAB, positive): calcd 253.1229 (C₁₇H₁₇O₂), found 253.1226. The ¹H

+

3.0 Hz, CH), 139.2 (d, J_CP= 13.1 Hz, CH), 139.7 (d, J_CP= 1.4 Hz, C), 140.4

ppm (d, J_CP= 3.3 Hz, C). ³¹P NMR (CD₂Cl₂, 162 MHz): δ 22.1 ppm.

HRMS (ESI, positive): calcd 483.2236 (C₃₅H₃₂P⁺), found 483.2235.

General Procedure for the Synthesis of (E)-(1,3-Diarylal-

lyl)triphenylphosphonium Triflates (1-PPh₃⁺TfO^ꢀ). Triphe-

nylphosphine (1 equiv) and trimethylsilyl triflate (1.2 equiv) were

successively added to a dichloromethane solution of (E)-((1,3-diaryl-

allyl)oxy)trimethylsilane (1-OTMS). The reaction mixture was stirred

for 30 min at rt. After evaporation of the solvent, the crude product was

recrystallized from a CH₂Cl₂/Et₂O mixture, affording the (diarylallyl)

triphenylphosphonium triflate.

NMR spectrum of 1g in 96% H₂SO₄has previously been reported.³⁶

(E)-1,3-Bis(4-methoxyphenyl)allyl Methyl Ether (1g-OMe).

A solution of 1g-BF₄(24.1 g, 71.0 mmol) in dichloromethane (250 mL)

was cooled to ꢀ70 °C before a 5.4 M sodium methoxide solution in

methanol (20.0 mL, 110 mmol) was added. The reaction mixture was

slowly brought to 0 °C using an ice bath and stirred overnight at this

temperature. The formed precipitate was filtered off, and the filtrate was

quenched with 2 M aqueous ammonia. The organic layer was separated,

and the water layer was extracted with diethyl ether (5ꢁ). The organic

phases were combined, and the solvents were removed in a rotary

evaporator. The crude product was purified by Kugelrohr distilla-

tion (250 °C, 10^ꢀ3mbar) affording 1g-OMe (6.0 g, 21 mmol, 30%).

(E)-(1,3-Bis(4-bromophenyl)allyl)triphenylphosphonium

Triflate (1c-PPh₃⁺TfO^ꢀ). From 1c-OTMS (620 mg, 1.41 mmol):

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ARTICLE

¹H NMR (CDCl₃, 400 MHz): δ 3.36 (s, 3 H, OMe), 3.80, 3.81 (2 s, 2 ꢁ

3 H, 2 ꢁ OMe), 4.74 (d, ³J_HH= 7.0 Hz, 1 H, ArCHCHCH(OMe)Ar),

EtOAc/NEt₃= 91/7/2) affording 4b (870 mg, 3.82 mmol, 19%). The

¹H NMR spectrum of 4b was in accord with the one described in ref 41.

(E)-1,3-Bis(julolidin-9-yl)allylium Tetrafluoroborate (1i-BF₄).

Magnesium (145 mg, 5.95 mmol) and lithium chloride (315 mg, 7.44

mmol) were slurried in THF (5 mL). Then DIBAL-H (1 M solution in

hexane, 220 μL, 0.223 mmol) was added to the resulting mixture followed by

dropwise addition of freshly sublimated (160 °C, 5 ꢁ 10^ꢀ3mbar) 4a (1.87g,

7.44 mmol). After completion of addition, the resulting mixture was kept

gently boiling until GCꢀMS analysis (analogous to the method described in

reference 28b) showed complete conversion of 4a. Asolutionof4b (780mg,

3.43 mmol) in THF was added dropwise to the reaction solution, and the

resulting mixture was refluxed for 3 h. After dissolving in conc acetic acid

(60 mL), the reaction mixture was poured into a 20% w/w aq solution of

sodium tetrafluoroborate (120 mL). A green precipitate formed which was

filtered, washed with water and diethyl ether, and dried in the vacuum to yield

1i-BF₄(0.95 g, 2.0 mmol, 59%) of as dark green powder (mp

151.6ꢀ152.5 °C, decomp). ¹H NMR (nitrobenzene-d₅, 400 MHz,

100 °C): δ 1.96ꢀ2.02 (m, 8 H, NCH₂CH₂CH₂), 2.73ꢀ2.79 (m, 8 H,

NCH₂CH₂CH₂), 3.49ꢀ3.55 (m, 8 H, NCH₂CH₂CH₂), 7.31 (s, 4 H, H_Ar),

7.43 (d, ³J_HH= 13.3 Hz, 2 H, ArCHCHCH⁺Ar), 7.67 ppm (t, ³J_HH= 13.3

Hz, 1 H, ArCHCHCH⁺Ar). ¹³C NMR (nitrobenzene-d₅, 101 MHz,

100 °C): δ 20.6 (CH₂), 26.9 (CH₂), 51.0 (CH₂), 119.0 (CH), 123.5

(C), 125.1 (C), 132.5 (CH), 151.1 (C), 156.5 ppm (CH). HRMS (ESI,

3

6.16 (dd, J_HH= 15.9, 7.0 Hz, 1 H, ArCHCHCH(OMe)Ar), 6.55 (d,

³J_HH= 15.9 Hz, 1 H, ArCHCHCH(OMe)Ar), 6.81ꢀ6.87 (m, 2 H, H_Ar),

6.88ꢀ6.94 (m, 2 H, H_Ar), 7.30ꢀ7.34 ppm (m, 4 H, H_Ar). ¹³C NMR

(CDCl₃, 101 MHz): δ 55.24 (CH₃), 55.25 (CH₃), 56.2 (CH₃), 84.0

(CH), 113.87 (CH), 113.92 (CH), 127.7 (CH), 128.1 (CH), 128.2

(CH), 129.4 (C), 130.8 (CH), 133.4 (C), 159.1 (C), 159.3 ppm (C).

Anal. Calcd for C₁₈H₂₀O₃: C, 76.03; H, 7.09. Found: C, 76.29; H, 7.03.

(E)-1,3-Bis(4-dimethylaminophenyl)allylium Tetrafluoro-

borate (1h-BF₄). Synthesized using Brieskorn’s procedure.³⁷4-Bro-

mo-N,N-dimethylaniline (9.11 g, 45.5 mmol) was added dropwise under

Ar atmosphere to lithium (1.20 g, 173 mmol) in dry diethyl ether

(100 mL) at ambient temperature. After 18 h of stirring, unreacted

lithium was filtered off, and (E)-3-(4-(dimethylamino)phenyl)propenal

(6.00 g, 34.2 mmol) was added dropwise to the filtrate (rt). After

refluxing for 3 h, subsequent cooling to rt, and dissolving in conc acetic

acid (250 mL), the reaction mixture was added to a 20% w/w aq solution

of sodium tetrafluoroborate (500 mL). A green precipitate formed

which was filtered, washed with water and diethyl ether, and dried in the

vacuum. Recrystallization from dichloromethane/pentane afforded 1h-

BF₄(7.04 g, 19.2 mmol, 56%) as a green powder with metallic gloss (mp

177ꢀ178 °C, decomp). In order to obtain crystals suitable for X-ray

diffraction analysis, 1h-BF₄was recrystallized from acetonitrile. ¹H

NMR (CD₃CN, 400 MHz): δ 3.22 (s, 12 H, 2 ꢁ NMe₂), 6.79ꢀ6.95

(m, 4 H, H_Ar), 7.65ꢀ7.86 ppm (m, 7 H). ¹³C NMR (CD₃CN, 101

MHz): δ 41.4 (CH₃), 115.0 (CH), 121.2 (CH), 126.2 (C), 137.3 (weak

broad peak which becomes sharper at 50 °C, CH), 157.7 (C), 161.5

+

positive): calcd 383.2482 (C₂₇H₃₁N₂), found 383.2479.

Product Studies

Reaction of 1,3-Diphenylallyl Cation (1e) with 2,3-Di-

methylbut-2-ene (2a). Zinc chloride (300 mg, 1.84 mmol), tetra-

butylammonium chloride (608 mg, 2.19 mmol), diethyl ether

(0.30 mL), and 2a (402 mg, 4.78 mmol) were dissolved in dichlor-

omethane (5 mL) and cooled to ꢀ78 °C. Then 1e-Cl (500 mg, 2.18

mmol) in dichloromethane (4 mL) was added dropwise. The reaction

solution was stirred at ꢀ78 °C for 2 h and then kept in a ꢀ60 °C fridge

for another 12 h. The resulting mixture was quenched with 2 M aqueous

ammonia. Diethyl ether was added to the organic phase followed by

washing with water and brine, drying (MgSO₄), and evaporation of the

solvents in a vacuum. The crude mixture (534 mg) contained (E)-(5-

chloro-4,4,5-trimethylhex-1-ene-1,3-diyl)dibenzene (3a) (ca. 350 mg,

ca. 1.1 mmol, ∼50%), (E)-(4,4,5-trimethylhexa-1,5-diene-1,3-diyl)-

dibenzene (3a⁰) (ca. 85 mg, ca. 0.3 mmol, ∼14%) and <20% of other

+

ppm (CH). HRMS (ESI, positive): calcd 279.1856 (C₁₉H₂₃N₂), found

279.1855.

(E)-1,3-Bis(julolidin-9-yl)allylium Tetrafluoroborate (1i-BF₄).

Synthesized using the following scheme:

1

products (all ratios are based on the H NMR spectrum of the crude

mixture). A portion of the crude product (298 mg) was purified by

column chromatography (silica gel, pentane/EtOAc = 99.3/0.7) afford-

ing 3a⁰(116 mg, 0.418 mmol). Assuming the same column efficiency for

the purification of the whole amount of the crude product one would

expect 35% (210 mg, 0.758 mmol) overall yield of 3a⁰.

The reaction under identical conditions but without Bu₄NCl aﬀorded

a complicated product mixture, which could not be resolved by using

column chromatography or distillation.

3a. ¹H NMR (CDCl₃, 599 MHz): δ 1.02, 1.28 (2 s, 2 ꢁ 3 H, 2 ꢁ

CH₃), 1.64, 1.66 (2 s, 2 ꢁ 3 H, 2 ꢁ CH₃), 3.87 (d, ³J_HH= 10.2 Hz, 1 H,

3

PhCHCHCH(R)Ph), 6.36 (d, J_HH= 15.7 Hz, 1 H, PhCHCHCH-

9-Bromo-1,2,3,5,6,7-hexahydropyrido[3,2,1-ij]quinoline

(4a). Julolidine (19.1 g, 110 mmol) was reacted with bromine (5.65 mL,

17.6 g, 110 mmol) in dichloromethane.³⁸Workup as described in ref 38

3

(R)Ph), 6.71 (dd, J_HH= 15.7, 10.2 Hz, 1 H, PhCHCHCH(R)Ph),

7.16ꢀ7.20 (m, 2 H, H_Ar), 7.23ꢀ7.31 (m, 6 H, H_Ar), 7.31ꢀ7.34 ppm

(m, 2 H, H_Ar). ¹³C NMR (CDCl₃, 151 MHz): δ 20.9 (CH₃), 23.7 (CH₃),

30.0 (CH₃), 30.2 (CH₃), 45.7 (C), 55.8 (CH), 80.6 (br. s, C), 126.1

(CH), 126.2 (CH), 127.1 (CH), 128.1 (CH), 128.5 (CH), 129.5 (CH),

130.6 (CH), 132.3 (CH), 137.7 (C), 143.9 ppm (C). ¹H and ¹³C NMR

spectra for 3a were obtained by comparing the spectra of the crude

mixture and those of isolated 3a⁰. HRMS of the crude mixture (EI,

positive): calcd 312.1639 (C₂₁H₂₅³⁵Cl, 3a), found 312.1631; calcd

276.1873 (C₂₁H₂₄, 3a⁰), found 276.1877.

1

afforded 4a (22.3 g, 88.3 mmol, 80%). The H NMR spectrum of

4a agreed with that described in the literature.³⁹

(E)-3-(1,2,3,5,6,7-Hexahydropyrido[3,2,1-ij]quinolin-9-

yl)acrylaldehyde (4b). 9-Bromojulolidine 4a (5.00 g, 19.8 mmol)

was reacted with acrolein diethylacetal (7.74 g, 59.4 mmol) in the

presence of tetrabutylammonium acetate (8.97 g, 29.7 mmol), potas-

sium acetate (0.97 g, 9.9 mmol), potassium carbonate (4.11 g, 29.7

mmol), potassium chloride (2.96 g, 39.7 mmol), and palladium acetate

(133 mg, 0.595 mmol) following a procedure as described in ref 40. The

reaction progress was monitored by TLC. After workup, the crude

product was purified by column chromatography (silica gel, hexane/

3a⁰. ¹H NMR (CDCl₃, 400 MHz): δ 1.01, 1.11 (2 s, 2 ꢁ 3 H, 2 ꢁ

3

CH₃), 1.77ꢀ1.78 (m, 3 H, CH₃), 3.52 (d, J_HH= 9.0 Hz, 1 H,

PhCHCHCH(R)Ph), 4.69ꢀ4.74 (m, 1 H, RR⁰CdCH₂), 4.77ꢀ4.82

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ARTICLE

3

(m, 1 H, RR⁰CdCH₂), 6.35 (d, J_HH= 15.7 Hz, 1 H, PhCHCHCH-

ylsilane (2d) (436 mg, 1.45 mmol), zinc chloride (100 mg, 0.612 mmol),

diethyl ether (0.1 mL), and dichloromethane (7 mL) at ꢀ78 °C. After

stirring for 30 min, the solution was allowed to warm up and quenched

with 2 M aq NH₃. The organic phase of the resulting mixture was

separated, washed with water and brine, and dried (MgSO₄) followed by

evaporation of solvents. The residue was dissolved in pentane and

filtered through a paper filter. The filtrate was freed from the solvent and

purified by column chromatography (silica gel, pentane/EtOAc = 98.4/

1.6) affording 3d (171 mg, 0.729 mmol, 53%) as a colorless oil. The ¹H

and ¹³C NMR spectra of 3d agreed with those described in ref 16.

HRMS (EI, positive): calcd 234.1403 (C₁₈H₁₈), found 234.1418. Anal.

Calcd for C₁₈H₁₈: C, 92.26; H, 7.74. Found: C, 92.10; H, 7.97.

3

(R)Ph), 6.57 (dd, J_HH= 15.7, 9.0 Hz, 1H, PhCHCHCH(R)Ph),

7.16ꢀ7.23 (m, 4 H, H_Ar), 7.24ꢀ7.29 (m, 4 H, H_Ar), 7.32ꢀ7.34 ppm (m,

2 H, H_Ar). ¹³C NMR (CDCl₃, 101 MHz): δ 20.1 (CH₃), 24.1 (CH₃),

25.7 (CH₃), 42.8 (C), 56.2 (CH), 111.3 (CH₂), 126.1 (2 ꢁ CH,

superimposed), 127.0 (CH), 127.6 (CH), 128.4 (CH), 129.7 (CH),

130.7 (CH), 131.2 (CH), 137.9 (C), 142.1 (C), 151.2 ppm (C). HRMS

(EI, positive): calcd 276.1873 (C₂₁H₂₄), found 276.1872.

(E)-(5-Chloro-5,6-dimethylhept-1-ene-1,3-diyl)dibenzene

(3b). Zinc chloride (300 mg, 1.84 mmol), tetrabutylammonium chlor-

ide (555 mg, 1.99 mmol), diethyl ether (0.30 mL), and 2,3-dimethylbut-

1-ene (2b) (370 mg, 4.40 mmol) were dissolved in dichloromethane

(5 mL). The mixture was cooled to ꢀ78 °C followed by dropwise

addition of 1e-Cl (455 mg, 1.99 mmol) in dichloromethane (4 mL).

After stirring for 30 min, the reaction was quenched with 2 M aq NH₃.

Diethyl ether was added to the organic phase followed by washing with

water and brine, drying (MgSO₄), and evaporation of the solvents in the

vacuum to afford 3b (481 mg) as a mixture of two diastereomers (dr ca.

1.4: 1) in ca. 70% purity (¹H NMR). Due to the presence of impurities in

(E)-4,4⁰-(Hexa-1,5-diene-1,3-diyl)bis(methoxybenzene) (3e).

Allyltrimethylsilane (2e) (913 mg, 7.99 mmol) was added to a solution of

1g-BF₄(1.36 g, 4.01 mmol) in dichloromethane (20 mL) at ambient

temperature. After stirring for 16 h, the reaction mixture was hydrolyzed

using 2 M aq NH₃and extracted with dichloromethane (2 ꢁ ). The

combined organic phases were washed with water and dried (MgSO₄).

Evaporation of the solvents in the vacuum afforded 3e (0.92 g, 3.1 mmol,

70%) as an oil. ¹H NMR (CDCl₃, 400 MHz): δ 2.51ꢀ2.56 (m, 2 H, CH₂),

3.45(ddd,³J_HH= 7.4, 7.4, 7.3 Hz, 1 H, ArCHCHCH(R)Ar), 3.78(2s, 2ꢁ 3

H, 2 ꢁ CH₃), 4.97(d, ³J_HH=10.2Hz, 1H, CHdCH₂), 5.03(d, ³J_HH=17.1

1

the crude product the yield could only be estimated to be ∼50%. H

3

NMR (CDCl₃, 300 MHz): 0.96 (d, J_HH= 6.69 Hz, 1.29 H, CH-

(CH₃)₂), 1.03 (d, ³J_HH= 6.73 Hz, 3.42 H, CH(CH₃)₂), 1.08 (d, ³J_HH

=

Hz, 1 H, CHdCH₂), 5.70ꢀ5.81 (m, 1 H, CHdCH₂), 6.19 (dd, ³J_HH

=

6.69 Hz, 1.29 H, CH(CH₃)₂), 1.40 (s, 1.71 H, CH₃), 1.48 (s, 1.29 H,

CH₃), 1.94ꢀ2.10 (m, 1 H, CH(CH₃)₂), 2.28ꢀ2.48 (m, 2 H, CH₂),

3.83ꢀ3.92 (m, 1 H, ArCHCHCH(R)Ar), 6.28ꢀ6.47 (m, 2 H,

ArCHCHCH(R)Ar), 7.15ꢀ7.38 ppm (m, 10 H, H_Ar). ¹³C NMR

(CDCl₃, 75.5 MHz): δ 18.07 (CH₃), 18.12 (CH₃), 18.16 (CH₃),

18.23 (CH₃), 27.7 (CH₃), 38.8 (CH), 39.2 (CH), 45.9 (CH), 46.2

(CH), 47.7 (CH₂), 48.2 (CH₂), 79.3 (C), 79.5 (C), 126.1 (CH), 126.3

(CH), 126.4 (CH), 127.09 (CH), 127.14 (CH), 127.6 (CH), 127.7

(CH), 128.4 (CH), 128.5 (CH), 128.69 (CH), 128.71 (CH), 129.1

(CH), 129.5 (CH), 134.9 (CH), 135.1 (CH), 137.4 (C), 145.1 (C),

145.4 ppm (C). HRMS (EI, positive): calcd 312.1639 (C₂₁H₂₅³⁵Cl),

found 312.1635.

3

15.8, 7.3 Hz, 1 H, ArCHCHCH(R)Ar), 6.30 (d, J_HH= 15.9 Hz, 1 H,

ArCHCHCH(R)Ar), 6.77ꢀ6.88 (m, 4 H, H_Ar), 7.13ꢀ7.18 (m, 2 H, H_Ar),

7.23ꢀ7.28 ppm (m, 2 H, H_Ar). ¹³C NMR (CDCl₃, 101 MHz): δ 40.4

(CH₂), 48.0 (CH), 55.2 (CH₃), 55.3 (CH₃), 113.86 (CH), 113.89 (CH),

116.1 (CH₂), 127.2 (CH), 128.6 (CH), 128.8 (CH), 130.4 (C), 131.7

(CH), 136.1 (CH), 136.8 (C), 158.0 (C), 158.9 ppm (C). Anal. Calcd for

C₂₀H₂₂O₂: C, 81.60; H, 7.53. Found: C, 81.77; H, 7.55.

Formation of 3e from 1g-BF₄and 2g. Allyltriphenylstannane (2g)

(385 mg, 0.985 mmol) was added successively to a dichloromethane

solution of 1g-BF₄(196 mg, 0.577 mmol) at room temperature. After

stirring for 30 min, the reaction mixture was hydrolyzed using 1 M aq

NH₃and then extracted with dichloromethane (2 ꢁ ). The combined

organic phases were washed with water, dried (MgSO₄) and freed from

solvents in the vacuum to yield the crude product (164 mg) for which ¹H

and ¹³C NMR spectra showed signals of 3e and some impurities (see pp

S163ꢀS164 of the Supporting Information).

(E)-(5-Chloro-5-methyloct-1-ene-1,3-diyl)dibenzene (3c).

According to procedure described in ref 42, 1e-Cl (1.25 g, 5.45 mmol)

was dissolved in dichloromethane (8 mL). This solution was added

dropwise to a mixture of 2-methylpent-1-ene (2c) (0.671 g, 7.96 mmol),

zinc chloride (300 mg, 1.84 mmol), diethyl ether (0.3 mL), and

dichloromethane (10 mL) at ꢀ78 °C. After stirring for 30 min, the

solution was allowed to warm up and quenched with 2 M aq NH₃. The

organic phase was separated, washed with water and brine, and dried

(MgSO₄). Evaporation of solvents in the vacuum afforded 3c (1.29 g) as

a mixture of two diastereomers (dr ca. 1.4: 1) of ca. 70% purity (¹H

NMR). Due to the presence of impurities in the crude product the yield

could only be estimated to be ∼50%. ¹H NMR (CDCl₃, 599 MHz): δ

0.84 (t, ³J_HH= 7.4 Hz, 1.74 H, CH₂CH₂CH₃), 0.87 (t, ³J_HH= 7.3 Hz,

1.26 H, CH₂CH₂CH₃), 1.34ꢀ1.52 (m, 2 H, CH₂CH₂CH₃), 1.45 (s,

1.26 H, CH₃), 1.53 (s, 1.74 H, CH₃), 1.65ꢀ1.82 (m, 2 H,

CH₂CH₂CH₃), 2.31ꢀ2.44 (m, 2 H, CH₂), 3.78ꢀ3.93 (m, 1 H,

PhCHCHCH(R)Ph), 6.35ꢀ6.41 (m, 2 H, PhCHCHCH(R)Ph),

7.16ꢀ7.39 ppm (m, 10 H, H_ar). ¹³C NMR (CDCl₃, 151 MHz): δ

14.07 (CH₃), 14.10 (CH₃), 18.1 (CH₂), 30.6 (CH₃), 30.8 (CH₃), 46.15

(CH), 46.21 (CH), 46.7 (CH₂), 47.1 (CH₂), 49.5 (CH₂), 49.7 (CH₂),

75.0 (C), 75.1 (C), 126.1 (CH), 126.34 (CH), 126.36 (CH), 127.11

(CH), 127.14 (CH), 127.66 (CH), 127.67 (CH), 128.40 (CH), 128.42

(CH), 128.67 (CH), 128.70 (CH), 129.3 (CH), 129.5 (CH), 134.75

(CH), 134.81 (CH), 137.4 (C), 137.5 (C), 145.0 (C), 145.1 ppm (C).

HRMS (EI, positive): calcd 312.1639 (C₂₁H₂₅³⁵Cl), found 312.1638.

Tables SX1 and SX2 of the Supporting Information compare the ¹H and

¹³C resonances found for 3c with those of the structurally related 3b.

(E)-Hexa-1,5-diene-1,3-diyldibenzene (3d). The allylium ion

precursor 1e-Cl (315 mg, 1.38 mmol) was dissolved in dichloromethane

(5 mL). This solution was added dropwise to a mixture of allyltriphen-

(E)-4,4⁰-(5-Methylhexa-1,5-diene-1,3-diyl)bis(methoxyben-

zene) (3f). (2-Methylallyl)-trimethylsilane (2f) (168mg, 1.31mmol) was

added to a solution of 1g-BF₄(223 mg, 0.656 mmol) in dichloromethane

(10 mL) at ambient temperature. After fading of the violet color, the

reaction mixture was filtered through a short column filled with alumina,

and the solvent was evaporated in the vacuum to yield 3f (190 mg, 0.616

mmol, 93%) asacolorlessoil. ¹HNMR(CDCl₃, 300MHz):δ1.72 (s, 3H,

CH₃), 2.50 (d, ³J_HH= 7.7 Hz, 2 H, CH₂), 3.60 (td, ³J_HH= 7.7, 6.8 Hz, 1 H,

ArCHCHCH(R)Ar), 3.79, 3.80 (2 s, 2 ꢁ 3 H, 2 ꢁ OCH₃), 4.67ꢀ4.68,

4.73ꢀ4.74 (2 m, 2 ꢁ 1 H, CdCH₂), 6.18 (dd, ³J_HH= 15.8, 6.8 Hz, 1 H,

ArCHCHCH(R)Ar), 6.28 (d, ³J_HH= 15.9 Hz, 1 H, ArCHCHCH(R)Ar),

6.79ꢀ6.83 (m, 2 H, H_Ar), 6.85ꢀ6.88 (m, 2 H, H_Ar), 7.15ꢀ7.19 (m, 2 H,

H_Ar), 7.23ꢀ7.28 ppm (m, 2 H, H_Ar). ¹³C NMR (CDCl₃, 75.5 MHz): δ

22.5 (CH₃), 44.5 (CH₂), 46.1 (CH), 55.2 (CH₃), 55.3 (CH₃), 112.4

(CH₂), 113.8 (CH), 113.9 (CH), 127.2 (CH), 128.5 (CH), 128.6 (CH),

130.4 (C), 132.1 (CH), 136.4 (C), 143.5 (C), 158.0 (C), 158.8 ppm (C).

HRMS (EI, positive): calcd 308.1771 (C₂₁H₂₄O₂), found 308.1762.

(E)-2-(1,3-Bis(4-methoxyphenyl)allyl)cyclohexanone (3h).

1-(Trimethylsiloxy)cyclohexene (2h) (1.00 mL, 204 mg, 1.92 mmol)

was added to a stirred solution of 1g-BF₄(204 mg, 0.600 mmol) in

dichloromethane (10 mL) at ꢀ78 °C. After the solution had changed

the color from intensive violet to red, the mixture was allowed to warm,

filtered through aluminum oxide using dichloromethane as solvent, and

freed from solvents in the vacuum. The crude mixture contained mainly

3h as mixture of diastereomers (dr 1.3:1, based on ¹H NMR).

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ARTICLE

Purification of the crude product by column chromatography (silica gel,

pentane/EtOAc = 85/15) afforded 3h in three fractions (overall yield of

isolated 3h: 24%).

135.1 (C), 158.1 (C), 159.0 (C), 219.3 ppm (C). HRMS (EI, positive):

calcd 336.1720 (C₂₂H₂₄O₃), found 336.1717.

Mixture of First and Second Diastereomer of 3i. Total 214 mg (0.635

mmol, 81%). ¹H and ¹³C NMR spectra are superpositions of the

corresponding spectra of both separately characterized diastereomers.

(E)-Phenyl 3,5-Bis(4-(dimethylamino)phenyl)pent-4-eno-

ate (3j). 1-Phenoxy-1-(trimethylsiloxy)ethene (2j) (340 μL, 341 mg,

1.64 mmol) was added to a suspension of 1h-BF₄(462 mg, 1.22 mmol)

in dichloromethane (5 mL). The mixture was stirred for 48 h and then

hydrolyzed with diluted aq NH₃. The organic layer was separated, and

the aqueous phase was extracted with dichloromethane (2ꢁ). The

combined organic phases were washed with water and dried (MgSO₄).

Evaporation of solvents followed by column chromatography (silica gel,

n-hexane/Et₂O = 3/1) afforded 3j (248 mg, 59.7 mmol, 47%) as an oily

First Diastereomer of 3h. Colorless oil, 20.4 mg (58.2 μmol, 10%).

¹H NMR (CDCl₃, 599 MHz): δ 1.37ꢀ1.43 (m, 1 H, CH₂), 1.57ꢀ1.64

(m, 1 H, CH₂), 1.73ꢀ1.86 (m, 3 H, CH₂), 1.90ꢀ1.98 (m, 1 H, CH₂),

2.33ꢀ2.38 (m, 1 H, CH₂), 2.42ꢀ2.46 (m, 1 H, CH₂), 2.79ꢀ2.83 (m, 1

H, CH), 3.77 (s, 3 H, OCH₃), 3.79 (s, 3 H, OCH₃), 3.80ꢀ3.81 (m, 1 H,

3

ArCHCHCH(R)Ar), 6.25 (d, J_HH= 15.9 Hz, 1 H, ArCHCHCH-

3

(R)Ar), 6.29 (dd, J_HH= 15.9, 6.5 Hz, 1 H, ArCHCHCH(R)Ar),

6.78ꢀ6.80 (m, 2 H, H_Ar), 6.85ꢀ6.87 (m, 2 H, H_Ar), 7.14ꢀ7.17 (m, 2 H,

H_Ar), 7.22ꢀ7.25 ppm (m, 2 H, H_Ar). ¹³C NMR (CDCl₃, 151 MHz): δ

23.8 (CH₂), 28.5 (CH₂), 32.0 (CH₂), 42.1 (CH₂), 47.4 (CH), 55.21

(CH₃), 55.24 (CH₃), 56.1 (CH), 113.8 (CH), 113.9 (CH), 127.3 (CH),

129.4 (CH), 129.5 (CH), 130.0 (CH), 130.2 (C), 134.1 (C), 158.1 (C),

158.8 (C), 212.7 ppm (C). HRMS (EI, positive): calcd 350.1876

(C₂₃H₂₆O₃), found 350.1864.

1

solid. H NMR (CDCl₃, 400 MHz): δ 2.94, 2.95 (2 s, 2 ꢁ 6 H, 2 ꢁ

NMe₂), 2.96ꢀ3.08 (m, 2 H, CH₂), 4.03ꢀ4.08 (m, 1 H, ArCHCHCH-

(R)Ar), 6.21 (dd, ³J_HH= 15.8, 7.5 Hz, 1 H, ArCHCHCH(R)Ar), 6.43

(d, ³J_HH= 15.8 Hz, 1 H, ArCHCHCH(R)Ar), 6.66ꢀ6.70 (m, 2 H, H_Ar),

6.73ꢀ6.79 (m, 2 H, H_Ar), 6.90ꢀ6.93 (m, 2 H, H_Ar), 7.16ꢀ7.33 ppm (m,

7 H, H_Ar). ¹³C NMR (CDCl₃, 101 MHz): δ 40.6 (CH₃), 46.8 (CH₃),

41.3 (CH₂), 44.5 (CH), 112.6 (CH), 113.1 (CH), 121.6 (CH), 125.6

(CH), 126.0 (C), 127.2 (CH), 128.1 (CH), 128.2 (CH), 129.3 (CH),

129.6 (CH), 131.0 (C), 149.5 (C), 149.9 (C), 150.7 (C), 170.7 ppm(C).

HRMS (EI, positive): calcd 414.2302 (C₂₇H₃₀N₂O₂), found 414.2308.

(E)-Methyl 3,5-Bis(4-(dimethylamino)phenyl)-2,2-dimethyl-

pent-4-enoate (3k). 1-Methoxy-2-methyl-1-(trimethylsiloxy)propene

(2k) (175 mg, 1.01 mmol) was added to a suspension of 1h-BF₄in

dichloromethane (10 mL) at room temperature. After stirring for 5 min, the

reaction mixture was washed with saturated aq NaHCO₃(3 ꢁ ), dried

(MgSO₄), and freed from the solvent. Recrystallization of the residue from

acetonitrile afforded 3k (192 mg, 0.505 mmol, 53%). ¹H NMR (CDCl₃, 400

MHz): δ 1.15, 1.21 (2 s, 2 ꢁ 3 H, 2 ꢁ CH₃), 2.92, 2.94 (2 s, 2 ꢁ 6 H, 2 ꢁ

NMe₂), 3.60 (s, 3 H, OCH₃), 3.65 (dd, ³J_HH= 5.7, ⁴J_HH= 3.0 Hz, 1 H,

ArCHCHCH(R)Ar), 6.29ꢀ6.40 (m, 2 H, ArCHCHCH(R)Ar), 6.65ꢀ6.70

Second Diastereomer of 3h. Colorless oil, 16.0 mg (45.7 μmol, 8%).

¹H NMR (CDCl₃, 599 MHz): δ 1.62ꢀ1.70 (m, 2 H, CH₂), 1.70ꢀ1.80

(m, 1 H, CH₂), 1.88ꢀ1.94 (m, 1 H, CH₂), 1.95ꢀ2.01 (m, 1 H, CH₂),

2.14ꢀ2.18 (m, 1 H, CH₂), 2.24ꢀ2.29 (m, 1 H, CH₂), 2.35ꢀ2.39 (m, 1

H, CH₂), 2.81ꢀ2.85 (m, 1 H, CH), 3.77 (s, 3 H, OCH₃), 3.79 (s, 3 H,

3

OCH₃), 3.90 (dd, J_HH= 8.9, 8.9 Hz, 1 H, ArCHCHCH(R)Ar), 6.09

(dd, ³J_HH= 15.7, 9.3 Hz, 1 H, ArCHCHCH(R)Ar), 6.37 (d, ³J_HH= 15.7

Hz, 1 H, ArCHCHCH(R)Ar), 6.80ꢀ6.84 (m, 4 H, H_Ar), 7.18ꢀ7.20 (m,

2 H, H_Ar), 7.25ꢀ7.28 ppm (m, 2 H, H_Ar). ¹³C NMR (CDCl₃, 151

MHz): δ 24.3 (CH₂), 28.4 (CH₂), 31.8 (CH₂), 42.3 (CH₂), 47.6 (CH),

55.2 (CH₃), 55.3 (CH₃), 55.9 (CH), 113.85 (CH), 113.87 (CH), 127.3

(CH), 128.8 (CH), 129.1 (CH), 130.1 (C), 130.3 (CH), 135.4 (C),

157.9 (C), 158.9 (C), 212.0 ppm (C). HRMS (EI, positive): calcd

350.1876 (C₂₃H₂₆O₃), found 350.1873.

Mixture of First and Second Diastereomer of 3h. Colorless oil (12.8

mg, 36.5 μmol, 6%). ¹H and ¹³C NMR spectra are superpositions of the

corresponding spectra of both separately characterized diastereomers.

(E)-2-(1,3-Bis(4-methoxyphenyl)allyl)cyclopentanone (3i).

Prepared analogously to 3h from 1g-BF₄(250 mg, 0.735 mmol) and

1-(trimethylsiloxy)cyclopentene (2i, 264 mg, 1.69 mmol) as a mixture of

diastereomers (dr 1:1.9, based on ¹H NMR of the crude product). After

column chromatography (silica gel, pentane/EtOAc = 85/15), three

fractions were obtained (overall yield of isolated 3i: 94%).

(m, 4H, H_Ar), 7.09ꢀ7.12 (m, 2 H, H_Ar), 7.23ꢀ7.26 ppm (m, 2 H, H_Ar). ¹³

C

NMR (CDCl₃, 101 MHz): δ 22.3 (CH₃), 23.2 (CH₃), 40.6 (CH₃), 40.7

(CH₃), 47.6 (C), 51.5 (CH₃), 56.1 (CH), 112.4 (CH), 112.5 (CH), 125.0

(CH), 126.5 (C), 127.1 (CH), 129.0 (C), 129.8 (CH), 131.7 (CH), 149.3

(C), 149.8 (C), 177.9 ppm (C). Anal. Calcd for C₂₄H₃₂N₂O₂: C, 75.75; H,

8.48; N, 7.36. Found: C, 75.53; H, 8.55; N, 7.38.

First Diastereomer of 3i. Colorless oil, 28.9 mg (0.0859 mmol, 11%).

¹H NMR (CDCl₃, 599 MHz): δ 1.60ꢀ1.68 (m, 1 H, CH₂), 1.69ꢀ1.73

(m, 1 H, CH₂), 1.76ꢀ1.82 (m, 1 H, CH₂), 1.86ꢀ1.92 (m, 1 H, CH₂),

2.08ꢀ2.13 (m, 1 H, CH₂), 2.22ꢀ2.27 (m, 1 H, CH₂), 2.59ꢀ2.63 (m, 1

H, CH), 3.78 (s, 3 H, OCH₃), 3.80 (s, 3 H, OCH₃), 4.00ꢀ4.02 (m, 1 H,

(E)-1,3-Bis(4-methoxyphenyl)prop-2-ene (3l). Dimethylphen-

ylsilane (2l) (1.40 mL, 1.25 g, 9.15 mmol) was added to a stirred

suspension of 1g-BF₄(1.06 g, 3.11 mmol) in dichloromethane at rt. After

complete decolorization, the reaction mixture was hydrolyzed with water

and extracted with dichloromethane (2ꢁ). The combined organic phases

were dried (MgSO₄) and freed from solvent. Kugelrohr distillation of the

crude product (240ꢀ250 °C, 1.1 ꢁ 10^ꢀ2mbar) gave 3l (0.648 g, 2.55

mmol, 82%) as an oil. The ¹H and ¹³C NMR spectra agreed with those

described in ref 43. Anal. Calcd for C₁₇H₁₈O₂: C, 80.28; H, 7.13. Found:

C, 80.61; H, 7.07.

3

ArCHCHCH(R)Ar), 6.36 (d, J_HH= 16.0 Hz, 1 H, ArCHCHCH-

3

(R)Ar), 6.43 (dd, J_HH= 16.0, 6.9 Hz, 1 H, ArCHCHCH(R)Ar),

6.82ꢀ6.85 (m, 4 H, H_Ar), 7.12ꢀ7.15 (m, 2 H, H_Ar), 7.29ꢀ7.31 ppm (m,

2 H, H_Ar). ¹³C NMR (CDCl₃, 151 MHz): δ 20.5 (CH₂), 26.3 (CH₂),

38.8 (CH₂), 46.7 (CH), 53.8 (CH), 55.2 (CH₃), 55.3 (CH₃), 113.6

(CH), 113.9 (CH), 127.3 (CH), 129.53 (CH), 129.54 (CH), 129.9

(CH), 130.2 (C), 133.5 (C), 158.2 (C), 158.9 (C), 219.6 ppm (C).

HRMS (EI, positive): calcd 336.1720 (C₂₂H₂₄O₃), found 336.1719.

Second Diastereomer of 3i. Colorless oil, 4.2 mg (0.012 mmol, 2%).

¹H NMR (CDCl₃, 599 MHz): δ 1.71ꢀ1.76 (m, 1 H, CH₂), 1.91ꢀ2.06

(m, 3 H, CH₂), 2.16ꢀ2.23 (m, 1 H, CH₂), 2.28ꢀ2.33 (m, 1 H, CH₂),

2.53ꢀ2.57 (m, 1 H, CH), 3.79 (s, 3 H, OCH₃), 3.80 (s, 3 H, OCH₃),

Reaction between 1g-BF₄and 1-Methyl-1H-pyrrole (2m).

A suspension of 1g-BF₄(162 mg, 0.478 mmol) in dichloromethane was

added dropwise to a solution of 1-methyl-1H-pyrrole (2m) (578 mg,

7.13 mmol) in dichloromethane (10 mL) at ꢀ78 °C. The resulting

mixture was allowed to warm, then washed with brine and water, dried

(MgSO₄), and freed from solvents in the vacuum. Based on its ¹H NMR

spectrum the crude mixture (183 mg) contained (E)-2-(1,3-bis(4-

methoxyphenyl)allyl)-1-methyl-1H-pyrrole (3m) (ca. 120 mg, 0.36 mmol,

∼70%), 2,5-bis((E)-1,3-bis(4-methoxyphenyl)allyl)-1-methyl-1H-pyrrole

(3 m⁰) (ca. 20 mg, 0.039 mmol, ∼15%), unreacted 1-methyl-1-H-pyrrole

(2m, ca. 9 mg, 0.1 mmol), and some impurities (ca. 10% w/w).

4.03 (dd, ³J_HH= 8.4, 4.1 Hz, 1 H, ArCHCHCH(R)Ar), 6.23 (dd, ³J_HH

=

15.7, 8.4 Hz, 1 H, ArCHCHCH(R)Ar), 6.33 (d, ³J_HH= 15.7 Hz, 1 H,

ArCHCHCH(R)Ar), 6.80ꢀ6.83 (m, 2 H, H_Ar), 6.85ꢀ6.88 (m, 2 H,

H_Ar), 7.20ꢀ7.24 (m, 2 H, H_Ar), 7.24ꢀ7.29 ppm (m, 2 H, H_Ar). ¹³C

NMR (CDCl₃, 151 MHz): δ 20.7 (CH₂), 25.9 (CH₂), 38.9 (CH₂), 47.0

(CH), 55.0 (CH), 55.25 (CH₃), 55.29 (CH₃), 113.86 (CH), 113.91

(CH), 127.2 (CH), 127.4 (CH), 128.9 (CH), 130.1 (C), 131.4 (CH),

3m. ¹H NMR (CDCl₃, 599 MHz): δ 3.42 (s, 3 H, NCH₃), 3.81 (s, 3

H, OCH₃), 3.82 (s, 3 H, OCH₃), 4.80 (d, ³J_HH= 6.9 Hz, ArCHCHCH-

(R)Ar), 5.93ꢀ5.98 (m, 1 H, H_Ar), 6.10ꢀ6.13 (m, 1 H, H_Ar), 6.19 (d,

9404

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ARTICLE

³J_HH= 15.8 Hz, 1 H, ArCHCHCH(R)Ar), 6.47 (dd, ³J_HH= 15.8, 6.9 Hz,

1 H, ArCHCHCH(R)Ar), 6.60ꢀ6.63 (m, 1 H, H_Ar), 6.82ꢀ6.90 (m, 4

2.35ꢀ2.43 (m, 1 H, CH₂), 2.80ꢀ2.85 (m, 1 H, CH), 2.91, 2.94 (2 s,

2 ꢁ 6 H, 2 ꢁ NMe₂), 3.88 (dd, ³J_HH= 9.0, 8.9 Hz, 1 H, ArCHCHCH-

(R)Ar), 6.03 (dd, ³J_HH= 15.6, 9.0 Hz, 1 H, ArCHCHCH(R)Ar), 6.35

(d, ³J_HH= 15.6 Hz, 1 H, ArCHCHCH(R)Ar), 6.66 (d, ³J_HH= 8.8 Hz, 2

H, H_Ar), 6.69 (d, ³J_HH= 8.7 Hz, 2 H, H_Ar), 7.16 (d, ³J_HH= 8.7 Hz, 2 H,

H_Ar), 7.24 ppm (d, ³J_HH= 8.8 Hz, 2 H, H_Ar). ¹³C NMR (CDCl₃, 151

MHz): δ 23.9 (CH₂), 28.4 (CH₂), 31.5 (CH₂), 40.6 (CH₃), 40.7

(CH₃), 42.0 (CH₂), 47.5 (CH), 56.0 (CH), 112.5 (CH), 112.8 (CH),

126.2 (C), 127.0 (CH), 127.5 (CH), 128.4 (CH), 130.4 (CH), 131.4

(C), 149.0 (C), 149.8 (C), 212.5 ppm (C). HRMS (EI, positive): calcd

376.2509 (C₂₅H₃₂N₂O), found 376.2502.

H, H_Ar), 7.09ꢀ7.15 (m, 2 H, H_Ar), 7.28ꢀ7.34 ppm (m, 2 H, H_Ar). ¹³

C

NMR (CDCl₃, 151 MHz): δ 33.9 (CH₃), 45.7 (CH), 55.2 (CH₃), 55.3

(CH₃), 106.4 (CH), 107.6 (CH), 113.8 (CH), 113.9 (CH), 122.0

(CH), 127.4 (CH), 129.4 (CH), 129.6 (CH), 130.0 (CH), 130.1 (C),

134.1 (C), 134.2 (C), 158.2 (C) 158.9 ppm (C). HRMS (ESI, positive):

calcd 333.1729 (C₂₂H₂₃NO₂), found 333.1720.

3 m⁰. ¹H NMR (CDCl₃, 599 MHz): δ 3.61 (s, 3 H, NCH₃), 3.81, 3.82

(2 s, 2 ꢁ 6 H, 4 ꢁ OCH₃), 4.70 (d, ³J_HH= 7.6 Hz, 2 H, ArCHCHCH-

(R)Ar), 6.34 (s, 2 H, H_Ar) overlapped with 6.36 (d, ³J_HH= 15.7 Hz, 2 H,

ArCHCHCH(R)Ar), 6.48 (dd, ³J_HH= 15.7, 7.6 Hz, 2 H, ArCHCHCH-

(R)Ar), 6.82ꢀ6.90 (m, 8 H, H_Ar), 7.21ꢀ7.28 (m, 4 H, H_Ar), 7.30ꢀ7.35

ppm (m, 4 H, H_Ar). ¹³C NMR (CDCl₃, 151 MHz): δ 36.1 (CH₃), 46.6

(CH), 55.21 (CH₃), 55.24 (CH₃), 113.6 (CH), 113.8 (CH), 119.8

(CH), 127.0 (C), 127.3 (CH), 128.8 (CH), 129.2 (CH), 130.5 (C),

131.9 (CH), 137.0 (C), 157.9 (C), 158.7 ppm (C).

Mixture of First and Second Diastereomer of 3n⁰. Yellowish oil, 12.4 mg

1

(0.0239 mmol, 4%). H and ¹³C NMR spectra are superpositions of the

corresponding spectra of both separately characterized diastereomers.

1

Overall yield of 3n⁰: 23%. As the H NMR spectrum of the crude

product (286 mg, ca. 100%) contains mainly the signals corresponding

to the mixture of two diastereomers described above, the much lower

yield of isolated material can be explained by puriﬁcation problems

(partial decomposition of 3n⁰on the column).

(E)-4-(2-(1,3-Bis(4-(dimethylamino)phenyl)allyl)cyclohe-

xylidene)morpholin-4-ium Tetrafluoroborate (3n, mixture

of diastereomers). The allylium tetrafluoroborate 1h-BF₄(68.1 mg,

0.186 mmol) and 1-(N-morpholino)cyclohexene (2n) (32.5 mg, 0.194

mmol) were mixed in CD₂Cl₂. The resulting solution was analyzed by

(E)-1-(2-(1,3-Bis(4-(dimethylamino)phenyl)allyl)cyclo-

pentylidene)piperidin-1-ium Tetrafluoroborate (3o, mixture

of diastereomers). The allylium tetrafluoroborate 1h-BF₄(70.2 mg,

0.192 mmol) and 1-(N-piperidino)cyclopentene (2o) (30.3 mg, 0.200

mmol) were mixed in CD₂Cl₂. The resulting solution was analyzed by

1

NMR and HRMS. H NMR (CD₂Cl₂, 400 MHz, only characteristic

resonances): δ 2.90, 2.93, 2.93, 2.94 (4 s, 12 H, 4 ꢁ NMe₂), 5.93 (dd,

³J_HH= 15.7, 9.9 Hz, 0.48 H, ArCHCHCH(R)Ar), 6.18 (dd, ³J_HH= 15.6,

9.5 Hz, 0.52 H, ArCHCHCH(R)Ar), 6.30 (d, ³J_HH= 15.7 Hz, 0.48 H,

1

NMR and HRMS. H NMR (CD₂Cl₂, 400 MHz, only characteristic

resonances): δ 2.92, 2.93, 2.94, 2.95 (4 s, 12 H, 4 ꢁ NMe₂), 6.06 (dd,

³J_HH= 15.6, 9.2 Hz, 0.48 H, ArCHCHCH(R)Ar), 6.20 (dd, ³J_HH= 15.6,

3

ArCHCHCH(R)Ar), 6.49 ppm (d, J_HH= 15.6 Hz, 0.52 H,

3

ArCHCHCH(R)Ar). ¹³C NMR (CD₂Cl₂, 101 MHz, only characteristic

resonances): δ 40.6, 40.7, 40.78, 40.82, (4 ꢁ CH₃, 2 ꢁ NMe₂), 48.0,

48.9 (2 ꢁ CH, CHCdN⁺), 50.8, 51.7 (2 ꢁ CH, ArCHCHCH(R)Ar),

124.0, 124.8 (2 ꢁ CH, ArCHCHCH(R)Ar), 131.6, 133.5 (2 ꢁ CH,

ArCHCHCH(R)Ar), 195.6, 195.7 ppm (2 ꢁ C, CdN⁺); the chemical

shifts of CdN⁺are close to those for products of reactions between

benzhydrylium ions and 2n (δ 195.1 ppm, see ref 8a). HRMS (ESI,

positive): calcd 446.3166 (C₂₉H₄₀N₃O), found 446.3163. Tables SX3

and SX4 of the Supporting Information compare the characteristic ¹H

and ¹³C resonances of compound 3n listed above with those of the

hydrolyzed product 3n⁰.

8.9 Hz, 0.52 H, ArCHCHCH(R)Ar), 6.31 (d, J_HH= 15.6 Hz, 0.48 H,

3

ArCHCHCH(R)Ar), 6.42 (d, J_HH= 15.6 Hz, 0.52 H, ArCHCHCH-

(R)Ar), 6.62ꢀ6.75 (m, 4 H, H_Ar), 7.06ꢀ7.11 (m, 1.04 H, H_Ar), 7.11ꢀ7.16

(m, 0.96 H, H_Ar), 7.21ꢀ7.25 (m, 0.96 H, H_Ar), 7.26ꢀ7.31 ppm (m, 1.04

H, H_Ar). ¹³C NMR (CD₂Cl₂, 101 MHz, only characteristic resonances): δ

40.61, 40.68, 40.80, 40.83 (4 ꢁ CH₃), 50.2, 51.3 (2 ꢁ CH, ArCHCHCH-

(R)Ar), 52.0, 52.3 (2 ꢁ CH, CHCdN⁺), 123.7, 125.4 (2 ꢁ CH,

ArCHCHCH(R)Ar), 132.0, 133.3 (2 ꢁ CH, ArCHCHCH(R)Ar),

198.4, 198.7 ppm (2 ꢁ C, CdN⁺). HRMS (ESI, positive): calcd

430.3217 (C₂₉H₄₀N₃), found 430.3219. Tables SX5 and SX6 of the

Supporting Information compare the characteristic ¹H and ¹³C

resonances of compound 3o listed above with those of the hydro-

lyzed product 3o⁰.

(E)-2-(1,3-Bis(N,N-dimethylaminophenyl)allyl)cyclopen-

tanone (3o⁰). Analogously to 3n⁰; from 1h-BF₄(208 mg, 0.568 mmol)

and 1-(N-piperidino)cyclopentene (2o) (90.2 mg, 0.597 mmol). The

crude product was purified by column chromatography (silica gel,

pentane/EtOAc = 3/1) affording three fractions of 3o⁰(overall yield

of isolated 3o⁰, 54%).

(E)-2-(1,3-Bis(4-(dimethylamino)phenyl)allyl)cyclohexanone

(3n⁰). A solution of 1h-BF₄(268 mg, 0.736 mmol) in dichloromethane

(30 mL) was prepared. Subsequently, 1-(N-morpholino)-cyclohexene (2n)

(129 mg, 0.772 mmol) and aqueous acetic acid (50 mL of a ca. 2% v/v

solution) were added. The resulting mixture was stirred for 48 h at rt. The

aqueous phase was separated and extracted with dichloromethane (2ꢁ).

The combined organic phases were then dried (MgSO₄) and freed from

solvents. The crude product was purified by column chromatography (silica

gel, pentane/EtOAc = 3/1) affording 3n⁰in three fractions:

First Diastereomer of 3o⁰. Colorless oil, 18.6 mg (0.0513 mmol, 9%).

¹H NMR (CDCl₃, 599 MHz): δ 1.65ꢀ1.73 (m, 2 H, CH₂), 1.73ꢀ1.80

(m, 1 H, CH₂), 1.81ꢀ1.92 (m, 1 H, CH₂), 2.07ꢀ2.17 (m, 1 H, CH₂),

2.16ꢀ2.27 (m, 1 H, CH₂), 2.56ꢀ2.66 (m, 1 H, CH), 2.91 (s, 6 H, NMe₂),

2.94 (s, 6 H, NMe₂), 3.99ꢀ4.02 (m, 1 H, ArCHCHCH(R)Ar),

6.31ꢀ6.38 (m, 2 H, ArCHCHCH(R)Ar), 6.63ꢀ6.70 (m, 4 H, H_Ar),

7.05ꢀ7.10 (m, 2 H, H_Ar), 7.23ꢀ7.28 ppm (m, 2 H, H_Ar). ¹³C NMR

(CDCl₃, 151 MHz): δ 20.6 (CH₂), 26.2 (CH₂), 38.9 (CH₂), 40.6

(CH₃), 40.7 (CH₃), 46.6 (CH), 54.0 (CH), 112.5 (CH), 112.6 (CH),

126.3 (C), 127.1 (CH), 127.9 (CH), 129.5 (CH), 129.6 (CH), 129.7

(C), 149.2 (C), 149.8 (C), 220.2 ppm (C). HRMS (EI, positive): calcd

362.2353 (C₂₄H₃₀N₂O), found 362.2363.

First Diastereomer of 3n⁰. Yellowish oil, 15.3 mg (0.0406 mmol, 6%).

¹H NMR (CDCl₃, 599 MHz): δ 1.43ꢀ1.50 (m, 1 H, CH₂), 1.54ꢀ1.63

(m, 1 H, CH₂), 1.70ꢀ1.80 (m, 1 H, CH₂), 1.78ꢀ1.87 (m, 2 H, CH₂),

1.87ꢀ1.95 (m, 1 H, CH₂), 2.28ꢀ2.37 (m, 1 H, CH₂), 2.40ꢀ2.49 (m, 1

H, CH₂), 2.76ꢀ2.83 (m, 1 H, CH), 2.91, 2.92 (2 s, 2 ꢁ 6 H, 2 ꢁ NMe₂),

3.77 (dd, ³J_HH= 9.5, 6.0 Hz, 1 H, ArCHCHCH(R)Ar), 6.16ꢀ6.26 (m, 2

H, ArCHCHCH(R)Ar), 6.60ꢀ6.65 (m, 2 H, H_Ar), 6.68ꢀ6.74 (m, 2 H,

H_Ar), 7.09ꢀ7.14 (m, 2 H, H_Ar), 7.17ꢀ7.21 ppm (m, 2 H, H_Ar). ¹³C

NMR (CDCl₃, 151 MHz): δ 23.4 (CH₂), 28.5 (CH₂), 31.7 (CH₂), 40.6

(CH₃), 40.7 (CH₃), 41.9 (CH₂), 47.4 (CH), 56.3 (CH), 112.5 (CH),

112.8 (CH), 126.3 (C), 127.1 (CH), 128.2 (CH), 129.0 (CH), 129.5

(CH), 130.2 (C), 149.2 (C), 149.8 (C), 213.2 ppm (C). HRMS (EI,

positive): calcd 376.2509 (C₂₅H₃₂N₂O), found 376.2492.

Second Diastereomer of 3o⁰. Colorless oil, 54.8 mg (0.151 mmol,

1

27%). H NMR (CDCl₃, 599 MHz): δ 1.67ꢀ1.77 (m, 1 H, CH₂),

Second Diastereomer of 3n⁰. Colorless solid, 36.5 mg (0.0969 mmol,

1.93ꢀ2.07 (m, 3 H, CH₂), 2.13ꢀ2.22 (m, 1 H, CH₂), 2.25ꢀ2.33 (m, 1

H, CH₂), 2.50ꢀ2.58 (m, 1 H, CH), 2.93, 2.93 (2 s, 2 ꢁ 6 H, 2 ꢁ NMe₂),

1

13%). H NMR (CDCl₃, 599 MHz): δ 1.59ꢀ1.69 (m, 1 H, CH₂),

1.69ꢀ1.77 (m, 1 H, CH₂), 1.77ꢀ1.86 (m, 1 H, CH₂), 1.86ꢀ2.00 (m, 2

H, CH₂), 2.09ꢀ2.17 (m, 1 H, CH₂), 2.21ꢀ2.30 (m, 1 H, CH₂),

4.01 (dd, ³J_HH= 8.5, 3.8 Hz, 1 H, ArCHCHCH(R)Ar), 6.16 (dd, ³J_HH

=

15.7, 8.5 Hz, 1 H, ArCHCHCH(R)Ar), 6.31 (d, ³J_HH= 15.7 Hz, 1 H,

9405

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The Journal of Organic Chemistry

ARTICLE

ArCHCHCH(R)Ar), 6.62ꢀ6.69 (m, 2 H, H_Ar), 6.69ꢀ6.77 (m, 2 H,

H_Ar), 7.17ꢀ7.21 (m, 2 H, H_Ar), 7.21ꢀ7.24 ppm (m, 2 H, H_Ar). ¹³C

NMR (CDCl₃, 151 MHz): δ 20.8 (CH₂), 25.7 (CH₂), 39.0 (CH₂), 40.6

(CH₃), 40.8 (CH₃), 46.9 (CH), 55.1 (CH), 112.4 (CH), 112.8 (CH),

125.5 (CH), 126.2 (C), 127.1 (CH), 128.5 (CH), 131.3 (C), 131.5

(CH), 149.2 (C), 149.9 (C), 219.9 ppm (C). HRMS (EI, positive): calcd

362.2353 (C₂₄H₃₀N₂O), found 362.2352.

to the crude product, and the resulting suspension was treated with

ultrasound for 30 min. Then the solid residue was filtered and dried in

the vacuum affording 3s (304 mg, 0.831 mmol, 93%) as a pale gray solid

(mp 76.8ꢀ78.1 °C, decomp). ¹H NMR (CDCl₃, 300 MHz): δ

2.37ꢀ2.44 (m, 2 H, NCH₂), 2.53ꢀ2.60 (m, 2 H, NCH₂), 2.95 (s, 12

H, 2 ꢁ NMe₂), 3.68 (d, ³J_HH= 8.9 Hz, 1 H, ArCHCHCH(R)Ar), 3.72

3

(t, J_HH= 4.7 Hz, 4 H, CH₂O), 6.10 (dd, J_HH= 15.7, 8.9 Hz, 1 H,

3

Mixture of First and Second Diastereomer of 3o⁰. Colorless oil,

ArCHCHCH(R)Ar), 6.45 (d, J_HH= 15.7 Hz, 1 H, ArCHCHCH-

1

36.8 mg (0.101 mmol, 18%). H and ¹³C NMR spectra are super-

(R)Ar), 6.67 (d, ³J_HH= 8.8 Hz, 2 H, H_Ar), 6.73 (d, ³J_HH= 8.8 Hz, 2 H,

H_Ar), 7.26 (d, ³J_HH= 8.8 Hz, 2 H, H_Ar), 7.27 ppm (d, ³J_HH= 8.8 Hz, 2 H,

H_Ar). ¹³C NMR (CDCl₃, 75.5 MHz): δ 40.5 (CH₃), 40.7 (CH₃), 52.2

(CH₂), 67.2 (CH₂), 74.4 (CH), 112.4 (CH), 112.7 (CH), 125.7 (C),

127.2 (CH), 127.4 (CH), 128.7 (CH), 129.7 (C), 130.9 (CH), 149.8

(C), 150.0 ppm (C). Anal. Calcd for C₂₃H₃₁N₃O: C, 75.58; H, 8.55; N,

11.50. Found: C, 75.37; H, 8.60; N, 11.21.

positions of the corresponding spectra of both separately characterized

diastereomers.

(E)-N-(1,3-Bis(4-(dimethylamino)phenyl)allyl)-2,2,2-tri-

fluoroethylamine (3p). Obtained from 1h-BF₄(134 mg, 0.365

mmol), 2,2,2-trifluoroethylamine (2p) (75.6 mg, 0.763 mmol), and

potassium carbonate (529 mg, 3.83 mmol) by using a procedure

1

(E)-9,9⁰-(3-(Piperidin-1-yl)prop-1-ene-1,3-diyl)bis(1,2,3,5,-

6,7-hexahydropyrido[3,2,1-ij]quinoline) (3t). Piperidine 2t

(12.0 mg, 0.141 mmol) was added to a stirred slurry of 1i-BF₄(30.6

mg, 65.1 μmol) and potassium carbonate (98.5 mg, 0.713 mmol) in

acetonitrile (10 mL). After fading of the green color, the mixture was

diluted with diethyl ether, washed with 2 M NaOH solution and dried

(MgSO₄). Evaporation of the solvent gave the crude product that was

analyzed by NMR spectroscopy. Because of the high instability of 3t in

the presence of proton sources (reaction between 1i and piperidine is

reversible) further attempts to purify 3t were not made. ¹H NMR

(CD₃CN, 400 MHz): δ 1.36ꢀ1.45 (m, 2 H, CH₂), 1.46ꢀ1.56 (m, 4 H,

CH₂), 1.85ꢀ1.92 (m, 8 H, CH₂), 2.30ꢀ2.46 (m, 4 H, CH₂), 2.64ꢀ2.70

(m, 8 H, CH₂), 3.06ꢀ3.11 (m, 8 H, CH₂), 3.47 (d, ³J_HH= 8.9 Hz, 1 H,

ArCHCHCH(R)Ar), 5.93 (dd, ³J_HH= 15.9, 8.9 Hz, 1 H, ArCHCHCH-

(R)Ar), 6.20 (d, ³J_HH= 15.9 Hz, 1 H, ArCHCHCH(R)Ar), 6.68 (s, 2 H,

H_Ar), 6.74 ppm (s, 2 H, H_Ar). ¹³C NMR (CD₃CN, 101 MHz): δ 23.0

(CH₂), 23.2 (CH₂), 25.7 (CH₂), 27.1 (CH₂), 28.4 (CH₂), 28.5 (CH₂),

50.7 (CH₂), 50.8 (CH₂), 53.4 (CH₂), 75.3 (CH), 122.4 (C), 122.5 (C),

125.75 (C), 125.81 (CH), 127.3 (CH), 128.8 (CH), 130.9 (CH), 131.3

(C), 142.9 (C), 143.4 ppm (C). Though signals of excess piperidine and

some other impurities are present in the NMR spectra, these spectra still

allow unambiguous identification of 3t as the major product formed in

the reaction.

described in ref 44: yellow oil, 133 mg (0.352 mmol, 96%). H NMR

(CD₂Cl₂, 400 MHz): δ 1.74 (s, 1 H, NH), 2.96, 2.96 (2 s, 2 ꢁ 6 H, 2 ꢁ

3

NMe₂), 3.29ꢀ3.14 (m, 2 H, CH₂), 4.38 (d, J_HH= 7.7 Hz, 1 H,

ArCHCHCH(R)Ar), 6.07 (dd, ³J_HH= 15.8, 7.7 Hz, 1 H, ArCHCHCH-

(R)Ar), 6.51 (d, ³J_HH= 15.8 Hz, 1 H, ArCHCHCH(R)Ar), 6.65ꢀ6.73

(m, 2 H, H_Ar), 6.73ꢀ6.80 (m, 2 H, H_Ar), 7.18ꢀ7.38 ppm (m, 4 H, H_Ar).

¹³C NMR (CDCl₃, 101 MHz): 40.8 (CH₃), 41.0 (CH₃), 48.3 (q, ²J_CF

=

30.9 Hz, CH₂), 64.8 (CH), 112.8 (CH), 113.3 (CH), 125.7 (C), 126.7

(q, ¹J_CF= 278.5 Hz, CF₃), 127.9 (CH), 128.2 (CH), 128.5 (CH), 130.7

(C), 131.0 (CH), 150.8 (C), 150.9 ppm (C). ¹⁹F NMR (CD₂Cl₂, 376

MHz) δ ꢀ71.7 to ꢀ71.6 ppm (m). HRMS (EI, positive): calcd

377.2073 (C₂₁H₂₆F₃N₃), found 377.2074.

(E)-N-(1,3-Bis(4-(dimethylamino)phenyl)allyl)isopropylamine

(3q). Obtained analogously to 3p from isopropylamine 2q (129 mg,

1.74 mmol) and 1h-BF₄(366 mg, 0.871 mmol) without use of K₂CO₃:

1

red oily solid, 243 mg (0.721 mmol, 83%). H NMR (CDCl₃, 599

MHz): δ 1.08 (d, ³J_HH= 6.3 Hz, 3 H, CH₃₃), 1.10 (d, ³J_HH= 6.3 Hz, 3 H,

CH₃), 1.35 (br. s, 1 H, NH), 2.83 (qq, J_HH= 6.3 Hz, 6.3 Hz, 1 H,

CH(CH₃)₂), 2.94, 2.94 (2 s, 2 ꢁ 6 H, 2 ꢁ NMe₂), 4.40 (d, ³J_HH= 7.4

3

Hz, 1 H, ArCHCHCH(R)Ar), 6.12 (dd, J_HH= 15.8, 7.4 Hz, 1 H,

3

ArCHCHCH(R)Ar), 6.41 (d, J_HH= 15.8 Hz, 1 H, ArCHCHCH-

(R)Ar), 6.63ꢀ6.69 (m, 2 H, H_Ar), 6.72ꢀ6.76 (m, 2 H, H_Ar), 7.24ꢀ7.29

ppm (m, 4 H, H_Ar). ¹³C NMR (CDCl₃, 151 MHz): δ 23.0 (CH₃), 23.4

(CH₃), 40.5 (CH₃), 40.7 (CH₃), 45.4 (CH), 61.9 (CH), 112.4 (CH),

112.7 (CH), 125.9 (C), 127.2 (CH), 127.9 (CH), 129.1 (CH), 129.6

(CH), 131.8 (C), 149.7 (C), 149.8 ppm (C). HRMS (EI, positive): calcd

337.2512 (C₂₂H₃₁N₃), found 337.2512.

5,5-Bis((E)-1,3-bis(4-(dimethylamino)phenyl)allyl)-2,2-di-

methyl-1,3-dioxane-4,6-dione (3u⁰). A solution of Meldrum’s

acid (H-2u) (62.4 mg, 0.432 mmol) and potassium tert-butoxide (110

mg, 0.900 mmol) in DMSO (2 mL) was added to a suspension of 1h-

BF₄(317 mg, 0.866 mmol) in DMSO at rt. The reaction mixture was

stirred for 10 min followed by addition of water. The precipitate

was filtered and dried in the vacuum affording 3u⁰(255 mg, 0.366

mmol, 85%) as a pale green solid. ¹H NMR (CD₂Cl₂, 400 MHz): δ 0.66

(s, 6 H, 2 ꢁ CH₃), 2.85 (s, 12 H, NMe₂), 2.97 (s, 12 H, NMe₂), 4.18

(d, ³J_HH= 10.1 Hz, 2 H, ArCHCHCH(R)Ar), 6.30 (d, ³J_HH= 15.7 Hz, 2

H, ArCHCHCH(R)Ar), 6.56ꢀ6.67 (m, 4 H, H_Ar), 6.68ꢀ6.75 (m, 4 H,

(E)-N-(1,3-Bis(4-(dimethylamino)phenyl)allyl)benzylamine

(3r). Obtained analogously to 3q from benzylamine 2r (150 mg, 1.40

mmol) and 1h-BF₄(251 mg, 0.685 mmol). Recrystallization of the crude

product from diethyl ether/pentane afforded 3r (201 mg, 0.522 mmol,

76%) as a pale red solid (mp 88.2ꢀ90.0 °C, decomp). Evaporation of the

solvents from the solution which was left after recrystallization afforded

additional 60 mg (0.16 mmol, 23%) of 3r in lower quality as yellow oil.

¹H NMR(CDCl₃, 599 MHz): δ1.83 (br. s, 1 H, NH), 2.96, 2.97 (2 s, 2 ꢁ 6H,

2 ꢁ NMe₂), 3.81 (d, 1 H, ²J_HH= 14.3 Hz, CH₂), 3.84 (d, ²J_HH= 14.3 Hz,

1 H, CH₂), 4.33 (d, ³J_HH= 7.6 Hz, 1 H, ArCHCHCH(R)Ar), 6.17 (dd,

³J_HH= 15.7, 7.6 Hz, 1 H, ArCHCHCH(R)Ar), 6.50 (d, ³J_HH= 15.7 Hz, 1

H, ArCHCHCH(R)Ar), 6.68ꢀ6.71 (m, 2 H, H_Ar), 6.74ꢀ6.82 (m, 2 H,

H_Ar), 7.15ꢀ7.50 ppm (m, 9 H, H_Ar). ¹³C NMR (CDCl₃, 151 MHz): δ

40.5 (CH₃), 40.7 (CH₃), 51.3 (CH₂), 64.1 (CH), 112.4 (CH) 112.7

(CH), 125.7 (C), 126.7 (CH), 127.2 (CH), 128.0 (CH), 128.1 (CH),

128.3 (CH), 128.8 (CH), 129.7 (CH), 131.3 (C), 140.7 (C), 149.8 (C),

149.9 ppm (C). HRMS (EI, positive): calcd 385.2513 (C₂₆H₃₁N₃), found

385.2528. Anal. Calcd for C₂₆H₃₁N₃: C, 81.00; H, 8.10; N, 10.90. Found:

C, 80.61; H, 8.27; N, 10.65.

3

H_Ar), 6.86 (dd, J_HH= 15.7, 10.1 Hz, 2 H, ArCHCHCH(R)Ar),

7.02ꢀ7.12 (m, 4 H, H_Ar), 7.26ꢀ7.34 ppm (m, 4 H, H_Ar). ¹³C NMR

(CD₂Cl₂, 101 MHz): δ 29.0 (CH₃), 40.88 (CH₃), 40.92 (CH₃), 54.6

(CH), 65.1 (C), 106.3 (C), 112.9 (CH), 113.3 (CH), 122.3 (CH), 126.4

(C), 128.0 (CH), 128.3 (C), 130.3 (CH), 134.5 (CH), 150.8 (2 ꢁ C),

168.1 ppm (C). HRMS (EI, positive): calcd 700.3983 (C₄₄H₅₂N₄O₄),

found 700.3998.

Reaction of 1h-BF₄with the potassium salt of Meldrum’s

acid (K-2u). According to ref 45, a solution of 1h-BF₄(104 mg, 0.285

mmol) in DMSO was added dropwise to a solution of K-2u (253 mg,

1.39 mmol) in the same solvent at rt. After decolorization followed by

addition of water, the precipitate was filtered, washed with water, and

dried in the vacuum affording a mixture of (E)-5-(1,3-bis(4-(dimethylamino)

phenyl)allyl)-2,2-dimethyl-1,3-dioxane-4,6-dione (3u) (29 mg, 0.069

mmol, 24%) and 3u⁰(39 mg, 0.056 mmol, 39%). The yields of 3u and

(E)-N-(1,3-Bis(4-(dimethylamino)phenyl)allyl)morpholine

(3s). Obtained analogously to 3q from morpholine 2s (328 mg, 3.77

mmol) and 1h-BF₄(329 mg, 0.897 mmol). Pentane (10 mL) was added

9406

dx.doi.org/10.1021/jo201668w |J. Org. Chem. 2011, 76, 9391–9408

The Journal of Organic Chemistry

ARTICLE

3u⁰are based on the signal ratios in the ¹H NMR spectrum and the mass

(68.5 mg) of the crude product mixture. 3u: H NMR (CD₂Cl₂, 400

2598. (c) Perez, P.; Domingo, L. R.; Aizman, A.; Contreras, R. Theor.

Comput. Chem. 2007, 19, 139–201 and references therein.

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1

MHz): 1.51, 1.71 (2 s, 2 ꢁ 3H,2ꢁ CH₃), 2.91, 2.94 (2 s, 2 ꢁ 6H,2ꢁ NMe₂),

3.95 (br. s, 1 H, COCHCO), 4.55ꢀ4.57 (br. m, 1 H, ArCHCHCH-

(R)Ar), 6.49 (d, ³J_HH= 16.1 Hz, 1 H, ArCHCHCH(R)Ar), 6.55ꢀ6.80

(m overlapped with signals of 3u⁰, 5 H, ArCHCHCH(R)Ar, H_Ar),

7.19ꢀ7.36 (m overlapped with signals of 3u⁰, 4 H, H_Ar). ¹³C NMR

(CD₂Cl₂, 101 MHz): δ 28.1 (CH₃), 28.7 (CH₃), 40.8 (CH₃), 40.9

(CH₃), 47.7 (CH), 53.4 (CH), 105.7 (C), 112.8 (CH), 113.0 (CH),

124.8 (CH), 125.7 (C), 127.8 (CH), 128.4 (C), 129.5 (CH), 132.9

(CH), 150.4 (C), 150.8 (C), 165.30 (C), 165.33 ppm (C). The ¹H and

¹³C NMR spectra of 3u were obtained comparing the corresponding

spectra of the crude mixture with those of isolated 3u⁰. HRMS (EI,

positive): calcd 422.2200 (C₂₅H₃₀N₂O₄), found 422.2193.

(15) CCDC 297424 contains the supplementary crystallographic

data for 1h-BF₄reported in this paper. These data can be obtained

free of charge from the Cambridge Crystallographic Data Centre via

www.ccdc.cam.ac.uk/data_request/cif.

(16) Sanz, R.; Martines, A.; Miguel, D.; Alvarez-Gutierrez, J. M.;

Rodriguez, F. Adv. Synth. Catal. 2006, 348, 1841–1845.

(17) Rys, P. Acc. Chem. Res. 1976, 9, 345–351.

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J. Am. Chem. Soc. 1990, 112, 4446–4454. (b) Hagen, G.; Mayr, H. J. Am.

Chem. Soc. 1991, 113, 4954–4961.

(19) ”What’sBest! 4.0 Commercial” by Lindo Systems Inc.

(20) Mayr, H.; M€uller, K.-H.; Oﬁal, A. R.; B€uhl, M. J. Am. Chem. Soc.

1999, 121, 2418–2424.

’ ASSOCIATED CONTENT

S

Supporting Information. Details of the kinetic experi-

b

ments, quantum chemical calculations, NMR spectra of all

characterized compounds, and crystallographic data in CIF

format for the compound 1h-BF₄. This material is available free

of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION

(21) Mayr, H.; Fichtner, C.; Oﬁal, A. R. J. Chem. Soc., Perkin Trans. 2

2002, 1435–1440.

(22) Nubbemeyer, U. Synthesis 2003, 961–1008.

(23) Miranda, M. A.; Pꢀerez-Prieto, J.; Font-Sanchis, E.; Kꢀonya, K.;

Scaiano, J. C. J. Phys. Chem. A 1998, 102, 5724–5727.

(24) Minegishi, S.; Kobayashi, S.; Mayr, H. J. Am. Chem. Soc. 2004,

126, 5174–5181.

Corresponding Author

*E-mail: herbert.mayr@cup.uni-muenchen.de.

’ ACKNOWLEDGMENT

(25) Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 91, 165–195.

(26) Wei, Y.; Singer, T.; Mayr, H.; Sastry, G. N.; Zipse, H. J. Comput.

Chem. 2008, 29, 291–297.

We acknowledge ﬁnancial support by the Deutsche For-

schungsgemeinschaft and the Fonds der Chemischen Industrie.

We are grateful to Dr. Thomas Singer and Dr. Carmen Nitu for

performing some of the kinetic experiments, Dr. Kurt Polborn

for collection of X-ray diﬀraction data and Dr. Peter Mayer for

help with their evaluation. We also thank Biplab Maji and

Dr. Armin R. Oﬁal for their help during preparation of this

manuscript.

(27) Horn, M.; Mayr, H. Chem.—Eur. J. 2010, 16, 7478–7487.

(28) (a) Olah, G. A.; Prakash, G. K. S.; Arvanaghi, M. Synthesis

1984, 228–230. (b) Samples taken from the reaction mixture were

quenched with a solution of iodine in THF. The resulting mixture was

dissolved in diethyl ether, washed with aqueous sodium thiosulfate

solution, and dried (MgSO₄). GCꢀMS analysis showed slow disap-

pearance of 1-bromo-3,5-diﬂuorobenzene while the peak of the product

of the reaction of the in situ generated (3,5-diﬂuorophenyl)magnesium

chloride with iodine, that is, 1,3-diﬂuoro-5-iodobenzene, increased

with time.

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Electrophilicities of symmetrically substituted 1,3-diarylallyl cations

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