Orthoamides and iminium salts, LXXXIX. Reactions of N,N,N',N',N'',N'',N''',N'''-octamethylacetylene-bis(carboxamidinium) tetrafluoroborate with nucleophilic reagents - New methods for the preparation of amidinium salts and ketene aminals

Z. Naturforsch. 2015; 70(4)b: 225–241

Konstantin Drandarov, Ioannis Tiritiris and Willi Kantlehner*

Orthoamides and iminium salts, LXXXIX.

Reactions of N,N,N′,N′,N″,N″,N′″,N′″-octamethyl-

acetylene-bis(carboxamidinium) tetrafluoroborate

with nucleophilic reagents – new methods for

the preparation of amidinium salts and ketene

aminals^a

Abstract: The acetylene-bis(carboxamidinium) salt 4 of quinoxaline-2-carboxamidinium salts 29 are acces-

dehydrates carboxylic acids to the corresponding anhy- sible from aromatic 1,2-diamines and compound 4. The

drides, as the byproduct 2-oxo-but-2-en-amidinium salt reaction of the CH₂/NH-acidic cyanoacetamide with the

6b was isolated. Aromatic hydroxy compounds and bis(amidinium) salt 4 produced the 3-pyrroline-2-on

2-furyl-methylmercaptan add to the triple bond of the derivatives 33.

salt 4 to give 2-aryloxy- and 2-alkylmercapto-but-2-ene-

bis(amidinium) salts 7–9. According to this reaction Keywords: acetylene; bis(amidinium) salts; CH₂- and XH-

principle, 2-organoamino-buten-2-ene-bis(amidinium) acidic compounds; ketene aminals; Michael-initiated ring

salts 10 and 11 were prepared from 4 and primary and closure reactions.

secondary amines, whereas 4-chlorobenzhydrazide

reacted with 4 to give the imidazole-3-carboxamidinium

DOI 10.1515/znb-2014-0204

salt 13. The reaction of CH₂-acidic compounds as malon-

Received September 7, 2014; accepted December 12, 2014

onitrile or ethyl cyanoacetate with the bis(amidinium)

salt

4 affords 2-cyanomethylene-but-3-enamidinium

salts 15. With the CH-acidic diethyl 2-bromomalonate,

compound 4 undergoes a Michael-initiated ring closure

cyclopropenation reaction with further ring opening

by the released Br^–to the corresponding 2-diethoxycar-

bonylmethylene-3-bromo-but-3-enamidinium salt 18.

Dedicated to: Professor Klaus Peseke on the occasion of his

75^thbirthday

^{Unlike cyclopentadiene and furane, the reaction of}1 Introduction

N-methylpyrrole and bis(amidinium) salt 4 does not lead

to Diels–Alder [4 + 2] cycloadduct but to the Michael- Only a few types of alkyne iminium salts are known

type 1:1 adduct 20. Pyrrole- and thiophene-2-carboxa- (Scheme 1). The methods for the preparation of alkyne

midinium salts 23–25 can be prepared from compound iminium salts 1, which can formally be derived from

4 and esters of glycine, N-methylglycine (sarcosine), aldehydes or ketones – or more exactly from vinylogous

and mercaptoacetic acid, respectively. The derivatives amides – have mainly been developed by Maas et al.

[2–8]. Alkinyl-alkoxymethyleniminium salts 2 have been

prepared by the alkylation of propiolamides with triethy-

loxonium tetrafluoroborate [9–14] or methyl fluorosul-

fonate [15]. The alkylation of propiolamidines seems to

be of low value for the preparation of propiolamidinium

salts [16]. In general, propiolamidinium salts are well

accessible by the cleavage of orthoamide derivatives of

alkyne carboxylic acids with benzoyl chloride [17–19],

triethylsilyl trifluoromethanesulfonate and trimethylsilyl

halides [18], or elemental bromine [20].

^aOrthoamides and Iminium Salts, LXXXVIII: see ref. [1]

*Corresponding author: Willi Kantlehner, Fakultät Chemie/

Organische Chemie, Hochschule für Technik und Wirtschaft,

Beethovenstr. 1, D-73430 Aalen, Germany and Institut für

Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55,

D-70569 Stuttgart, Germany, Fax: +49-7361-5762250,

e-mail: willi.kantlehner@htw-aalen.de

Konstantin Drandarov and Ioannis Tiritiris: Institut für Organische

Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569

Stuttgart, Germany

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ꢀK. Drandarov et al.: Orthoamides and iminium salts, LXXXIX

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R³

1, R³= alkyl, aryl

2, R³= OEt

3, R³= NR¹R²

2 Results and discussion

R

C

X

NR¹R²

As in propyne iminium salts 1 [21] and propiolamidinium

salts 3 [18], the cation of the salt 4 can be regarded as an

ambident electrophile, because nucleophilic reagents can

add to the triple bond (Michael-addition analogue) or to

the carbon in the center of the amidinium function. As far

as investigated in nucleophilic addition reactions to pro-

pioliminium systems 1 and 3, the Michael-type addition

reactions predominate in most cases. Thus, in addition

to the reactions of mercaptanes or morpholine to 3a, the

conjugated addition products were formed solely [18, 19].

In the course of our investigations on nucleophilic

a: R = C₆H₅, R¹= R²= Me

Me₂N

NMe₂

C

2 BF₄

NMe₂

4

Scheme 1:ꢁAlkyne iminium salts.

A number of chemical reactions have been performed

with propyne iminium salts 1 [4, 5, 8, 21–34]. In contrast, addition reactions to the cation of the salt 4, we made

only few reactions of propiolamidinium salts 3 are known. analogous observations.

Examples are the addition reactions of primary [19] and

secondary amines [18, 19] and thiols [18].

The salt 4 can act as a neutral strong dehydrating

reagent. When phthalic acid was reacted with salt 4 in

Recently, we have described the preparation of N,N, the presence of triethylamine in acetonitrile, phthalic acid

N′,N′,N″,N″,N′″,N′″-octamethyl-acetylene-bis(carbox- anhydride was formed in quantitative yield [thin-layer

amidinium)-bis(tetrafluoroborate) (4) by the cleavage chromatography (TLC) detection]. As a second product,

of 1,1,1,4,4,4-hexakis(dimethylamino)-2-butyne with tri- the amidinium salt 6a was formed, which was isolated

fluoroacetic anhydride [35]. Heterocyclic bis(amidinium) easily as the well crystallizing tetraphenylborate 6b

salts could be prepared from the bis(amidinium) salt 4 by (Scheme 2). The amidinium salt 6a was prepared advan-

cycloaddition reactions [36].

tageously from acetic acid and salt 4 in the presence of

N,N,N′,N′-peralkylated amidinium salts are of general excessive triethylamine, and 6b was similarly precipitated

interest in preparative organic chemistry [37–39], because by the addition of sodium tetraphenylborate to the filtered

they can be used for the preparation of nearly all kinds reaction mixture (Scheme 2). Possibly, the high dehydrat-

of orthoamide derivatives [40] and ketene aminals [41, ing power of the bis(amidinium) salt 4 can be used for the

42], which are of high synthetic importance. Thus, the formation of peptides, glycosides, or esters (in analogy to

precursors for very useful formylating reagents, such as the Mitsunobu reaction [44–47]). However, at present, we

N,N-dimethylformamide acetals, the Bredereck-Simchen do not examine this question. Colorless single crystals of

esters, or tris(dialkylamino)methanes, are N,N,N′,N′- 6b were obtained by recrystallization from hot acetonitrile

tetraalkyl-formamidinium salts.

solution. The crystal structure of compound 6b is shown

From this point of view, bis(orthoamide) deriva- in Fig. 1. The compound crystallizes in the monoclinic

tives with close neighborhood of the orthoamide func- space group P2₁/n with Z ꢀ=ꢀ 4 (Table 1). The crystal struc-

tions (e.g., 1,2 or 1,3-position) are potentially interesting ture analysis (Fig. 1) reveals that the planes built up from

+

building blocks, especially for cyclization reactions. The the amidine and the N···C ···N unit are twisted against

compounds of this type should be available from the cor- each other with an angle of 56.5°. The bond lengths in the

+

responding bis(amidinium) salts. Unfortunately, only N···C ···N moiety are 1.321(4) and 1.326(4) Å, as expected

a few methods for the preparation of N-peralkylated for charge delocalization between both dimethylamino

bis(amidinium) salts of this type are known [35]. Addi- groups. The distance of 1.535(4) Å between the carbon

tionally, some of the known procedures are hardly suited atoms C7 and C8 is characteristic for a C–C single bond.

for preparative purposes because expensive silver salts The bond lengths of 1.409(4) Å for the C5–C6 double bond

are used as reagents in stoichiometric amounts [43]. In and 1.389(4) Å for the C6–C7 bond are in a similar range.

contrast, the above-mentioned cycloaddition reactions of Also, the Cꢀ=ꢀO distance with 1.253(3) Å is typical for a car-

the bis(amidinium)salt 4 give access to isocyclic and het- bonyl group. The C–N bond lengths in the amidine unit

erocyclic 1,2-bis(carboxamidinium) salts on a preparative [d(C–N) ꢀ=ꢀ 1.348(4) and 1.356(4) Å] are slightly longer.

scale [35, 36].

Compared with the bisamidinium salt 4, the four-carbon

In the present paper, we report on the reactions of the atoms chain in 6b is not linear anymore, and the C–C–C

salt 4 with nucleophilic reagents, furnishing various ami- angles with 119.2(3)° and 124.0(3)° indicate a trigonal-

dinium and bis(amidinium) salts and ketene aminals.

planar environment of the carbon atoms. The shortest

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K. Drandarov et al.: Orthoamides and iminium salts, LXXXIXꢀ

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CO₂H

O

HNEt₃

NMe₂

O

− NEt₃⋅HBF₄

NEt₃

2 BF₄

Me₂N

O

+

NMe₂

5

O

NMe₂

X

Me₂N

CH₃CN

r. t.

4

NMe₂

6a, X = BF₄

+ NaB(C₆H₅)₄

− NaBF₄

34 %

6b, X = B(C₆H₅)₄

O

CH₃CO₂H

NEt₃

+

6a

6b

Scheme 2:ꢁTransformation of carboxylic acids to anhydrides by salt 4.

addition of 2-furylmethanthiol to 4 follows the same reac-

tion pattern, delivering the bis(amidinium) salt 9a, which

was isolated as tetraphenylborate 9b (Scheme 3).

The bis(amidinium) salts 10 and 11 are accessible by

the addition of aliphatic amines as dimethylamine, mor-

pholine, and aminoacetonitrile and aromatic amines as

aniline and methyl anthranilate to the salt 4 (Scheme 4).

Very likely from 4-chlorobenzhydrazide and 4, the adduct

12 is formed, which undergoes further cyclization under

the applied reaction conditions to give the imidazolcar-

boxamidinium system of 13 (which was isolated as tetrap-

henylborate, Scheme 4).

Usually, CH₂-acidic compounds react with N,N,N′,N′-

tetraalkyl-formamidinium salts in the presence of a base

under condensation, giving rise to the formation of enam-

ines. However, this reaction type was not observed in the

reaction of the bis(amidinium) salt 4 with malononitrile

or ethyl cyanoacetate in acetonitrile in the presence of

sodium carbonate as a base (Scheme 5). Obviously, in the

first step, the adducts 14 are formed, which correspond to

compounds 5 and 7–11. The adducts 14 are further depro-

Fig. 1:ꢁOrtep plot (50 % probability ellipsoids) of the cation in

N,N,N′,N′-tetramethyl-4,4-bis(dimethylamino)-2-oxo-but-3-en-

amidinium tetraphenylborate (6b) in the crystal.

hydrogen-bonding interactions are observable between tonated by the base yielding the amidinium tetrafluorobo-

an oxygen atom of the carbonyl and a methyl hydrogen rates 15, which are substituted by a “push-pull” system in

atom of a neighboring cation [d(H11C···O1) ꢀ=ꢀ 2.46 Å]. the α-position. Compound 15b was converted to the tetra-

Finally, the tetraphenylborate ion does not interact with phenylborate before isolation (Scheme 5).

the cation; it serves only for charge compensation.

An attempt was made for the cyclopropenation of

The bis(amidinium) salts 7a–c are formed by the con- the alkyne bis(amidinium) salt 4 with diethyl 2-bromo-

jugated addition of phenol or naphthols to the acetylene- malonate in MeCN at r.t. in the presence of Na₂CO₃as

bis(carboxamidinium) salt 4 in nearly quantitative yield base (Scheme 6). The TLC analysis of the reaction mixture

at room temperature (r.t.) (Scheme 3). Obviously, this type showed a quick appearance of a colorless intermediate,

of reaction is also possible with polyhydric phenols, as which was transformed stepwise into a bright orange final

could be demonstrated by the formation of the six-fold product. The product was identified as the amidinium

charged salt 8 from compound 4 and phloroglucinol. The tetrafluoroborate 18, which analogous to compounds

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ꢀK. Drandarov et al.: Orthoamides and iminium salts, LXXXIX

228ꢀ

Table 1:ꢁCrystallographic data for 6b, 20, and 29a.

ꢀ

6b

ꢀ

20

ꢀ

29a

Formula

ꢃ

C₃₆H₄₅BN₄O

560.57

ꢃ

C₆₅H₇₁B₂N₅

943.89

ꢃ

C₁₆H₂₅B₂F₈N₅

461.03

M_r

Temperature, K

100(2)

293(2)

Crystal size, mm³

0.23 ꢃ×ꢃ 0.19 ꢃ×ꢃ 0.15 ꢃ

0.22 ꢃ×ꢃ 0.18 ꢃ×ꢃ 0.12ꢃ

triclinic

0.17 ꢃ×ꢃ 0.13 ꢃ×ꢃ 0.10

orthorhombic

Pbca (no. 61)

13.0525(4)

24.6540(9)

13.8657(5)

90

Crystal system

monoclinic

P2₁/n (no. 14)

10.8824(3)

14.7536(5)

20.0654(8)

90

ꢃ

Space group

P1̅ (no. 2)

11.5276(3)

12.9323(5)

18.5259(6)

100.128(3)

97.756(2)

91.669(2)

2689.95(16)

2

a, Å

b, Å

c, Å

α, °

β, °

γ, °

V, Å³

Z

97.262(2)

90

3195.75(19)

4

4461.9(3)

8

D

_calcd., g cm^–3

1.165

1.373

μ, mm^–1

0.1

F(000), e

1208

1012

1904

θ range, °

2.45–28.28

14, 19, 26

9486/7904

0.0470/0.0534

6499

4.81–28.17

15, 17, 24

24 559/13 098

0.0283/0.0419

8742

2.21–28.28

17, 32, 18

6141/5518

0.0651/0.0814

4502

hkl range

Reflections measured/unique

R_int/R_σ

Reflections with [I ꢃ≥ꢃ 2σ(I)]

Parameters refined

391

670

290

R₁/wR₂for reflections with [I ꢃ≥ꢃ 2σ(I)]ꢃ

0.0419/0.0830

0.0711/0.0969

1.112

0.0576/0.1184

0.0986/0.1386

1.059

0.0516/0.0902

0.0893/0.1091

1.058

R₁/wR₂(all reflections)

ꢃ

GoF (F²)

Δρ_fin(max/min), e Å^–3

0.17/–0.22

0.20/–0.18

0.27/–0.17

Ar

15 bears in the α-position a “push-pull” 1,3-butadiene

system. Apparently, as an initial step, a deprotonation of

the strongly CH-acidic 2-bromomalonate takes place. The

formed resonance-stabilized carbanion attacks the acti-

vated triple bond of compound 4 leading to the allenic

intermediate 16. As a typical example of a Michael-ini-

tiated ring closure reaction [48, 49], the intermediate 16

undergoes an intramolecular S_n2 reaction leading to the

highly substituted cyclopropene intermediate 17. Cyclo-

propenes are highly strained carbocyclic compounds

[50, 51]. Therefore, the released bromide anion, as a good

nucleophile, further attacks the cyclopropene moiety of

the intermediate 17, causing its ring opening to compound

18 (Scheme 6). Similar Br^–- and I^–-induced ring openings

of cyclopropenes have been reported recently in the litera-

ture [50, 51].

As we have reported earlier, the reactions of com-

pound 4 with cyclopentadiene and furane led to the cor-

responding Diels–Alder [4 + 2] cycloadducts 19a and 19b

(Scheme 7) [35]. In contrast, the reaction with N-methyl-

pyrrole led to the formation of the Michael-type 1:1 adduct

20 as a sole product. Compound 20 was isolated as the

well crystallizing tetraphenylborate salt (Scheme 7).

Yellow single crystals of the N-methyl-pyrrol-2-yl

O

NMe₂

ArOH

Me₂N

2 BF₄

NMe₂

7

b

c

7

a

Ph

1-naph 2-naph

Ar

yield 79 % 40 %

93 %

NMe₂

OH

Me₂N

NMe₂

O

NMe₂

O

NMe₂

HO

OH

Me₂HN

Me₂N

CH₃CN

r. t.

4

6 BF₄

94 %

O

NMe₂

Me₂N

NMe₂

8

O

S

NMe₂

CH₂SH

O

Me₂N

2 X

NMe₂

9a, X = BF₄

+ 2 NaB(C₆H₅)₄

− 2 NaBF₄

93 %

9b, X = B(C₆H₅)₄

Scheme 3:ꢁAddition of hydroxy aromatic compounds and 2-furyl-

methylmercaptan to the salt 4.

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K. Drandarov et al.: Orthoamides and iminium salts, LXXXIXꢀ

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R²R¹N

Me₂N

NMe₂

HNR¹R²

X

XCH₂CN

Na₂CO₃, CH₃CN

NC

Me₂N

H

2 BF₄

NMe₂

4

2 BF₄

10

NMe₂

r. t.

14

NMe₂

a^*

10

R¹

R²

b

c

H

Me

(CH₂)₂O(CH₂)₂

Na₂CO₃− NaBF₄

CH₂CN

1.5/1

57 %

E/Z 1.5/1

yield

6/1

98 %

92 %

NC

Me₂N

X

NMe₂

^*isolated as tetraphenylborate

BF₄

HNAr NMe₂

15

NMe₂

ArNH₂

CH₃CN

r. t.

Me₂N

2 BF₄

4

NMe₂

a

b^*

15

11

NMe₂

CO₂C₂H₅

88 %

CN

X

11

a

yield

84 %

b

^*isolated as tetraphenylborate

Ar

CO₂Me

98 %

Scheme 5:ꢁCondensation of the bis(amidinium) salt 4 with malonic

acid derivatives in the presence of a base.

yield

92 %

Cl

O

2 BF₄

NH NMe₂

NMe₂

O

NHNH₂

at an angle of 59.8°. Typically, both tetraphenylborate

ions show no significant interactions with the bisami-

dinium ion.

HN

Me₂N

NMe₂12

It could be assumed that, from compound 4 and the

methyl esters of glycine, N-methylglycine (sarcosine), or

mercaptoacetic acid, all bearing an electron-withdrawing

group in the α-position, adducts such as 21 would be

formed (Scheme 8). However, in these adducts, the meth-

ylene groups in the α-position to the ester function are

CH₂-acidic and carbanions, obtained from them by depro-

tonation, should be able to attack the amidinium function

located in the γ-position to the amino or mercapto group,

respectively, giving the intermediates 22. The correspon-

ding heterocyclic amidinium salts 23–25 could be formed

from these “aminals” by the loss of dimethylamine. These

considerations were confirmed completely by the cor-

+ NaB(C₆H₅)₄− NaBF₄

40 %

− HNMe₂⋅HBF₄

Cl

O

BF₄

N

NMe₂

N

Me₂N

13

NMe₂

Scheme 4:ꢁAddition reactions of amines, amine derivates, and an

acylhydrazine to the bis(amidinium)salt 4.

bis(tetraphenylborate) salt 20 were obtained by recrystal- responding experiments, from which the expected het-

lization from a hot acetonitrile solution. Its X-ray struc- erocyclic amidinium salts resulted, which were isolated

ture is depicted in Fig. 2. The compound crystallizes in as tetraphenylborates 23b, 24b, and 25b (Scheme 8).

the triclinic space group P1

̅

with Zꢀ=ꢀ 2 (Table 1). Figure Analogously, the cyanomethylamine adduct 10c

2 shows a view of the bisamidinium ion. As expected for (Scheme 4) was expected to undergo a similar ring closure

such type of compounds, the C–N bond lengths in both reaction. Unfortunately, the intermediate Michael adduct

amidinium units are d(N1–C5) ꢀ=ꢀ 1.320(2), d(N2–C5) ꢀ=ꢀ 10c and its products showed instability after a prolonged

1.333(2), d(N3–C8) ꢀ=ꢀ 1.319(2), and d(N4–C8) ꢀ=ꢀ 1.320(2) exposure to the base (Na₂CO₃) in the reaction mixture

Å, exhibiting also, in this case, charge delocalization (Scheme 8). Therefore, the expected pyrrole-5-carbonitrile

between the dimethylamino groups. The distances of derived product could not be isolated. However, the elec-

1.480(2) Å between the carbon atoms C5–C6 and 1.495(2) trospray ionization-mass spectrometry (ESI-MS) spectrum

Å between C7–C8 are typical for C–C single bonds sepa- of compound 10c confirmed that the intramolecular ring

rated by a double bond [d(C6–C7) ꢀ=ꢀ 1.343(2) Å]. The ami- closure reaction is indeed favored by showing the signal

dinium moieties show a trans-orientation with respect to of the expected pyrrole-5-carbonitrile product as a major

the C–C double bond and are twisted against each other MS fragment (Scheme 8, highlighted, fragment b).

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230ꢀ

ꢀK. Drandarov et al.: Orthoamides and iminium salts, LXXXIX

O

OEt

EtO

OEt

Na

EtO

O

Br

O

OEt

4

Me₂N

NMe₂

− NaBF₄

MeCN, Na₂CO₃

r. t.

EtO

Me₂N

•

Br

2 BF₄

Me₂N

− NaHCO₃

NMe₂

16

BF₄

O O

EtO

OEt

Br

Me₂N

NMe₂

NMe₂NMe₂

BF₄

17

94 %

O

OEt

Br

O

OEt

Br

EtO

Me₂N

NMe₂

Me₂N

NMe₂

Me₂N NMe₂

BF₄

a

18

b

Scheme 6:ꢁCondensation of the bis(amidinium) salt 4 with diethyl-2-bromomalonate in the presence of a base.

NMe₂

X

2 BF₄

NMe₂

19

NMe₂

X = CH₂or O

Me₂N

19

X

a

CH₂

b

O

X

4

MeCN, r. t.

X = NMe

71 %

+ NaBPh₄

− NaBF₄

MeN

Me₂N

NMe₂

NMe₂2 BPh₄

20

NMe₂

Scheme 7:ꢁReactions of bis(amidinium) salt 4 with cyclopentadi-

ene, furane, and N-methylpyrrole.

In analogy to these reactions, the addition products

26 from the bis(amidinium) salt 4 and o-phenylenedi-

amine or 2,3-diaminonaphthalene, respectively, undergo

further cyclization reactions (Scheme 9). However, in

these cases, the amidinium function in the β-position to

the added amino group reacts with the second aromatic

amino group to form the condensation products 27, which

Fig. 2:ꢁOrtep plot (30 % probability ellipsoids) of the cation

showing the trans-orientation of the amidinium units in N,N,N′,N′,

N″,N″,N′″,N′″-octamethyl-2-(N-methyl-pyrrol-2-yl)-2-butene-1,4-

bis(amidinium) bis(tetraphenylborate) (20).

The hydrogen atoms (except of H6′) were omitted for clarity.

after deprotonation deliver the intensively orange-colored 29b. Presumably, the cyclizations 26 → 27 are facilitated

quinoxaline derivatives 28a and 28b in good yields due to the proper spatial orientation of the two amino

(Scheme 9). The crude ketenaminals 28a and 28b were groups allowing the formation of a sterically favored six-

converted to the stable bis(tetrafluoroborates) 29a and membered transition state leading to the formation of

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ꢀ231

CO₂Me

HXCH₂EWG

EWG = CO₂Me

Na₂CO₃, CH₃CN

X

NMe₂

NMe₂2 BF₄

4

Me₂N

r. t.

21

NMe₂

ESI-MS

CN

− NaBF₄

Na₂CO₃

HN

NMe₂

Me₂N

2 BF₄

H

X

CO₂Me

NMe₂

10c

NMe₂

Me₂N

− HBF₄

− BF₄

NMe₂BF₄

22

− BF₄

NMe₂

− HNMe₂

Na₂CO₃− HNMe₂

CN

NMe₂

HN

CO₂Me

X

N

NMe₂

Me₂N

NMe₂

Me₂N

NMe₂

Y

NMe₂

a m/z = 279 (100)

23−25

NMe₂

b m/z = 234 (100)

23 X = NH, a (Y = BF₄)

AE

b [Y = B(C₆H₅)₄], 77 %

AE

b [Y = B(C₆H₅)₄], 41 %

b [Y = B(C₆H₅)₄], 61 %

23 X = NMe, a (Y = BF₄)

23 X = S, a (Y = BF₄)

EWG = electron withdrawing group

AE = anion exchange with NaB(C₆H₅)₄

Scheme 8:ꢁHeterocyclic carboxamidinium salts 23–25 from the bis(amidinium) salt 4 and the methyl esters of glycine, N-methylglycine

(sarcosine), and mercaptoacetic acid (EWG ꢃ=ꢃ COOMe). The ESI-MS fragmentation pattern of compound 10c is highlighted in the insert.

six-membered heteroaromatic systems. Yellow single crys-

tals of the quinoxalin-2-yl bis(tetrafluoroborate) salt 29a

were obtained by recrystallization from a hot methanol

solution (Scheme 9). The crystal structure of compound

29a is depicted in Fig. 3. The compound crystallizes in the

orthorhombic space group Pbca with Z ꢀ=ꢀ 8 (Table 1). A

view of the cation is shown in Fig. 3. The structure analy-

sis shows an almost planar quinoxaline ring system, with

the amidinium unit being twisted at an angle of 74.6° with

+

respect to the ring plane. The bond lengths in the N···C ···N

moiety are 1.295(5) and 1.313(6) Å, indicating a charge delo-

calization between both dimethylamino groups similar to

compound 29a. The presence of C–C single bonds [d(C5–

C6) ꢀ=ꢀ 1.511(6) Å, d(C6–C7) ꢀ=ꢀ 1.481(6) Å, and d(C7–C8) ꢀ=ꢀ

1.471(6) Å] is clearly indicated. The C–N double bond in the

quinoxaline ring is localized between the atoms N5 and C7

[d(C–N) ꢀ=ꢀ 1.298(5) Å]. In contrast, the nitrogen atom N4 is

now protonated [d(N4–C8) ꢀ=ꢀ 1.350(5) Å]. The distance of

1.319(5) Å between N3 and C8 reveals also charge delocali-

zation within the plane defined by the atoms N3–C8–N4

(see Fig. 3). A strong N–H···F hydrogen bond is observed

Fig. 3:ꢁOrtep plot (30 % probability ellipsoids) of the cation in

between the protonated nitrogen atom N4 and a fluorine

N,N,N′,N′-tetramethyl-2-(3-dimethylammonio-quinoxalin-2-yl)aceta-

atom of the tetrafluoroborate ion [d(H···F) ꢀ=ꢀ 2.19 Å]. In midinium bis(tetrafluoroborate) (29a).

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addition, much weaker C–H···F hydrogen bonds between the salt 4 under cyclization in the presence of a base. The

the hydrogen atoms of methyl groups and a neighboring reaction of compound 4 with cyanoacetamide led to a

BF₄^–ion were detected [d(H···F) ꢀ=ꢀ 2.41 and 2.51 Å].

transient bright yellow adduct, which could be detected

Such conditions are missing in the molecule of 1,8-diami- by TLC of the reaction mixture besides two more prod-

nonapthalene, where in analogous reactions only unfa- ucts. When the reaction was performed with an excess

vorable seven- or eight-membered rings could be formed. (2–3 mole equivalents) of cyanoacetamide for 18 h at r.t.

Thus, when the salt 4 and 1,8-diaminonapthalene were and 3 h at 80 °C, only one deep purple-colored product

reacted in acetonitrile, a deep orange color of the reaction was present, which was identified as compound 33a

mixture appeared, which is typical for the formation of the (Scheme 10). Obviously, in the first step, cyanoacetamide

first adduct 30. After a short time, the color of the mixtures is added to the activated triple bond of bisamidinium salt

turned to brown-black. Very likely, intermolecular nucleo- 4, producing an adduct 31, which undergoes further cycli-

philic addition/substitution reactions dominate, giving rise zation to give the transient pyrrolidone-4-carboxamidin-

to the formation of polymeric products (Scheme 9).

ium salt 32 (which under the condensation reacts with

Cyanoacetamide is a 1,3-difunctional CH₂- and NH₂- a second cyanoacetamide equivalent at the amidinium

acidic compound, which could be expected to react with function to yield the final pyrrolidone-derivative 33a).

NH₂

NH NMe₂

2 BF₄

4

Me₂N

CH₃CN, r. t.,15 h

NMe₂

26

NMe₂

− HNMe₂⋅HBF₄

NH NMe₂

BF₄

N

NMe₂

27

NMe₂

− HBF₄

Me₂N

N

NMe₂

N

NMe₂

28a, b

+ 2 HBF₄

Me₂N

N

NMe₂

2 BF₄

N

NMe₂

H

29a, b (41 and 47 %, resp.)

NH₂NH₂

NH₂

NH NMe₂

2 BF₄

4

undefined products

CH₃CN, r. t.,15 h

Me₂N

NMe₂

30

NMe₂

Scheme 9:ꢁReaction of aromatic diamines with bis(amidinium) salt 4.

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O

CN

RHN

NMe₂

BF₄

RHN

NMe₂

BF₄

4

RN

Me₂N

Na₂CO₃, CH₃CN

r. t.,18 h; 80°C, 3 h

− HBF₄

− HNMe₂

NMe₂

31

NMe₂

32

NMe₂

O

− HNMe₂

CN − HBF₄

RHN

O

CN

NMe₂

RN

NMe₂

NHR

NC

O

33a, R = H, 99 %

b, R = Ph, 79 %

Scheme 10:ꢁReaction of the amidinium salt 4 with cyanoacetamides.

In full analogy to this reaction, the N-phenylpyrrolidone of the nucleophilic center – initially present in the react-

derivative 33b could be obtained from the salt 4 and ing compounds or formed from them by the added base –

N-phenyl-cyanoacetamide (Scheme 10).

at C-2 of the bis(amidinium) salt 4. This addition step can

be followed by further condensation reactions between an

amidinium function of 4 and an acidic group (NH₂, CH₂) if

also present in the used nucleophilic reagent.

All these reactions demonstrate that compounds of

type 4 represent valuable precursors for the preparation

of heterocyclic amidinium salts and ketenaminals, respec-

tively, which at present are not accessible by other methods.

3 Conclusion

In summary, we could show that, in the presence of a base

compound, 4 dehydrates carboxylic acids to their anhy-

drides with the formation of compound 6a. The latter

could be regarded as a formal water adduct to the triple

bond of compound 4, which otherwise does not react

directly with water. Other nucleophilic reagents, such as

aromatic hydroxy compounds, mercaptans, aliphatic and

4 Experimental section

aromatic amines, and an acylhydrazine, can be added to 4.1 General procedures

the acetylenic bis(iminium) salt 4, yielding new, hitherto

unknown, 2-butene-bis(amidinium) salts 7–12 and the The nuclear magnetic resonance (NMR) spectra were

pyrazole-carboxamidinium salt 13. CH₂-acidic compounds recorded on a Bruker ARX 500 instrument (operating at

1

such as malononitrile and cyanoacetic acid ester react 500.1 MHz for H and 125.7 MHz for ¹³C). The spectra were

similarly. However, in the presence of a base, the initially calibrated using tetramethylsilane as internal stand-

1

formed adducts are deprotonated to give 3-butene-ami- ard. For the assignment of H and ¹³C NMR signals, dis-

dinium salts 15. The reaction of compound 4 with diethyl tortionless enhancement by polarization transfer and

bromomalonate apparently involves a cyclopropene inter- two-dimensional ¹H,¹H-COSY, ¹H,¹³C correlation spectra

mediate, which is further opened by the released bromide (heteronuclear single-quantum correlation and hetero-

anion to the open-chain “push-pull” butadiene 18. Unlike nuclear multiple-bond correlation spectroscopy) were

cyclopentadiene and furane, the reaction of N-methyl- recorded. The melting points were determined with a

pyrrole with compound 4 did not give a [4 + 2] cycload- Büchi 510 apparatus (Büchi Laboratoriumstechnik AG,

duct but yielded merely the Michael-type 1:1 adduct 20. Flawil, Switzerland) and are uncorrected. Elemental anal-

From bis-nucleophilic compounds such as esters of amino yses were performed by the service of the Institut für Orga-

acids, mercaptoacetic acid or aromatic 1,2-diamines, and nische Chemie, University of Stuttgart. The ESI-MS spectra

the bis(amidinium) salt 4, heterocyclic carboxamidinium were measured on a micrOTOF-Q instrument (Bruker Dal-

salts 23–25 and 29 or ketene aminals 28, respectively, can tonics). Solvents and liquid reagents were purified and

be prepared. All these reactions are started by the addition dried according to the established procedures.

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4.2 X-ray structure determinations

and 164.1 (BC_Ph), 136.7, 126.5, and 122.7 [o-, m-, p-Ar C,

+

B(Ph)₄], 85.3 [C(3)], 43.1 [C N(CH₃)₂], 41.6 [N(CH₃)₂] ppm.

X-ray single crystal diffraction data were collected on C₃₆H₄₅N₄BO (560.58): calcd. C 77.13, H 8.09, N 9.99; found

a Bruker-Nonius κ CCD diffractometer, which employs C 76.68, H 8.03, N 9.90.

graphite-monochromated MoK_αradiation (λ ꢀ=ꢀ 0.71073 Å).

The data collection for compounds 20 and 29a was per-

formed at 293 K and that for compound 6b was performed 4.4 N,N,N′,N′,N″,N″,N′″,N′″-octamethyl-2-

at 100 K. Unit cell parameters were obtained by indexing

phenoxy-2-butene-1,4-bis(amidinium)

the peaks in the first 10 frames and refined by employing

bis-(tetrafluoroborate) (7a)

the whole data set. All frames were integrated and cor-

rected for Lorentz and polarization effects. The structures A solution of phenol (100 mg, 1 mmol) in acetonitrile

were solved by Direct Methods using the SHELXS-97 [52] (2 mL) and finely powdered anhydrous Na₂CO₃(100 mg,

structure solution package. All non-hydrogen atoms were 9.4 mmol) were added to a solution of the bis(amidinium)

located and refined anisotropically with full-matrix least salt 4 (400 mg, 1.0 mmol) in acetonitrile (2 mL), and

squares using the program SHELXL-97 [53]. The position the mixture was stirred 18 h at r.t. The mixture was fil-

of hydrogen atoms belonging to the carbon atoms was tered. The filtrate was evaporated in vacuo, and the

geometrically optimized by applying the riding model. solid residue was recrystallized from ethanol to afford

The crystallographic data and details of the data collec- compound 7a. Yield: 390 mg (79 %), colorless crystals;

1

tion and structure refinement are listed in Table 1. The m.p. 144–146 °C. H NMR (500 MHz, CD₃CN): δ ꢀ=ꢀ 7.52 (t,

molecular graphics were drawn with the program Ortep- J ꢀ=ꢀ 8 Hz, 2H, m-ArH), 7.37 (t, J ꢀ=ꢀ 8 Hz, 1H, p-ArH), 7.13

III [54, 55].

(d, J ꢀ=ꢀ 8 Hz, 2H, o-ArH), 6.30 [s, 1H, C(3)H], 3.26 [br. s,

CCDC 796286 (6b), 796287 (20), and 796288 (29a) 6H, N(CH₃)₂], 3.18 [br. s, 12H, 2 N(CH₃)₂], 3.01 [br. s, 6H,

contain the supplementary crystallographic data for this N(CH₃)₂] ppm. ¹³C NMR (125 MHz, CD₃CN): δ ꢀ=ꢀ 162.6, 162.5

paper. These data can be obtained free of charge from The [C(1), C(4)], 153.6 (ArC), 150.3 [C(2)], 131.8, 127.7, and 118.8

Cambridge Crystallographic Data Centre via http://www. (ArC), 111.9 [C(3)], 44.1, 43.5 [N(CH₃)₂] ppm. C₁₈H₃₀N₄B₂F₈O

ccdc.cam.ac.uk/data_request/cif.

(492.07): calcd. C 43.94, H 6.15, N 11.39; found C 43.96, H

6.07, N 11.23.

4.3 N,N,N′,N′-tetramethyl-4,4-

bis(dimethylamino)-2-oxo-but-3-en-

amidinium tetraphenylborate (6b)

4.5 N,N,N′,N′,N″,N″,N′″,N′″-octamethyl-

2-(1-naphthyloxy)-2-butene-1,4-

bis(amidinium) bis-(tetrafluoroborate)

(7b)

Acetic acid (0.50 mL, 520 mg, 8.7 mmol) and triethyl-

amine (0.15 mL, 109 mg, 1 mmol) were added to a solu-

tion of the bis(amidinium) tetrafluoroborate 4 (400 mg, 1-Naphthol (160 mg, 1.1 mmol) was added to a solution of

1 mmol) in acetonitrile (3 mL) and the mixture was stirred compound 4 (400 mg, 1.0 mmol) in acetonitrile (3 mL).

at r.t. for 19 h. The volatile compounds were removed The yellow mixture was stirred at r.t. overnight. The vola-

in vacuo. The residue was dissolved in acetonitrile. A tile compounds were removed in vacuo. The solid residue

solution of sodium tetraphenylborate (0.7 g, 2 mmol) in was recrystallized from ethanol to give the salt 7b. Yield:

acetonitrile (3 mL) was added. The precipitated sodium 220 mg (40 %), yellow crystals; m.p. 182–184 °C (dec.). ¹H

tetrafluoroborate was removed by filtration. The filtrate NMR (500 MHz, CD₃CN): δ ꢀ=ꢀ 8.32–8.27 (m, 1H, ArH), 8.04–

was evaporated in vacuo. Methanol was added to the 7.99 (m, 1H, ArH), 7.86 (d, J ꢀ=ꢀ 8.3 Hz, 1H, ArH), 7.7–7.65 (m,

residue. The crystalline material was collected by fil- 2H, ArH), 7.53 (t, J ꢀ=ꢀ 8.2 Hz, 1H, ArH), 6.90 (d, J ꢀ=ꢀ 7.7 Hz,

tration and recrystallized from methanol to afford the 1H, ArH), 6.51 (s, 1H, ꢀ=ꢀCH-), 3.25 [br. s, 6H, N(CH₃)₂], 3.18

amidinium salt 6b. Yield: 195 mg (34 %), colorless crys- [s, 12H, 2N(CH₃)₂], 3.05 [br. s, 6H, N(CH₃)₂] ppm. ¹³C NMR

tals; m.p. 168 °C. ¹H NMR (500 MHz, CD₃CN): δ ꢀ=ꢀ 7.27 (m, (125 MHz, CD₃CN): δ ꢀ=ꢀ 162.8, 162.7 [C(1), C(4)], 149.6 [C(2)],

8H, ArH), 6.99 (t, J ꢀ=ꢀ 7.5 Hz, 8H, ArH), 6.84 (t, J ꢀ=ꢀ 7.2 Hz, 149.5, 136.2, 129.2, 128.8, 128.4, 127.1, 126.8, 125.5, 122.0

4H, ArH), 4.51 [s, 1H, C(3)H], 3.12 [s, 12H, 2N(CH₃)₂], 2.92 (ArH), 114.3 [C(3)], 111.9 (ArH), 44.4, 43.7 [N(CH₃)₂] ppm.

[s, 12H, 2N(CH₃)₂] ppm. ¹³C NMR (125 MHz, CD₃CN): δ ꢀ=ꢀ C₂₂H₃₂N₄B₂F₈O (542.12): C 48.74, H 5.95, N 10.33; found

170.9 (Cꢀ=ꢀO), 170.1 [C(1)], 168.5 [C(4)], 165.3, 164.9, 164.5, C 48.53, H 5.92, N 10.33.

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in acetonitrile (3 mL). The yellow mixture was stirred

2 h at r.t. A solution of sodium tetraphenylborate (0.7 g,

2 mmol) in acetonitrile (5 mL) was added. The mixture

was filtered, and the filtrate was evaporated in vacuo.

4.6 N,N,N′,N′,N″,N″,N′″,N′″-octamethyl-

2-(2-naphthyloxy)-2-butene-1,4-

bis(amidinium) bis-(tetrafluoroborate) (7c)

The bis(amidinium) salt 7c was obtained from compound The crystalline residue was triturated twice with hot

4 (400 mg, 1.0 mmol) and 2-naphthol (150 mg, 1.0 mmol) methanol, filtered, and washed several times with cold

in acetonitrile (3 mL) as described for 7b. Yield: 510 mg (93 methanol and then dried to afford the bis(amidinium)

1

%), yellow crystals; m.p. 178–180 °C. H NMR (500 MHz, salt 9b. Yield: 0.91 g (93 %), yellow solid; m.p. 192 °C

CD₃CN): δ ꢀ=ꢀ 8.06 (d, J ꢀ=ꢀ 9 Hz, 1H, ArH), 8.0–7.96 (m, 1H, (dec.). ¹H NMR (500 MHz, CD₃CN): δ ꢀ=ꢀ 7.49 [s, 1H, C(3)H],

ArH), 7.65–7.55 (m, 3H, ArH), 7.32 (d, J ꢀ=ꢀ 9 Hz, 1H, ArH), 7.28 (br. s, 16H, o-ArH), 6.99 (t, J ꢀ=ꢀ 7.6 Hz, 16H, m-ArH),

6.38 [s, 1H, C(3)H], 3.34 [br. s, 6H, N(CH₃)₂], 3.20 [s, 12H, 6.84 (t, J ꢀ=ꢀ 7.6 Hz, 8H, p-ArH), 6.43–6.38 (m, 3H, furane

2N(CH₃)₂], 2.98 [br. s, 6H, N(CH₃)₂] ppm. ¹³C NMR (125 MHz, H), 4.02 (s, 2H, CH₂S), 3.24 [br. s, 6H, N(CH₃)₂], 3.02 [s,

CD₃CN): δ ꢀ=ꢀ 162.8, 162.7 [C(1), C(4)], 151.5 (ArH), 150.4 [C(2)], 12H, 2N(CH₃)₂], 3.00 [br. s, 6H, N(CH₃)₂] ppm. ¹³C NMR

134.7, 132.6, 132.5, 128.9, 128.8, 128.7, 127.7, 118.5, 115.5 (ArH), (125 MHz, CD₃CN): δ ꢀ=ꢀ 165.3, 164.9, 164.5, 164,1 (BC_Ph),

+

112.7 [C(3)], 44.3, 43.7 [N(CH₃)₂] ppm. C₂₂H₃₂N₄B₂F₈O (542.12): 163.6, 163.5 [C (NCH₃)₂], 148.6, 145.2 [C(2), C(3)], 144.9

C 48.74, H 5.95, N 10.33; found C 47.67, H 6.08, N 10.18.

[furane C(2)], 136.7 (ArC), 126.5 (ArC), 125.5 [furane C(5)],

122.7 (ArC), 112.3, 111.1 [furane C(3) and C(4)], 44.6, 43,9,

43.2 [N(CH₃)₂], 29.7 (CH₂S) ppm. C₆₅H₇₀N₄B₂OS (976.96): C

79.91, H 7.22, N 5.73, S 3,28; found C 79.76, H 7.22, N 5.58,

S 3.21.

4.7 2-(1,3,5-Benzenetrioxytris-)-

[N,N,N′,N′,N″,N″,N′″,N′″-octamethyl-

(but-2-en)-1,4-bis(amidinium]

hexakis(tetrafluoroborate) (8)

4.9 (2,3-E/Z)-N,N,N′,N′,N″,N″,N′″,N′″-

octamethyl-2-dimethylamino-

2-butene-1,4-bis(amidinium)

bis(tetraphenylborate) (10a)

1,3,5-Benzenetriol (phloroglucinol) (50 mg, 0.4 mmol) was

added to a solution of the bis(amidinium) salt 4 (500 mg,

1.26 mmol) in acetonitrile (3 mL). The mixture was stirred

at r.t. for 48 h. The volatile compounds were removed in

vacuo. Methanol (10 mL) was added to the residue, and the Dimethylamine hydrochloride (170 mg, 2.1 mmol) and

suspension was stirred at r.t. for 24 h. The solid was col- Na₂CO₃(150 mg, 1.4 mmol) were added to a solution of

lected by filtration, washed several times with methanol, compound 4 (400 mg, 1.0 mmol) in acetonitrile (3 mL). The

and dried to afford the tetrafluoroborate 8. Yield: 490 mg mixture was stirred at r.t. for 3 h and then filtered. A solu-

(94 %), yellowish powder; m.p. 248–250 °C (dec.). ¹H NMR tion of NaBPh₄(0.7 g, 2 mmol) in acetonitrile (3 mL) was

(500 MHz, CD₃CN), mixture of rotamers: δ ꢀ=ꢀ 6.59–6.30 (m, added. The precipitated NaBF₄was removed by filtration.

+

6H, ArH ꢀ=ꢀ CH-), 3.41–3.04 [m, 72 H, 12N(CH₃)₂] ppm. ¹³C The filtrate was concentrated under reduced pressure.

NMR (125 MHz, CD₃CN), mixture of rotamers: δ ꢀ=ꢀ 162.6, Methanol was added to the residue and the mixture was

162.4, 162.3, 162.2, 161.8, 161.7, 161.6, 161.4, 161.2, 156.1, 155.8, refluxed for few minutes. After cooling to ambient temper-

155.6, 155.2, 149.7, 149.1, 147.3, 118.0, 117.0, 114.5, 113.2, 109.6, ature, the crystalline material was collected by filtration,

105.9, 103.8, 103.7, 101.3, 99.3, 44.7, 44.6, 44.5, 44.4, 44.3, 44.0, washed several times with methanol, and dried to afford

43.9, 43.8, 43.7 ppm. High-resolution mass spectra (HRMS) (2,3-E/Z)-10a (1.5:1 ratio). Yield: 849 mg (92 %), yellow

1

[(+)-time-of-flight electrospray ionization (TOF-ESI)]: m/z ꢀ=ꢀ crystals; m.p. 260 °C (dec.). H NMR (500 MHz, CD₃CN),

+

1232.6516 {calcd. 1232.6511 for C₄₂H₇₈N₁₂O₃·(BF₄)₅[M-BF₄] }.

(2,3-E/Z)-mixture: δ ꢀ=ꢀ 7.27 (br. s, 16H, o-ArH), 6.99 (t, J ꢀ=ꢀ

7.3 Hz, 16H, m-ArH), 6.84 (t, J ꢀ=ꢀ 7.3 Hz, 8H, p-ArH), 4.81 [s,

0.4H, (2,3-Z)-10a, C(3)H], 4.61 [s, 0.6H, (2,3-E)-10a, C(3)H],

3.24 [br. s, 2.4H, (2,3-Z)-10a, C(2)N(CH₃)₂], 3.20 [br. s, 3.6H,

(2,3-E)-10a, C(2)N(CH₃)₂], 3.10–2.70 [m, 24H, 4N(CH₃)₂]

ppm. ¹³C NMR (125 MHz, CD₃CN): δ ꢀ=ꢀ 166.9 + 166.8 [C(1)],

165.4, 165.0, 164.6, 164.2 (BC_Ph), 165.1 + 162.2 [C(4)], 150.7 +

150.3 [C(2)], 136.8 (ArC), 126.6 (ArC), 122.8 (ArC), 92.6 + 90.6

[C(3)], 44.4, 44,3, 44.1, 43.8, 43.4, 43.1, 41.5, 41.2 [N(CH₃)₂]

4.8 N,N,N′,N′,N″,N″,N′″,N′″-octamethyl-

2-(2-furyl-methylthio)-2-butene-1,4-

bis(amidinium)) bis(tetraphenylborate)

(9b)

2-Furyl-methanthiol (124 mg, 1.09 mmol) was added to a ppm. C₆₂H₇₁N₅B₂(907.88): C 82.02, H 7.88, N 7.71; found C

solution of the bis(amidinium) salt 4 (400 mg, 1.0 mmol) 79.00, H 7.67, N 8.20.

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4.10 (2,3-E/Z)-N,N,N′,N′,N″,N″,N′″,

N′″-octamethyl-2-(morpholin-

4-yl)-2-butene-1,4-bis(amidinium)

bis(tetrafluoroborate (10b)

(454.02): C 37.04, H 6.22, N 18.51; found C 37.00, H 6.19, N

18.52.

4.12 N,N,N′,N′,N″,N″,N′″,N′″-octamethyl-

2-phenylamino-2-butene-1,4-

bis(amidinium) bis(tetrafluoroborate)

(11a)

A mixture of morpholine (180 mg, 2.0 mmol) and ace-

tonitrile (1.5 mL) was added to a solution of compound

4 (400 mg, 1.0 mmol) in acetonitrile (1.5 mL) and the

mixture was stirred at r.t. for 19 h. The volatile compounds

were removed under reduced pressure. The residual foam A mixture of aniline (200 mg, 2.0 mmol) and acetonitrile

was washed twice with boiling tetrahydrofuran (THF) (1.5 mL) was added to a solution of compound 4 (400 mg,

and suspended in diethylether. The pale yellow-white 1.0 mmol) in acetonitrile (1.5 mL) and the mixture was

solid was isolated by filtration, washed several times with stirred at r.t. for 19 h. The volatile compounds were

diethylether, and dried to afford (2,3-E/Z)-10b (6:1 ratio). removed under reduced pressure. The residual yellow

Yield: 480 mg (98 %), pale yellow solid; m.p. 232–234 °C. oil was triturated twice with boiling THF. After cooling

¹H NMR (500 MHz, CD₃CN), (2,3-E/Z)-mixture: δ ꢀ=ꢀ 5.29 [s, to ambient temperature, the solidified residue was sus-

0.14H, (2,3-Z)-10b, C(3)H], 4.90 (s, 0.86H, (2,3-E)-10b, C(3) pended in diethylether, isolated by filtration, washed

H], 3.84–3.66 (m, 4H, CH₂OCH₂), 3.42–3.0 (m, 28H, 4N(CH₃)₂several times with diethylether, and dried to afford com-

and CH₂NCH₂) ppm. ¹³C NMR (125 MHz, CD₃CN): δ ꢀ=ꢀ 166.6, pound 11a. Yield: 470 mg (95 %), yellow solid; m.p. 218 °C.

166.4 [C(4)], 165.2, 162.3 [C(2)], 150.5, 148.9 [C(1)], 97.6, 93.1 ¹H NMR (500 MHz, CD₃CN): δ ꢀ=ꢀ 7.88 (s, 1H, NH), 7.44 (t,

[C(3)], 66.7 (CH₂OCH₂), 49.7 (CH₂NCH₂), 44.8, 44.5, 44.4, J ꢀ=ꢀ 7.8 Hz, 2H, m-ArH), 7.26 (t, J ꢀ=ꢀ 7.6 Hz, 1H, p-ArH), 7.00

44.2, 43.6, 43.3 (NCH₃) ppm. C₁₆H₃₃N₅B₂F₈O (485.07): C (d, J ꢀ=ꢀ 7.6 Hz, 2H, o-ArH), 5.31 [s, 1H, C(3)H], 3.35–2.70 (m,

39.62, H 6.86, N 14.44; found C 39.79, H 6.78, N 14.40.

24H, 8NCH₃) ppm. ¹³C NMR (125 MHz, CD₃CN): δ ꢀ=ꢀ 165.6,

165.2 [C(1) and C(4)], 142.4 [C(2)], 138.8, 130.9, 126.8, 121.1

(ArC), 98.0 [C(3)], 44.2, 43.7, 42.8 (NCH₃) ppm. C₁₈H₃₁N₅B₂F₈

(491.08): C 44.02, H 6.36, N 14.26; found C 44.10, H 6.34,

N 14.36.

4.11 (2,3-E/Z)-N,N,N′,N′,N″,N″,N′″,N′″-

octamethyl-2-cyanomethylamino-

2-butene-1,4-bis(amidinium)

4.13 N,N,N′,N′,N″,N″,N′″,N′″-octamethyl-

2-(2-methoxycarbonylanilino)-

2-butene-1,4-bis(amidinium)

bis(tetrafluoroborate) (10c)

A mixture of compound 4 (400 mg, 1.0 mmol), aminoace-

tonitrile hydrochloride (110 mg, 1.2 mmol), and Na₂CO₃

(150 mg, 1.4 mmol) in acetonitrile (3 mL) was stirred at

bis(tetrafluoroborate) (11b)

r.t. for 1 h and then filtered. The filtrate was concentrated A mixture of methyl 2-aminobenzoate (methyl anthra-

under reduced pressure. Methanol was added to the nilate) (200 mg, 1.3 mmol) and methanol (3 mL) was

residue. The crystalline product was isolated by filtration, added to a suspension of compound 4 (400 mg, 1 mmol)

washed several times with methanol, and dried to afford of in methanol (3 mL). The mixture was heated shortly to

(2,3-E/Z)-10c (3:2 ratio). Yield: 260 mg (57 %), light purple reflux until a clear yellow solution resulted, which was

1

crystals; m.p. 168–170 °C. H NMR (500 MHz, CD₃CN), stirred at r.t. for 48 h. The volatile compounds were

(2,3-E/Z)-mixture: δ ꢀ=ꢀ 6.3 (br. s, 1H, NH), 5.25 [br. s, 0.4H, removed under reduced pressure. Ethanol (5 mL) was

(2,3-Z)-10c, C(3)H], 5.11 [br. s, 0.6H, (2,3-E)-10c, C(3)H], added to the residual yellow oil and the mixture was

4.35 and 4.16 (2 br. s, 0.8H and 1.2H, CH₂CN), 3.36, 3.32, heated for a few minutes. The clear yellow solution was

3.19 (3 br. s, 9H, 3NCH₃), 3.14 (br. s, 15H, 5NCH₃) ppm. ¹³C kept at 5 °C for 2 days. The yellow crystalline material

NMR (125 MHz, CD₃CN): δ ꢀ=ꢀ 165.9, 165.4 [C(4)], 162.6, 161.9 formed was collected by filtration, washed twice with

[C(1)], 145.9, 145.7 [C(2)], 116.7, 115.8 (CN), 94.9, 94.7 [C(3)], cold ethanol, and dried to afford compound 11b. Yield:

1

44.4, 44.3, 44.2, 43.6, 43.1 [N(CH₃)₂], 33.9, 32.8 (CH₂CN) 500 mg (90 %), yellow crystals; m.p. 172–174 °C. H NMR

ppm. HRMS [(+)-TOF-ESI]: m/z ꢀ=ꢀ 279.2294 {calcd. 279.2292 (500 MHz, CD₃CN): δ ꢀ=ꢀ 10.25 (s, 1H, NH), 8.10 (d, J ꢀ=ꢀ 8 Hz,

+

for C₁₄H₂₇N₆, [M-HBF₄-BF₄] , (100)], 234.17 {calcd. 234.17 1H, ArH), 7.65 (t, J ꢀ=ꢀ 7.8, 1H, ArH), 7.27 (t, J ꢀ=ꢀ 7.7, 1H, ArH),

+

for C₁₂H₂₀N₅, [M-HBF₄-BF₄-HNMe₂] , (100)}. C₁₄H₂₈N₆B₂F₈6.75 (d, J ꢀ=ꢀ 8 Hz, 1H, ArH), 5.55 [s, 1H, C(3)H], 3.93 (s, 3H,

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COCH₃), 3.4–3.0 (m, 24H, 8NCH₃) ppm. ¹³C NMR (125 MHz, to afford compound 15a. Yield: 320 mg (84 %), yellow

1

CD₃CN): δ ꢀ=ꢀ 169.1 (Cꢀ=ꢀO), 164.7, 164.6 [C(1), C(4)], 140.4 needles; m.p. 158–160 °C. H NMR (500 MHz, CD₃CN): δ ꢀ=ꢀ

(ArC), 140.3 [C(2)], 136.0, 133.0, 124.9, 117.9, 117.4 (ArC), 4.73 [s, 1H, C(3)H], 3.21 [br. s, 12H, 2N(CH₃)₂], 3.11 [s, 12H,

101.9 [C(3)], 53.5 (COCH₃), 44.3, 43.9. 43.1 (NCH₃) ppm. 2N(CH₃)₂] ppm. ¹³C NMR (125 MHz, CD₃CN): δ ꢀ=ꢀ 169.1 [C(4)],

C₂₀H₃₃N₅B₂F₈O₂(549.12): C 43.75, H 6.06, N 12.75; found C 167.6 [C(1)], 147.7 [C(2)], 119.7, 119.5, 119.1, 95.2 [C(3)], 44.4,

43.06, H 6.00, N 12.60.

43.3, 42.5 (NCH₃) ppm. C₁₅H₂₅N₆BF₄·H₂O (394.22): C 45.70, H

6.90, N 21.32; found C 44.21, H 6.17, N 20.61.

4.14 N,N,N′,N′-tetramethyl-1-(4-

chlorbenzoyl)hydrazino]-5-dimethyl-

amino-2H-pyrazole-3-carboxamidinium

tetraphenylborate (13)

4.16 N,N,N′,N′-tetramethyl-

2-cyan-ethoxycarbonylmethylene-

4,4-bis(dimethylamino)-3-buten-

amidinium tetraphenylborate (15b)

A mixture of compounds 4 (400 mg, 1.0 mmol), 4-chlo-

robenzohydrazide (170 mg, 1.0 mmol) and acetonitrile A mixture of compound 4 (400 mg, 1.0 mmol), ethyl

(3 mL) was heated at 50 °C with stirring for a few minutes cyanoacetate (220 mg, 1.9 mmol), Na₂CO₃(100 mg,

until the solids were dissolved and then stirring was con- 0.95 mmol), and acetonitrile (3 mL) was stirred at r.t. for

tinued at r.t. for 19 h. The mixture was filtered. A solution 24 h. The mixture was diluted with acetonitrile (2 mL) and

of NaBPh₄(0.7 g, 2 mmol) was added. The mixture was fil- filtered. A solution of NaBPh₄(360 mg, 1 mmol) in ace-

tered and the filtrate was evaporated in vacuo. Methanol tonitrile (4 mL) was added to the yellow-orange filtrate.

was added to the residue. The crystallized product was The mixture was filtered and the filtrate was concentrated

collected by filtration, washed several times with metha- under reduced pressure. The residue was dissolved in hot

nol and dried to afford compound 13, which was recrys- methanol. After cooling to ambient temperature, the crys-

tallized from acetonitrile. Yield: 290 mg (40 %), yellow talline material was collected by filtration, washed several

crystals; m.p. 258–260 °C. ¹H NMR (500 MHz, CD₃CN): δ ꢀ=ꢀ times with methanol, and dried to afford compound 15b.

7.90 (d, J ꢀ=ꢀ 8.6 Hz, 2H, ArH), 7.55 (d, J ꢀ=ꢀ 8.6 Hz, 2H, ArH), Yield: 580 mg (88 %), yellow needles; m.p. 184–186 °C. ¹H

7.27 (br. s, 8H, ArH, BPh₄), 6.99 [t, J ꢀ=ꢀ 7.4 Hz, 8H, ArH, NMR (500 MHz, CD₃CN): δ ꢀ=ꢀ 7.27 (br. s, 8H, o-ArH), 6.99

BPh₄], 6.83 [t, J ꢀ=ꢀ 7.3 Hz, 4H, ArH, BPh₄), 5.95 (s, 1H, pyra- (t, J ꢀ=ꢀ 7.4 Hz, 8H, m-ArH), 6.84 (t, J ꢀ=ꢀ 7.3 Hz, 4H, p-ArH),

zole ꢀ=ꢀCH-), 3.12 [br. s, 12H, 2N(CH₃)₂], 2.90 [s, 6H, N(CH₃)₂] 4.55 [s, 1H, C(3)H], 4.07 (q, J ꢀ=ꢀ 7 Hz, 2H, OCH₂), 3.20–2.90

ppm. ¹³C NMR (125 MHz, CD₃CN): δ ꢀ=ꢀ 167.29, 165.42, 165.05, [m, 24H, 4N(CH₃)₂], 1.21 (t, J ꢀ=ꢀ 7 Hz, 3H, CH₂CH₃) ppm. ¹³C

164.65, 164.25, 163.41, 158.65, 144.31, 140.29, 136.84, 133.62, NMR (125 MHz, CD₃CN): δ ꢀ=ꢀ 173.2 [C(2)], 168.2 [C(4)], 167.6

132.26, 129.54, 126.63, 122.81, 94.19, 44.09, 43.39 ppm. (Cꢀ=ꢀO), 165.4, 165.0, 164.6, 164.2 (BC_Ph), 148.3 (CCN), 136.8,

C₄₁H₄₃N₅BClO (668.08): C 73.71, H 6.49, N 10.48; found C 126.6, 122.8 (ArC), 121.2 (CN), 95.7 [C(3)], 60.8 (OCH₂), 44.1,

73.73, H 6.50, N 10.65.

43.1, 42.3 (NCH₃), 15.0 (CH₂CH₃) ppm. C₄₁H₅₀N₅BO₂(655.68):

C 75.10, H 7.69, N 10.68; found C 73.86, H 7.65, N 10.63.

4.15 N,N,N′,N′-tetramethyl-2-

dicyanomethylene-4,4-

4.17 N,N,N′,N′-tetramethyl-

2-diethoxymethylene-3-bromo-

4,4-bis(dimethylamino)-3-buten-

amidinium tetrafluoroborate (18)

bis(dimethylamino)-3-buten-

amidinium tetrafluoroborate (15a)

A solution of malononitrile (100 mg, 1.5 mmol) in acetoni-

trile (1.5 mL) was added to a stirred mixture of compound A mixture of compound 4 (200 mg, 0.5 mmol), diethyl bro-

4 (400 mg, 1.0 mmol) and Na₂CO₃(100 mg, 0.95 mmol) momalonate (90 μL, 126 mg, 0.53 mmol), Na₂CO₃(150 mg,

in acetonitrile (1.5 mL), and stirring was continued at r.t. 1.4 mmol), and acetonitrile (3 mL) was stirred at r.t. for

for 20 h. The mixture was filtered and the yellow-orange 24 h. The mixture was filtered and the filtrate concen-

filtrate was concentrated under vacuum. The residue trated under reduced pressure. 2-Propanol was added to

was dissolved in hot ethanol and then filtered hot. After the residue and the mixture was heated shortly until a

cooling to r.t., the crystalline material was collected by clear solution was obtained. The solution was cooled to

filtration, washed several times with ethanol, and dried 5 °C. The crystalline product was collected by filtration,

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238ꢀ

washed few times with 2-propanol, and dried to afford at r.t. and then for 1 h at 80 °C. The mixture was diluted

compound 18. Yield: 260 mg (94 %), bright orange crys- with acetonitrile and filtered. A solution of NaBPh₄(350

tals; m.p. 176–178 °C. ¹H NMR (500 MHz, CD₃CN): δ ꢀ=ꢀ 4.03 mg, 1 mmol) in acetonitrile (3 mL) was added to the

(m, 4H, OCH₂), 3.17 [s, 6H, N(CH₃)₂], 3.07 [s, 6H, N(CH₃)₂], yellow filtrate. The mixture was filtered and the filtrate

3.06 [s, 6H, N(CH₃)₂], 2.97 [s, 6H, N(CH₃)₂], 1.20 (m, 6H, was concentrated under reduced pressure. The residue

2OCH₂CH₃) ppm. ¹³C NMR (125 MHz, CD₃CN): δ ꢀ=ꢀ 174.3, was dissolved in hot ethanol. After cooling to r.t., the

169.6, 169.3, 168.1, 147.4, 91.9, 83.3, 60.6, 60.2, 44.4, 42.7, crystalline material was collected by filtration, washed

42.6, 42.2, 14.9, 14.6. HRMS [(+)-TOF-ESI]: isotope distribu- several times with ethanol, and dried to afford the salt

+

tion m/z ꢀ=ꢀ for C₁₉H₃₄BrN₄O₄[M-BF₄] , rel. int. (%).

23b. Yield: 455 mg (77 %), yellow crystals; m.p. 196–198

1

°C. H NMR (500 MHz, CD₃CN): δ ꢀ=ꢀ 10.9–9.0 (br. s, 1H,

Calcd.

Found

461.1758

(100)

461.1750

(100)

462.1788

(20.5)

462.1779

(22)

463.1740

(97.5)

463.1726

(100)

464.1769

(20)

464.1742

(22)

NH), 7.27 (br. s, 8H, o-ArH), 6.98 (t, J ꢀ=ꢀ 7.3 Hz, 8H, m-ArH),

6.83 (t, J ꢀ=ꢀ 7.3 Hz, 4H, p-ArH), 6.38 (s, 1H, pyrrole ꢀ=ꢀCH-),

3.81 (s, 3H, COOCH₃), 3.04 [br. s, 12H, 2N(CH₃)₂], 2.78

[s, 6H, N(CH₃)₂] ppm. ¹³C NMR (125 MHz, CD₃CN): δ ꢀ=ꢀ

+

165.4, 165.0, 164.6, 164.2 (BC_Ph), 162.2 (C ) 160.5 (Cꢀ=ꢀO),

148.1 [C(4)], 136.8, 126.6, 122.8 (ArC), 120.1, 115.9 [C(2),

C(5)], 108.9 [C(3)], 52.1 (OCH₃), 44.4, 43.7 (NCH₃) ppm.

C₃₇H₄₃N₄BO₂(586.57): C 75.76, H 7.39, N 9.55; found C 75.51,

H 7.38, N 9.42.

4.18 N,N,N′,N′,N″,N″,N′″,N′″-octamethyl-

2-(1-methyl-1H-pyrrol-2-yl)-

2-butene-1,4-bis(amidinium)

bis(tetraphenylborate) (20)

A mixture of compound 4 (400 mg, 1 mmol), N-methyl- 4.20 N,N,N′,N′-tetramethyl-4-dimethylamin

pyrrole (450 mg, 5.5 mmol), and acetonitrile (3 mL) was

o-5-methoxycarbonyl-N-methylpyrrole

stirred at r.t. for 7 days. A solution of NaBPh₄(700 mg,

-2-carboxamidinium tetraphenylborate

2 mmol) in acetonitrile (5 mL) was added. The mixture was

filtered and the filtrate was concentrated under reduced

(24b)

pressure. Methanol was added to the residue, and the

A mixture of compound 4 (400 mg, 1.0 mmol), 2-(N-meth-

mixture was heated to reflux and left at r.t. The crystalline

ylamino)acetate hydrochloride (N-methylglycine methyl

product was collected by filtration, washed several times

ester hydrochloride, 170 mg, 1.2 mmol), Na₂CO₃(150 mg,

with methanol, and dried to afford compound 20. Yield:

1.4 mmol), and acetonitrile (3 mL) was stirred 24 h at r.t.

670 mg (71 %), yellow-brown crystals; m.p. 254 °C (dec.).

and further 24 h at 80 °C. The mixture was diluted with

¹H NMR (500 MHz, CD₃CN): δ ꢀ=ꢀ 7.27 (br. s, 16H, o-ArH), 7.04

acetonitrile and filtered. A solution of NaBPh₄(350 mg,

(m, 1H, pyrrole CH), 6.99 (t, J ꢀ=ꢀ 7.4 Hz, 16H, m-ArH), 6.84

1 mmol) in acetonitrile (3 mL) was added to the yellow

(t, J ꢀ=ꢀ 7.2 Hz, 8H, p-ArH), 6.35 (m, 1H, pyrrole CH), 6.29

filtrate. The mixture was filtered and the filtrate was

(m, 1H, pyrrole CH), 6.25 [s, 1H, C(3)H], 3.43 (s, 3H, pyrrole

concentrated under vacuum. The residue was dissolved

NCH₃), 3.35–2.79 [m, 24H, 4N(CH₃)₂] ppm. ¹³C NMR (125

in hot methanol. After cooling to 5 °C, the crystalline

MHz, CD₃CN): δ ꢀ=ꢀ 167.9, 165.8, 165.4, 165.0, 164.6, 164.2,

material was collected by filtration, washed several

136.8, 136.5, 132.4, 126.7, 125.0, 124.7, 122.8, 111.8, 44.9, 44.0,

times with methanol, and dried to afford the salt 24b.

42.6, 35.7 ppm. C₆₅H₇₁N₅B₂(943.91): C 82.71, H 7.58, N 7.42;

found C 82.47, H 7.58, N 7.52.

1

Yield: 250 mg (41 %), yellow plates; m.p. 174–176 °C. H

NMR (500 MHz, CD₃CN): δ ꢀ=ꢀ 7.27 (br. s, 8H, o-ArH), 6.98

(t, J ꢀ=ꢀ 7.5 Hz, 8H, m-ArH), 6.83 (t, J ꢀ=ꢀ 7.3 Hz, 4H, p-ArH),

6.32 (s, 1H, pyrrole ꢀ=ꢀCH-), 3.84 (s, 3H, COOCH₃), 3.61

4.19 N,N,N′,N′-tetramethyl-4-dimethylamino (s, 3H, pyrrole NCH₃), 3.19 [s, 6H, N(CH₃)₂], 2.85 [s, 6H,

N(CH₃)₂], 2.69 [s, 6H, N(CH₃)₂] ppm. ¹³C NMR (125 MHz,

-5-methoxycarbonyl-pyrrole-2-carboxa-

+

CD₃CN): δ ꢀ=ꢀ 165.4, 165.0, 164.6, 164.2 (BC_Ph), 161.8 (C ),

midinium tetraphenylborate (23b)

161.7 (Cꢀ=ꢀO), 148.7 [C(4)], 136.8 (ArC), 126.6 (ArC), 124.2

mixture of methyl 2-aminoacetate hydrochloride [C(2)], 122.8 (ArC), 118.6 [C(5)], 107.0 [C(3)], 52.0 (OCH₃),

A

(glycine methyl ester hydrochloride, 150 mg, 1.2 mmol), 45.0 [N(CH₃)₂], 43.6, 43.4 [N(CH₃)₂], 35.6 (pyrrole NCH₃)

compound 4 (400 mg, 1.0 mmol), Na₂CO₃(150 mg, 1.4 ppm. C₃₈H₄₅N₄BO₂(600.60): C 75.99, H 7.55, N 9.33; found

mmol), and acetonitrile (3 mL) was stirred first for 24 h C75.97, H 7.49, N 9.33.

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4.21 N,N,N′,N′-tetramethyl-3-dimethylamino C(7)H], 4.55 (s, 2H, CH₂), 3.55 [s, 6H, N(CH₃)₂], 3.18 [s, 12H,

2N(CH₃)₂] ppm. ¹³C NMR (125 MHz, CD₃CN): δ ꢀ=ꢀ 170.7, 148.4,

-5-methoxycarbonyl-thiophene-2-carbo

146.0, 135.0, 134.7, 130.3, 129.3, 128.8, 43.9, 43.6, 40.8 ppm.

xamidinium tetraphenylborate (25b)

C₁₆H₂₅N₅B₂F₈·H₂O (479.03): C 40.12, H 5.68, N 14.62; found C

A mixture of compound 4 (560 mg, 1.4 mmol), methyl 40.59, H 5.55, N 14.70.

thioglycolate (150 mg, 1.41 mmol), Na₂CO₃(150 mg, 1.4

mmol), and acetonitrile (3 mL) was stirred 24 h at r.t. The

mixture was diluted with acetonitrile and filtered. A solu- 4.23 N,N,N′,N′-tetramethyl-

tion of NaBPh₄(480 mg, 1.4 mmol) in acetonitrile (3 mL)

2-(3-dimethylammonio-benzo[g]

was added to the yellow filtrate. The mixture was filtered

quinoxalin-2-yl)acetamidinium

and the filtrate was evaporated in vacuo. The residue was

bis(tetrafluoroborate) (29b)

dissolved in hot methanol. After cooling to r.t., the crystal-

line material was collected by filtration, washed several

A mixture of compound 4 (240 mg, 0.6 mmol), naphtha-

times with methanol, and dried to afford compound 25b.

lene-2,3-diamine (80 mg, 0.5 mmol), triethylamine (0.5 mL,

1

Yield: 510 mg (61 %), yellow plates; m.p. 174–176 °C. H

360 mg, 3.6 mmol), and acetonitrile (7 mL) was stirred at

NMR (500 MHz, CD₃CN): δ ꢀ=ꢀ 7.27 (br. s, 8H, o-ArH),7.18 (s,

r.t. for 18 h. The solvent was removed under reduced pres-

1H, thiophene ꢀ=ꢀCH-), 6.98 (t, J ꢀ=ꢀ 7.3 Hz, 8H, m-ArH), 6.83

sure. The residue was dissolved in CH₂Cl₂and the solu-

(t, J ꢀ=ꢀ 7.3 Hz, 4H, p-ArH), 3.78 (s, 3H, COOCH₃), 3.08 [br.

tion was washed consecutively with an aqueous solution

s, 12H, 2N(CH₃)₂], 2.97 [s, 6H, N(CH₃)₂] ppm. ¹³C NMR (125

of K₂CO₃and water, dried over Na₂SO₄, and concentrated

MHz, CD₃CN): δ ꢀ=ꢀ 165.4, 165.0, 164.6, 164.3 (BC_Ph), 164.2

under vacuum. The residual bright orange glass-like solid

+

(C ), 162.3 (Cꢀ=ꢀO), 157.5 [C(4)], 136.7 (ArC) 131.7 [C(2)], 128.8

(28b, 110 mg) was dissolved in 4 mL acetonitrile. The

[C(3)], 126.5 (ArC), 122.7 (ArC), 111.1 [C(5)], 52,6 (OCH₃),

solution was acidified with 50 % aqueous HBF₄, and the

44.3 [N(CH₃)₂], 44.2 [N(CH₃)₂] ppm. C₃₇H₄₂N₃BO₂S (603.62):

solvent was evaporated to dryness. The residue was dried

C 73.62, H 7.01, N 6.96, S 5.31; found C 73.43, H 7.07, N 6.91,

by thrice dissolving in acetonitrile and vacuum evapo-

S 5.1 7.

ration. Methanol was added to the residue. The mixture

was refluxed for a few minutes and left at r.t. The crystal-

line product formed was collected by filtration, washed

4.22 N,N,N′,N′-tetramethyl-2-(3-

several times with methanol, and dried to afford the

dimethylammonioquinoxalin-2-yl)

acetamidinium bis(tetrafluoroborate)

(29a)

hydrotetrafluoroborate-tetrafluoroborate salt 29b. Yield:

1

80 mg (47 %), orange crystals; m.p. 248–252 °C. H NMR

(500 MHz, CD₃CN) [an equilibrium mixture of differently

protonated species (∼1:1) in CD₃CN solution]: δ ꢀ=ꢀ 8.56 (br.

+

A mixture of compound 4 (480 mg, 1.2 mmol), benzene- s, 0.5H, NH ), 8.54 [s, 0.5H, C(10)H], 8.33 [s, 0.5H, C(5)H],

1,2-diamine (130 mg, 1.2 mmol), and acetonitrile (3 mL) was 8.14 [d, J ꢀ=ꢀ 8.4 Hz, 0.5H, C(6)H], 8.10 [d, J ꢀ=ꢀ 8.4 Hz, 0.5H,

stirred at r.t. for 15 h and then concentrated under reduced C(9)], 7.96 [s, 0.5H, C(10)H], 7.87 [d, J ꢀ=ꢀ 8.2 Hz, 0.5H, C(6)],

pressure. The bright yellow glass-like residual solid (28a) 7.82 [d, J ꢀ=ꢀ 8.2 Hz, 0.5H, C(9)], 7.73 [t, J ꢀ=ꢀ 8 Hz, 0.5H, C(7)H],

was dissolved in a minimal amount of methanol. The solu- 7.68 [s, 0.5H, C(5)], 7.65 [t, J ꢀ=ꢀ 7.7 Hz, 0.5H, C(8)H], 7.51 [t, J ꢀ=ꢀ

tion was acidified with 50 % aqueous solution of HBF₄and 7.6 Hz, 0.5H, C(7)H], 7.46 [t, J ꢀ=ꢀ 7.8 Hz, 0.5H, C(8)H], 5.56 (s,

concentrated under reduced pressure. The residue was 0.5H, ꢀ=ꢀCH-), 4.59 (s, 1H, -CH₂-), 3.61 (s, 3H, NCH₃), 3.50 (s,

dried by triple dissolving in absolute ethanol and vacuum 3H, NCH₃), 3.22 [s, 6H, N(CH₃)₂], 3.21[s, 6H, N(CH₃)₂] ppm.

evaporation. The resulting light yellow glass-like solid C₂₀H₂₇N₅B₂F₈·H₂O (529.09): C 45.40, H 5.52, N 13.24; found C

was dissolved in the minimal amount of methanol, heated 45.70 H 5.51, N 13.31.

for a few minutes until a clear solution was obtained,

and left overnight at 5 °C. The crystalline product was

collected by filtration, washed several times with chilled 4.24 2-{3-[2,2-Bis(dimethylamino)vinyl]-

methanol, and dried to afford the hydrotetrafluoroborate-

4-cyano-5-oxo-2,5-dihydro-pyrrol-

tetrafluoroborate salt 29a. Yield: 230 mg (41 %), yellow

2-ylidene}-cyanoacetamide (33a)

crystals; m.p. 260–264 °C. ¹H NMR (500 MHz, CD₃CN): δ ꢀ=ꢀ

+

11.12 (br. s, 1H, NH ), 7.94 and 7.93 [2d, J ꢀ=ꢀ 8.3 Hz, 2H, C(5) A mixture of compound 4 (400 mg, 1.0 mmol), cyanoacet-

H and C(8)H], 7.85 and 7.68 (2t, J ꢀ=ꢀ 8.1 Hz, 2H, C(6)H and amide (330 mg, 3.9 mmol), triethylamine (0.5 mL), and

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ꢀK. Drandarov et al.: Orthoamides and iminium salts, LXXXIX

Me₂N

N

NMe₂

Me₂N

N

NMe₂

H

1'

10

5

2'

2

H

BF₄

N

NMe₂

N

NMe₂

6

H

*

28b⋅HBF₄

+

C(5)H C(6)H

C(7)H

C(8)H

C(9)H

C(10)H C(2′)

NH

C(3)

C(1′)

H/H₂

NMe₂N(Me)₂

28b·HBF₄8.33 (s) 8.14 (d), J ꢃ=ꢃ 8.4 Hz 7.73 (t), J ꢃ=ꢃ 8 Hz 7.65 (t), J ꢃ=ꢃ 7.7 Hz 8.10 (d), J ꢃ=ꢃ 8.4 Hz 8.54 (s) 5.56 (s) 8.56 (br. s) 3.61 (s) 3.22 (s)

28b·HBF₄* 7.68 (s) 7.87 (d), J ꢃ=ꢃ 8.2 Hz 7.51 (t), J ꢃ=ꢃ 7.6 Hz 7.46 (t), J ꢃ=ꢃ 7.8 Hz 7.82 (d), J ꢃ=ꢃ 8.2 Hz 7.96 (s) 4.59 (s)

–

3.50 (s) 3.21 (s)

acetonitrile (4 mL) was stirred at r.t. for 18 h and then

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K. Drandarov et al.: Orthoamides and iminium salts, LXXXIXꢀ

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Orthoamides and iminium salts, LXXXIX. Reactions of N,N,N',N',N'',N'',N''',N'''-octamethylacetylene-bis(carboxamidinium) tetrafluoroborate with nucleophilic reagents - New methods for the preparation of amidinium salts and ketene aminals

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