Terminal acetylenic iminium salts – Synthesis and reactivity

A Journal of

Accepted Article

Title: Terminal Acetylenic Iminium Salts – Synthesis and Reactivity

Michael Keim,[a] Philipp Kratzer,[a] Helena Derksen,[a] Dajana

Isakov,[a] Gerhard Maas*[a]

Authors: Michael Keim, Philipp Kratzer, Helena Derksen, Dajana

Isakov, and Gerhard Maas

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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201801511

Link to VoR: http://dx.doi.org/10.1002/ejoc.201801511

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10.1002/ejoc.201801511

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Terminal Acetylenic Iminium Salts – Synthesis and Reactivity

Michael Keim,^[a]Philipp Kratzer,^[a]Helena Derksen,^[a]Dajana Isakov,^[a]Gerhard Maas*^[a]

Abstract: Various types of terminal acetylenic iminium triflates

(propyne iminium salts) featuring a ketiminium or an aldiminium

group have been prepared for the first time by protiodesilylation of

the corresponding trimethylsilyl-substituted acetylenic iminium salts

using triflic acid and catalytic silver(I) triflate. The high reactivity of

the terminal C,C-triple bond is documented herein by the facile

Michael addition of nucleophiles and the exceptionally high

dienophilic reactivity in Diels-Alder reactions.

(Figure 1), depending on the status of their functional group.

Propyne iminium salts I are proper iminium salts, which are

derived from ketones or aldehydes, while amidium (II) and

amidinium (III) salts are derivatives of carboxylic acids. Due to

the better stabilization of the positive charge in II and III, the

iminium activation in these ions should activate the acetylenic

bond less effectively than in iminium ions, and this is confirmed

by the available experimental results.

Introduction

Iminium salts play a major role in organic synthesis.^[1,2]While the

iminium function is, in general, rather sensitive toward hydrolysis,

many iminium salts can be isolated and stored under anhydrous

conditions. The electrophilicity of iminium ions is by far higher

than that of the corresponding carbonyl compounds (aldehydes,

ketones) and imines.^[3]They can be used in diverse chemical

transformations, among which electrophilic aminoalkylations of

Grignard reagents, CH-acidic compounds, electron-rich arenes

and hetarenes, enamines, enolethers and O-silyl ketene acetals

are the most important ones. The electrophilic activation of

carbonyl compounds by (reversible) conversion into iminium

salts can be performed with preformed iminium salts^[4,5]or in a

catalytic cycle where the catalyst is a secondary or (less

frequently) primary amine (“iminium catalysis”^[6]). While iminium-

catalyzed reactions involving amines such as piperidine, proline

and aniline have been known for more than a century, only

recently they have gained new and strong attention with a focus

on the electrophilic reactivity of ,-unsaturated iminium salts in

general and their asymmetric transformations in particular.^[6]

In ,-unsaturated iminium ions, the  conjugation of the

iminium function with an adjacent C,C-double or triple bond

widens the synthetic potential as compared to simple iminium

salts. The iminium function lowers the LUMO level and causes a

significant polarization of the multiple bond. As a consequence,

these ions are ambident electrophiles with reaction centers at C-

1 and C-3, and the olefinic or acetylenic bond offers dienophilic

and dipolarophilic reactivity toward sufficiently electron-rich

dienes and 1,3-dipoles. The high electrophilicity power at the C-

3 position has been established by a kinetic study of the Michael

reaction of cinnamaldehyde-derived iminium salts with the cyclic

ketene acetal 6-TMS-3,4-dihydro-2H-pyran.^[7]

Figure 1. Acetylenic iminium, amidium, and amidinium salts.

As was stated above, some reports on iminium-catalyzed

transformations can be found in the earlier 20^thcentury literature,

but mainly with the seminal publications by the Yamaguchi

group in 1991^[8](lithium prolinate catalyzed Michael addition of

dimethyl malonate to ,-unsaturated aldehydes) and the

MacMillan group in 2000 and 2002 (enantioselective Diels-Alder

reactions of ,-unsaturated aldehydes^[9a]and ketones^[9b]

catalyzed by chiral acyclic secondary amines and

imidazolidinones) the new and prosperous field of

(enantioselective) organocatalysis by iminium activation of ,-

unsaturated carbonyl compounds was opened.^[6,10]

In contrast to the large number of reports on olefinic iminium

salts participating in catalytic cycles, analogous reactions of

alkynals/acetylenic iminium salts have become known only

recently.^[11]In a total synthesis of the Strychnos alkaloid (+)-

minfiensine by MacMillan and coworkers, an acetylenic iminium

salt was generated by iminium activation of propiolaldehyde with

a chiral imidazolidinone catalyst, which subsequently underwent

an intermolecular Diels-Alder reaction with a 2-vinylindole

derivative at -40 ^oC.^[12]In subsequent studies, similar terminal or

internal acetylenic iminium ion intermediates derived from

propiolaldehyde itself or from 3-substituted derivatives thereof

were postulated for the catalytic cycle, which were trapped by

oxa-Michael addition on the way to 4H-chromenes.^[13]

Our group has prepared and isolated quite a number of propyne

iminium salts with an internal (i.e. disubstituted) triple bond, and

we have studied their reactivity in stoichiometric reactions in a

range of transformations such as addition of diverse

nucleophiles at C-1 and C-3,^[14]Diels-Alder,^[15]1,3-dipolar

cycloaddition^[16]and [2+2] cycloaddition^[17]reactions. The results

of this preformed iminium salt strategy could be useful for the

design and understanding of related iminium-activated catalytic

procedures.

Acetylenic iminium salts can be divided in three major groups

[a]

Dr. M. Keim, Dr. P. Kratzer, Dipl.-Chem. H. Derksen, M.Sc. D.

Isakov, Prof. Dr. G. Maas*

Institute of Organic Chemistry I, University of Ulm

Albert-Einstein-Allee 11, D-89081 Ulm, Germany

E-mail: gerhard.maas@uni-ulm.de

http://www.uni-ulm.de/nawi/oc1.html

Supporting information for this article is given via a link at the end of

the document.

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The isolation and characterization of acetylenic iminium salts I

however, could not be separated from by-products without

featuring a terminal C,C-triple bond has not been reported so far. partial decomposition.^[21]

The closest analogy is represented by the terminal acetylenic

amidium salts II-BF₄, reported by Baum and Viehe,^18]and an

N,N,N’,N’-tetramethyl-propiolamidinium tetraphenylborate III,

reported by our group.^[19]While iminium ions II clearly exhibited

an enhanced reactivity as dienophiles and dipolarophiles

compared to propiolaldehyde, the amidinium ion salt gave

merely

a

somewhat better performance in the [3+2]

cycloaddition with C-phenyl-N-methyl nitrone or benzyl azide,

and it underwent the Diels-Alder reaction with common

dienophiles only under forcing conditions (with cyclopentadiene)

or not at all. Here, we introduce terminal acetylenic ketiminium

(Figure 2, 1 and 3) and aldiminium (2) triflate salts and we

highlight the excellent reactivity of their C,C-triple bond in the

Michael addition and as dienophiles in Diels-Alder reactions.

Scheme 1. Preparation of acetylenic ketiminium salts 1a,b. Conditions: a) 1.

EtMgBr (1 equiv), THF, 10 ^oC, 2 h; 2. CuBr·SMe₂(5 mol-%), THF, rt, 10 min; 3.

PhC(=NMe)Cl or (2-thienyl)C(N=Me)Cl, THF, rt, 18 h; 81 and 54% yield,

respectively. b) KF (1.5 equiv)/18-crown-6 (0.06 equiv), CH₂Cl₂, rt, 36 h (74%

yield for a and b). c) Methyl triflate was added slowly to imine 4 in CH₂Cl₂, for

a: -20 ^oC  rt, 18 h, 96%; for b: rt, 18 h, 70%. d) HOTf (1 equiv), AgOTf (1

mol-%), CH₂Cl₂, protection from light, rt, 79 days, 89% (a) and 84% (b). TMS



= Me₃Si, TfO^= CF₃SO₃

.

In an analogous manner as before, the novel cross-conjugated

bis(alkynyl)iminium salts 1c and 1d were prepared from imines 7,

which were obtained by TiCl₄-assisted condensation^[22]of the

corresponding bis(ethynyl)ketones and methylamine (Scheme 2).

The desilylation of 8a was advantageously performed with a

catalyst concentration of 5 mol-% and delivered 1c in high yield

within two days. On the other hand, a significantly higher amount

of AgOTf was required for the conversion 8b  1d, but even

with 21 mol-% of catalyst, 1d was obtained in only 63% yield

after five days. Like the other terminal acetylenic iminium salts,

Figure 2. Terminal acetylenic ketiminium and aldiminium salts prepared in this

study.

Results and Discussion

N-alkylation of acetylenic imines with strong alkylating reagents,

such as methyl triflate and triethyloxonium tetrafluoroborate, is

an effective method to prepare acetylenic iminium salts. While a

number of iminium salts with an internal C,C-triple bond (3-

substituted propyne iminium salts) have been prepared in this

manner,^[15b,17a,20]the isolation of terminal acetylenic iminium salts

has not been reported so far. In order to arrive at 1-arylethynyl

iminium salts 1a,b, we first prepared the 1-aryl-3-

(trimethylsilyl)propyne imines 4a,b from trimethylsilyl-acetylene

according to our published procedure (Scheme 1, for 4a^[20]).

Desilylation and N-methylation, in that order, were expected to

deliver the terminal acetylenic iminium triflates 1a,b. While the

o

1c and 1d can be stored for several weeks at -25 C under an

inert atmosphere. It has been reported that di(ethynyl)ketone,

the precursor of 1d, can be stored for some time at -80 ^oC,

undergoes a color change to yellow and black within a few

minutes at room temperature, and decomposes on warming by

deflagration accompanied by a black soot.^[23]Therefore, as a

matter of precaution, the preparation of 1d from 8b was carried

out on the sub-millimolar scale. Beginning decomposition of neat

1d around 60 ^oC was indicated by a color change from colorless

to yellow and finally black, but the salt appeared to be

insensitive toward scratching with a metallic spatula or to

mechanical impact.

desilylation

using

KF/catalytic

18-crown-6

proceeded

successfully, the N-methylation of so formed ethynyl imines 5a,b

unexpectedly failed to provide the desired N,N-dimethyl-iminium

triflates 1a,b. Under carefully controlled reaction conditions

o

(temperature at  0 C, HOTf-free methyl triflate and anhydrous

solvent) and with variations of addition rate and sequence, a

yellow solution or suspension was initially formed which quickly

went through several color changes, and finally a black solid

oligomeric/polymeric material was formed (vide infra).

Alternatively, imines 4 were first converted into iminium salts 6

by N-methylation with methyl triflate.^[20]The protiodesilylation of

6 was then achieved using an equimolar amount of triflic acid in

the presence of a catalytic amount of silver triflate, and the

desired terminal acetylenic iminium triflates 1a,b were obtained.

With 1 mol-% of the catalyst, the reaction required 79 days for

completion, but shorter conversion times could be achieved with

a higher concentration of the catalyst. The catalytic cycle is likely

to include an alkynyl silver(I) species; in fact, treatment of salts

6a,b with a stoichiometric amount of AgF or AgNO₃in

chloroform or acetonitrile generated silver acetylides which,

Scheme 2. Preparation of bis(alkynyl)iminium triflates 1c,d. Conditions: a)

MeNH₂(4 equiv), TiCl₄(0.7 equiv), toluene/THF, -20 ^oC  rt, 1 h, 67 and 94%

yield, respectively. b) CH₃OTf, CH₂Cl₂, -40 ^oC  rt, 86 and 89% yield,

respectively. c) For 8a  1c: HOTf (1 equiv), AgOTf (5 mol-%), CH₂Cl₂,

protection from light, rt, 2 days, 98%; for 8b  1d: HOTf (1 equiv), AgOTf (21

mol-%), 5 d, 63%.

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Acetylenic aldiminium salts with an internal C,C-triple bond can

be prepared by thermal elimination of HOTf from 3-

trifloxypropene iminium salts.^[24]They have also been generated

by de-amination of acetylenic amidines with triflic anhydride and

reacted in situ with Grignard reagents to form propargyl

amines.^[25]Following our synthetic strategy, we were able to

convert also the TMS-substituted acetylenic aldimine 9 into

imines and their N-methylated relatives 1a,b in the course of the

reaction.

acetylenic aldiminium triflate

2

by the high-yielding N-

methylation/desilylation sequence via 10 as shown in Scheme 3.

Imine 9^[26]was prepared in two steps from TMS-acetylene via

TMS-propynal.^[27]

.

Figure 3. NMR chemical shifts of iminium salts 1, 2 (in CD₃CN, /ppm) and

imine 5a (in CDCl₃); ¹H in black, ¹³C in red.

In fact, when equimolar amounts of 5a and 1a were combined in

CH₂Cl₂at room temperature, the solution turned black

immediately and a black solid could be isolated, the ¹H NMR

spectra of which showed broad absorption ranges at  3.54.5

and 68.5 ppm which were superposed by several sharp

singlets between 2.62 and 3.42 ppm and a triplet at  = 2.66

ppm for H₂N⁺Me₂. In addition, the major part of imine 5a was

recovered on work-up. A MALDI mass spectrum of the black

solid isolated from a reaction of 5a with methyl triflate showed

peaks with m/z = n  143, corresponding to an oligomer

consisting of 410 C=CH-C(=NMe₂)Ph units. These and other

observations suggest that imines 5a,b initiate the polymerization

of iminium cations 1a,b resulting in poly(acetylene iminium

cations). The initiating step is a conjugate addition (Michael

addition) of the imine nitrogen atom at the terminal acetylenic

position of 5a,b. (A formula scheme of a possible polymerization

pathway is shown in the Supporting Information.) We have

reported earlier that acetylenic iminium salts with an internal

triple bond undergo a controlled Michael addition with N-

phenylbenzaldimine^[28]and isoquinoline.^[14a]The stronger

polarization and better accessibility of the terminal alkynes 5

could be factors causing the reaction not to terminate after the

first conjugate addition step.

Scheme 3. Preparation of acetylenic aldiminium salt 2. Conditions: a) MeNH₂,

MgSO₄, CH₂Cl₂, 78% yield. b) Imine 9 was added to CH₃OTf (1 equiv) in Et₂O,

-78 ^oC  rt, 90%. c) HOTf (1 equiv), AgOTf (1 mol-%), CH₂Cl₂, protection from

light, rt, 6 days, 95%.

In contrast to the failure of a controlled N-methylation of alkynyl

imines 5a,b, their N-protonation can be achieved with the

superacid HOTf at low temperature to provide NH-iminium

triflates (E)-3a,b in almost quantitative yield (Scheme 4). The

use of anhydrous solvent and triflic acid as well as freshly

distilled imines is mandatory in order to avoid the formation of

polymeric (by-)products. The hygroscopic salts 3a,b can be

stored for at least several weeks at -25 ^oC under an inert

atmosphere without detoriation, whereas they deliquesce to form

a black oil in a short time on exposure to air.

Scheme 4. Preparation of terminal N-methyl propyne iminium salts 3.

Acetylenic iminium ions are ambident cations, which can accept

nucleophiles at the acetylenic -position or at the iminium carbon

atom.^[14]As the few examples shown in Scheme 5 reveal,

acetylenic iminium salts with a terminal C,C-triple bond behave

in the same manner as those with an internal one. On exposure

of salt 1a to water vapor, the 3-hydroxypropene iminium triflate

11 (also to be considered as O-protonated 3-dimethylamino-

cinnamaldehyde) is formed in high yield, while the iminium group

does not undergo hydrolysis under these conditions.

Analogously, traces of water that were present in [D₃]acetonitrile

in an NMR tube were sufficient to convert salt 1d into 15 by

addition of water at one of the triple bonds. Water addition at the

C,C-triple bond of an acetylenic iminium ion has also been

postulated as an intermediate step in the self-condensation of

propynals in the presence of a prolinol catalyst.^[29]

For reference purposes, NMR chemical shifts of acetylenic

iminium triflates 1a,b and 2 are shown in Figure 3. By

comparison with the data of imine 5a, it is noted that the

acetylenic proton is strongly deshielded (by 1.8 ppm in 1a);

furthermore, the acetylenic carbon atom C-3 is deshielded by

21.5 ppm while the C-1 chemical shift is almost the same in the

iminium ion and the imine. These data indicate the strong

polarization of the triple bond in the iminium salts (for example,

_C= 31.9 ppm in iminium salt 1a vs. 12.6 ppm in imine 5) with

significantly increased positive charge at the C-3 position. We

reasoned that the formation of oligomers/polymers instead of

clean N-methylation of terminal acetylenic imines 5a,b (see

above) can be attributed to the simultaneous presence of these

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Scheme 6. Silver-catalyzed reaction of Me₃Si-propyne iminium salt 6a with

alcohols.

We have studied earlier the reactivity of propyne iminium ions

with an internal C,C-triple bond in Diels-Alder reactions with

common 1,3-dienes, anthracene and furan.^[15]Their dienophilic

reactivity was certainly higher than that of the related acetylenic

ketones, but not as much as we had expected based mainly on

their lowered LUMO level. We speculated that the increased

steric demand of the iminium group in comparison with the

carbonyl group negatively influences the formation of the

reaction’s transition state and therefore counteracts the

electronic advantage. Therefore, we had a great interest in

studying the dienophilic performance of terminal propyne

iminium salts 1a, 1c, 2, and 3a in [4+2] cycloaddition reactions

with normal electron demand. To our delight, the Diels-Alder

reactions listed in Table 1 occurred under very mild conditions in

all cases. In particular, Diels-Alder reactions with anthracene as

the diene component were finished after 14 hours at room

temperature, whereby the secondary iminium salt 3a reacted

faster than the ketiminium salts 1a and 1c.

The reaction of 1a and 3a with 1,3-diphenylisobenzofuran

(DBPF, 21) furnished the naphthalen-1(2H)-one derivatives

23a,b as the major products and 1-naphthols 24a,b as the minor

ones, instead of the expected [4+2] cycloaddition products 22

(Scheme 7). In the case of the reaction of 3a with 21, a third

product resulted, wich could not be clearly identified. Containig

an iminiun as well as a keto function it may by a constitutional

isomer of naphthalen-1(2H)-ones 23. The identity of 23b and

24a was firmly established by X-ray structure analysis (Figures 4

and 5). Not surprisingly, the separation of the iminium salts

turned out to be difficult. Nevertheless, iminium salt 23b could

be isolated in pure form; for details see Experimental Section.

With 23a in particular, slow hydrolysis was noticed when

moisture was not rigorously excluded. Therefore, we decided to

speed up this reaction using aqueous potassium carbonate.

NMR spectra indicated the formation of 2,4-diphenyl-1-

naphthol^[37]25 and benzoate, i. e., a reaction analogous to the

well-known base-assisted de-acylation of 1,3-diketones had

occurred. In contrast to 23, the iminium function of isomeric salts

24 was not hydrolyzed on contact with moist air; the absence of

a -ketoiminium unit and a hindered access of the nucleophile to

the iminium carbon atom are likely reasons.

Scheme 5. Reactions of propyne iminium salts 1a,d with nucleophiles.

With enamino ester 12, conjugate addition of the enamine

moiety occurs readily to form the pentamethinium derivative 13.

On the other hand, propargylamine 14 results from the addition

of CN^at the iminium carbon atom, as expected. The structure

of salt 13 can be derived from the NMR spectra. The Z

configuration of the enaminic double bond is indicated by the

large chemical shift difference of the NH₂protons ( = 9.10 and

10.20 ppm), which is consistent with an intramolecular NH···O

hydrogen bond. The E configuration of the CH=CH bond follows

3

from the large J_HHcoupling constant (14.0 Hz). [2D] NMR

spectra reveal the connectivity of the molecular framework,

which is different from constitutionally isomeric cations which are

formed from internal propyne iminium salts with enaminoketones

[15b, 17b]

by [2+2] cycloaddition at the enaminic double bond

followed by ring-opening. Salt 13 is the iminium analogue of the

ketone intermediate in the Bohlmann-Rahtz pyridine synthesis.^[30,

31]

In fact, a 1-(amino acid substituted)-4-amino-but-3-yn-2-one

reacts with 12 at room temperature to a product analogous to 13

(with C=O instead of C=N⁺Me₂), which undergoes

cyclocondensation to a 2,3,6-trisubstituted pyridine in refluxing

ethanol.^[32]In contrast, salt 13 did not undergo

a

o

cyclocondensation in acetonitrile at 80 C, perhaps because the

necessary E  Z isomerization of the olefinic bond does not

occur under these conditions.

It has been reported that trimethylsilyl-alkynes undergo a Ag(I)-

catalyzed SiMe₃/H exchange with protic reagents as proton

donors.^[33,34]This method would be a cheaper alternative to the

protiodesilylation with triflic acid. However, with aliphatic

alcohols as proton donors, Me₃Si-alkyne 6a under the published

conditions (but in the absence of H₂O) is converted into 3-

alkoxypropene iminium triflates 16a,b rather than terminal

alkyne 1a (Scheme 6). According to the proposed

mechanism,^[35]1a is formed in the catalytic cycle, and it is

trapped immediately by addition of ROH at the triple bond.

Notably, even less nucleophilic 4-nitrophenol adds to the

acetylenic bond of 1a and delivers the adduct 16c. These

observations underline again the high Michael reactivity of the

triple bond of terminal acetylenes 1 toward protic nucleophiles.

The products 23 and 24 could result from a spontaneous

rearrangement of the initially formed Diels-Alder adducts. It is

known that the [4+2] cycloaddition adducts of DPBF and

acetylenic dienophiles can undergo different rearrangements

mainly under thermal, acidic (refluxing HOAc, HOAc/HCl at

ambient temperature, chromatography on silica gel) and

photochemical conditions.^[38-42]Thermal and acid-catalyzed

rearrangements can afford naphthalen-1(2H)-ones and

naphthalen-2(1H)-ones, as in the case of DPBF/alkynylsulfone

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adducts.^[42]In other cases, annelated benzoylindenes are

isolated.^[38,40]

require significant thermal activation,^[38]whereas 23 and 24 are

formed already at or below ambient temperature.

With the Diels-Alder adduct 22 as the precursor, the formation of

23 and 24 can be explained as shown in Scheme 8, in

accordance with earlier proposals.^[39,42]A surprisingly fast

heterolytic cleavage of one of the two CO bonds (path A or B)

would yield intermediates 26 or 27. A 1,2-phenyl shift follows,

which converts 26 directly into 23 and in the case of 27 is

followed by aromatization through keto-enol tautomerization. As

far as the CO bond cleavage is concerned, path A should be

disfavored, because only in 26 the carbocationic center is at an

unfavorable position, namely adjacent to the electron-deficient -

C atom of the ,-unsaturated iminium unit. In order to explain

the formation of 26 as the major product, other factors, such as

the reversibility of the first step and steric factors would have to

be considered; a comparison of the molecular structures

(Figures 4 and 5) suggests that the steric congestion in the

cation of 27 is higher than in 26.

Scheme 7. Reaction of alkynes 1a and 3a with DPBF (21). Reaction details:

21 + 1a: CH₂Cl₂, -40 ^oC, 90 min, 91% conversion, 23a : 24a = 1 : 0.42. 21 +

3a: CH₂Cl₂, 0 ^oC, 5 min, 95% conversion, 23b : 24b = 1 : 0.38.

Scheme 8. Possible mechanism for the formation of 23 and 24.

Figure 4. ORTEP plot of 23b in the solid state. Hydrogen bond: N1···O2

2.766(2) Å, (N1H)···O2 1.98 Å, <(N1H···O2) 147.6 ^o.

Alternative mechanisms leading to intermediates 26 and 27,

which circumvent the initial formation of Diels-Alder adduct 22,

cannot be excluded. Thus, an electrophilic attack of 1a/3a at the

furan ring of DPBF followed by ring-opening would generate a

benzoylaminoallene intermediate, which could readily deliver

26 by a carbonylenamine cyclization.

In Table 2, a comparison is made for Diels-Alder reactions of

cyclopentadiene and anthracene with terminal acetylenic

iminium or amidium salts and other common electron-deficient

acetylenic and olefinic dienophiles. It can be seen that the

acetylenic iminium salts are extremely reactive dienophiles,

even more reactive than corresponding amidium salts. It is also

obvious that [4+2] cycloaddition reactions of anthracene with

dienophiles other than the terminal acetylenic iminium salts

rarely proceed at room temperature; only the very electron-

deficient tetracyanoethylene (TCNE) has a comparable reactivity.

Activation parameters for the [4+2] cycloaddition of acetylenic

iminium salts are not known. Therefore, we monitored the

kinetics of the reaction of iminium salts 1a, 3a as well as

(ethynyl)phenylketone (28) with tetraphenyl-cyclopentadienone

(tetracyclone) by ¹H NMR spectroscopy; anthracene was not

suited as the diene component because of its insufficient

solubility. Solutions of the iminium salt (1 equiv) and a large

excess of tetracyclone (14 equiv) in CDCl₃at pre-adjusted

temperature were combined, and the formation of the

Figure 5. ORTEP plot of 24a in the solid state. Hydrogen bond: O1···O2 2.750

(2) Å, (O1)H···O2 2.00 Å, <(O1H···O2) 146.3 ^o.

It appears, however, that general predictions cannot be made

and it is not always clear at which stage, i.e. during the reaction

itself or on work-up, the rearranged products are formed.

Isomerization reactions related to ours are known, but they

1

cycloadduct was monitored by H NMR in the range 233–258 K

(for 1a and 3a) and 308–326 K (for 28) (Figure 6).

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Table 1. Diels-Alder reactions of terminal propyne iminium salts 1a, 1c, 3a.

1,3-Diene

Alkyne

Product

R¹

R²

Conditions

Yield (%)

96

Cyclopentadiene

1a

17a

17b

Ph

Me

-68 °C  rt, 5 min

3a

Ph

H

-14 °C, 30 min

86

Tetracyclone

Anthracene

1a

3a

1c

18a^[36]

18b^[36]

18c^[36]

Ph

Me

H

-20 °C, 3 h

0 °C, 30 min

rt,15 min

93

83

87

Ph

C≡C-Ph

Me

1a

3a

1c

19a

19b

19c

Ph

Me

H

92

75

87

-20 °C  rt, 4 h

rt, 2 h

Ph

C≡C-Ph

Me

rt, 2 h

1. -20 °C, 8 h

2. o-chloranil

Isoprene

1a

20a

Ph

Me

81^a

[a] The product was isolated after in-situ oxidation of the initially formed 1,4-cyclohexadiene derivative with o-chloranil; a 96:4 mixture of the 4-Me and 3-Me

regioisomers was obtained.

Table 2. A comparison of the dienophilic reactivity of acetylenic iminium salts and other dienophiles toward cyclopentadiene and anthracene

.

Dienophile

Conditions

Yield (%)

Ref.

With cyclopentadiene

R¹

X

Ph

OTf

BF₄

B(Ph)₄

96

87

77

This work

[18]

-68 °C  rt, 5 min

rt, 20 min

OEt

NMe₂

105 °C, microwave, 45 min

[19]

-20 °C, 30 min

86

This work

55

61

[43]

[44]

0 °C  rt, 19 h

rt, 72 h

With anthracene

R = Me

R = H

92

75

This work

-20 °C  rt, 4 h

rt, 2 h

rt, 1 h

98^a

53

This work

[45]

140 °C, 168 h

dimethyl acetylenedicarboxylate

170–180 °C, 1 h

80

71

[46]

[47]

200 °C, 2 h

120 °C, 52 h

79

[48]

tetracyanoethylene (TCNE)

maleic anhydride

rt, 12 h

quant.

67

[49]

[50]

100 °C, 2 h

[a] Reduction to amine with LiAlH₄.

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(45.1  1.7) kJ mol^-1and A = 4.14  10⁴s^-1; H^‡= (42.7  1.7) kJ

mol^-1, S^‡= (-164.9  5.9) J K^-1mol^-1.^[51]Of course, a valid

comparison of the two types of iminium-activated Diels-Alder

reactions cannot be made, since both the reaction partners and

the constitution of the dienophiles (terminal acetylenic vs.

internal olefinic bond) are different.

The iminium group of the Diels-Alder adducts shown in Table 1

can be converted subsequently into other functional groups in

high yields without isolation of these adducts. Representative

examples are shown in Scheme 9 for cycloaddition products

resulting from aldiminium salt 2. Hydride reduction generated the

dimethylamino-methyl derivatives which were isolated as HBr

salts 29 or 30. It may be noted that 29 has been prepared before

from ethyl propiolate in five steps with about 30% overall

yield,^[52,53]whereas we could obtain 29 in five steps from TMS-

acetylene in 60% overall yield. Tetraphenyl-benzaldehyde 31, on

the other hand, readily shows that propyne iminium salt 2 may

be preferable as a synthetic equivalent of propiolaldehyde which

has several disadvantages as a reagent (lacrimatory, prone to

polymerize explosively, should not be stored neat).^[54]

The controlled deprotonation of the cycloaddition products

bearing secondary iminium groups is not trivial in all cases.

Deprotonation of 18b and 19b with triethylamine in CH₂Cl₂

yielded the expected imines 32 and 33, respectively,

accompanied by some polymeric material, whereas an

unexpected subsequent reaction occurred for iminium salt 17b

(vide infra). Only with the stronger and non-nucleophilic base

LiHMDS, imine 34 could be isolated as an oil in good yield

(Figure 7); however, purification efforts by chromatography or

Figure 6. Formation of the cycloadduct 18a as a function of time (upper

graphic) and pseudo-first-order plot for the cycloaddition at three different

temperatures (c_CA= concentration of cycloadduct, c₀= c_CA+ c_Dienophil).

A pseudo-first order treatment of the data (see Supporting

Information) revealed the kinetics and activation parameters for

the three different cycloaddition reactions (Table 3).^[36]

distillation were not

successful.

The formation of

oligomeric/polymeric by-products in the deprotonation reactions

of 17b, 18b and 19b with NEt₃is likely a result of the

simultaneous presence of the imine and its iminium precursor

and is reminescent of the presumed imine-triggered

polymerization of acetylenic iminium salts 1a,b, as discussed

above.

Table 3. Activation parameters for the [4+2] cycloaddition of tetracyclone and

iminium salts 1a, 3a, and ketone 28; [a]: at -15 °C, [b]: at 53 °C.

S^‡

(J·K^-1·mol^-1)

H^‡

(kJ·mol^-1)

k₂

E_A

log A

(10^-4L·mol^-1·s^-1) (kJ·mol^-1)

1a 14.95±0.84^[a]

3a 35.69±1.70^[a]

28 5.03±0.26^[b]

35.2±1.4 4.29±0.30

36.4±2.5 4.94±0.52

55.1±1.7 5.52±0.28

33.2±1.4

34.3±2.5

52.4±1.7

-169.4±5.7

-157.0±10.1

-148.0±5.3

The calculated values confirm the impressively high reactivity of

the two acetylenic iminium salts compared with the acetylenic

o

ketone; thus, these Diels-Alder reactions of 1a and 3a at -15 C

are already 37 times faster than that of the acetylenic ketone

o

28 at 53 C. The considerably lower Arrhenius energy (E_A) and

activation enthalpy (H^‡) of the iminium salts vs. the ketone are

attributed to the lower LUMO energy level of the former

dienophiles. The S^‡values correspond to the size of the

activating substituents on the acetylenic bond [C(Ph)N⁺Me₂

>

C(Ph)N⁺HMe > C(=O)CF₃], but due to the relatively large

standard deviations the differences between the calculated

values should not be overemphasized.

As far as we know, our kinetic study is the first one documenting

quanitatively the iminium activation of the acetylenic bond. As far

1

as olefinic iminium salts are concerned, a H NMR kinetic study

Scheme 9. In-situ transformations of Diels-Alder iminium salts formed from

alkyne 2.

(T = 293303 K) of the Diels-Alder reaction of cyclopentadiene

with the olefinic iminium-PF₆salt derived from cinnamaldehyde

and 2-CF₃-pyrrolidine gave the following parameters: second-

order rate constant k₂₉₃= (3.74  0.02)  10^-4dm³mol^-1s^-1; E_a=

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Figure 7. Imines obtained by deprotonation of secondary iminium salts; HMDS

= N(SiMe₃)₂.

Figure 8. Solid-state structure of 1,5-diazocine derivatives 35A/35B (ORTEP

plot). The solid bonds in the “disordered” norbornene system are for 35A, the

dashed bonds for 35B; A:B = 3.8:1.

We concluded that, in order to avoid subsequent reactions of the

already formed imine with the iminium salt, the deprotonation

reaction should be fast and the concentration of the iminium salt

in the reaction solution should be kept as low as possible. These

ideas were confirmed but at the same time gave unexpected

results when sodium methanolate was used as the base

(Scheme 10). To a solution of iminium salt 17b was added one

equivalent of NaOMe in CH₂Cl₂. After work-up by column

chromatography, a mixture of three diastereomeric diazocine-

derived polycycles, the non-symmetrical isomer 35A and the C₂-

symmetrical forms 35B and 35C, was obtained in 68% yield.

After crystallization from CH₂Cl₂/pentane, single crystals

containing both 35A and 35B were obtained whose structures

were established by XRD analysis (Figure 8) and are in

agreement with the NMR and MS data. Both diastereomers

were found in the same crystal, and the occupancy factors agree

quite well with the ratio determined on the crystalline material by

¹H NMR (NMR: A:B = 3.5:1; XRD: 3.8:1), compared with 2.2:1 in

the original product mixture. Notably, the deprotonation of 17b in

the presence of a 40-fold excess of the weak base NEt₃also

furnished 1,5-diazocine derivatives 35, but only with a 41% yield.

On the other hand, when iminium salt 17b was gradually added

to a large excess of NaOMe in methanol, thereby avoiding the

The formation of 1,5-diazocine derivatives 35 under conditions,

where both iminium salt 17b and imine 34 are present in the

reaction solution, presumably starts with a Michael addition of

the imine nitrogen atom at the ,-unsaturated iminium group of

17b and continues by a 1,8-azacyclization and subsequent

HOTf elimination (Scheme 11). Under stereochemical aspects,

the formation of diastereomers 35A/B begins with an endo

attack in the first Michael addition; exo or endo approach to the

norbornadiene double bond of intermediates 37A and 37b,

respectively, takes place in the ring-closure step and yields

mainly the exo product 35A. If the first Michael addition occurs

by an exo approach, two further diastereomers are possible, one

of which should be the C₂-symmetrical 35C, which results from

an exo ring-closure. Comparable formal [4+4] cycloadditions

have recently been detected: the [4+4] cycloaddition of 1-benzyl-

1-aza-1,3-butadiene induced by benzylamine yielded a 2,6,9-

triazabicyclo[3.3.1]nonane^[55]and a 1,5-diazacyclooctane when

triggered by an alcohol.^[56]

presence of unreacted 17b in the reaction solution,

a

diastereomeric mixture of norbornene derivatives 36A and 36B

was isolated after work-up. The configuration of the two

diastereomers was derived from the ¹H NMR data (see Exp.

Section).

Scheme 10. Deprotonation of norbornadiene iminium salt 17b with NaOMe.

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Scheme 11. Proposed mechanism for the formation of 1,5-diazocine derivatives 35A,B

.

signal of the solvent. If necessary, ¹³C signals were assigned by means

of DEPT-135, HMBC and HSQC experiments. Mass spectra were

recorded with the following instruments: Finnigan-MAT SSQ-7000 (CI,

100 eV) and SolariX (HRMS, ESI). Elemental analyses were carried out

with an elementar Hanau vario MICRO cube analyser. Column

chromatography was performed on silica gel (63-200 mesh).

The norbornene derivatives 36, on the other hand, result from a

conjugate addition of methanolate/methanol at the ,-

unsaturated imine 34, followed by conversion of the imine into a

carbonyl group.

Conclusions

N-Methyl-N-(1-phenylprop-2-yn-1-ylidene)methanaminium

Triflate

(1a): Propyne iminium salt 6a (9.11 g, 24.0 mmol) was dissolved in

CH₂Cl₂(40 mL). To the solution HOTf (2.1 mL, 24.0 mmol) and silver(I)

triflate (62 mg, 0.24 mmol) were added, and the mixture was stirred for

five days under exclusion of light. Thereafter n-pentane was added

whereupon an orange oil separated. Decantation and trituration of the oil

with ether led to crystallization. Drying of the solid at 0.01 mbar/20 °C

gave 1a (7.23 g, 23.5 mmol, 98%) as an off-white solid. Note: With 5 mol-

% of catalyst, a reaction time of 1 day was achieved. M.p. 76.8–78.4 °C

(dec.). ¹H NMR (CD₃CN, 500.14 MHz): [ppm] = 3.63 (s, 3 H, NCH₃),

3.93 (s, 3 H, NCH₃), 5.49 (s, 1 H, C≡CH), 7.63–7.66 (m, 2 H, H_Ph), 7.73–

Acetylenic iminium ions featuring a terminal triple bond (propyne

iminium ions) have been isolated as triflate salts for the first time.

As was reported in earlier studies, such iminium ions are

considered as intermediates in catalytic cycles of some iminium-

activated transformations. Stoichiometric reactions of the

isolated salts confirm their anticipated reactivity. They were

found to be exceptionally reactive dienophiles in Diels-Alder

reaction thanks to the electronic activation of the C,C triple bond

and the reduced steric hindrance of the diene/dienophile

approach as compared to internal acetylenic propyne iminium

ions. Furthermore, Michael addition reactions also occur with

great ease, as demonstrated with water and alcohols as

nucleophiles; these results corroborate a mechanistic proposal

for the prolinol-catalyzed self-condensation of propynals.^[29]

7.77 (m, 3 H, H_Ph). ¹³C NMR (CD₃CN, 125.79 MHz):  [ppm] = 46.97

(NCH₃), 49.39 (NCH₃), 76.99 (C≡C), 108.89 (HC≡C), 122.04 (q, J_C,F

1

=

321.3 Hz, TfO^–), 130.32 (C_Ph), 130.37 (C_Ph), 131.25 (C_Ph), 135.16 (C_Ph),

164.02 (C=N). IR (KBr): 휈̃ [cm^-1] = 3197 (m, C(sp)H), 2108 (s, CC),

1632 (s), 1597 (s), 1451 (m), 1344 (m), 1263 (s), 1226 (s), 1162 (s), 1032

(s), 764 (m), 698 (m), 640 (s), 574 (m), 517 (m). MS ((+)-ESI): m/z (%) =

158.10 (100) [M - OTf]⁺. C₁₂H₁₂F₃NO₃S (307.29 g/mol): calcd. C 46.90, H

3.94, N 4.56; found C 46.84, H 4.03, N 4.50.

Finally, the iminium group, which is still present in the

cycloaddition product, offers opportunities for further

transformations that are not compatible with catalytic iminium-

activated processes.

N-Methyl-N-(1-(thiophen-2-yl)prop-2-yn-1-ylidene)methanaminium

Triflate (1b): Prepared from 6b (1.58 g, 4.09 mmol) according to 1a,

reaction time 9 days. Yield: 1.08 g (3.44 mmol, 84%), brownish solid, m.p.

71.2–72.1 °C (dec.). ¹H NMR (CD₃CN, 400.13 MHz):  [ppm] = 3.83 (s, 3

H, NCH₃), 3.92 (s, 3 H, NCH₃), 5.26 (s, 1 H, C≡CH), 7.45–7.48 (m, 1 H,

H_thienyl), 8.27 (d, ³J = 4.00 Hz, 1 H, H_thienyl), 8.41 (d, ³J = 4.94 Hz, 1 H,

H_thienyl). ¹³C NMR (CD₃CN, 100.61 MHz):  [ppm] = 46.95 (NCH₃), 50.27

(NCH₃), 75.70 (C≡CThie), 103.56 (HC≡C), 121.99 (q, ¹J_C,F= 320.95 Hz,

TfO^–), 131.21 (C_thienyl), 133.50 (C_thienyl), 143.56 (C_thienyl), 143.99 (C_thienyl),

152.74 (C=N). IR (KBr): 휈̃ [cm^-1] = 3206 (m, C(sp)H), 3089 (m), 2112 (s,

CC), 1600 (s), 1510 (m), 1407 (s), 1382 (s), 1362 (m), 1259 (s), 1225

(s), 1157 (s), 1081 (m), 1029 (s), 870 (m), 753 (m), 691 (m), 637 (s), 572

(m), 517 (m). MS ((+)-ESI): m/z (%) = 164.05 [M - OTf]⁺. C₁₀H₁₀F₃NO₃S₂

(313.31 g/mol): calcd. C 38.34, H 3.22, N 4.47; found C 38.32, H 3.35, N

4.33.

Experimental Section

Methods and materials. All reactions involving moisture-sensitive

compounds were carried out in rigorously dried glassware under an

argon atmosphere. Solvents were dried by established procedures and

stored over molecular sieves (4 Å; 3 Å for acetonitrile). All chemicals,

except where stated, were purchased from commercial sources and used

without

(trimethylsilyl)penta-1,4-diyn-3-one,^[58]

diyn-3-one,^[59]

further

purification.

Imidoyl

chlorides,^[57]

1-phenyl-5-

1,5-bis(trimethylsilyl)penta-1,4-

3-(trimethylsilyl)propiolaldehyde,^[27]

N-methyl-3-

(trimethylsilyl)prop-2-yn-1-imine (9)^[26]and 1-phenylprop-2-yn-1-one

(28)^[60]were prepared by literature methods. Melting points were

determined in open capillaries with a Büchi B-540 instrument at a heating

rate of 1 °C/min. IR spectra of solid samples prepared as KBr pellets or

oils between NaCl plates were recorded on a Bruker Vector 22 FT-IR

instrument. NMR spectra were recorded on

spectrometer operating at 400.13 MHz for ¹H and 100.61 MHz for ¹³C

and on a Bruker AMX 500 spectrometer operating at 500.14 MHz for H

and 125.79 MHz for ¹³C and were referenced to the residual proton

N-Methyl-N-(1-phenylpenta-1,4-diyn-3-ylidene)methanaminium

Triflate (1c): Prepared from 8a (2.24 g, 5.55 mmol) according to 1a with

2 mol% of silver(I) triflate, reaction time 5 days. Yield: 1.18 g (5.46 mmol,

98%), brown solid, dec. at 102 °C. ¹H NMR (CD₃CN, 500.14 MHz): 

[ppm] = 3.84 (s, 3 H, NCH₃), 3.87 (s, 3 H, NCH₃), 5.26 (s, 1 H, C≡CH),

7.57–7.60 (m, 2 H, H_Ph), 7.71–7.74 (m, 1 H, H_Ph), 7.82–7.84 (m, 2 H, H_Ph).

¹³C NMR (CD₃CN, 125.79 MHz):  [ppm] = 47.31 (NCH₃), 47.36 (NCH₃),

a Bruker DRX 400

1

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74.97 (C≡C), 83.59 (C≡C), 103.58 (C≡CH), 115.99 (C≡CPh), 118.37

N-Methyl-1-phenyl-3-(trimethylsilyl)prop-2-yn-1-imine (4a): To

a

1

(C_Ph), 121.89 (q, J_C,F= 320.5 Hz, TfO^–), 130.36 (C_Ph), 134.91 (C_Ph),

solution of ethylmagnesium bromide (prepared from magnesium (480 mg,

19.7 mmol) and bromoethane (1.6 mL, 21 mmol) in THF (30 mL)) was

added trimethylsilylacetylene (2.8 mL, 20 mmol) at 0 °C. After stirring for

2 h, CuBr·SMe₂(210 mg, 1.0 mmol) was added followed by the dropwise

addition of N-methylbenzimidoyl chloride (3.03 g, 19.7 mmol). Thereafter,

the solution was stirred for 16 h at room temperature followed by addition

of ether (100 mL) and extraction with aqueous NaHCO₃. Drying of the

organic phase with Na₂SO₄and evaporation of the volatile components

gave a dark oil, which was purified by vacuum destillation (0.02 mbar,

65 °C). Imine 4a (3.39 g, 15.8 mmol, 80%) could be obtained as a slightly

yellow oil, which quickly changed color to dark-brown at room

temperature. ¹H NMR (CDCl₃, 400.13 MHz):  [ppm] = 0.32 (s, 9 H,

Si(CH₃)₃), 3.65 (s, 3 H, NCH₃), 7.38–7.43 (m, 3 H, H_Ph), 7.99–8.02 (m, 2

H, H_Ph). ¹³C NMR (CDCl₃,100.61 MHz):  [ppm] = -0.14 (Si(CH₃)₃), 43.8

(NCH₃), 95.9 (C≡C), 106.2 (C≡C), 127.4 (C_thienyl), 128.3 (C_thienyl), 130.4

(C_thienyl), 137.3 (C_thienyl), 152.5 (C=N). The spectroscopic data are in

accordance with published values.^[20]

134.97 (C_Ph), 142.76 (C=N). IR (KBr): 휈̃ [cm^-1] = 3180 (w, C(sp)H), 2204

(s, HCC), 2109 (m, CC), 1612 (m), 1590 (m), 1261 (s), 1225 (m), 1157

(s), 1030 (s), 638 (m). HRMS ((+)-ESI): m/z = 182.09695 (calcd.

182.09643 for C₁₃H₁₂N⁺, [M - OTf]⁺). C₁₄H₁₂F₃NO₃S (331.31 g/mol): calcd.

C

50.75, H 3.65, N 4.23; found C 48.63, H 4.19, N 3.97.

C₁₄H₁₂F₃NO₃S·0.80 H₂O (689.55 + 0.80·18.02 g/mol): calcd. C 48.64, H

3.96, N 4.05.

N-Methyl-N-(penta-1,4-diyn-3-ylidene)methanaminium Triflate (1d):

Prepared from 8b (150 mg, 0.375 mmol) according to 1a with 21 mol% of

AgOTf, reaction time

5 days. The salt was obtained as a very

hygroscopic off-white solid. Yield: 60.5 mg (0.237 mmol, 63%), m.p.

80 °C (dec. starts at 60 °C). ¹H NMR (CD₃CN, 500.14 MHz):  [ppm] =

3.82 (s, 6 H, NCH₃), 5.31 (s, 2 H, C≡CH). ¹³C NMR (CD₃CN, 125.79

MHz):  [ppm] = 47.84 (NCH₃), 74.93 (C≡CH), 105.08 (C≡CH), 121.71 (q,

¹J_C,F= 320.27 Hz, TfO^–), 175.44 (C=N). IR (KBr): 휈̃ [cm^-1] = 3191 (m,

C(sp)H), 2115 (s, HC≡C), 1624 (m), 1264 (s), 1160 (s), 1033 (s), 761

(m), 638 (s), 518 (m). C₈H₈F₃NO₃S (255.21 g/mol): calcd. C 37.65, H

3.16, N 5.49. As the salt was very hygroscopic, a correct elemental

analysis could not be obtained.

N-Methyl-1-(thiophen-2-yl)-3-(trimethylsilyl)prop-2-yn-1-imine (4b):

To a solution of ethylmagnesium bromide (prepared from magnesium

(682 mg, 28.0 mmol) and bromoethane (2.24 mL, 30.0 mmol) in THF (30

mL)) was added trimethylsilylacetylene (3.77 mL, 26.5 mmol) at 0 °C.

After stirring for 2 h, CuBr·SMe₂(250 mg, 1.22 mmol) was added

followed by the dropwise addition of N-methylthiophene-2-carbimidoyl

chloride (4.35 g, 27.3 mmol). Thereafter, the solution was stirred for 16 h

at room temperature followed by addition of ether (100 mL) and

extraction with aqueous NaHCO₃. Drying of the organic phase with

Na₂SO₄and evaporation of the volatile components gave a dark oil,

which was purified by vacuum destillation (0.03 mbar, 53 °C). Imine 4b

(3.14 g, 14.2 mmol, 54%) could be obtained as a yellow oil, which quickly

changed its color to dark-brown at room temperature. ¹H NMR (CDCl₃,

400.13 MHz):  [ppm] = 0.30 (s, 9 H, Si(CH₃)₃), 3.56 (s, 3 H, NCH₃), 7.05

(dd, J = 5.04, 3.70 Hz, 1 H, 4-H_thienyl), 7.35 (dd, J = 5.05, 1.14 Hz, 1 H, 3-

N-Methyl-N-(prop-2-yn-1-ylidene)methanaminium

Triflate

(2):

Prepared from 10 (303 mg, 1.00 mmol) according to 1a, reaction time 6

days. Yield: 220 mg (0.95 mmol, 95%), dark oil which could not be

purified further. ¹H NMR (CD₃CN, 400.13 MHz):  [ppm] = 3.70 (s, 3 H,

CH₃), 3.72 (s, 3 H, CH₃), 5.37 (s, 1 H, HC≡C), 8.11–8.13 (m, 1 H, HC=N).

¹³C NMR (CD₃CN, 100.61 MHz):  [ppm] = 46.15–46.26 (m, NCH₃),

49.71–49.81 (m, NCH₃), 73.76 (C≡C), 108.74 (HC≡C), 155.91–156.21 (m,

C=N). IR (NaCl): 휈̃ [cm^-1] = 2132 (w, CC), 1667 (s), 1629 (s), 1474 (m),

1415 (m), 1254 (s), 1168 (s), 1032 (s), 649 (m). MS ((+)-CI, 100 eV): m/z

= 82 [M - OTf]⁺. C₆H₈F₃NO₃S (231.19 g/mol): calcd. C 31.17, H 3.49, N

6.06. A correct elemental analysis was not obtained.

H_thienyl), 7.48 (dd,

J = 4.05, 0.96 Hz, 1

H, 5-H_thienyl). ¹³C NMR

(CDCl₃,100.61 MHz):  [ppm] = -0.23 (Si(CH₃)₃), 43.31 (NCH₃), 94.89

(C≡C), 104.65 (C≡C), 127.32 (C_thienyl), 128.81 (C_thienyl), 129.59 (C_thienyl),

144.32 (C_thienyl), 147.08 (C=N). IR (NaCl): 휈̃ [cm^-1] = 2961 (m), 1582 (s),

1430 (m), 1287 (s), 1253 (s), 1084 (m), 1062 (m), 1029 (m), 944 (m), 845

(s), 761 (m), 708 (s). HRMS ((+)-ESI): m/z = 222.07682 (calcd.

222.07672 for C₁₁H₁₆NSSi⁺, [M + H]⁺). C₁₁H₁₅NSSi (221.39 g/mol): calcd.

C 59.68, H 6.83, N 6.33; found C 58.93, H 6.66, N 6.55.

(E)-N-(1-Phenylprop-2-yn-1-ylidene)methanaminium Triflate (3a):

Propyne imine 5a (1.10 g, 7.86 mmol) was dissolved in CH₂Cl₂(20 mL)

and slowly added to a solution of HOTf (1.00 mL, 11.3 mmol) in CH₂Cl₂

(10 mL) at -20 °C. Stirring of the mixture was continued for 30 min at this

temperature. Then, the solution was poured into n-pentane/ether (5:1)

whereupon a precipitate formed. Decantation, washing of the precipitate

with ether and drying at 0.01 mbar/20 °C gave 3a (2.18 g, 7.43 mmol,

1

95%) as an ocherous solid, m.p. 90.3–91.5 °C. H NMR (CDCl₃, 400.13

3

N-Methyl-1-phenylprop-2-yn-1-imine (5a): Propyne imine 4a (4.20 g,

19.5 mmol) was diluted with CH₂Cl₂(80 mL) and cooled to -20 °C. 18-

Crown-6 (309 mg, 1.17 mmol) was added followed by the addition of KF

(1.70 g, 29.3 mmol) in portions over 5 min. After stirring for 30 min at -

20 °C and for 3 h at room temperature, the reaction was quenched with

aqueous NaHCO₃. Extraction with CH₂Cl₂, drying of the organic layer and

evaporation of the volatile components gave a dark oil, which was

purified by vacuum destillation (0.02 mbar, 70 °C). Imine 5a (2.46 g, 17.6

mmol, 88%) could be obtained as a white solid, which quickly changed its

MHz):  [ppm] = 3.79 (d, J = 5.16 Hz, 3 H, NCH₃), 5.07 (s, 1 H, HC≡C),

7.60–7.64 (m, 2 H, H_Ph), 7.79–7.82 (m, 1 H, H_Ph), 8.21–8.22 (m, 2 H, H_Ph),

13.00 (s, br, 1 H, NH). ¹³C NMR (CDCl₃, 100.61 MHz):  [ppm] = 37.91

(NCH₃), 73.18 (C≡C), 106.36 (HC≡C), 120.42 (q, ¹J_C,F= 319.25 Hz, TfO^–),

128.28 (C_Ph), 130.23 (C_Ph), 130.87 (C_Ph), 137.81 (C_Ph), 162.02 (C=N). IR

(KBr): 휈̃ [cm^-1] = 3206 (s, C(sp)H), 3030 (m), 2944 (m), 2114 (s, HC≡C),

1652 (s), 1596 (m), 1446 (m), 1289 (s), 1243 (s), 1159 (s), 1059 (m),

1031 (s), 765 (m), 686 (m), 639 (s), 575 (m), 519 (m). MS ((+)-ESI): m/z

(%) = 144.08 (100) [M - OTf]⁺. C₁₁H₁₀F₃NO₃S (293.26 g/mol): calcd. C

45.05, H 3.44, N 4.78; found C 45.09, H 3.57, N 4.87.

1

color to orange-brown at room temperature. M.p. 36.6–37.6 °C. H NMR

(CDCl₃, 500.14 MHz):  [ppm] = 3.66 (s, 1 H, C≡CH), 3.67 (s, 3 H, NCH₃),

7.40–7.46 (m, 3 H, H_Ph), 8.02–8.04 (m, 2 H, H_Ph). ¹³C NMR (CDCl₃,

125.79 MHz):  [ppm] = 43.84 (NCH₃), 75.10 (C≡C), 87.41 (HC≡C),

127.35 (C_Ph), 128.39 (C_Ph), 130.64 (C_Ph), 137.03 (C_Ph), 151.72 (C=N). IR

(KBr): 휈̃ [cm^-1] = 3160 (m, C(sp)H), 2084 (m, C≡C), 1715 (m), 1596 (m),

1572 (m), 1446 (m), 1275 (s), 1052 (m), 1026 (m), 775 (m), 715 (m), 692

(s), 666 (m), 656 (m). C₁₀H₉N (143.19 g/mol); calcd. C 83.88, H 6.34, N

9.78; found C 82.32, H 6.73, N 9.47; calcd. for C₁₀H₉N·0.15H₂O: C 82.33,

H 6.43, N 9.60.

(E)-N-(1-(Thiophen-2-yl)prop-2-yn-1-ylidene)methanaminium Triflate

(3b): Prepared from 5b (170 mg, 1.14 mmol) according to 3a. Yield: 331

1

mg (1.11 mmol, 97%); yellow solid, m.p. 83.2–84.6 °C. H NMR (CDCl₃,

3

400.13 MHz):  [ppm] = 3.69 (d, J = 4.05 Hz, 3 H, NCH₃), 4.90 (s, 1 H,

3

HC≡C), 7.37 (t, ³J = 4.53 Hz, 1 H, 4-H_thienyl), 8.15 (dd, J = 4.82, 0.67 Hz,

1 H, 3-H_thienyl), 8.45 (d, ³J = 4.10 Hz, 1 H, 5-H_thienyl), 12.54 (s, br, 1 H, NH).

¹³C NMR (CDCl₃, 100.61 MHz):  [ppm] = 36.96 (NCH₃), 72.88 (C≡C),

1

102.87 (HC≡C), 120.44 (q, J_C,F= 319.24 Hz, TfO^–), 131.53 (C_thienyl),

133.30 (C_thienyl), 139.10 (C_thienyl), 142.95 (C_thienyl), 152.66 (C=N). IR (KBr):

휈̃ [cm^-1] = 3208 (s, C(sp)H), 3121 (m), 3042 (m), 2929 (m), 2116 (s,

HC≡C), 1627 (s), 1516 (m), 1413 (m), 1373 (m), 1282 (s), 1245 (s), 1157

(s), 1070 (m), 1032 (s), 860 (m), 747 (m), 639 (s), 517 (m). MS ((+)-ESI):

m/z (%) = 150.04 (100) [M - OTf]⁺. C₉H₈F₃NO₃S₂(299.28 g/mol): calcd. C

36.12, H 2.69, N 4.68; found C 35.90, H 2.86, N 4.66.

N-Methyl-1-(thiophen-2-yl)prop-2-yn-1-imine (5b): Prepared form 4b

(1.00 g, 4.52 mmol) according to 5a. Yield: 500 mg (3.35 mmol, 74%),

slightly orange solid, m.p. 44.6–45.4 °C. ¹H NMR (CDCl₃, 400.13 MHz): 

[ppm] = 3.58 (s, 1 H, HC≡C), 3.59 (s, 3 H, NCH₃), 7.06 (dd, ³J = 5.01,

3.67 Hz, 1 H, 4-H_thienyl), 7.36–7.38 (m, 1 H, 3-H_thienyl), 7.56–7.57 (m, 1 H,

5-H_thienyl). ¹³C NMR (CDCl₃, 100.61 MHz):  [ppm] = 43.32 (NCH₃), 74.35

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(C≡C), 85.81 (HC≡C), 127.44 (C_thienyl), 129.07 (C_thienyl), 129.82 (C_thienyl),

144.04 (C_thienyl), 146.30 (C=N). IR (KBr): 휈̃ [cm^-1] = 3160 (s, C(sp)H),

2086 (s, C≡C), 1584 (s), 1428 (s), 1391 (m), 1284 (m), 1056 (m), 1022

(m), 849 (m), 748 (m), 706 (s), 677 (m). C₈H₇NS (149.21 g/mol): calcd. C

64.40, H 4.73, N 9.39; found C 64.22, H 4.76, N 9.28.

7b (3.70 g, 11.8 mmol, 94%) resulted as an orange-brown oil. Purification

of 7b by destillation (0.15 mbar, 100 °C) is possible but the colorless oil

changes its color to orange-brown very fast again. ¹H NMR (CDCl₃,

400.13 MHz):  [ppm] = 0.22 (s, 9 H, Si(CH₃)₃), 0.25 (s, 9 H, Si(CH₃)₃),

3.47 (s, 3 H, NCH₃). ¹³C NMR (CDCl₃, 100.62 MHz):  [ppm] = -0.37

(Si(CH₃)₃), -0.35 (Si(CH₃)₃), 43.80 (NCH₃), 93.53 (C≡C), 95.56 (C≡C),

101.85 (C≡C), 104.13 (C≡C), 136.94 (C=N). IR (NaCl): 휈̃ [cm^-1] = 2963

(m), 2160 (w, C≡C), 1561 (m), 1252 (s), 1224 (s), 846 (s), 761 (m).

C₁₂H₂₁NSi₂(235.48 g/mol): calcd. C 61.21, H 8.99, N 5.95; found C 60.26,

H 8.99, N 7.09.

N-Methyl-N-(1-phenyl-3-(trimethylsilyl)prop-2-yn-1-

ylidene)methanaminium Triflate (6a): This compund was synthesized

according to a published procedure^[20]but in CH₂Cl₂instead of Et₂O:

Propyne imine 4a (6.20 g, 28.8 mmol) was diluted with CH₂Cl₂(25 mL)

and cooled to -20 °C. After addition of methyl triflate (3.30 mL, 29.4

mmol) the solution was stirred for 1 h at this temperature and for 18 h at

room temerature. The solution was poured into n-pentane/ether (1:1)

whereupon a white precipitate formed. Washing with ether and drying at

0.01 mbar/20 °C gave 4a (10.47 g, 27.6 mmol, 96%) as a colorless solid,

m.p. 84.7 °C. ¹H NMR (CDCl₃, 400.13 MHz):  [ppm] = 0.30 (s, 9 H,

Si(CH₃)₃), 3.77 (s, 3 H, NCH₃), 4.05 (s, 3 H, NCH₃), 7.53–7.57 (m, 2 H,

H_Ph), 7.61–7.65 (m, 1 H, H_Ph), 7.72–7.74 (m, 2 H, H_Ph). ¹³C NMR (CDCl₃,

100.62 MHz):  [ppm] = -1.14 (Si(CH₃)₃), 46.09 (NCH₃), 48.46 (NCH₃),

N-Methyl-N-(1-phenyl-5-(trimethylsilyl)penta-1,4-diyn-3-

ylidene)methanaminium Triflate (8a): Propyne imine 7a (1.64 g, 6.87

mmol) was diluted with CH₂Cl₂(12 mL) and cooled to -40 °C. After

addition of methyl triflate (1.24 mL, 11.1 mmol) the solution was stirred

for 20 min at -40 ^oC and for 15 min at room temperature. The solution

was poured into n-pentane/ether (1:1), whereupon a brown precipitate

formed. Washing with ether and drying at 0.02 mbar/20 °C gave 8a (2.38

g, 5.90 mmol, 86%) as a brownish solid. M.p. 138.1–139.5 °C (dec. starts

at 125 °C). ¹H NMR (CDCl₃, 400.13 MHz):  [ppm] = 0.35 (s, 9 H,

Si(CH₃)₃), 3.96–3.97 (m, 3 H, NCH₃), 4.00–4.01 (m, 3 H, NCH₃), 7.46–

1

96.45 (C≡C–SiMe₃), 120.92 (q, J_C,F= 320.50 Hz, TfO^–), 129.46 (C_Ph),

129.51 (C_Ph), 130.63 (C_Ph), 130.64 (C≡C–SiMe₃), 133.96 (C_Ph), 162.86

(C=N). The analytical data are in accordance with the literature.^[20]

7.50 (m, 2 H, H_Ph), 7.59–7.63 (m, 1 H, H_Ph), 7.69–7.71 (m, 2 H, H_Ph). ¹³

C

NMR (CDCl₃, 100.62 MHz):  [ppm] = -1.12 (Si(CH₃)₃), 46.43 (NCH₃),

46.50 (NCH₃), 83.01 (C≡C), 94.43 (C≡C), 115.40 (C≡C), 117.73 (C≡C),

120.90 (¹J_C,F= 320.52 Hz, TfO^–), 125.39 (C_Ph), 129.31 (C_Ph), 133.74

(C_Ph), 134.05 (C_Ph), 141.45 (C=N). IR (KBr): 휈̃ [cm^-1] = 2202 (s, C≡C),

2168 (m, C≡C), 1608 (m), 1591 (m), 1373 (m), 1270 (s), 1224 (m), 1157

(s), 1031 (s), 851 (s), 764 (m), 637 (m). C₁₇H₂₀F₃NO₃SSi (403.49 g/mol):

calcd. C 50.61, H 5.00, N 3.47; found C 50.83, H 5.10, N 3.52.

N-Methyl-N-(1-(thiophen-2-yl)-3-(trimethylsilyl)prop-2-yn-1-

ylidene)methanaminium Triflate (6b): Prepared form 4b (1.63 g, 7.36

mmol) according to 6a. Yield: 1.99 g (5.15 mmol, 70%), greyish solid,

m.p. 104.9–105.7 °C. ¹H NMR (CDCl₃, 400.13 MHz):  [ppm] = 0.33 (s, 9

H, Si(CH₃)₃), 3.94 (s, 3 H, NCH₃), 4.00 (s, 3 H, NCH₃), 7.38 (dd, ³J = 4.94,

4.21 Hz, 1 H, H_thienyl), 8.17–8.19 (m, 2 H, H_thienyl). ¹³C NMR (CDCl₃,

100.61 MHz):  [ppm] = -1.16 (Si(CH₃)₃), 46.23 (NCH₃), 49.42 (NCH₃),

1

95.36 (C≡C-SiMe₃), 120.82 (q, J_C,F= 320.61 Hz, TfO^–), 124.72 (C≡C–

N-(1,5-Bis(trimethylsilyl)penta-1,4-diyn-3-ylidene)-N-

SiMe₃); 130.49 132.82, 141.64, 142.02 (all C_thienyl); 151.59 (C=N). IR

(KBr): 휈̃ [cm^-1] = 3096 (m), 2966 (m), 2163 (m, C≡C), 1594 (s), 1409 (s),

1380 (m), 1359 (s), 1273 (s), 1223 (s), 1148 (s), 1078 (m), 1032 (s), 858

(s), 769 (s), 752 (s), 713 (m), 690 (m), 637 (s). MS ((+)-ESI): m/z (%) =

236.09 (100) [M - OTf]⁺. C₁₃H₁₈F₃NO₃S₂Si (385.49 g/mol): calcd. C 40.50,

H 4.71, N 3.63; found C 40.60, H 4.66, N 3.62.

methylmethanaminium Triflate (8b): Prepared from 7b (1.80 g, 7.66

mmol) according to 8a. Yield: 2.72 g (6.82 mmol, 89%), colorless solid,

dec. starts at 148 °C. ¹H NMR (CDCl₃, 400.13 MHz):  [ppm] = 0.35 (s,

18 H, Si(CH₃)₃), 3.97 (s, 6 H, NCH₃). ¹³C NMR (CDCl₃, 100.62 MHz): 

[ppm] = -1.14 (Si(CH₃)₃), 46.76 (NCH₃), 94.49 (C≡C), 126.57 (C≡C),

141.03 (C=N). The quartet signal of the triflate ion was not observed. IR

(KBr): 휈̃ [cm^-1] = 2168 (m, C≡C), 1615 (m), 1327 (s), 1273 (s), 1225 (m),

1151 (s), 1035 (s), 853 (s), 764 (m), 637 (s). HRMS ((+)-ESI): m/z =

N-Methyl-1-phenyl-5-(trimethylsilyl)penta-1,4-diyn-3-imine (7a): 1-

Phenyl-5-(trimethylsilyl)penta-1,4-diyn-3-one was prepared from 3-

phenylpropioloyl chloride, bis(trimethylsilyl)acetylene and AlCl₃in CH₂Cl₂

according to the literature^[56][but with stirring overnight at room

temperature, 88% yield (lit.: 47%)]. The ketone (5.78 g, 25.5 mmol) was

dissolved in toluene (150 mL) and cooled to -30 °C. Then methylamine

(60 mL, 102 mmol, 1.7 M in THF) was added followed by the addition of

TiCl₄(1.99 mL, 17.9 mmol). After stirring for 30 min at -20 °C and 1 h at

room temperature, the brown suspension was diluted with n-hexane.

Repeated filtration and evaporation of the volatiles gave an orange oil

which was purified by flash chromatography (cyclohexane/ethyl acetate =

20:1). Yield: 4.09 g (17.1 mmol, 67%), orange oil. Mixture of E/Z

+

250.14395 (calcd. 250.14418 for C₁₃H₂₄NSi₂

,

[M

-

OTf]⁺).

C₁₄H₂₄F₃NO₃SSi₂(399.58 g/mol): calcd. C 42.08, H 6.05, N 3.51; found C

42.06, H 6.11, N 3.60.

N-Methyl-N-(3-(trimethylsilyl)prop-2-yn-1-ylidene)methanaminium

Triflate (10): Methyl triflate (1.1 mL, 10.0 mmol) was diluted with ether

(18 mL) and cooled to -78 °C. A solution of 9 (1.39 g, 10.0 mmol) in ether

(2 mL) was added dropwise over a period of 25 min. After stirring for 1 h

at room temperature the precipitate was collected under argon

atmosphere, washed with ether and dried at 0.06 mbar. Yield: 2.73 g

(9.00 mmol, 90%), off-white solid, m.p. 83.2–84.4 °C. ¹H NMR (CDCl₃,

400.13 MHz):  [ppm] = 0.32 (s, 9 H, Si(CH₃)₃), 3.77 (m, 3 H, NCH₃), 3.89

(m, 3 H, CH₃), 8.34–8.35 (m, 1 H, HC=N). ¹³C NMR (CDCl₃, 100.61

MHz):  [ppm] = -1.19 (Si(CH₃)₃), 45.21 (NCH₃), 49.10 (NCH₃), 93.49

1

diastereomers in the ratio 1:0.97. H NMR (CDCl₃, 400.13 MHz):  [ppm]

= 0.25 (s, 9 H, Si(CH₃)₃), 0.28 (s, 9 H, Si(CH₃)₃), 3.55 (s, 3 H, NCH₃),

3.57 (s, 3 H, NCH₃), 7.31–7.44 (m, 6 H, H_Ph), 7.54–7.57 (m, 4 H, H_Ph).

¹³C NMR (CDCl₃, 100.62 MHz):  [ppm] = -0.33 (Si(CH₃)₃), -0.32

(Si(CH₃)₃), 43.79 (NCH₃), 43.92 (NCH₃); 81.66, 87.46, 87.51, 93.50,

95.73, 96.99, 102.00, 104.03 (all C≡C); 121.07–132.47 (8 C_Phsignals),

136.98 (C=N), 137.12 (C=N). IR (NaCl): 휈̃ [cm^-1] = 2961 (m), 2214 (s,

C≡C), 1560 (s), 1490 (m), 1443 (m), 1302 (s), 1252 (s), 1188 (m), 1163

(m), 1118 (m), 869 (s), 844 (s), 758 (s), 691 (m). C₁₅H₁₇NSi (239.39

g/mol): calcd. C 75.26, H 7.16, N 5.85; found C 75.28, H 7.29, N 5.82.

1

(C≡C–SiMe₃), 120.74 (q, J_C,F= 319.97 Hz, TfO^–), 132.05 (C≡C–SiMe₃),

155.30–155.55 (m, C=N). IR (KBr): 휈̃ [cm^-1] = 2184 (w, C≡C), 1666 (m),

1268 (s), 1159 (s), 1083 (m), 1034 (s), 848 (s), 649 (s). HRMS ((+)-ESI):

m/z

= -

154.10478 (calcd. 154.10465 for C₈H₁₆NSi⁺, [M OTf]⁺).

C₉H₁₆F₃NO₃SSi (329.41 g/mol): calcd. C 35.63, H 5.32, N 4.62; found C

35.79, H 5.12, N 4.57.

(E)-N-(3-Hydroxy-1-phenylallylidene)-N-methyl-methanaminium

Triflate (11): Propyne iminium salt 1a (180 mg, 0.586 mmol) was spread

in a crystallization dish. After standing for 15 min at air, the dish was

placed over water vapor and the formed red oil was well mixed. Then, it

was dissolved in acetonitrile (5 mL) and Na₂SO₄was added. Filtration

and evaporation of the volatiles gave a red oil, which was washed with

several portions of ether and precipitated from CH₂Cl₂/ether. Drying at

0.01 mbar/20 °C gave 11 (181 mg, 0.556 mmol, 95%) as a red oil which

was slightly contaminated with dimethylammonium triflate. ¹H NMR

N-Methyl-1,5-bis(trimethylsilyl)penta-1,4-diyn-3-imine

(7b):

1,5-

Bis(trimethylsilyl)penta-1,4-diyn-3-one (2.80 g, 12.6 mmol) was dissolved

in toluene (80 mL) and cooled to -20 °C. Methylamine (30 mL, 51 mmol,

1.7 M in THF) was added followed by the addition of TiCl₄(0.94 mL, 8.56

mmol). After stirring for 30 min at -20 °C and 1 h at room temperature the

brown suspension was diluted with n-hexane. Filtration through celite and

evaporation of the volatiles gave an orange oil which was diluted with

ether and filtrated over flash silica gel. After evaporation of the solvents,

11

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(CD₃CN, 400.13 MHz):  [ppm] = 3.08 (s, 3 H, NCH₃), 3.46 (s, 3 H,

NCH₃), 6.30 (d, ³J = 11.30 Hz, 1 H, HC=CH), 7.10 (d, ³J = 11.29 Hz, 1 H,

HC=CH), 7.36–7.38 (m, 2 H, H_Ph), 7.56–7.65 (m, 3 H, H_Ph). ¹³C NMR

(CD₃CN, 100.61 MHz):  [ppm] = 42.95 (NCH₃), 45.29 (NCH₃), 103.87

mmol, 92%) as an orange solid, m.p. 111.3–112.3 °C. ¹H NMR (CDCl₃,

400.13 MHz):  [ppm] = 3.29 (s, 3 H, NCH₃), 3.76 (s, 3 H, NCH₃), 4.04 (s,

3 H, OCH₃), 6.44 (d, ³J = 11.77 Hz, 1 H, HC²=C), 6.95 (d, ³J = 11.77 Hz,

1 H, HC³=C), 7.43–7.45 (m, 2 H, H_Ph), 7.56–7.62 (m, 3 H, H_Ph). ¹³C NMR

(CDCl₃, 100.61 MHz):  [ppm] = 43.62 (NCH₃), 45.74 (NCH₃), 60.71

(OCH₃), 102.35 (C²=C), 120.93 (q, ¹J_C,F= 320.95 Hz, TfO^–), 128.45 (C_Ph),

129.62 (C_Ph), 130.29 (C_Ph), 132.00 (C_Ph), 175.49 (MeOC=C), 177.21

(C=N). IR (KBr): 휈̃ [cm^-1] = 1610 (s), 1444 (m), 1391 (m), 1306 (s), 1285

(s), 1223 (m), 1148 (s), 1033 (s), 971 (m), 920 (m), 849 (m), 753 (m), 705

(m), 637 (s). MS (CI, 100 eV): m/z (%) = 190 (7) [M - OTf]⁺, 176 (100) [M

–OTf - CH₃+ H]⁺. C₁₃H₁₆F₃NO₄S (339.33 g/mol): calcd. C 46.02, H 4.75,

N 4.13; found C 45.94, H 4.79, N 4.17.

1

(HC=C), 121.45 (q, J_C,F= 319.76 Hz, TfO^–), 129.04 (C_Ph), 129.84 (C_Ph),

131.32 (C_Ph), 132.08 (C_Ph), 175.81 (HOC=C), 177.60 (C=N). IR (KBr): 휈̃

[cm^-1] = 1633 (m), 1599 (s), 1447 (m), 1422 (m), 1281 (s), 1167 (s), 1029

(s), 795 (m), 638 (s). HRMS ((+)-ESI): m/z = 176.10780 (calcd.

176.10699 for C₁₁H₁₄NO⁺, [M - OTf]⁺), 198.08978 (calcd. 198.08894 for

C₁₁H₁₃NNaO⁺, [M – H - OTf + Na]⁺). C₁₂H₁₄F₃NO₄S (325.30 g/mol): calcd.

C

44.31, H 4.34, N 4.31; found C 41.93, H 4.46, N 4.27.

C₁₂H₁₄F₃NO₄S·0.16 C₃H₈F₃NO₃S (373.39 + 0.16·196.16 g/mol) calcd. C

42.07, H 4.32, N 4.56.

(E)-N-(3-(Tert-butyloxy)-1-phenylallylidene)-N-methyl-

N-((2E,4Z)-5-Amino-4-(methoxycarbonyl)-1-phenylhexa-2,4-dien-1-

ylidene)-N-methy-lmethanaminium Triflate (13): Propyne iminium salt

1a (206 mg, 0.67 mmol) was dissolved in CH₂Cl₂(5 mL) and methyl 3-

aminocrotonate (12) (77.2 mg, 0.67 mmol) in CH₂Cl₂(2 mL) was added

at room temperature. After stirring for 20 min ether was added dropwise

under vigorous stirring whereby an orange precipitate formed.

Decantation and drying at 0.01 mbar gave 13 (277 mg, 0.66 mmol, 98%)

as an orange solid, m.p. 143.9–145.1 °C. ¹H NMR (CDCl₃, 400.13 MHz):

 [ppm] = 1.88 (s, 3 H, CH₃), 3.16 (s, 3 H, NCH₃), 3.53 (s, 3 H, NCH₃),

methanaminium Triflate (6b): Propyne iminium salt 6a (577 mg, 1.52

mmol) was dissolved in CH₂Cl₂(2 mL), and AgNO₃(25.8 mg, 0.152

mmol) and tert-butanol (570 µL, 6.08 mmol) were added. After stirring for

19 h at room temperature under exclusion of light, the volatiles were

removed at 0.001 mbar. The solid residue was dissolved in a minimum

amount of CH₂Cl₂and filtrated under argon. Removal of the solvent gave

16b (533 mg, 1.40 mmol, 92%) as a red oil. ¹H NMR (CDCl₃, 400.13

MHz):  [ppm] = 1.22 (s, 9 H, CH₃-t-Bu), 3.24 (s, 3 H, NCH₃), 3.58 (s, 3 H,

NCH₃), 6.24 (d, ³J = 11.12 Hz, 1 H, HC²=C), 6.93 (d, ³J = 11.12 Hz, 1 H,

HC³=C), 7.41–7.43 (m, 2 H, H_Ph), 7.52–7.59 (m, 3 H, H_Ph). ¹³C NMR

(CDCl₃,100.61 MHz):  [ppm] = 27.92 (CH₃-t-Bu), 42.94 (NCH₃), 45.34

3

3.85 (s, 3 H, OCH₃), 6.97 (d, J = 14.05 Hz, 1 H, HC=CH), 7.00 (d, J =

13.99 Hz, 1 H, HC=CH), 7.26–7.26 (m, 2 H, H_Ph), 7.53–7.61 (m, 3 H, H_Ph),

9.10 (s, br, 1 H, NH₂), 10.20 (s, br, 1 H, NH₂). ¹³C NMR (CDCl₃, 100.62

1

(NCH₃), 85.65 (C_q-t-Bu), 104.44 (C²=C), 120.77 (q, J_C,F= 320.95 Hz,

MHz):  [ppm] = 20.76 (CH₃), 41.77 (NCH₃), 44.78 (NCH₃), 51.77 (OCH₃),

TfO^–), 128.49 (C_Ph), 129.40 (C_Ph), 130.34 (C_Ph), 131.93 (C_Ph), 171.55

(^tBuOC=C), 176.45 (C=N). IR (NaCl): 휈̃ [cm^-1] = 2981 (m), 1610 (s), 1540

(m), 1448 (m), 1398 (m), 1377 (m), 1272 (s), 1225 (s), 1140 (s), 1031 (s),

857 (m), 795 (m), 764 (m), 705 (m), 638 (s). MS (CI, 100 eV): m/z (%) =

176 (100) [M – OTf - t-Bu + H]⁺. C₁₆H₂₂F₃NO₄S (381.41 g/mol): calcd. C

50.39, H 5.81, N 3.67; found C 47.72, H 5.09, N 3.71. (Tert-butanol could

not be removed completely.)

1

99.62 (MeOOC-C=CNH₂), 108.25 (Me₂N=CC=C), 120.68 (q, J_C,F

=

320.09 Hz, TfO^–), 128.54 (C_Ph), 129.32 (C_Ph), 131.25 (C_Ph), 131.88 (C_Ph),

156.96, 168.23, 174.42, 175.00. IR (KBr): 휈̃ [cm^-1] = 3313 (m), 3173 (m),

1670 (m), 1566 (s), 1489 (m), 1457 (m), 1417 (m), 1346 (m), 1321 (s),

1287 (s), 1246 (s), 1224 (s), 1159 (s), 1029 (s), 989 (m), 892 (m), 774

(m), 706 (m) 637 (m). HRMS ((+)-ESI): m/z = 273.15972 (calcd.

273.15975 for C₁₆H₂₁N₂O₂⁺, [M - OTf]⁺). C₁₇H₂₁F₃N₂O₅S (422.42 g/mol):

calcd. C 48.34, H 5.01, N 6.63; found C 48.24, H 4.93, N 6.60.

(E)-N-Methyl-N-(3-(4-nitrophenoxy)-1-

phenylallylidene)methanaminium Triflate (16c): Propyne iminium salt

6a (640 mg, 1.69 mmol) was dissolved in CH₂Cl₂(5 mL), and AgNO₃

(44.0 mg, 0.259 mmol) and 4-nitrophenol (587 mg, 4.23 mmol) were

added. After stirring for 22 h at room temperature under exclusion of light

the volatiles were removed at 0.01 mbar. The solid residue was dissolved

in a minimum amount of CH₂Cl₂and filtrated under argon. The solvent

was evaporated and the residue was washed with several portions of

ether. Drying at 0.01 mbar gave 16c (641 mg, 1.44 mmol, 85%) as a very

2-(Dimethylamino)-2-phenylbut-3-ynenitrile (14): Propyne iminium salt

1a (143 mg, 0.465 mmol) was dissolved in MeCN (2 mL) and slowly

added to a suspension of KCN (151 mg, 2.32 mmol) in acetonitrile (25

mL). After stirring for 1 h, the volatiles were removed at 0.02 mbar and

the residue was treated with n-pentane (20 mL). Filtration and

evaporation of the solvent gave 14 (82 mg, 0.445 mmol, 96%) as a

yellow oil which solidified at 4 °C. ¹H NMR (CDCl₃, 400.13 MHz):  [ppm]

= 2.33 (s, 6 H, NCH₃), 2.78 (s, 1 H, HC≡C), 7.40–7.44 (m, 3 H, H_Ph),

7.72–7.74 (m, 2 H, H_Ph). ¹³C NMR (CDCl₃, 100.61 MHz):  [ppm] = 40.53

(NCH₃), 64.31 (C_q), 77.10 and 77.38 (C≡C), 115.08 (C≡N), 127.11 (C_Ph),

128.98 (C_Ph), 129.66 (C_Ph), 136.55 (C_Ph). IR (KBr): 휈̃ [cm^-1] = 3291 (s,

C(sp)H), 2996 (m), 2961 (s), 2872 (s), 2833 (s), 2791 (s), 2116 (m),

1490 (m), 1453 (s), 1230 (s), 1182 (m), 1042 (s), 999 (s), 952 (m), 879

(m), 758 (s), 697 (s). MS ((+)-ESI): m/z (%) = 185.11 (100) [M + H]⁺,

158.09 (46) [M - CN]⁺, 140.05 (27) [M - NMe₂]⁺. C₁₂H₁₂N₂(184.24 g/mol):

calcd. C 78.23, H 6.57, N 15.21; found C 77.85, H 6.62, N 15.16.

1

hygroscopic orange solid. H NMR (CDCl₃, 400.13 MHz):  [ppm] = 3.39

(s, 3 H, NCH₃), 3.77 (s, 3 H, NCH₃), 6.81 and 7.06 (two d, ³J = 11.45 Hz,

2 H, HC=CH), 7.16–7.20 (m, 2 H, H_Ph), 7.59–7.63 (m, 5 H, H_Ph), 8.21–

8.25 (m, 2 H, H_Ph). ¹³C NMR (CDCl₃,100.61 MHz):  [ppm] = 44.19

1

(NCH₃), 46.45 (NCH₃), 109.02 (C_olef), 118.81 (C_Ph), 120.74 (q, J_C,F

=

320.01 Hz, TfO^–); 126.38, 128.72, 129.78, 129.85, 132.63, 145.58,

159.15 (all C_Ph);167.75 (C_olef), 177.12 (C=N). IR (KBr): 휈̃ [cm^-1] = 1636 (s),

1615 (s), 1585 (s), 1525 (m), 1490 (m), 1448 (m), 1420 (m), 1384 (m),

1348 (s), 1267 (s), 1244 (s), 1148 (s), 1031 (s), 863 (m), 638 (m). MS

((+)-ESI): m/z (%) = 297.12 (100) [M - OTf]⁺. C₁₈H₁₇F₃N₂O₆S (446.08

g/mol): calcd. C 48.43, H 3.84, N 6.28; found C 48.31, H 3.84, N 6.10.

(E)-N-(1-Hydroxy-5-phenylpent-1-en-4-yn-3-ylidene)-N-

methylmethanaminium Triflate (15): Propyne iminium salt 1d (2.0 mg,

7.3 µmol) was dissolved in CD₃CN (500 µL) and placed into an NMR

tube. After 15 h in the sealed tube the conversion into 15 was complete.

¹H NMR (CD₃CN, 400.13 MHz):  [ppm] = 3.37 (s, 3 H, NCH₃), 3.62 (s, 3

H, NCH₃), 4.75 (s, 1 H, C≡CH), 6.23 (d, ³J = 11.23 Hz, HC=CH(OH)),

8.25 (d, ³J = 11.24 Hz, HC=CH(OH)). C₈H₁₀F₃NO₄S (273.23 g/mol): calcd.

C 35.17, H 3.69, N 5.13.

N-((Bicyclo[2.2.1]hepta-2,5-dien-2-yl)(phenyl)methylene)-N-

methylmethanaminium Triflate (17a): Propyne iminium salt 1a (702 mg,

2.28 mmol) was dissolved in CH₂Cl₂(7 mL) and cyclopentadiene (208 µL,

2.51 mmol) was added at -68 °C. Thereafter the solution was warmed to

0 °C, the volatiles were removed at 0.02 mbar, and the residue was

washed with ether several times. Drying of the residue at 0.001 mbar

gave 17a (817 mg, 2.19 mmol, 96%) as a brownish oil which could not be

crystallized. ¹H NMR (CDCl₃, 400.13 MHz):  [ppm] = 2.22 (d, J = 7.05

Hz, 1 H, CH₂), 2.31 (m, 1 H, CH₂), 3.53 (s, 3 H, NCH₃), 3.82 (s, 3 H,

NCH₃), 3.92 and 3.95 (each s, 1 H, CH_bridgehead); 6.79–6.83 (m, 2 H,

HC=CH), 7.39–7.41 (m, 2 H, H_Ph), 7.52–7.55 (m, 2 H, H_Ph), 7.58–7.62 (m,

1 H, H_Ph), 7.72 (d, ³J = 3.31 Hz, 1 H, HC=C). ¹³C NMR (CDCl₃, 100.61

(E)-N-(3-Methoxy-1-phenylallylidene)-N-methylmethanaminium

Triflate (16a): Propyne iminium salt 6a (776 mg, 2.04 mmol) was

dissolved in CH₂Cl₂(16 mL), and AgNO₃(34.7 mg, 0.204 mmol) and

MeOH (9.0 mL, 222 mmol) were added. After stirring for 23 h at room

temperature under exclusion of light the volatiles were removed at 0.01

mbar. The solid residue was dissolved in a minimum amount of CH₂Cl₂

and filtrated under argon. Removal of the solvent gave 16a (637 mg, 1.88

MHz):

 [ppm] = 46.56 (NCH₃), 47.39 (NCH₃) 53.26 and 54.08

(CH_bridgehead), 73.38 (CH₂), 128.89 (C_Ph), 129.40 (C_Ph), 131.91 (C_Ph),

12

10.1002/ejoc.201801511

European Journal of Organic Chemistry

FULL PAPER

132.79 (C_Ph), 142.47 (HC=CH), 143.11 (HC=CH), 152.32 (C=CH),

169.81 (HC=C), 178.02 (C=N). IR (NaCl): 휈̃ [cm^-1] = 3067 (m), 2963 (s),

2877 (m), 1619 (s), 1547 (s), 1448 (s) 1415 (m), 1372 (m), 1339 (m),

1261 (s), 1224 (s), 1154 (s), 1082 (s), 1031 (s), 795 (m), 767 (m), 727

(m), 705 (m), 638 (s), 572 (m). MS ((+)-ESI): m/z (%) = 224.14 (100) [M -

OTf]⁺. C₁₇H₁₈F₃NO₃S (373.39 g/mol): calcd. C 54.68, H 4.86, N 3.75;

found C 52.29, H 5.17, N 3.72. C₁₇H₁₈F₃NO₃S·0.95 H₂O (373.39 +

0.95·18.01 g/mol): calcd. C 52.29, H 5.14, N 3.59.

MS ((+)-ESI): m/z (%) = 500.23 (100) [M - OTf]⁺. C₃₉H₃₀F₃NO₃S (649.73

g/mol): calcd. C 72.10, H 4.65, N 2.16; found C 72.08, H 4.58, N 2.21.

N-(1-(3',6'-Diphenyl-[1,1':2',1''-terphenyl]-4'-yl)-3-phenylprop-2-yn-1-

ylidene)-N-methylmethanaminium Triflate (18c): Propyne iminium salt

1c (227 mg, 0.68 mmol) was dissovled in CH₂Cl₂(8 mL), and acetonitrile

(2 mL) and tetraphenylcyclopentadienone (263 mg, 0.68 mmol) were

added at room temperature. After stirring for 15 min cyclohexane was

added until a black oil precipitated. The mother liquor was collected and

more cyclohexane was added to it, whereby a solid precipitated.

Decantation and drying at 0.02 mbar gave 18c (186 mg, 0.27 mmol, 40%

in the first fraction; 112 mg, 24% in the second fraction by adding more

cyclohexane to the mother liquor) as a dark solid which decomposed at

123 °C. ¹H NMR (CDCl₃, 400.13 MHz):  [ppm] = 3.66 (s, 3 H, NCH₃),

3.88 (s, 3 H, NCH₃), 6.75–6.85 (m, 4 H, H_Ph), 6.91–6.98 (m, 7 H, H_Ph),

7.05–7.16 (m, 8 H, H_Ph), 7.23–7.25 (m, 1 H, H_Ph), 7.39–7.42 (m, 2 H, H_Ph),

7.51–7.55 (m, 3 H, H_Ph), 7.88 (s, 1 H, H_Ph). ¹³C NMR (CDCl₃, 100.62

MHz):  [ppm] = 45.86 (NCH₃), 47.18 (NCH₃), 84.13 (C≡C), 118.22 (C≡C),

120.13–144.90 (30 C_Phsignals), 163.67 (C=N). IR (KBr): 휈̃ [cm^-1] = 2195

(s, C≡C), 1620 (m), 1444 (m), 1369 (m), 1263 (s), 1224 (s), 1153 (s),

1029 (s), 762 (m), 701 (m), 637 (s). HRMS ((+)-ESI): m/z = 538.25589

(calcd. 538.25293 for C₄₁H₃₂N⁺, [M - OTf]⁺). C₄₂H₃₂F₃NO₃S (687.78

g/mol): calcd. C 73.35, H 4.69, N 2.04.

N-((Bicyclo[2.2.1]hepta-2,5-dien-2-

yl)(phenyl)methylene)methanaminium Triflate (17b): Propyne iminium

salt 3a (1.28 g, 4.35 mmol) was dissolved in CH₂Cl₂(8 mL) and

cyclopentadiene (360 µL, 4.35 mmol) was added at -14 °C. After stirring

for 30 min at this temperature, the solution was poured into ether. The

brownish precipitate was washed with three portions of ether and dried at

0.01 mbar to obtain 17b (1.35 g, 3.74 mmol, 86%). M.p. 101 °C (dec.

started 82 °C). ¹H NMR (CDCl₃, 400.13 MHz):  [ppm] = 2.35 (d, J = 7.07

Hz, 1 H, CH₂), 2.43 (d, J = 7.08 Hz, 1 H, CH₂), 3.51 (d, ³J = 5.45 Hz, 3 H,

NCH₃), 4.01 and 4.04 (two s, 1 H each, 1-H, 4-H), 6.93–6.95 (m, 1 H,

HC=CH), 7.00–7.01 (m, 1 H, HC=CH), 7.49–7.53 (m, 2 H, H_Ph), 7.57–

3

7.59 (m, 2 H, H_Ph), 7.66–7.70 (m, 1 H, H_Ph), 7.83 (d, J = 3.07 Hz, 1 H,

HC=C), 11.39 (s, br, 1 H, NH). ¹³C NMR (CDCl₃, 100.61 MHz):  [ppm] =

1

36.27 (NCH₃), 53.29 and 53.79 (C_bridgehead), 74.50 (CH₂), 120.49 (q, J_C,F

= 318.93 Hz, TfO^–), 129.57 (C_Ph), 130.47 (C_Ph), 131.81 (C_Ph), 135.33

(C_Ph), 143.14 (HC=CH), 143.30 (HC=CH), 149.16 (C=CH), 170.49

(HC=C), 177.05 (C=N). IR (KBr): 휈̃ [cm^-1] = 3149 (m), 3062 (m), 3017 (m),

1637 (s), 1596 (m), 1554 (m), 1445 (m), 1330 (m), 1293 (s), 1248 (s),

1224 (s), 1175 (s), 1155 (s), 1031 (s), 774 (m), 727 (m), 697 (m), 638 (s),

MS ((+)-ESI): m/z (%) = 210.13 (100) [M - OTf]⁺. C₁₆H₁₆F₃NO₃S (359.36

g/mol): calcd. C 53.48, H 4.49, N 3.90; found C 53.20, H 4.45, N 3.97.

N-((9,10-Dihydro-9,10-ethenoanthracen-11-yl)(phenyl)methylene)-N-

methylmethanaminium Triflate (19a): Propyne iminium salt 1a (611 mg,

1.99 mmol) was dissolved in CH₂Cl₂(22 mL) and anthracene (363 mg,

2.04 mmol) was added at -20 °C. After stirring for 4 h at this temperature

the solvent was removed at 0.01 mbar, and the residue was washed with

ethyl acetate/cyclohexane (1:4) and ether. Drying at 0.01 mbar gave 20a

(889 mg, 1.83 mmol, 92%) as a white solid, m.p. 193.6–195.4 °C. ¹H

NMR (CDCl₃, 400.13 MHz):  [ppm] = 3.61 (s, 3 H, NCH₃), 3.63 (s, 3 H,

NCH₃), 5.39–5.41 (m, 2 H, H_bridgeheads(overlap)), 6.95–7.03 (m, 4 H, H_Ph),

7.19 (d, ³J = 7.47 Hz, 2 H, H_Ph), 7.27 (d, ³J = 6.99 Hz, 2 H, H_Ph), 7.34 (d,

³J = 6.89 Hz, 2 H, H_Ph), 7.39 (t, ³J = 7.82 Hz, 2 H, H_Ph), 7.56 (t, ³J = 7.52

Hz, 1 H, H_Ph), 7.70 (dd, J = 6.22, 1.78 Hz, 1 H, HC=C). ¹³C NMR (CDCl₃,

100.61 MHz):  [ppm] = 47.18 (NCH₃), 47.65 (NCH₃), 52.23 and 53.18

N-((3',6'-Diphenyl-[1,1':2',1''-terphenyl]-4'-yl)(phenyl)methylene)-N-

methylmethanaminium Triflate (18a): Propyne iminium salt 1a (503 mg,

1.64

mmol)

was

dissovled

in

CH₂Cl₂

(5

mL)

and

tetraphenylcyclopentadienone (637 mg, 1.65 mmol) was added at -20 °C.

After stirring for 3 h at this temperature the volatiles were removed at

0.01 mbar and the residue was dissolved in ethyl acetate and

precipitated with ether. Decantation and drying at 0.01 mbar gave 18a

(1.01 g, 1.52 mmol, 93%) as a beige solid, m.p. 268.2–270.0 °C. ¹H NMR

(CDCl₃, 400.13 MHz):  [ppm] = 3.72 (s, 3 H, NCH₃), 3.95 (s, 3 H, NCH₃),

6.00 (d, ³J = 7.70 Hz, 1 H, H_Ph), 6.58 (t, ³J = 7.54 Hz, 1 H, H_Ph), 6.65–

1

(C_bridgehead), 120.93 (q, J_C,F= 320.95 Hz, TfO^–), 123.98–147.54 (9 C_Ph

signals), 125.67 (C=CH), 155.87 (C=CH), 180.90 (C=N). IR (KBr): 휈̃ [cm^-

¹] = 1634 (m), 1458 (m), 1269 (s), 1219 (m), 1146 (s), 1030 (s), 770 (m),

752 (m), 705 (m), 636 (m). MS ((+)-ESI): m/z (%) = 336.17 (100) [M -

OTf]⁺. C₂₆H₂₂F₃NO₃S (485.52 g/mol): calcd. C 64.32, H 4.57, N 2.88;

found C 64.27, H 4.43, N 2.84.

3

6.68 (m, 1 H, H_Ph), 6.70–6.72 (m, 1 H, H_Ph), 6.77 (d, J = 7.31 Hz, 1 H,

H_Ph), 6.81–6.86 (m, 3 H, H_Ph), 6.88–6.91 (m, 1 H, H_Ph), 6.92–7.05 (m, 6 H,

H_Ph), 7.15–7.21 (m, 6 H, H_Ph), 7.21–7.25 (m, 2 H, H_Ph), 7.35–7.42 (m, 2 H,

H_Ph), 7.93 (s, 1 H, H_Ph). ¹³C NMR (CDCl₃, 100.61 MHz):  [ppm] = 47.27

N-((9,10-Dihydro-9,10-ethenoanthracen-11-

1

(NCH₃), 48.44 (NCH₃), 120.97 (q, J_C,F= 320.54 Hz, TfO^–), 126.33–

yl)(phenyl)methylene)methanaminium Triflate (19b): Propyne iminium

salt 3a (988 mg, 3.37 mmol) was dissovled in CH₂Cl₂(11 mL) and

anthracene (600 mg, 3.37 mmol) was added at room temperature. After

stirring for 2 h the solvent was removed at 0.01 mbar, and the residue

was washed with ether and cyclohexane several times, then dissolved in

ethyl acetate. By addition with n-pentane, 20b (1.19 g, 2.53 mmol, 75%)

was precipitated as an ocherous solid which decomposed at 155 °C. ¹H

144.96 (29 C_Phsignals), 184.24 (C=N). IR (KBr): 휈̃ [cm^-1] = 3055 (m),

1644 (m), 1599 (m), 1447 (m), 1355 (m), 1266 (s), 1223 (m), 1151 (s),

1031 (s), 771 (m), 723 (m), 700 (s), 637 (s). MS (CI, 100 eV): m/z (%) =

514 (19) [M - OTf]⁺. C₄₀H₃₂F₃NO₃S (663.76 g/mol): calcd. C 72.38, H

4.86, N 2.11; found C 72.34, H 4.95, N 2.10.

3

N-((3',6'-Diphenyl-[1,1':2',1''-terphenyl]-4'-

NMR (CDCl₃, 400.13 MHz):  [ppm] = 3.39 (d, J = 5.34 Hz, 3 H, NCH₃),

yl)(phenyl)methylene)methanaminium Triflate (18b): Propyne iminium

salt 3a (746 mg, 2.54 mmol) was dissovled in CH₂Cl₂(14 mL) and

tetraphenylcyclopentadienone (978 mg, 2.54 mmol) was added at 0 °C.

After stirring for 30 min at this temperature, the volatiles were removed at

0.01 mbar and the residue was washed with ether/cyclohexane several

times. Drying of the residue at 0.01 mbar gave 18b (1.37 g, 2.11 mmol,

83%) as a dark-red solid, which began to decompose at 140 °C. ¹H NMR

5.37 (d, ⁴J = 1.57 Hz, 1 H, H_bridgehead), 5.50 (d, ³J = 6.24 Hz, 1 H,

H_bridgehead), 7.05–7.10 (m, 4 H, H_Ph), 7.35–7.43 (m, 8 H, H_Ph+ HC=C),

7.63–7.69 (m, 2 H, H_Ph), 11.81 (s, br, 1 H, NH). ¹³C NMR (CDCl₃, 100.61

MHz):  [ppm] = 37.35 (NCH₃), 52.24 and 53.35 (CH_bridgehead), 120.48 (q,

¹J_C,F= 319.94 Hz, TfO^–), 124.20–143.78 (10 C_Phsignals), 144.05 (C=CH),

156.18 (C=CH), 179.57 (C=N). IR (KBr): 휈̃ [cm^-1] = 3066 (m), 1640 (s),

1597 (m), 1581 (m), 1459 (m), 1287 (s), 1245 (s), 1224 (s), 1160 (s),

1030 (s), 768 (m), 752 (m), 705 (m), 637 (s). MS ((+)-ESI): m/z (%) =

322.16 (100) [M - OTf]⁺. C₂₅H₂₀F₃NO₃S (471.49 g/mol): calcd. C 63.69, H

4.28, N 2.97; found C 62.14, H 4.29, N 3.23.

3

(CDCl₃, 400.13 MHz):  [ppm] = 3.57 (d, J = 5.17 Hz, 3 H, NCH₃), 6.41

(s, br, 1 H, H_Ph), 6.73–6.77 (m, 3 H, H_Ph), 6.84–6.85 (m, 1 H, H_Ph), 6.90–

6.91 (m, 5 H, H_Ph), 6.96–7.02 (m, 4 H, H_Ph), 7.12–7.16 (m, 3 H, H_Ph),

7.20–7.22 (m, 3 H, H_Ph), 7.40–7.44 (m, 2 H, H_Ph), 7.51 (s, 1 H, H_Ph),

7.57–7.63 (m, 3 H, H_Ph), 12.36 (s, br, 1 H, NH). ¹³C NMR (CDCl₃, 100.61

MHz):  [ppm] = 37.36 (NCH₃), 126.55–145.06 (26 C_Phsignals), 182.82

(C=N). The quartet signal of the triflate anion was not detected. IR (KBr):

휈̃ [cm^-1] = 3057 (m), 1649 (s), 1597 (m), 1494 (m), 1444 (m), 1341 (m),

1290 (s), 1241 (s), 1156 (s), 1074 (m), 1029 (s), 762 (m), 700 (s), 637 (s).

N-(1-(9,10-Dihydro-9,10-ethenoanthracen-11-yl)-3-phenylprop-2-yn-

1-ylidene)-N-methylmethanaminium Triflate (19c): Propyne iminium

salt 1c (283 mg, 0.85 mmol) was dissovled in CH₂Cl₂(9 mL), and

acetonitrile (3 mL) and anthracene (152 mg, 0.85 mmol) were added at

room temperature. After stirring for 2 h cyclohexane was added until a

13

10.1002/ejoc.201801511

European Journal of Organic Chemistry

FULL PAPER

black oil precipitated. The mother liquor was collected and more

cyclohexane was added to it, whereby a solid precipitated. Decantation,

washing with cyclohexane and drying at 0.02 mbar gave 20c (378 mg,

0.74 mmol, 87%) as a beige solid. M.p. 173 °C (dec. starts at 160 °C). ¹H

NMR (CDCl₃, 400.13 MHz):  [ppm] = 3.61 (s, 3 H, NCH₃), 3.92 (s, 3 H,

NCH₃), 5.49 (d, ³J = 6.32 Hz, 1 H, H_bridgehead), 5.69 (d, ⁴J = 2.05 Hz, 1 H,

H_bridgehead), 7.02–7.07 (m, 4 H, H_Ph), 7.37–7.39 (m, 2 H, H_Ph), 7.44–7.49

(m, 4 H, H_Ph), 7.57–7.61 (m, 3 H, H_Ph+ C=CH). ¹³C NMR (CDCl₃, 100.62

N-((1-Oxo-2,4-diphenyl-1,2-dihydronaphthalen-2-yl)(phenyl)methyl-

ene)methanaminium

Triflate

(23b)

and

N-((4-Hydroxy-1,3-

diphenylnaphthalen-2-yl)(phenyl)methylene)methanaminium Triflate

(24b): Propyne iminium salt 3a (505 mg, 1.72 mmol) was dissolved in

CH₂Cl₂(12 mL) and 1,3-diphenylisobenzofuran (465 mg, 1.72 mmol) was

added at 0 °C. After stirring for 5 min at this temperature, the volatile

components were removed at 0.01 mbar and the solid residue was

washed with several portions of ether to obtain a mixture of 23b, 24b and

another isomeric species (921 mg, 1.63 mmol, 95%, 1:0.33:0.21). By

dissolving in EtOAc and addition of Et₂O, 23b could be selectively

precipitated as a slight beige solid (533 mg, 0.95 mmol, 55%); m.p.

176.1–177.5 °C. Contact of 23b with moist air gave 1-naphthol 25 (see

below). ¹H NMR (CDCl₃, 400.13 MHz): 23b:  [ppm] = 3.32 (d, J = 5.36

Hz, 3 H, NCH₃), 6.40 (s, 1 H, HC=C), 7.27–7.42 (m, 12 H, H_Ph), 7.50–

7.53 (m, 5 H, H_Ph), 7.64–7.68 (m, 1 H, H_Ph), 8.08 (d, J = 7.62 Hz, 1 H,

H_Ph), 12.93 (s, br, 1 H, NH); selected signals of 24b and unknown isomer

in the original product mixture:  [ppm] = 3.20 (d, J = 5.31 Hz, 1.34 H,

NCH₃), 3.46 (d, J = 5.14 Hz, 0.65 H, NCH₃), 5.75 (broad signal, 0.76 H,

OH), 8.09 (d, J = 8.57 Hz, 0.21 H, H_Ph), 8.46 (d, J = 8.43 Hz, 0.35 H, H_Ph),

11.90 (s, br, 0.33 H, NH), 12.33 (s, br, 0.21 H, NH). ¹³C NMR (CDCl₃,

100.61 MHz): 23b:  [ppm] = 37.98 (NCH₃), 65.52 (C_sp3), 120.35 (q, ¹J_C,F

MHz):

 [ppm] = 46.07 (NCH₃), 47.67 (NCH₃), 52.31 and 53.37

(C_bridgehead), 81.97 (C≡C), 117.73 (C≡C), 118.24 (HC=C), 120.75 (¹J_C,F

=

320.11 Hz, TfO^–), 124.08–144.81 (10 C_Phsignals), 155.14 (HC=C),

160.49 (C=N). IR (KBr): 휈̃ [cm^-1] = 2199 (s, C≡C), 1611 (m), 1591 (m),

1268 (s), 1225 (m), 1151 (s), 1030 (s), 759 (m), 638 (s). HRMS ((+)-ESI):

m/z

C₂₈H₂₂F₃NO₃S (509.54 g/mol): calcd. C 66.00, H 4.35, N 2.75.

= -

360.17475 (calcd. 360.17468 for C₂₇H₂₂N⁺, [M OTf]⁺).

N-Methyl-N-(phenyl(p-tolyl)methylene)methanaminium Triflate (20a):

Propyne iminium salt 1a (533 mg, 1.74 mmol) was dissolved in CH₂Cl₂

(10 mL) and isoprene (128 mg, 1.88 mmol) was added at -20 °C. After

stirring for 8 h at this temperature, o-chloranil (428 mg, 1.74 mmol) was

added and stirring was continued for 18 h at room temperature.

Thereafter the volatiles were removed at 0.01 mbar and the residue was

dissolved in CH₂Cl₂. The solid obtained by addition of ether was re-

dissolved in ethyl acetate and precipitated again with ether. The greenish

solid was dried at 0.01 mbar to furnish 21a (526 mg, 1.41 mmol, 81%)

contaminated with 4 mol% of the meta-isomer and polymeric species.

M.p. 148.1–150.0 °C. NMR data for the para-isomer: ¹H NMR (CDCl₃,

400.13 MHz):  [ppm] = 2.40 (s, 3 H, CH₃), 3.77 (s, 3 H, NCH₃), 3.82 (s, 3

H, NCH₃), 7.29 (d, ³J = 8.13 Hz, 2 H, H_Ph), 7.38 (d, ³J = 8.27 Hz, 2 H,

H_Ph), 7.47–7.53 (m, 5 H, H_Ph). ¹³C NMR (CDCl₃, 100.61 MHz):  [ppm] =

= 318.93 Hz, TfO^–), 126.48 (HC=C), 127.96141.51 (18 signals, C_Ph

+

C=C), 189.45 (C=N), 192.93 (C=O); selected signals of 24b and

unknown isomer:  [ppm] = 37.29 (NCH₃), 37.45 (NCH₃), 149.40, 181.83,

183.20, 196.74. IR (KBr): 휈̃ [cm^-1] = 3057 (m), 1677 (s), 1642 (m), 1594

(m), 1490 (m), 1446 (m), 1293 (s), 1240 (s), 1163 (s), 1029 (s), 784 (m),

738 (m), 697 (m), 637 (s), 578 (m), 519 (m). MS ((+)-ESI): m/z (%) =

414.18 (100) [M - OTf]⁺. Elemental analysis for 23b: C₃₁H₂₄F₃NO₄S

(563.59 g/mol) calcd. C 66.07, H 4.29, N 2.49; found C 64.84, H 4.41, N

2.68. The discrepancies may arise from some hydrolysis during

manipulation.

1

21.87 (CH₃), 47.93 (NCH₃), 47.95 (NCH₃), 120.79 (q, J_C,F= 320.36 Hz,

TfO^–); 129.16, 129.85, 130.24, 130.35, 130.88, 133.40, 133.66, 145.43

(all C_Ph); 183.99 (C=N). IR (KBr): 휈̃ [cm^-1] = 1632 (s), 1450 (m), 1350 (m),

1265 (s), 1224 (m), 1156 (s), 1031 (s), 704 (m), 638 (s). MS ((+)-ESI):

m/z (%) = 224.1426 (calcd. 224.14338 for C₁₆H₁₈N⁺, [M - OTf]⁺).

C₁₇H₁₈F₃NO₃S (373.39 g/mol): calcd. C 54.68, H 4.86, N 3.75.

2,4-Diphenylnaphthalen-1-ol (25): The mixture of 23a and 24a (861 mg,

1.49 mmol) was dissolved in CH₂Cl₂(10 mL) and extracted with

saturated aqueous K₂CO₃. The organic layer was separated, dried with

Na₂SO₄, and the volatile components were removed at reduced pressure.

The residue was dissolved in cyclohexane/EtOAc (10:1) and filtrated

through SiO₂. The filtrate was purified via HPLC (cyclohexane/EtOAc =

95:5) to furnish 25 (210 mg, 0.709 mmol, 68% (based on amount of 23a))

as a colorless oil. ¹H NMR (CDCl₃, 400.13 MHz):  [ppm] = 5.91 (s, 1 H,

OH), 7.36 (s, 1 H, H_Ph), 7.42–7.61 (m, 12 H, H_Ph), 7.93 (d, J = 8.43 Hz, 1

H, H_Ph), 8.40 (d, J = 8.35 Hz, 1 H, H_Ph). ¹³C NMR (CDCl₃, 100.61 MHz): 

[ppm] = 120.92–147.44 (18 C_Phsignals). The spectroscopic data are in

accordance with published values.^[37]MS ((+)-ESI): m/z (%) = 297.13

(100) [M + H]⁺. C₂₂H₁₆O (296.37 g/mol): calcd. C 86.08, H 7.22, N 6.69.

N-Methyl-N-((1-oxo-2,4-diphenyl-1,2-dihydronaphthalen-2-

yl)(phenyl)methylene)methanaminium Triflate (23a) and N-((4-

Hydroxy-1,3-diphenylnaphthalen-2-yl)(phenyl)methylene)-N-

methylmethanaminium Triflate (24a): Propyne iminium salt 1a (583 mg,

1.90 mmol) was dissolved in CH₂Cl₂(10 mL) and 1,3-

diphenylisobenzofuran (518 mg, 1.92 mmol) was added at -40 °C. After

stirring for 90 min at this temperature, the volatiles were removed at 0.01

mbar and the residue was washed with ether several times, then

dissolved in ethyl acetate, and ether/n-pentane (1:1) was added to

precipitate 23a and 24a (999 mg, 1.73 mmol, 91%, 1:0.42) as a yellow

solid. Contact of the mixture of 23a and 24a in CH₂Cl₂with moist air

leads to selective hydrolysis of 23a to give 1-naphthol 25,

dimethylammonium triflate and benzoid acid, whereas 24a did not react.

Salt 24a could be purified by precipitation with n-pentane and

crystallization using the vapor diffusion method (CH₂Cl₂/Et₂O). M.p. of the

mixture (23a + 24a) 175.9–177.3 °C; m.p. of 24a 168.8–170.8 °C. ¹H

NMR (CDCl₃, 500.14 MHz), for 23a:  [ppm] = 3.66 (s, 3 H, NCH₃), 3.73

(s, 3 H, NCH₃), 7.08–7.09 (m, 1 H, H_Ph), 7.10–7.12 (m, 3 H, H_Ph), 7.23–

7.30 (m, 6 H, H_Ph+HC=C), 7.35–7.50 (m, 7 H, H_Ph), 7.58–7.61 (m, 1 H,

H_Ph), 7.72–7.75 (m, 1 H, H_Ph), 8.15 (dd, J = 7.75, 1.10 Hz, 1 H, H_Ph); for

24A: 3.40 (s, 3 H, NCH₃), 3.46 (s, 3 H, NCH₃), 8.97–6.98 (m, 1H, H_Ph),

8.49–8.50 (m, 1 H, H_Ph), all other signals covered by those of 23a. ¹³C

NMR (CDCl₃, 125.79 MHz): signals of 23a and 24a:  [ppm] = 46.81

(NCH₃, 24a), 47.47 (NCH₃, 23a), 48.54 (NCH₃, 24a), 50.88 (NCH₃, 23a),

67.92 (C_sp3, 23a), 120.75 (q, ¹J_C,F= 320.49 Hz, TfO^–), 119.72–149.85 (41

signals, C_Ph+ C=CH), 183.71 (C=N, 24a), 190.57 (C=N, 23a), 195.56

(C=O, 23a). IR (KBr): 23a + 24a: 휈̃ [cm^-1] = 3060 (m), 1681 (m), 1631 (m),

1593 (m), 1447 (m), 1276 (s), 1226 (s), 1156 (s), 1029 (s), 781 (m), 700

(m), 637 (s); 24a: 휈̃ [cm^-1] = 3178 (m, broad), 1614 (m), 1447 (m), 1384

(m), 1250 (s), 1161 (s), 1072 (m), 1030 (s), 744 (m), 698 (m), 638 (s). MS

((+)-ESI): m/z (%) = 428.20 (100) [M - OTf]⁺. C₃₂H₂₆F₃NO₄S (577.62

g/mol) calcd. C 66.54, H 4.54, N 2.42; found C 65.99, H 4.93, N 2.41.

1-(9,10-Dihydro-9,10-ethenoanthracen-11-yl)-N,N-

dimethylmethanaminium Bromide (29): Propyne iminium salt 2 (386

mg, 1.67 mmol) was dissolved in CH₂Cl₂(12 mL), and acetonitrile (2 mL)

and anthracene (298 mg, 1.67 mmol) were added at room temperature.

After stirring for 1 h, the solution was cooled to -78 °C and LiAlH₄(696 µL,

1.67 mmol, 2.4 M in THF) was added dropwise. After 5 min the reaction

was quenched with acetone at -78 °C, brought to room temperature and

extracted with ether/brine. The organic phase was collected, dried with

Na₂SO₄, and the volatile components were removed under reduced

pressure. The residue was dissolved in ether, and conc. HBr was added

dropwise until pH 1 was reached. The resulting solid was filtered off,

washed with ether and dried at 0.01 mbar to obtain 29 (560 mg, 1.64

mmol, 98%) as a brownish solid. Slow evaporation of a CHCl₃solution

furnished 29 as colorless crystals. M.p. 242 °C (dec. started at 235 °C).

¹H NMR (CDCl₃, 500.14 MHz):  [ppm] = 2.53 (d, ³J = 4.95 Hz, 6 H,

3

N(CH₃)₂), 3.80 (d, J = 5.79 Hz, 2 H, NCH₂), 5.13 (d, J = 5.87 Hz, 1 H,

H_bridgehead), 5.91 (s, 1 H, H_bridgehead), 6.93–6.95 (m, 4 H, H_Ph), 7.15 (d, ³J =

5.87 Hz, 1 H, C=CH), 7.25–7.26 (m, 2 H, H_Ph), 7.55–7.57 (m, 2 H, H_Ph),

11.51 (s, br, 1 H, NH). ¹³C NMR (CDCl₃, 125.79 MHz):  [ppm] = 42.69

(N(CH₃)₂), 51.32 and 52.53 (C_bridgehead), 59.49 (NCH₂), 123.31 (C_Ph),

124.23 (C_Ph), 125.08 (C_Ph), 125.15 (C_Ph), 142.92 (C=CH), 144.77 (C_Ph),

144.92 (C_Ph), 145.38 (C=CH). IR (KBr): 휈̃ [cm^-1] = 2914 (m), 2651 (s),

2562 (m), 2469 (m), 1457 (s), 1426 (m), 1147 (m), 943 (m), 748 (s), 563

14

10.1002/ejoc.201801511

European Journal of Organic Chemistry

FULL PAPER

(m), 536 (m). HRMS ((+)-ESI): m/z = 217.10131 (calcd. 217.10118 for

C₁₇H₁₃, [cation - HNMe₂]⁺, 262.15896 (calcd. 262.15903 for C₁₉H₂₀N⁺,

[cation + H]⁺), 603.23742 (calcd. 603.23694 for C₃₈H₄₀BrN₂⁺, [2cation +

2H + ⁷⁹Br^-]⁺, 605.23628 (calcd. 605.23550 for C₃₈H₄₀BrN₂⁺, [2cation + 2H

(NCH₃), 51.29 and 54.47 (CH_bridgehead), 123.25–145.77 (10 C_Phsignals),

129.99 (C=C), 147.37 (C=C), 167.82 (C=N). IR (KBr): 휈̃ [cm^-1] = 3061 (m),

3019 (m), 2965 (m), 2911 (m), 2858 (m), 1602 (s), 1456 (s), 1340 (m),

1276 (m), 1254 (s), 1229 (m), 1188 (m), 1149 (m), 1016 (m), 907 (m),

835 (m), 748 (s), 701 (s), 624 (m), 586 (s). HRMS ((+)-ESI): m/z =

322.15969 (calcd. 322.15903 for C₂₄H₂₀N⁺, [M + H]⁺). C₂₄H₁₉N (321.42

g/mol) calcd. C 89.68, H 5.96, N 4.36; found C 87.01, H 5.94, N 3.20.

+

⁸¹Br^-]⁺. C₁₉H₂₀BrN (342.28 g/mol): calcd. C 66.67, H 5.89, N 4.09; found

C 65.52, H 5.83, N 4.47.

1-(3',6'-Diphenyl-[1,1':2',1''-terphenyl]-4'-yl)-N,N-

dimethylmethanaminium Bromide (30): Preparation as described for

29 from propyne iminium salt 2 (278 mg, 1.20 mmol), tetracyclone (462

mg, 1.20 mmol) and LiAlH₄(500 µL, 1.20 mmol, 2.4 M in THF). Yield:

609 mg (1.17 mmol, 98%), off-white solid, m.p. 284.0–285.2 °C. ¹H NMR

(CDCl₃, 500.14 MHz):  [ppm] = 2.61 (d, ³J = 4.99 Hz, 6 H, N(CH₃)₂),

4.29 (d, ³J = 5.61 Hz, 2 H, NCH₂), 6.66–6.68 (m, 2 H, H_Ph), 6.77–6.79 (m,

2 H, H_Ph), 6.83–6.84 (m, 3 H, H_Ph), 6.90–6.91 (m, 3 H, H_Ph), 6.97–6.98 (m.

2 H, H_Ph), 7.09–7.21 (m, 6 H, H_Ph), 7.30–7.31 (m, 2 H, H_Ph), 8.18 (s, 1 H,

H_Ph), 11.40 (s, br, 1 H, NH). ¹³C NMR (CDCl₃, 125.79 MHz):  [ppm] =

42.87 (N(CH₃)₂), 58.42 (NCH₂), 125.82–142.65 (21 C_Phsignals). IR (KBr):

휈̃ [cm^-1] = 1440 (m), 699 (s). HRMS ((+)-ESI): m/z = 440.23696 (calcd.

440.23728 for C₃₃H₃₀N⁺, [cation + H]⁺). C₃₃H₃₀BrN (520.51 g/mol): calcd.

C 76.15, H 5.81, N 2.69; found C 75.82, H 5.94, N 2.79.

1-(Bicyclo[2.2.1]hepta-2,5-dien-2-yl)-N-methyl-1-phenylmethanimine

(34): Iminium salt 17b (1.39 g, 3.87 mmol) was dissolved in THF (9 mL)

and added dropwise to LiHMDS (10.0 mL, 10.0 mmol, 1 M in THF) at

room temperature. Stirring was continued for 5 min whereupon the

reaction was quenched with aqueous Na₂CO₃and extraced with CH₂Cl₂.

The organic phase was separated, dried over Na₂SO₄and evaporated to

dryness under reduced pressure. The residue was dissolved in

cyclohexane/ethyl acetate (2:1) and quickly filtered through a short pad of

Al₂O₃. Removal of the solvent gave the crude imine 28 (655 mg, 3.13

mmol, 81%) as an orange oil. Further purification failed because of the

instability of 34. ¹H NMR (CDCl₃, 400.13 MHz):  [ppm] = 2.00–2.03 (m, 2

H, CH₂), 3.05 (s, 3 H, NCH₃), 3.49 (s, 1 H, H_bridgehead), 4.11 (s, 1 H,

H_bridgehead), 6.34 (d, ³J = 3.06 Hz, 1 H, HC=C), 6.63–6.65 (m, 1 H,

HC=CH), 6.88–6.90 (m, 1 H, HC=CH), 6.95–6.97 (m, 2 H, H_Ph), 7.24–

7.28 (m, 3 H, H_Ph). ¹³C NMR (CDCl₃, 100.61 MHz):  [ppm] = 40.10

(NCH₃), 49.58 and 51.20 (C_bridgehead), 72.72 (CH₂), 127.46 (C_Ph), 127.97

(C_Ph), 128.16 (C_Ph), 137.03 (C_Ph), 142.97 (HC=CH), 143.41 (HC=CH),

149.87 (C=CH), 160.05 (C=CH), 167.22 (C=N). IR (NaCl): 휈̃ [cm^-1] =

3057 (s), 3022 (s), 2970 (s), 2936 (s), 2865 (s), 2799 (m), 1635 (s), 1598

(s), 1553 (m), 1490 (m), 1446 (s), 1380 (m), 1328 (s), 1299 (s), 1250 (m),

1180 (m), 1091 (m), 1053 (m), 999 (m), 916 (m), 840 (m), 765 (m), 702

(s), 675 (m). MS ((+)-ESI): m/z (%) = 210.13 (100) [M + H]⁺. C₁₅H₁₅N

(209.29 g/mol): calcd. C 86.08, H 7.22, N 6.69.

5',6'-Diphenyl-[1,1':2',1''-terphenyl]-3'-carbaldehyde (31): Propyne

iminium salt 2 (109 mg, 0.47 mmol) was dissolved in CH₂Cl₂(5 mL) and

MeCN (2 mL) and tetraphenylcyclopentadienone (181 mg, 0.47 mmol)

was added. After stirring for 15 min, a saturated aqueous K₂CO₃solution

was added and the mixture was extracted with ether. The organic layer

was separated, dried with Na₂SO₄, and the volatiles were removed under

reduced pressure. The residue was purified by flash chromatography

(cyclohexane/EtOAc = 80:1) which gave 31 (183 mg, 0.45 mmol, 95%)

as a slightly violet solid. M.p. 205.1–207.0 °C. ¹H NMR (CDCl₃, 400.13

MHz):  [ppm] = 6.77–6.84 (m, 4 H, H_Ph), 6.90–6.95 (m, 6 H, H_Ph), 7.11–

7.21 (m, 10 H, H_Ph), 8.18 (s, 1 H, H_Ph), 9.84 (s, 1 H, C(O)H). ¹³C NMR

(CDCl₃, 100.62 MHz):  [ppm] = 126.00–145.71 (22 C_Phsignals), 192.69

(C=O). IR (KBr): 휈̃ [cm^-1] = 1689 (s), 1577 (m), 1443 (m), 1385 (m), 1074

(m), 761 (m), 702 (s). MS (CI, 100 eV): m/z (%) = 411 (100) [M + H]⁺.

C₃₁H₂₂O (410.52 g/mol): calcd. C 90.70, H 5.40; found C 90.80, H 5.56.

(6Z,12Z)-5,11-Dimethyl-6,12-diphenyl-1,4,4a,5,7,10,10a,11-octahydro-

1,4:7,10-dimethanodibenzo[b,f][1,5]diazocine (35): Norbornadiene

17b (850 mg, 2.37 mmol) was dissolved in CH₂Cl₂(40 mL) and NaOMe

(439 µL, 2.39 mmol, 30 wt. % in MeOH) was added at room temperature.

After stirring for 10 min, the mixture was filtrated and the volatiles were

evaporated under reduced pressure. The brown residue was purified by

chromatography (SiO₂, cyclohexane/EtOAc

= 40:1, R_f= 0.45). A

1-(3',6'-Diphenyl-[1,1':2',1''-terphenyl]-4'-yl)-N-methyl-1-

colorless solid was obtained, which was a mixture of the diastereomeric

diazocine derivatives 35 (337 mg, 0.81 mmol, 68%);with a molar ratio of

35A, 35B and 35C = 1 : 0.45 : 0.30. M.p. 205 °C. ¹H NMR (CDCl₃,

400.13 MHz): 35A:  [ppm] = 1.49–1.59 (m, 2 H), 1.62–1.65 (m, 2 H),

1.97 (s, 3 H, NCH₃), 2.28 (s, 3 H, NCH₃), 3.03 (s, 1 H, H_bridgehead), 3.08–

3,09 (m, 1 H, H_bridgehead), 3.09–3.10 (m, 1 H, H_bridgehead), 3.52 (s, 1 H,

H_bridgehead), 3.83 (s, 1 H, NCH), 4.49 (d, J = 3.63 Hz, 1 H, NCH), 6.06 (dd,

J = 5.44, 2.99 Hz, 1 H, HC=CH), 6.14 (dd, J = 5.52, 2.83 Hz, 1 H,

HC=CH), 6.38 (dd, J = 5.40, 3.28 Hz, 1 H, HC=CH), 6.43 (dd, J = 5.58,

3.44 Hz, 1 H, HC=CH), 7.27–7.47 (m, 10 H, H_Ph); selected signals of 35B

and 35C: (CDCl₃, 500.14 MHz): [ppm] = 2.00 (s, 6 H, NCH₃, 35B), 2.24

(s, 6 H, NCH₃, 35C), 2.98 (s, 2 H, H_bridgehead, 35C), 3.08–3.09 (m, 2 H,

phenylmethanimine (32): Iminium salt 18b (1.00 g, 1.54 mmol) was

dissolved in CH₂Cl₂(8 mL) and added dropwise to triethylamine (10 mL,

72 mmol) in CH₂Cl₂(50 mL). After stirring for 15 min, the volatile

components were removed under reduced pressure and the residue was

washed with several portions of cyclohexane. The combined organic

extracts were evaporated to dryness and the residue was purified by

column chromatography (cyclohexane/ethyl acetate = 10:1, R_f= 0.36).

Yield: 546 mg (1.09 mmol, 71%), white solid, m.p. 199.3–200.4 °C. ¹H

NMR (CDCl₃, 400.13 MHz):  [ppm] = 3.25 (s, 3 H, NCH₃), 6.60 (s, br, 1

H, H_Ph), 6.71–6.75 (m, 3 H, H_Ph), 6.79–6.91 (m, 11 H, H_Ph), 7.09–7.12 (m,

5 H, H_Ph), 7.19–7.25 (m, 4 H, H_Ph), 7.49–7.52 (m, 2 H, H_Ph). ¹³C NMR

(CDCl₃, 100.61 MHz):  [ppm] = 42.21 (NCH₃), 125.64–142.14 (26 C_Ph

signals), 169.39 (C=N). IR (KBr): 휈̃ [cm^-1] = 3056 (m), 3026 (m), 2925 (s),

2849 (s), 1711 (m), 1626 (m), 1599 (m), 1493 (m), 1444 (s), 1265 (m),

1027 (m), 762 (m), 697 (s). MS (CI, 100 eV): m/z (%) = 500 (100) [M]⁺,

422 (7) [M - Ph]⁺. C₃₈H₂₉N (499.66 g/mol): calcd. C 91.35, H 5.85, N 2.80;

found C 91.49, H 6.03, N 2.68.

H_bridgehead, 35B), 3.16 (s, 2 H, H_bridgehead, 35B), 3.45 (s, 2 H, H_bridgehead

,

35C), 3.68 (s, 2 H, NCH, 35C), 4.65 (d, J = 3.59 Hz, 2 H, NCH, 35B),

6.01 (dd, J = 5.51, 2.90 Hz, 2 H, HC=CH, 35C), 6.19 (dd, J = 5.52, 2.84

Hz, 2 H, HC=CH, 35B), 6.33 (dd, J = 5.50, 3.10 Hz, 2 H, HC=CH, 35C),

6.44 (dd, J = 5.61, 3.10 Hz, 2 H, HC=CH, 35B). ¹³C NMR (CDCl₃, 125.79

MHz), signals of all isomers:  [ppm] = 33.30, 33.62, 34.15, 34.31, 46.75,

47.59, 48.83, 48.86, 50.02, 50.10, 50.29, 51.68, 51.84, 115.47, 117.23,

120.47, 122.10, 127.11–138.19 (20 signals), 140.58, 140.69, 140.87,

141.01, 142.87, 143.59, 143.85, 144.62. IR (KBr): 휈̃ [cm^-1] = 3056 (m),

3015 (m), 2969 (s), 2943 (s), 2867 (s), 2799 (m), 1635 (s), 1597 (m),

1444 (s), 1379 (s), 1324 (s), 1055 (s). MS (CI, 100 eV): m/z (%) = 419

(37) [M + H]⁺, 352 (24) [M - C₅H₆]⁺, 286 (100) [M - 2C₅H₆]⁺, 210 (42) [M/2

+ H]⁺. C₃₀H₃₀N₂(418.58 g/mol): calcd. C 86.08, H 7.22, N 6.69; found C

85.96, H 7.38, N 6.70.

1-(9,10-Dihydro-9,10-ethenoanthracen-11-yl)-N-methyl-1-

phenylmethanimine (33): Iminium salt 19b (868 mg, 1.84 mmol) was

dissolved in CH₂Cl₂(6 mL) and triethylamine (306 µL, 2.21 mmol) was

added. After stirring for 5 min, aqueous Na₂CO₃was added followed by

extraction with CH₂Cl₂. The organic layer was dried over Na₂SO₄and

filtered through Al₂O₃. Evaporation of the solvent gave crude 33 (467 mg,

1.45 mmol, 79%). Further purification by column chromatography or

recrystallization failed. M.p. 165.8–167.9 °C. ¹H NMR (CDCl₃, 400.13

MHz):  [ppm] = 3.12 (s, 3 H, NCH₃), 5.02 (d, ³J = 1.55 Hz, 1 H,

H_bridgehead), 5.33 (d, ³J = 5.95 Hz, 1 H, H_bridgehead), 6.95 (dd, J = 5.97, 1.73

Hz, 1 H, HC=C), 7.02–7.10 (m, 4 H, H_Ph), 7.28–7.31 (m, 4 H, H_Ph), 7.36–

7.42 (m, 5 H, H_Ph). ¹³C NMR (CDCl₃, 100.61 MHz):  [ppm] = 42.18

(3-Methoxybicyclo[2.2.1]hept-5-en-2-yl)(phenyl)methanone

(36):

Norbornadiene 17b (1.26 g, 3.49 mmol) was dissolved in MeOH (10 mL)

and slowly added to a solution of NaOMe (6.48 mL, 35 mmol, 30 wt. % in

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MeOH) in MeOH (7 mL) at -10 °C. After stirring for 5 min the reaction

was quenched with solid NH₄Cl (3.74 g, 70 mmol). The mixture was

filtered, the solvent was removed under reduced pressure and the

residue was filtered through silica gel (cyclohexane/EtOAc/acetone =

90:5:5). Norbornene 36 (524 mg, 2.30 mmol, 66%) resulted as a

colorless oil which was a mixture of diastereomers 36A and 36B (1:0.24).

¹H NMR (CDCl₃, 400.13 MHz), A/B:  [ppm] = 1.68–1.70 (m, 1.47 H, 7-H,

A/B), 1.95–1.97 (m, 1 H, 7-H, A), 2.96 (dd, J = 2.94 Hz, 0.26 H, 2-H, B),

3.02 (s, 1.23 H, H_bridgehead, A/B), 3.12 (s, 1 H, H_bridgehead, A), 3.19 (s, 0.24

H, H_bridgehead, B), 3.29 (s, 0.74 H, OCH₃, B), 3.35 (s, 3 H, OCH₃, A), 3.55

(dd, ³J = 3.07 Hz, 1 H, 2-H, A), 3.73 (dd, J = 2.02 Hz, 1 H, 3-H, A), 4.32

(dd, J = 3.50 Hz, 0.23 H, 3-H, B), 6.036.05 (m, 1 H, HC=CH, A),

6.086.10 (m, 1 H, HC=CH, A), 6.24–6.26 (m, 0.24 H, HC=CH, B), 6.49–

6.51(m, 0.23 H, HC=CH, B), 7.44–7.48 (m, 2.52 H, H_Ph, A/B), 7.54–7.57

Acknowledgements

We thank U. Ziegler and Dr. R. Werz for recording some NMR

spectra, M. Wunderlin for the mass spectra, and B. Müller for the

XRD data collection.

Keywords: Alkynes;  Cycloaddition  Synthetic Methods 

Iminium Salts  Michael addition  Diels-Alder reaction

Supporting Information

¹H and ¹³C NMR spectra of all new compounds, data of the

kinetic measurements, proposed reaction scheme for

oligomerization/polymerization of 1a.

(m, 1.23 H, H_Ph, A/B), 8.02–8.06 (m, 2.47 H, H_Ph, A/B). The

configurational assignment for A and B is based on the following ¹H NMR

data: a) The trans configuration at C-2 and C-3 follows from the small

³J(2-H, 3-H) coupling constant. b) The exo position of the methoxy group

in 36A is derived from the observation of a significant ⁵J(3-H,7-H^anti

)

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K. Abbaspour Tehrani, N. De Kimpe, in Science of Synthesis, Vol. 27,

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348.

5

coupling and the absence of a J(2-H,7-H^anti) coupling. ¹³C NMR (CDCl₃,

100.61 MHz), A:  [ppm] = 45.46 (C-1), 46.66 (C-4), 47.12 (CH₂), 56.80

(C-2), 57.51 (OCH₃), 84.15 (C-3), 128.62 (C_Ph), 128.65 (C_Ph), 133.00

(C_Ph), 133.65 (C-5), 136.93 (C_Ph), 137.42 (C-6), 200.26 (C=O). B:  [ppm]

= 45.01 (C-1), 45.04 (CH₂), 47.14 (C-4), 54.87 (C-2), 57.34 (OCH₃),

84.81 (C-3), 128.69 (C_Ph), 128.71 (C_Ph), 133.17 (C_Ph), 134.87 (C-5),

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2977 (s), 2937 (m), 2824 (m), 1679 (s), 1597 (m), 1580 (m), 1448 (s),

1328 (m), 1269 (m), 1208 (s), 1120 (m), 1090 (s), 1017 (m), 722 (m), 696

(s), 665 (m). MS (CI, 100 eV): m/z (%) = 197 (7) [M - OCH₃]^·+, 163 (100)

[M - C₅H₆+H]⁺, 105 (16) [Ph-C=O]⁺, 85 (54) [M - C₅H₆- Ph]⁺. C₁₅H₁₆O₂

(228.29 g/mol): calcd. C 78.92, H 7.06; found C 78.91, H 7.06.

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X-ray Crystallographic Data of 23b, 24A, and 35A/B. Suitable crystals

were obtained by crystallization from ethyl acetate/ether (23b),

CH₂Cl₂/ether (24a) or dichloromethane/pentane (35A/B) by slow

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Entry for the Table of Contents (Please choose one layout)

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Iminium Salts

Michael Keim, Philipp Kratzer, Helena

Derksen, Dajana Isakov, Gerhard Maas*

Page No. – Page No.

Terminal Acetylenic Iminium Salts –

Synthesis and Reactivity

Simple structures – high reactivity: various types of terminal acetylenic iminium triflate

salts have been prepared and isolated. First reactivity studies show that they are more than

just synthetic equivalents of acetylenic ketones or aldehydes. They are exceedingly

reactive dienophiles in Diels-Alder reactions, undergo smooth conjugate addition with X-

H nucleophiles and can lead to unexpected products.

18

Article Doi

Terminal acetylenic iminium salts – Synthesis and reactivity

DOI: 10.1002/ejoc.201801511

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Article abstract of DOI:10.1002/ejoc.201801511

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