Proximity effects in the mass spectra of crowded bis(dimethylamino)arenes, I, intramolecular cyclization of ‘proton sponges’ under electron impact

Tetrahedron Letters,Vo1.27,No.47,pp Printed in Great Britain

5715-5718,1986

0040-4039/86 $3.00 + .OO Pergamon Journals Ltd.

PROXIMITY EFFECTS IN THE MASS SPECTRA OF CROWDED BIS(DIMETHYLAMINO)ARENES, INTRAMOLECULAR

CYCLIZATION

Marina

Rentzea*,

I,

OF 'PROTON SPONGES' Thomas

Abteilung Max-Planck-Institut Jahnstrasse

UNDER ELECTRON

IMPACT

Saupe and Heinz A. Staab

Organische

Chemie

fiir medizinische

Forschung

29, D-6900 Heidelberg

Abstract: EI mass spectra of 4,5-bis(dimethylaqino)phenanthrene (1) and the related compounds 2-S show base peaks corresponding to an Ma-Me2NH-H fragmentation for which the following iechanism is proposed: intramolecular hydrogen migration from one of the methyl groups to the nitrogen of the adjacent dimethylamino group, intramolecular cyclization with ejection of dimethylamine, and aromatization involving loss of H* and leading to stable N-methyl thebenidinium and phenanthridinium ions, respectively. The unusual

basicity

of

'proton sponges'

4,5-bis(dimethylamino)fluorene quence

salts. These such

2, and 4,5_bis(dimethylamino)phenanthrene

of the strong destabilizing

free bases and of the formation interesting

'proton sponges'

properties

led us to examine

1.

Relative

Intensities

(Corrected

of the two dimethylamino hydrogen

groups

of the Principal

for 13C and 37C1 Contents).

5715

in the

bond in their protonated

the mass spectrometrical

4

,

(1) 3, is a conse-

behaviour

effects.

=2

1

Table

steric compression

of a very strong N---H---N

with regard to proximity

1)

such as 1,8-bis(dimethylamino)naphthalene

iL

Ions in the EI Mass Spectra of 2-2

of

571.6

For 4,5_bis(dimethylamino)phenanthrene abundant

ionic species

routes as determined in Scheme

(1) and the related compounds

in the EI mass spectra

are listed in Table

z - 2 3) the most

1. For

1 the fragmentation = by means of linked scans and exact mass measurements are given in detail

1.

m/z

\ * -

261127%)

-

m/z 2L9 12%)

(W&N’

*

\

J\ -u-+j)gl4

ml2 219 (30%

H*

* -

1

(CH&NH

m/z 218 (lOO%l

m/z

203 111% 1

-HCN

1: General

Fragmentation

Pattern

m/217 7 (3%)

L

m/z 176 IL%) Scheme

._. m/z 2L813%

of l.

m/z 150 (1%

I

5717

The fragmentation

pattern

tion routes. The predominant

of l can be rationalized

gives rise to the base peak. To explain following a)

mechanism

intramolecular leading

subsequent

c)

aromatization

He migration

this consecutive

from an N-methyl

(or synchronous)

cyclization

tion by -CH2. with extrusion

and aromatic

The formation impact is strongly thebenidinium

of 19 to c_ involving

and He the

supported

nitrogen

substitu-

and ion g which

then, leads to thebenidine

ion d and of thebenidine

by the comparison (Figure

dimethylamino

an intramolecular

to an N-methylthebenidinium

of N-methylthebenidinium

H3 H$ c\ ...N

80

loss of dimethylamine

group to an adjacent

ion. Demethylation,

iodide and thebenidine

100

fragmenta-

ion d at m/z 218 which

ion 1,

of dimethylamine,

by loss of H. leading

even-electron

two competing

is suggested:

to the isomer 12 of the molecular

b)

by assuming

route leads to an intense even-electron

is a stable

D.

!j from _1 under electron

of the EI mass spectra

of 1 with N-methyl=

1).

W &+,

1

60

264 204

220

I”..’ 240

260

203 Cl-l

1’

f_

\/ \/ : . (23 lN

*I’

CH

2

0”

142

88

102

127 141 150 ’I _ _ ! II’ ~“1’“~,““1”“,““‘““l”“l”“i”“~““i 100 120 140 160

176 tu 180

*

u

20; -

204 218 .-

‘(1.. i-

200

220

240

260

203

Thcbcnidine

176

150 80

100

,‘.‘.““‘I’...~~~~~,~,~~~~~~~,~~~~....,...~ 1

120

140

160

180

200

1”“‘““1”“‘““1”‘1

220

240

260

m/z Figure

1.

EI Mass Spectra of 1, N-Methylthebenidinium

Iodide

4)

and Thebenidine

5) .

571-B

The less favoured

fragmentation

route of i probably ion b. This latter

tion to the N,N-dimethylcarbazolium the thebenidiniun proper

ion g and thebenidine

N-methylcarbazole

of perimidine

The fragmentations

results

system has recently

such as m is only a minor fragmentation

of g-5

exact mass measurements, _1. Similar

5 itself. The corresponding

to the phenanthridine

radical-ions

leads by loss of Me2N. and cyclizaion $ shows further

under electron

see Table

impact

(obtained

1) follow closely

were also obtained

lene and 4,5-bis(dimethylamino)fluorene

for the 7) .

iMH]+ as base peak and 1~: with relative

by means of linked scans and pattern

discussed

showed the quasi-molecular

between

for

1,8-bis(dimethylamino)naphtha=

'proton sponges'

intensities

to

process.

the fragmentation

CI mass spectra (isobutane) of L -2 and of thebenidine

demethylation

rearrangement of the 6) been shown . Formation

ion

10 and 67%; only minor fragmenta-

tions were observed. All 70eV EI and CI mass spectra were recorded instrument

1)

(source

R. W. Alder,

temperature

P. S. Bowman,

using a Finnigan

W. R. S. Steele,

D. R. Winterman,

1968, 723; R. W. Alder, M. R. Bryce, N. C. Goode, Perkin Trans.

2)

H. A. Staab,

I X@j, ----

2840, and literature

T. Saupe,

XAT 212 double focussing

150 - 25OOC).

N. Miller,

J. Chem. Sot. Chem. Commun.

J. Owen, J. Chem. Sot.

cited therein.

C. Krieger,

Angew.

Chem. 22 (1983) 748; Angew.

H. A. Staab,

Angew.

Chem. zg (1986) 460;

Chem.

Int. Ed. -

Engl. 22 (1983) 731. 3)

T. Saupe, C. Krieger, Engl. 22 (1986)

4)

The mass spectrum was obtained ments,

5)

LC-MS-DS

The authors Professor

6)

of the intact N-methylthebenidinium

by using the thermospray

Tudor Road, Altrincham,

VG20-250

7)

M. Rentzea, (Received

Cheshire

thank Dr.M. Haenel,

a thermal

A. Pictet,

Shiue, W. T. Smith, T. Saupe, in

cation with m/z 218 as base peak

We thank Mr. M. A. McDowall,

WA 145RZ, for recording

Germany

Max-Planck-Institut

Rutgers-Werke

to be published;

dine has been reported: Chyng-Yann

technique.

VG Instru-

this spectrunl on a

mass spectrometer,

Dr. M. Zander,

M. Rentzea,

Angew.Cheril. Int. Ed. -____ -

451.

rearrangement

for samples

Mblheim,

and

of thebenidine.

of N-methylcarbazole

to phenanthri=

Ber. Dtsch. Chem. Ges. zl (1905) 1946; 3. M. Patterson,

Jr., 3. Org. Chem. 25 (1973) 2447.

H. A. Staab, 5

fur Kohlenforschung

AG, Castrop-Rauxel,

to be published.

September 1986)