Mass spectra of new heterocycles: XII. Main fragmentation pathways of the molecular ions of 5-methylsulfanyl-1-vinyl-1H-pyrrol-2-amines under electron impact and chemical ionization

Article abstract of DOI:10.1134/S1070428014010072

Fragmentation patterns of 5-methylsulfanyl-1-vinyl-1H-pyrrol-2-amines under electron impact (70 eV) and chemical ionization (methane as reactant gas) were studied for the first time. The electron impact mass spectra of all the examined compounds contained a strong peak of molecular ion which decomposed along four pathways. Two pathways involved cleavage of the C-S bonds with elimination of methyl (major) and MeS radicals (minor), and the two others, decomposition of the pyrrole ring. The chemical ionization mass spectra displayed strong molecular, [M + H]⁺, and odd-electron [M + H - SMe]⁺ ion peaks. N,N-Dimethyl-5-methylsulfanyl-4-phenyl-1-vinyl-1H-pyrrol-2-amine under chemical ionization with methane as reactant gas characteristically decomposed with formation of [M - C₄H₉N]⁺ as the only fragment ion.

Full text of DOI:10.1134/S1070428014010072

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2014, Vol. 50, No. 1, pp. 35–44. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © L.V. Klyba, N.A. Nedolya, O.A. Tarasova, E.R. Sanzheeva, 2014, published in Zhurnal Organicheskoi Khimii, 2014, Vol. 50, No. 1,
pp. 43–51.
Mass Spectra of New Heterocycles:
XII.* Main Fragmentation Pathways of the Molecular Ions
of 5-Methylsulfanyl-1-vinyl-1H-pyrrol-2-amines under Electron
Impact and Chemical Ionization
L. V. Klyba, N. A. Nedolya, O. A. Tarasova, and E. R. Sanzheeva
Favorskii Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
e-mail: klyba@irioch.irk.ru
Received August 12, 2013
Abstract—Fragmentation patterns of 5-methylsulfanyl-1-vinyl-1H-pyrrol-2-amines under electron impact
(70 eV) and chemical ionization (methane as reactant gas) were studied for the first time. The electron impact
mass spectra of all the examined compounds contained a strong peak of molecular ion which decomposed
along four pathways. Two pathways involved cleavage of the C–S bonds with elimination of methyl (major)
and MeS radicals (minor), and the two others, decomposition of the pyrrole ring. The chemical ionization mass
spectra displayed strong molecular, [M + H]+, and odd-electron [M + H – SMe]+ ion peaks. N,N-Dimethyl-5-
methylsulfanyl-4-phenyl-1-vinyl-1H-pyrrol-2-amine under chemical ionization with methane as reactant gas
characteristically decomposed with formation of [M – C4H9N]+ as the only fragment ion.
DOI: 10.1134/S1070428014010072
Due to extensive and diverse applications of pyrrole
derivatives [2], including 1-vinylpyrroles [3–6], in
organic synthesis, medicine, pharmacology, materials
science, supramolecular chemistry, optoelectronics,
etc., development of new efficient procedures for the
preparation of these compounds, especially of those
containing rare substituents, and studies of their prop-
erties still remain important [4–6]. One of the simplest
and most effective methods for the synthesis of
1-vinylpyrrole derivatives is based on the reaction of
ketoximes with alkynes in superbasic system
(Trofimov reaction) [5]. Up to now, new versions of
the Trofimov reaction have been proposed, which
ensure one-pot synthesis of 1-vinylpyrroles directly
from ketones and acetylene (through the corresponding
oximes) [6]. Another synthetically attractive general
approach allowing simultaneous construction and
functionalization of pyrrole ring to be accomplished in
one preparative step is based on reactions of allenic
and acetylenic carbanions with isothiocyanates [7].
When 2-(vinyloxy)ethyl isothiocyanate is used as
starting compound, the products are 2-alkylsulfanyl-1-
[2-(vinyloxy)ethyl]pyrroles [7, 8]; treatment of the
latter with t-BuOK–DMSO at room or slightly elevat-
ed temperature smoothly produces 2,3-di-, 2,5-di-, and
2,3,5-tri- or 2,4,5-trihetero-substituted 1-vinylpyrroles
[9] which are difficult to obtain by other methods.
In the preceding communication [1] we described
the synthesis of 5-methylsulfanyl-1-[2-(vinyloxy)-
ethyl]-1H-pyrrol-2-amines and fragmentation of their
molecular ions under electron impact and chemical
ionization. The present work continues our systematic
studies on the mass spectra of heterocycles [1, 10]
obtained from allyl isothiocyanate [11] or other
isothiocyanates and allenic or acetylenic compounds
[7, 8, 12]. We now report for the first time on the
fragmentation of molecular ions of 5-methylsulfanyl-
1-vinyl-1H-pyrrol-2-amines I–VII under electron im-
pact (70 eV) and chemical ionization (using methane
as reactant gas).
5-Methylsulfanyl-1-vinyl-1H-pyrrol-2-amines I–
VII were synthesized in 86–97% yield from readily
accessible 5-methylsulfanyl-1-[2-(vinyloxy)ethyl]-1H-
pyrrol-2-amines VIII–XIV via cleavage of the
2-(vinyloxy)ethyl group by the action of t-BuOK–
* For communication XI, see [1].
35

KLYBA et al.
36
Scheme 1.
R2
R2
t-BuOK–DMSO
22°C, 1 h
R12N
SMe
O
R12N
SMe
CH2
N
N
CH2
VIII–XIV
I–VII
I, VI, VII, R1 = Me; II, R1 = Et; III, R1 = Pr; IV, R12N = pyrrolidin-1-yl; V, R12N = piperidin-1-yl;
I–V, R2 = H; VI, R2 = Ph; VII, R2 = H2C=C(Me).
DMSO, which was accompanied by elimination of
allyl alcohol (Scheme 1) [9]. Compounds VIII–XII
were prepared in turn from monolithiated propargyl-
amines and 2-(vinyloxy)ethyl isothiocyanate (through
recyclization of intermediate thienylamide anion A) in
one preparative step (yield 77–84%) according to the
procedure developed by us previously [13] (Scheme 2).
4-Substituted 1-[2-(vinyloxy)ethyl]pyrrol-2-amines
XIII and XIV (precursors of VI and VII) were syn-
thesized in 52 and 59% yield from 2-(vinyloxy)ethyl
isothiocyanate and lithiated N,N-dimethyl-3-phenyl-
prop-2-yn-1-amine and N,N,4-trimethylpent-4-en-2-
yn-1-amine, respectively, through allenyl imidothioate
B which was subjected to cyclization catalyzed by
copper(I) salts (Scheme 2) [14, 15].
of IV and V decreased from 78 and 94% for XI and
XII [1] to 66 and 56%, respectively. The complete lists
of ion peaks in the mass spectra of 5-methylsulfanyl-1-
vinyl-1H-pyrrol-2-amines I–VII and 4-isopropenyl-
N,N-dimethyl-5-methylsulfanyl-1-[2-(vinyloxy)ethyl]-
1H-pyrrol-2-amine (XIV) (which was not described in
[1]) are given in Table 1.
Another essential feature that makes compounds
I–VII different from VIII–XIV is the character of
fragmentation of their molecular ions under electron
impact. The molecular ions of 1-[2-(vinyloxy)ethyl]-
pyrrol-2-amines decompose according to three main
pathways: (1) elimination of EtS radical, (2) expulsion
of methyl radical from the MeS group, and (3) cleav-
age of the C–N and/or C–C bonds, which is accom-
panied by rearrangement processes [1]. The intensity
of the resulting [M – EtS]+, [M – Me]+, and [M –
C4H7O]+ ion peaks ranges within 96–100, 23–53, and
6–13%, respectively.
The electron impact mass spectra of I–VII, as well
as the spectra of 1-(2-vinyloxy)ethyl precursors VIII–
XIII [1] and XIV (Table 1; [M1]+·, Irel 53–100%),
displayed intense molecular ion peaks (Irel 56–100%);
however, there is no similarity in the variation of the
molecular ion stabilities in the series I–VII and VIII–
XIV. In particular, the abundance of the molecular
ions of 1-vinylpyrroles I, II, and VI increased from
53–97% for compounds VIII, IX, and XIII [1] to
100%, whereas the intensity of the molecular ion peaks
The electron ionization mass spectra of 1-vinyl-
pyrrol-2-amines I–VII revealed formation of several
ion series. Primary decomposition of the molecular ion
[M1]+· involves cleavage of both C–S bonds (Me–S
and C5–S) with elimination of Me and MeS radicals,
respectively, and formation of [M – Me]+ (C–C″) and
Scheme 2.
K
t-BuOH
(1) ~50°C, ~5 min
(2) MeI
R12N
N
R12N
SMe
O
t-BuOK–DMSO
S
N
R21N
O
CH2
H2C
(1) BuLi, THF–hexane
(2) H2C=CHOCH2CH2N=C=S
A
VIII–XII
R2
R2
R2
SMe
R12N
SMe
Me2N
·
MeI
CuBr
CH2
N
N
CH2
O
O
B
XIII, XIV
VIII, XIII, XIV, R1 = Me; IX, R1 = Et; X, R1 = Pr; XI, R12N = pyrrolidin-1-yl; XII, R12N = piperidin-1-yl;
VIII–XII, R2 = H; XIII, R2 = Ph; XIV, R2 = H2C=C(Me).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 1 2014

MASS SPECTRA OF NEW HETEROCYCLES: XII.
37
[M – MeS]+ (D, D′) ions (Scheme 3, Table 2). Unlike
1-[2-(vinyloxy)ethyl]pyrrol-2-amines, the formation of
[M – Me]+ ions is the major fragmentation pathway of
1-vinylpyrrole derivatives. The abundance of the
[M – Me]+ ions ranges from 74 to 100% against 23–
53% for 1-[2-(vinyloxy)ethyl] analogs [1]. The two
other ion series which were not observed in the mass
spectra of 1-[2-(vinyloxy)ethyl]pyrrol-2-amines [1]
originate from decomposition of the pyrrole ring,
leading to ions E and F and products of their further
fragmentation (Scheme 4, Table 2). In addition, there
are three decomposition channels, most probably relat-
ed to rearranged molecular ion [M2]+·; cleavage of the
C–N bonds in the latter gives rise to odd-electron
Scheme 3.
R2
R2
R1
R1
–MeS·
N
N
N
N
+·
R2
R3
R3
R1
D
D'
N
SMe
CH2
N
R2
R2
R2
R3
R1
R1
R1
[M1]+·
–Me·
N
S
S
N
N
N
N
N
S
I, R1 = Me, R2 = R3 = H; m/z 182 (100)
II, R1 = Et, R2 = H, R3 = Me; m/z 210 (100)
III, R1 = Pr, R2 = H, R3 = Et; m/z 238 (100)
IV, R1R3 = (CH2)3, R2 = H; m/z 208 (66)
V, R1R3 = (CH2)4, R2 = H; m/z 222 (56)
VI, R1 = Me, R2 = Ph, R3 = H; m/z 258 (100)
R3
R3
R3
CH2
C
C'
C''
VII, R1 = Me, R2 = H2C=C(Me), R3 = H; m/z 222 (100)
R2
–HCN
S
R2
R2
M
I, II, IV, V, m/z 97
–[R1N=CHR3]
S
VI, m/z 173; VII, m/z 137
N
N
S
R2
+·
R2
CH2
K
K'
–HCS·
N
S
I–V, m/z 124
VI, m/z 200
VII, m/z 164
N
K''
O
I–IV, m/z 79
VI, m/z 155
VII, m/z 119
C
+·
R2
–HCN
S
+·
R2
N
+·
I–V, m/z 96
VI, m/z 172
VII, m/z 136
R2
–R1(R3CH2)N·
S
N
N
S
+·
R2
L
L'
I–V, m/z 123
VI, m/z 199
VII, m/z 163
N
S
L''
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KLYBA et al.
38
Table 1. Electron impact (70 eV) mass spectra of 5-methylsulfanyl-1-vinyl-1H-pyrrol-2-amines I–VII and 4-isopropenyl-
N,N-dimethyl-5-methylsulfanyl-1-[2-(vinyloxy)ethyl]-1H-pyrrol-2-amine (XIV)
Comp. no.
m/z (Irel, %)a
I
182 (100) [M]+·, 183 (11), 184 (5), 169 (4), 168 (8), 167 (85), 165 (4), 155 (3), 152 (10), 151 (10), 141 (4), 140
(28), 139 (5), 138 (3), 137 (6), 136 (5), 135 (19), 134 (7), 133 (12), 126 (14), 125 (7), 124 (23), 123 (54), 121
(7), 120 (12), 119 (5), 114 (8), 111 (4), 110 (4), 108 (4), 107 (6), 106 (4), 105 (6), 100 (3), 99 (5), 98 (4), 97
(10), 96 (21), 94 (8), 93 (19), 92 (5), 91 (5), 85 (5), 84 (3), 83 (4), 82 (17), 81 (5), 80 (9), 79 (11), 78 (5), 76
(5), 73 (5), 72 (3), 71 (11), 70 (14), 69 (13), 68 (6), 67 (8), 66 (18), 65 (6), 64 (3), 59 (5), 58 (4), 56 (3), 55 (4),
54 (5), 53 (5), 52 (10), 51 (3), 47 (4), 46 (3), 45 (16), 44 (14).
II
210 (100) [M]+·, 211 (16), 212 (5), 197 (4), 196 (8), 195 (74), 181 (4), 180 (8), 168 (9), 167 (9), 166 (34), 165
(10), 164 (5), 163 (16), 162 (6), 161 (3), 154 (13), 153 (5), 152 (6), 151 (21), 149 (3), 148 (4), 147 (7), 141 (4),
140 (25), 139 (6), 138 (8), 137 (19), 136 (7), 135 (7), 134 (28), 133 (14), 132 (3), 128 (3), 126 (22), 125 (5),
124 (19), 123 (6), 121 (4), 119 (6), 118 (3), 112 (7), 111 (3), 110 (8), 108 (8), 107 (7), 106 (12), 105 (16), 100
(15), 99 (8), 98 (4), 97 (8), 96 (22), 94 (4), 93 (5), 86 (4), 85 (6), 84 (3), 82 (5), 81 (3), 80 (12), 79 (34), 78 (7),
73 (4), 72 (5), 71 (6), 70 (11), 69 (7), 68 (4), 67 (3), 66 (3), 65 (3), 61 (3), 59 (9), 58 (4), 56 (14), 55 (3), 54 (8),
53 (9), 52 (16), 47 (4), 45 (14), 44 (5), 42 (10), 41 (8), 40 (3), 39 (11), 38 (3).
III
IV
238 (100) [M]+·, 224 (12), 223 (84), 191 (16), 181 (8), 180 (17), 179 (5), 168 (6), 166 (6), 162 (8), 161 (4), 154
(16), 152 (4), 151 (12), 149 (11), 138 (11), 137 (10), 133 (19), 126 (16), 124 (10), 123 (5), 120 (6), 119 (7),
112 (8), 106 (6), 105 (10), 100 (7), 96 (9), 80 (4), 79 (15), 70 (4), 54 (3), 52 (30).
208 (66) [M]+·, 209 (8), 210 (4), 195 (5), 194 (12), 193 (100), 191 (3), 178 (6), 166 (9), 165 (13), 161 (11), 160
(10), 159 (9), 153 (3), 152 (4), 151 (6), 150 (3), 149 (14), 147 (5), 138 (4), 137 (4), 136 (3), 134 (4), 133 (4),
132 (5), 131 (3), 126 (4), 125 (4), 124 (29), 123 (5), 119 (4), 118 (4), 112 (3), 110 (3), 108 (7), 107 (5), 106
(8), 105 (10), 104 (3), 100 (3), 98 (5), 97 (13), 96 (23), 94 (3), 93 (5), 92 (3), 85 (4), 83 (4), 81 (4), 80 (12), 79
(22), 78 (5), 71 (9), 70 (19), 69 (8), 68 (4), 67 (3), 66 (5), 65 (4), 61 (3), 59 (8), 58 (3), 56 (3), 55 (16), 54 (8),
53 (10), 52 (14), 51 (4), 47 (5), 46 (3), 45 (18), 43 (4), 42 (9), 41 (26), 40 (6), 39 (25), 38 (4).
V
222 (56) [M]+·, 223 (8), 224 (4), 209 (4), 208 (10), 207 (77), 192 (5), 180 (5), 179 (5), 175 (11), 174 (5), 173
(5), 163 (8), 161 (3), 153 (3), 152 (3), 151 (5), 148 (3), 147 (4), 145 (3), 139 (7), 138 (3), 137 (4), 133 (3), 132
(3), 126 (5), 125 (4), 124 (20), 123 (8), 122 (11), 120 (4), 119 (5), 118 (7), 117 (4), 112 (6), 111 (4), 110 (3),
107 (7), 106 (7), 105 (10), 100 (3), 98 (4), 97 (10), 96 (21), 95 (5), 94 (4), 93 (5), 92 (4), 85 (5), 84 (14),
83 (3), 82 (3), 80 (10), 79 (17), 78 (4), 71 (6), 70 (7), 69 (11), 68 (4), 67 (5), 66 (6), 65 (6), 61 (9), 59 (8),
58 (3), 56 (6), 55 (13), 54 (11), 53 (12), 52 (15), 51 (4), 47 (6), 46 (3), 45 (23), 43 (5), 42 (25), 41 (100),
40 (11), 39 (40), 38 (5).
VI
258 (100) [M]+·, 259 (16), 260 (6), 252 (4), 245 (5), 244 (20), 243 (93), 241 (3), 231 (3), 229 (3), 228 (11), 227
(9), 217 (3), 216 (12), 215 (3), 213 (4), 212 (14), 211 (51), 210 (15), 209 (8), 202 (5), 201 (7), 200 (18), 199
(24), 198 (8), 197 (6), 196 (8), 195 (20), 191 (3), 190 (20), 187 (4), 186 (10), 185 (9), 184 (24), 183 (22), 182
(11), 181 (36), 180 (3), 174 (7), 173 (11), 172 (11), 171 (8), 170 (6), 169 (18), 168 (20), 167 (25), 166 (5), 160
(4), 159 (8), 158 (14), 157 (4), 156 (6), 155 (6), 154 (10), 153 (5), 147 (10), 146 (7), 145 (7), 144 (5), 143 (7),
142 (9), 141 (8), 140 (23), 139 (4), 134 (14), 130 (4), 129 (15), 128 (34), 127 (17), 121 (10), 117 (3), 116 (11),
115 (43), 114 (8), 113 (6), 110 (3), 108 (3), 105 (3), 104 (4), 103 (8), 102 (56), 101 (17), 100 (8), 99 (12), 98
(4), 95 (10), 94 (5), 93 (5), 91 (6), 90 (6), 89 (11), 88 (18), 87 (4), 86 (4), 82 (4), 81 (4), 80 (4), 79 (8), 78 (8),
77 (26), 76 (15), 75 (12), 74 (11), 73 (6), 72 (5), 71 (11), 70 (9), 69 (12), 68 (7), 67 (5), 66 (3), 65 (8), 64 (6),
63 (17), 62 (8), 61 (5), 59 (15), 58 (7), 56 (7), 55 (5), 54 (7), 53 (3), 52 (12), 51 (25), 50 (12).
VII
222 (100) [M]+·, 223 (15), 224 (6), 209 (5), 208 (13), 207 (96), 205 (4), 192 (11), 191 (7), 180 (3), 179 (4), 178
(6), 177 (7), 176 (6), 175 (35), 174 (20), 173 (13), 166 (5), 165 (13), 164 (37), 163 (11), 162 (15), 161 (5), 160
(12), 159 (14), 155 (4), 154 (31), 152 (3), 151 (7), 150 (17), 149 (11), 148 (27), 147 (12), 146 (5), 145 (12),
144 (4), 139 (5), 138 (29), 137 (12), 136 (13), 135 (7), 134 (6), 133 (14), 132 (12), 131 (15), 130 (10), 124 (5),
123 (7), 122 (17), 121 (7), 120 (5), 119 (5), 118 (8), 117 (9), 111 (11), 110 (5), 109 (7), 108 (4), 107 (6), 106
(8), 105 (7), 103 (31), 99 (4), 98 (4), 97 (7), 96 (8), 95 (6), 94 (8), 93 (6), 92 (14), 91 (9), 90 (7), 89 (4), 88 (8),
87 (4), 85 (8), 83 (6), 82 (6), 81 (7), 80 (7), 79 (13), 78 (9), 77 (18), 76 (5), 75 (3), 74 (4), 73 (3), 71 (11), 70
(96), 69 (13), 68 (10), 67 (8), 66 (17), 65 (29), 64 (7), 63 (9), 62 (3), 61 (6), 59 (12), 58 (9), 56 (4), 55 (9), 54
(6), 53 (10), 52 (10), 51 (13), 50 (4), 47 (3), 46 (3), 45 (13), 44 (20).
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MASS SPECTRA OF NEW HETEROCYCLES: XII.
39
Table 1. (Contd.).
Comp. no.
m/z (Irel, %)a
XIV
266 (100) [M]+·, 267 (19), 268 (7), 253 (5), 252 (13), 251 (74), 237 (3), 236 (3), 223 (3), 222 (6), 221 (3), 220
(10), 219(57), 217 (6), 209 (3), 208 (15), 207 (13), 206 (15), 205 (13), 195 (11), 194 (7), 193 (17), 192 (43),
189 (3), 181 (8), 180 (27), 179 (22), 178 (11), 177 (7), 176 (4), 175 (8), 174 (4), 173 (4), 167 (3), 166 (11), 165
(19), 164 (43), 163 (11), 162 (15), 161 (7), 160 (3), 159 (3), 155 (3), 154 (30), 152 (9), 151 (15), 150 (14), 149
(15), 148 (9), 147 (16), 146 (6), 145 (4), 139 (4), 138 (15), 137 (11), 136 (21), 135 (5), 134 (5), 133 (11), 132
(6), 131 (7), 130 (3), 125 (3), 124 (5), 123 (5), 122 (9), 121 (4), 120 (5), 119 (5), 118 (5), 117 (3), 111 (6), 110
(4), 109 (5), 108 (4), 107 (5), 106 (7), 105 (6), 104 (26), 96 (14), 95 (7), 94 (6), 93 (4), 92 (9), 91 (7), 90 (5),
89 (5), 87 (8), 86 (4), 85 (3), 84 (7), 83 (4), 82 (6), 81 (5), 80 (6), 79 (9), 78 (6), 77 (14), 75 (3), 74 (3), 72 (9),
71 (5), 70 (14), 69 (6), 68 (5), 67 (5), 66 (8), 65 (16), 64 (3), 63 (4), 61 (5), 59 (5), 58 (8), 57 (4), 56 (4), 55
(5), 54 (4), 53 (6), 52 (4), 51 (8), 49 (7), 47 (4), 46 (4), 45 (30), 44 (18).
a
Given are ion peaks with a relative intensity of no less than 3%.
[M – R3C3H5]+· (G) and [M – R1NH2]+· (H) ions and
[M – R1NH]+ ion (J), which are common for com-
pounds I–III, VI, and VII (Scheme 5, Table 2).
Radical cations G and H are likely to have the struc-
tures of 5-methylsulfanyl-2H-pyrrol-2-imine and
2-methylsulfanyl-1-(prop-2-yn-1-yl)-1H-pyrrole,
respectively.
pounds under electron impact. The subsequent decom-
position of ion C follows two pathways via expulsion
of imine molecule or dialkylamine radical to give,
respectively, [C – R1N=CHR3]+ (possible structures
K–K″) and [C – R1(R3CH2)N]+· ions (possible struc-
tures L–L″) (Scheme 3). Elimination of HCN mole-
cule or HCS radical from the latter yields ions M
[K – HCN]+, N [L – HCN]+·, and O [K – HCS]+·. The
contribution of each of the other common decom-
position channels of [M1]+· to the total ion current is
considerably smaller than that of the channel leading
to ion C; it ranges within 11–51 (D), 7–17 (E), and
3–30% (F) (Schemes 3, 4; Table 2).
Scheme 4.
F
+·
R2
R1
N
SMe
N
The effect of the substituent on the amino nitrogen
atom in pyrroles I–VII on their fragmentation pattern
under electron impact was seen most clearly in the
molecular ion decomposition pathways involving
cleavage of C–N bonds (Scheme 5). In this case, com-
pounds IV and V containing pyrrolidinyl and piperi-
dinyl substituents behaved differently. This is not
R3
E
CH2
[M1]+· (I–VII)
As we already noted, elimination of methyl radical
from the molecular ion to form ion C is the major
primary fragmentation act for all the examined com-
Scheme 5.
+·
R2
SMe
–R1NH2
N
+·
R2
+·
R2
R3
R1
N
R1
–R3C3H5
SMe
H
N
N
SMe
R2
N
R3
[M2]+· (I–III, VI, VII)
G
SMe
R3
–R1NH·
N
J
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 1 2014

KLYBA et al.
40
Table 2. Characteristic ions in the electron impact (70 eV) mass spectra of 5-methylsulfanyl-1-vinyl-1H-pyrrol-2-amines I–VII
m/z (Irel, %)
Ion
I
II
III
IV
V
VI
VII
[M]+·
[M – Me]+, C
[M – MeS]+, D
182 (100)
167 (85)
135 (19)
210 (100)
195 (74)
163 (16)
110 (8)
238 (100)
223 (84)0
191 (16)
138 (11)
154 (16)
168 (6)
208 (66)
193 (100)
161 (11)
108 (7)
124 (30)
000–
222 (56)
207 (77)
175 (11)
122 (11)
138 (3)
000–
258 (100)
243 (93)
211 (51)
158 (14)
098 (4)
222 (100)
207 (96)
175 (35)
122 (17)
098 (4)
[M – C2H3NCSMe]+, E 082 (17)
[M – R2C3SMe]+, F
[M – R3C3H5]+·, G
[M – R1NH2]+·, H
[M – R1NH]+, J
098 (4)
126 (22)
154 (14)
165 (11)
166 (34)
124 (19)
123 (6)
140 (28)
151 (10)
152 (10)
124 (23)
123 (54)
097 (10)
096 (21)
079 (11)
216 (12)
227 (9)
180 (3)
179 (5)
000–
000–
191 (7)
180 (17)
124 (10)
123 (5)
000–
000–
228 (11)
200 (18)
199 (24)
173 (11)
172 (11)
155 (6)
192 (11)
164 (37)
163 (11)
137 (12)
136 (13)
119 (5)
[C – R1N=CHR3]+, K
[C – R1NCH2R3]+·, L
[K – HCN]+, M
[L – HCN]+·, N
[K – HCS]+·, O
124a (30)
123 (5)
097 (13)
096 (23)
079 (22)
124 (20)
123 (8)
097 (10)
096 (21)
079 (17)
097 (8)
000–
096 (22)
079 (34)
096 (9)
079 (15)
a
Coincides with ion F in m/z value.
surprising, taking into account the absence of separate
R1 and R3 substituents in their molecules. Therefore,
no [M – R3C3H5]+·, [M – R1NH2]+·, or [M – R1NH]+ ion
can be formed from fused polycyclic rearranged
molecular ions of IV and V.
peak in the spectra of I–V does not exceed 19%
(Table 2). Presumably, stabilizing effect of these sub-
stituents is determined by the formation of polycyclic
conjugated structures like 1-methyl-1,2,3,4-tetrahydro-
benzo[3′,4′]cyclobuta[1′,2′:4,5]pyrrolo[1,2-a]pyrimi-
din-5-ium (P) and 1,7-dimethyl-1,2,3,4-tetrahydro-
cyclobuta[4,5]pyrrolo[1,2-a]pyrimidin-5-ium (Q) or
1-methyl-1,3,4,8-tetrahydro-2H-cyclopenta[4,5]pyr-
rolo[1,2-a]pyrimidin-5-ium (R) as a result of loss of
methylsulfanyl radical (Scheme 6).
The substituent in the amino group also has an ap-
preciable effect on the stability of all ions observed in
the mass spectra; however, no any distinct relation can
be found (Table 2). The presence of a phenyl or iso-
propenyl substituent on C4 (VI, VII) did not affect the
general fragmentation pattern, but in some cases appre-
ciable stabilization of fragment ions was observed. In
the mass spectra of VI and VII, the [M – MeS]+ ion
peak has the maximum intensity (51 and 35%, respec-
tively), whereas the intensity of the corresponding ion
Like their precursors VIII–XIV [1], chemical
ionization of compounds I–VII using methane as
reactant gas involves protonation and charge exchange
processes. As a result, the molecular ions (Irel 97–
100%) and [M + H]+ ions (Irel 62–100%) are generally
Scheme 6.
Me
R2 = Ph (VI)
+·
N
N
R2
H
Me
P
–MeS·
SMe
N
N
Me
Me
Me
[M2]+· (VI, VII)
R2 = H2C=C(Me) (VII)
N
N
N
N
H
H
Q
R
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MASS SPECTRA OF NEW HETEROCYCLES: XII.
41
Scheme 7.
+·
+·
R2
R2
R2
R1
R1
CH5
R1
[M + H]+
N
SMe
CH2
N
N
–CH4
–MeS·
N
SMe
N
N
R3
R3
CH2
R3
I–V, VII
S
S'
I, m/z 136; II, m/z 164
III, m/z 192; IV, m/z 162
V, VII, m/z 176
Scheme 8.
+·
R2
R2
CH5
R1
N
R1
+
CH4
SMe
N
S
N
N
R3
R3
CH2
[M1]+· (I–V, VII)
CH2
C
most abundant (Table 3). The main fragment ion (S or
S′, Irel 37–95%) is formed via elimination of MeS
radical from protonated molecular ion [M + H]+
(Scheme 7). The [M + C2H5]+ ion generated by elec-
trophilic addition also ejects MeS radical, but the con-
tribution of this fragmentation pathway is relatively
small (Irel 6–11%; Scheme 7).
may be localized on either amine or pyrrole nitrogen
atom. Ions W derived from compounds I and VII have
the same m/z values as those of ions T; in the spectrum
of III, the m/z values of ions U and W coincide with
each other.
The most essential difference of the chemical
ionization mass spectrum of VII from the spectra of
I–V is the presence in the former of a strong ion peak
with m/z 177 (Irel 79%), [M – HCS]+, (Z). Ion Z is
likely to result from rearrangement of the molecular
ion of VII into bicyclic structure [M3]+· with participa-
tion of the methylsulfanyl group and isopropenyl sub-
stituent in position 4 of the pyrrole ring (Scheme 10).
Unlike electron ionization, the formation of
[M – Me]+ ion (Irel 11–14%) under chemical ionization
is not the main fragmentation pathway of pyrroles I–
VII (Scheme 8, Table 3).
Further decomposition of the [M + H – MeS]+ ion
(S) generated from I–III and VII follows the amine
pattern. Expulsion of R1N molecule (as imine) from
ion S gives radical cation T, while elimination of alkyl
radicals or propene (cyclopropane) molecule yields
ions U, W, and Y (Scheme 9). The charge in ions U
The behavior of 1-vinylpyrrol-2-amine VI under
chemical ionization deviates from the general pattern
observed for compounds I–VII. It is characterized by
charge exchange involving the phenyl and methyl-
Table 3. Characteristic ions in the chemical ionization (reactant gas methane) mass spectra of 5-methylsulfanyl-1-vinyl-1H-
pyrrol-2-amines I–V and VII
m/z (Irel, %)
Ion
I
II
III
IV
V
VII
[M]+.
182 (100)
183 (62)
167 (11)
136 (95)
211 (2)
210 (100)
211 (68)
195 (12)
164 (37)
239 (4)
238 (97)
239 (100)
223 (12)
192 (40)
267 (7)
208 (100)
209 (63)
193 (14)
162 (64)
237 (2)
222 (100)
223 (86)
207 (11)
176 (64)
251 (5)
222 (100)
223 (88)
207 (14)
176 (92)
251 (4)
[M + H]+
[M – Me]+, C
[M + N – MeS]+·, S
[M + C2H5]+
[M + C2H5 – MeS]+.
164 (11)
192 (6)
220 (6)
190 (8)
204 (9)
204 (8)
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 1 2014

KLYBA et al.
42
Scheme 9.
+·
R2
R3
–R1N
N
T
m/z (Irel, %): I, 107 (21); II, 121 (14)
III, 135 (5); VII, 147 (18)
R2
R2
R1
R1
+·
+·
R2
R2
N
N
–R3·
N
N
R1
R1
N
N
N
N
U
U'
R3
m/z (Irel, %): I, 135 (5); II, 149 (5)
III, 163 (19); VII, 175 (13)
R3
CH2
S'
S
[S – C2H5]+
I–III, VII
·
–C2H5
W
m/z (Irel, %): I, 107 (21); II, 135 (5)
III, 163 (19); VII, 147 (18)
+·
+·
H
H
N
N
N
N
–C3H6 (III)
Pr
Et
CH2
Y
Y'
m/z 150 (Irel 5%)
Scheme 10.
+·
+·
Me
Me
CH2
SMe
Me
Me
Me
N
S
N
N
N
N
–HCS·
N
CH2
Me
Me
Me
H
CH2
[M1]+· (VII)
CH2
[M3]+·
Z
m/z 177 (Irel 79%)
sulfanyl substituents. Obviously, the formation of the
only fragment ion [M – C4H9N]+· with m/z 187 (as-
sumingly having the structure of 3,5-dihydroisothio-
chromeno[3,4-b]pyrrole) is possible only from rear-
ranged molecular ion [M4]+· with a probable structure
of 11-methyl-4a,8,9,10,11,12b-hexahydro-5H-iso-
thiochromeno[4′,3′:4,5]pyrrolo[1,2-a]pyrimidine
(Scheme 11). By contrast, the precursor of VI,
1-[2-(vinyloxy)ethyl]pyrrol-2-amine XIII, revealed no
specific behavior under chemical ionization, i.e., the
presence of a phenyl group in molecule XIII did not
affect the general fragmentation pattern [1].
To conclude, the fragmentation patterns of the
molecular ions of 5-methylsulfanyl-1-vinyl-1H-pyrrol-
2-amines I–VII under both electron impact and chem-
ical ionization radically differ from the decomposition
pathways of the corresponding 1-[2-(vinyloxy)ethyl]-
pyrrol-2-amines [1]. Electron ionization of I–VII gives
rise to seven ion series. The two major series result
from elimination of Me and MeS radicals from the
molecular ions. The other two series are related to
decomposition of the pyrrole ring. Three more ion
series observed in the mass spectra of I–III, VI, and
VII reflect cleavage of C–N bonds. The nature of the
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 1 2014

MASS SPECTRA OF NEW HETEROCYCLES: XII.
43
Scheme 11.
+·
+·
+·
Ph
Me
Me
S
N
SMe
N
–C4H9N
N
N
Me
S
N
CH2
H
[M1]+·, m/z 258 (100%) (VI)
[M4]+·
m/z 187 (Irel 10%)
substituent on C4 [R2 = H, Ph, H2C=C(Me)] almost
does not affect the fragmentation pattern of I–VII
under electron impact.
Sciences, project no. 8.17) using the facilities of the
Baikal Joint Analytical Center (Siberian Branch,
Russian Academy of Sciences).
Chemical ionization of I–VII is accompanied by
protonation, charge exchange, and electrophilic addi-
tion processes. The major fragment ions are formed
via elimination of MeS radical from [M + H]+ and
[M + C2H5]+ ions and of Me radical from [M1]+ ·.
Unlike electron ionization, the fragmentation pattern
of I–VII under chemical ionization with methane
strongly depends on the nature of the R2 substituent. In
particular, compound VII [R2 = H2C=C(Me)] revealed
an additional fragmentation pathway leading to
[M – HCS]+ ion, and 4-phenyl derivative VI (R2 = Ph)
gave only one fragment ion [M – C4H9N]+·.
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