Decomposition of alkene adducts of thianthrene cation radical in nitrile solvents. Formation of alkyl-2-oxazolines and a new class of four-component products: 5-[(1-alkoxyalkylidene) ammonio]alkylthianthrenium diperchlorates

Article abstract of DOI:10.1021/jo0402125

The monoadducts (4a-d) of thianthrene cation radical perchlorate (1a) and isobutene, 2-methyl-butene, 2-methyl-2-butene, and 2-methylpentene decompose spontaneously in acetonitrile (MeCN) solution, with the formation of thianthrene (Th). Decomposition of 4a (1,2-(5,10-thianthreniumdiyl)-2-methylpropane diperchlorate) and 4a', the corresponding dihexafluorophosphate, was studied in depth and extensively with ¹H and ¹³C NMR spectroscopy. Decomposition of 4a was found to involve the solvent itself as well as water in the solvent, remaining from incomplete drying, and gave, apart from Th, successively, the perchlorate salts of 2,4,4-trimethyl-2-oxazoline (6) and 2-amino-2-methylpropyl acetate (7). These salts, 6-HCIO₄ and 7-HCIO₄, respectively, were prepared and used in understanding the reactions of 4a as well as the relationships among 6, 7, and 2-(acetylamino)-2-methyl propanol (8) in acidified MeCN solution. Decompositions of 4a-d in MeCN and other nitriles (RCN) containing an added alcohol (ROH) led to new products, 5-[(1-alkoxyalkylidene)ammonio]alkylthianthrenium diperchlorates (5a-u). These compounds were identified with ¹H and ¹³C NMR spectroscopy and, in part, with X-ray crystallography and elemental analysis. The mechanisms of formation of 5-7 are discussed.

Full text of DOI:10.1021/jo0402125

Decomposition of Alkene Adducts of Thianthrene Cation Radical
in Nitrile Solvents. Formation of Alkyl-2-oxazolines and a New
Class of Four-Component Products:
5-[(1-Alkoxyalkylidene)ammonio]alkylthianthrenium
Diperchlorates
Henry J. Shine,*,† Bing-Jun Zhao,† John N. Marx,† Teyeb Ould-Ely,‡ and
Kenton H. Whitmire‡
Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, and
Department of Chemistry, Rice University, Houston, Texas 77005
henry.shine@ttu.edu
Received June 7, 2004
The monoadducts (4a-d) of thianthrene cation radical perchlorate (1a) and isobutene, 2-methyl-
butene, 2-methyl-2-butene, and 2-methylpentene decompose spontaneously in acetonitrile (MeCN)
solution, with the formation of thianthrene (Th). Decomposition of 4a (1,2-(5,10-thianthreniumdiyl)-
2-methylpropane diperchlorate) and 4a′, the corresponding dihexafluorophosphate, was studied in
depth and extensively with 1H and 13C NMR spectroscopy. Decomposition of 4a was found to involve
the solvent itself as well as water in the solvent, remaining from incomplete drying, and gave,
apart from Th, successively, the perchlorate salts of 2,4,4-trimethyl-2-oxazoline (6) and 2-amino-
2-methylpropyl acetate (7). These salts, 6-HClO4 and 7-HClO4, respectively, were prepared and
used in understanding the reactions of 4a as well as the relationships among 6, 7, and
2-(acetylamino)-2-methyl propanol (8) in acidified MeCN solution. Decompositions of 4a-d in MeCN
and other nitriles (RCN) containing an added alcohol (R′OH) led to new products, 5-[(1-
alkoxyalkylidene)ammonio]alkylthianthrenium diperchlorates (5a-u). These compounds were
identified with 1H and 13C NMR spectroscopy and, in part, with X-ray crystallography and elemental
analysis. The mechanisms of formation of 5-7 are discussed.
SCHEME 1
Introduction
Salts of thianthrene cation radical (Th•+X-, 1), X-
)
ClO4-, PF6-, BF4-, SbF6-, add to cycloalkenes and alkenes
(2) to form bis- (3) and monoadducts (4). The additions
are stereospecific, in which, as far as alkenes are con-
cerned, the geometry of the alkene is retained.1-3 This is
illustrated with Scheme 1. The addition reactions are
carried out in dry acetonitrile (MeCN) solution, from
which the adducts are precipitated with ether.
When we began our work on addition of 1a (X-
)
ClO4-) to isobutene, we used isobutene that, unknown
to us, was contaminated in its cylinder with methanol.
Consequently, reaction with 1a led not only to a monoad-
duct (4a) but also, serendipitously, to a second product
that was shown with X-ray crystallography and elemen-
tal analysis to be a new compound, 5-[2-[(1-methoxyeth-
ylidene)ammonio]-2-methylpropyl]thianthrenium diper-
chlorate (5a). As far as we know, this class of compounds
† Texas Tech University.
‡ Rice University.
(1) Lee, W. K.; Liu, B.; Park, C. W.; Shine, H. J.; Guzman-Jimenez,
I. Y.; Whitmire, K. H. J. Org. Chem. 1999, 64, 9206-9210.
(2) Qian, D.-Q.; Shine, H. J.; Guzman-Jimenez, I. Y.; Thurston, J.
H.; Whitmire, K. H. J. Org. Chem. 2002, 67, 4030-4039.
(3) Shine, H. J.; Zhao, B.-J.; Qian, D.-Q.; Marx, J. N.; Guzman-
Jimenez, I. Y.; Thurston, J. H.; Ould-Ely, T.; Whitmire, K. H. J. Org.
Chem. 2003, 68, 8910-8917.
has not been reported before. Identification of 5a led us
to an extensive study of reactions of 1a with alkenes in
nitrile solvents (RCN) containing small amounts of a
deliberately added alcohol (R′OH). We found that suc-
10.1021/jo0402125 CCC: $27.50 © 2004 American Chemical Society
Published on Web 12/02/2004
J. Org. Chem. 2004, 69, 9255-9261
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Shine et al.
TABLE 1. Products 5a-u
cessful reactions were limited to branched alkenes con-
taining small alkyl groups, i.e., isobutene, 2-methyl-
butene, 2-methyl-2-butene, and 2-methylpentene. We
found also that isolated monoadducts of these alkenes
reacted with R′OH in RCN to give compounds 5. These
results led us in turn to study the spontaneous decom-
position of monoadducts in nitrile solvents, illustrated
here with the use of 4a in MeCN. We found that this
decomposition gave successively 2,4,4-trimethyl-2-oxazo-
line (6) and 2-amino-2-methylpropyl acetate (7), each in
its protonated form. This finding caused us to study the
reactions of 6 itself in MeCN containing an equivalent
amount of HClO4 and also the relationships among 6, 7,
and 2-(acetylamino)-2-methylpropanol (8) that affected
our work with 4a. We now explain how 6 and 7 are
formed from 4a and how their formation is diverted in
part into formation of 5 when R′OH is present.
compounda
A
B
C
D
R
R′
yield (%)b methodc
5a
5a
5b
5c
5d
5e
5f
Me
H
H
Me Me Me
30
23
25
20
13
24
9
2
1
2
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
1
Me Et
Me Pr
Me i-Pr
Me Bu
Me cC6
Et Me
Pr Me
d
5g
5h
5i
14
5
Me
H
H
H
H
Et Me Me
Me Et
10
15
15
6
5j
5k
5l
Me Pr
Results
Me i-Pr
Me Bu
5m
5n
5o
5p
5q
5r
5s
5t
7
Preparations of 5a-u. Two methods of preparing
these compounds were used: the addition of 1a to an
alkene in RCN containing R′OH (method 1) and the
decomposition of a monoadduct (4) in RCN containing
R′OH (method 2). The alkenes (or their monoadducts)
that could be used were limited by structure to isobutene,
2-methylbutene, 2-methyl-2-butene, and 2-methylpen-
tene. Other alkenes, such as cis-2-butene and trans-3-
hexene and their monoadducts, 2-ethylbutene and (E)-
and (Z)-3-methyl-2-pentene, failed to give 5. Instead, the
cis-2-butene and trans-3-hexene had stable adducts,
while adduct formation was not obtained with the more
branched alkenes. Both methods 1 and 2 gave only small
yields of 5, from 5 to 30%. Method 1 was best used with
isobutene and 2-methylbutene. It gave very poor yields
with 2-methyl-2-butene, so that products corresponding
with this alkene (5o-t) were prepared with method 2.
The reason for the very poor yields of 5o-t when using
method 1 is not known. 2-Methyl-2-butene was available
only as a 2 M solution in tetrahydrofuran (THF). Pos-
sibly, therefore, the sequence of reactions that led to
compounds 5 was affected by the change in solvent from
MeCN to a mixture of MeCN and THF; however, the
effect of solvent in general on preparing 5 was not
explored.
Methanol, ethanol, propanol, isopropyl alcohol, butanol,
and cyclohexanol were used successfully, whereas tert-
butyl alcohol failed to give 5. In method 1, the amount
of alcohol used had to be small in comparison with the
amount of alkene to avoid competitive reaction of the
alcohol with 1a. Therefore, the concentration of methanol
in the first-used, contaminated supply of isobutene was
measured and approximately that concentration was
used in all other reactions. Use of equal amounts of
methanol and isobutene in the reaction with 1a in MeCN
gave, in fact, only the known4 5-methoxythianthrenium
perchlorate.
Et Me
6
Me Me
Me Me Me
Me Et
6
12
12
10
9
Me Pr
Me i-Pr
Me Bu
Et Me
8
15
5u
Me
H
Pr Me Me
a Series 5a-h corresponds with isobutene; series 5i-n with
2-methyl-1-butene; series 5o-t with 2-methyl-2-butene; 5u with
2-methyl-1-pentene. b Amount of 1a that was converted into 5.c In
-
method 1, reaction of Th•+ClO4 with alkene in RCN containing
R′OH; in method 2, reaction of monoadduct with R′OH in RCN.
d Cyclohexyl.
a reaction mixture overnight at room temperature, most
of the monoadducts decomposed, leaving only the corre-
sponding 5 to be precipitated by adding ether. In that
way, tedious fractional precipitation could be avoided.
This technique was used for preparing 5a (run 2),c,d,f,i-
n. In using method 2 for preparing 5o-u, we again
continued stirring overnight at room temperature to
ensure loss of all of the monoadduct before precipitating
the 5. Method 2 was also used for preparing 5a (run 1)
and 5b.
For the most part, MeCN was the solvent. Propionitrile
(EtCN) was used to prepare 5g,n,t, while butyronitrile
was used for 5h.
In all, therefore, 21 members of this new class of
compounds were isolated. They are listed in Table 1. All
1
were characterized with H, 13C, and DEPT NMR spec-
troscopy in a 500 MHz spectrometer. We were able to
grow single crystals of 15 compounds (5a-c,e-g,i-l,
n-r) for X-ray crystallography (Figures S1-S15). Two
(5a,g) had satisfactory elemental analyses. Analyses of
other 5 products were not sought.
Decomposition of Monoadducts (4) in RCN. For-
mation of 6-H+ and 7-H+. In the absence of added R′OH,
4a-d decomposed in MeCN solution with the formation
of thianthrene (Th). We used 4a and 4a′ (X- ) PF6-) as
models for studying this decomposition, which was fol-
lowed mainly with NMR spectroscopy, including DEPT.
The NMR spectrum of 4a in CD3CN, for example,
changed completely during a period of 5 days. The
When method 1 was used with ice-cold solutions of
reactants, mixtures of 4 and 5 were obtained, from which
it was necessary to separate 5 with fractional precipita-
tion from MeCN solution by adding ether. This technique
was used for preparing 5e,g,h. We found that by stirring
1
(4) Zhao, W.; Shine, H. J. Can. J. Chem. 1998, 76, 695-702.
9256 J. Org. Chem., Vol. 69, No. 26, 2004
aromatic H signals of 4a were replaced with the two

Formation of Alkyl-2-oxazolines
1
characteristic dd of Th, while the alkyl signals were
CD3CN. Within 20 h, the initial H spectrum of δ 4.56,
replaced with two singlets at δ 4.67 (2H) and 1.50 (6H)
2.22, and 1.35 ppm had changed almost completely into
δ 4.00, 2.02, and 1.25 ppm. The change was complete
after 66 h, at which time the 13C spectrum showed δ 173
(-CdO), 68.1 (CH2), 53.0 (quat), 21.3 (2 CH3), and 19.5
1
ppm. 13C peaks related to the new H spectrum, apart
from those from Th, characterized with DEPT, were at δ
182.0, 85.2 (CH2), 64.2 (quaternary), and 26.4 (CH3) ppm.
The data are consistent with the loss of 4a and the
formation of protonated 6 (6-H+), the group on C-2 of 6
being CD3 rather than CH3.
1
(CH3) ppm. The H spectrum was indentical with that
reported for 7-HCl.5
Reaction of 2-(Acetylamino)-2-methylpropanol (8)
in CD3CN/HClO4. Addition of HClO4 to a solution of 8
An analogous experiment was carried out on a larger
scale with 4a′ in MeCN. The solution was kept for 25
days after which the Th was removed from the recovered
products by washing with ether. The remaining product,
1
in CD3CN caused an immediate shift in H NMR peaks
to δ 3.67 (CH2), 2.28 (CH3), and 1.35 (2 CH3) ppm. The
intensities of these peaks decreased over a period of 10
days, at which point they were too small to be integrated.
During this period, peaks attributable to 6-H+ and 7-H+
appeared, those for 6-H+ being dominant at all times.
a sticky solid, was deduced to be the PF6 salt of 6-H+.
-
That is, the 1H NMR spectrum consisted of three singlets
at δ 4.64 (CH2), 2.33 (CH3), and 1.49 (2 CH3) ppm. This
product was kept in CD3CN for an additional 5 days, after
which new signals appeared, accompanying the earlier
signals, at 4.03 (CH2), 2.08 (CH3), and 1.35 (2 CH3) ppm.
The 13C spectrum at this stage consisted of two sets of
five peaks, the larger set at 177.9, 85.0, 64.2, 26.4, and
14.4 ppm and the smaller set at 171.3, 68.6, 56.3, 22.8,
and 20.8 ppm. The two sets of 1H and 13C peaks are
consistent with the formation of 6-H+ and, subsequently,
7-H+.
Discussion
Decomposition of 4: A. Formation of 5. The
chemistry that we report here originates in the instability
of selected monoadducts in MeCN solution. The instabil-
ity of such a monoadduct is detectable when the monoad-
duct is used directly (method 2) and when it is formed in
situ in method 1. The instability of 4c was reported
briefly earlier3 but was not followed further. Among the
others with which we are now concerned, 4a was suf-
Preparation of 6-HClO4. Crystalline 6-HClO4, mp
118-121 °C, was isolated with silica gel chromatography
of a solution of 6 in 70% HClO4. Its NMR spectra were
recorded in CD3CN and in D2O, and these data were used
in understanding the behavior of 4a in CH3CN. The
changes that occurred in 6, itself, when its solutions in
CD3CN and D2O were acidified with HClO4 were also
used in understanding the behavior of 4a.
Preparation of 7-HClO4. Crystalline 7-HClO4, mp
117-118 °C, was isolated after complete conversion of
6-H+ into 7-H+ in D2O. Its NMR spectra, recorded in
CD3CN and in D2O were used along with those of
6-HClO4 in understanding the behavior of 4a. However,
when a solution of 7-HClO4 in D2O was neutralized with
solid NaOH, 7 was not formed. Instead, the solution’s
NMR spectrum was consistent only with the formation
of 8.
1
ficiently stable in CD3CN to allow reliable H and 13C
NMR spectra to be recorded, 4b was too unstable for
time-consuming acquisition of 13C NMR data and for
preparing 5 in reasonable yields, and 4c was usable for
recording its 1H NMR spectrum and for preparing 5o-t;
preparation of 4d was not attempted. The formation of
5a, discovered serendipitously with 4a, prompted us to
ask what happens to monoadducts that decompose in
MeCN in the absence of R′OH. Therefore, the discussion
that follows is largely concerned with that decomposition,
which, when understood clearly, showed also how de-
composition was divertible in part to 5 by adding R′OH
to the solution. Decomposition of only 4a was studied in
depth, to serve as a model. We have not studied the
analogous decompositions of 4b,c in the absence or RO′H
but regard them as being similar to that of 4a, the link
being that the decompositions of all four monoadducts
(4a-d) in the presence of RO′H have a common pathway,
leading to 5.
Reaction of 6 in CD3CN/HClO4. When a solution of
6 in CD3CN was acidified with an equimolar amount of
HClO4, the 1H and 13C NMR spectra of 6 changed quickly.
1
The H spectrum consisted of two sets of three singlets,
There are several striking features in the reactions that
lead to compounds 5. First, the alkenes from which 5 can
be obtained, and whose monoadducts (4) can lead to 5,
have two alkyl groups on C-2 (4a,b,d) or C-3 (4c). Second,
the first product detectable with NMR spectroscopy in
the decomposition of 4a in the absence of R′OH was the
d3-analogue of protonated 2,4,4-trimethyl-2-oxazoline (6-
H+). That is, the C-2 of the former alkene (isobutene) was
now bonded to the N atom of the solvent CD3CN.
Similarly, the final product of decomposition of a com-
pound 4 in RCN containing R′OH is 5, in which the C-2
(C-3) of a former alkene is again bonded to the solvent’s
N atom. Third, in the decomposition of 4, the thi-
anthrenium group is converted into thianthrene (Th);
that is, it is reduced.
the larger set at δ 4.64, 2.33, and 1.48 ppm and the
smaller set at δ 4.03, 2.08, 1.36 ppm. Each set integrated
for proton ratios of 2:3:6. The intensities of the larger
set decreased with time, while those of the smaller set
increased. This change was followed at 300 MHz. The
ratio of peak intensities was 1/1 after 1 day and 1/5 after
16 days. The initial effect of HClO4 on 6 was also seen in
its 13C NMR spectrum, divisible with the aid of DEPT
and HMQC into two sets of five peaks. The larger set
and its associated proton signals had δ 177.6, 84.9 (4.64),
64.3, 26.5 (1.48), and 14.5 (2.33) ppm, while the
smaller set had δ 171.2, 68.5 (4.03), 56.7, 22.8 (1.36), and
1
20.8 (2.08 ppm). The two sets of H and 13C data are
attributable to 6-H+ and 7-H+.
The solvent CD3CN was evaporated from this solution
and replaced with D2O. The 1H NMR spectrum was now
identical with that when starting with 6 in D2O/HClO4.
Reaction of 6 in D2O/HClO4. The effect of HClO4 on
6 in D2O was analogous to but much faster than that in
These features suggest that the first step in the
decomposition of 4 is the opening of the bond between
(5) Kaminski, J. J.; Bodor, N.; Higuchi, T. J. Pharm. Sci. 1976, 65,
1733-1736.
J. Org. Chem, Vol. 69, No. 26, 2004 9257

Shine et al.
SCHEME 2
and reclosing would be detectable in a monoadduct whose
configuration would change thereby. That is, an erythro
adduct could be changed into a threo adduct, and vice
versa. Unfortunately, that criterion cannot be applied to
4a-d, whose configuration would not be changed by bond
opening and reclosing. Adducts of cis-2-butene and trans-
3-hexene, which we have made earlier,3 would serve as
tests for bond opening and reclosing, but they did not
undergo the reactions now reported. Reactions of cis-2-
butene and trans-3-hexene with 1a′ in MeCN containing
MeOH gave only the monoadducts and none of 5. At-
tempts to make testable adducts of other suitable alkenes
such as (E)- and (Z)-3-methyl-2-pentene failed. Thus, we
are not able to say now if bond opening is reversible.
B. Role of 6 and 7. The conversion of 2-substituted-
2-oxazolines into esters of amino alcohols in acidic
solution is reported in the older6 and more recent
literature.7-10 These reports have guided us in deducing
the behavior of 4a in MeCN. To confirm the literature’s
guidance, we studied the chemistry of 6 in acid solutions
and its conversion in such solutions into 7. Thereby, we
have been able to characterize authentic 6-H+ in CD3CN.
Similarly, having been able to convert 6-HClO4 com-
pletely into 7-HClO4, we were able to isolate the latter
and characterize authentic 7-H+ in CD3CN, too. In these
ways, we have been able to confirm our deductions
(Schemes 2 and 3) about the decomposition of 4a in
MeCN, monitored with NMR spectroscopy in CD3CN. The
work with 4a serves as a model for the decomposition of
the other monoadducts (4b-d) and for understanding
how, in the presence of R′OH, they were converted into
their corresponding four-component adducts (5).
SCHEME 3
Our searches of the literature have failed to find the
isolation and characterization of 7 itself. The preparation,
but not isolation and characterization, of 7 by transes-
terification of 2-amino-2-methylpropanol with ethyl 2-(2,4-
dinitrophenyl)aceto acetate (12) has been reported re-
cently.11 We tried to prepare 7 by that method, but in
our hands, the reaction gave only a mixture of 6 and 8.
This was shown with column chromatography of products
formed in CHCl3 and also by following the reaction in
CDCl3 with NMR spectroscopy rather than with isolation.
The possibility that, in our hands, 7 had been formed and
had rearranged immediately into 8 cannot be ruled out;
but we found that tert-butylamine, used as a model, was
acetylated when heated with 12 in CDCl3, so that by
analogy direct N-acetylation of 2-amino-2-methylpro-
panol by 12 may also have occurred. Earlier reports on
the relationships between 2-oxazolines and the corre-
sponding esters of amino alcohols show that the esters
are stable in acidic solution but isomerize easily into
isomeric acylamino alcohols as the pH of the solution is
increased.7,8,10 Thus, it may be questionable that 7 itself
was prepared as reported.11
the geminally substituted C atom and the sulfur atom.
This is shown with 4a decomposing in MeCN (Scheme
2). The driving force for bond opening is the formation
of the tertiary cation (9). Once formed, that reacts with
the most available nucleophile present, the solvent,
giving 10. Direct attack of MeCN on 4a does not occur,
for if that were to occur, the position of attack should be
the former alkene’s C-1 carbon atom. If that mode of
attack were to occur, furthermore, the same reaction
should be expected of monoadducts of all unsubstituted
alkenes; instead, they are stable to storage in MeCN.
In the presence of R′OH, 10 leads directly to 5. In the
absence of R′OH, 10 can react with the small amount of
water in the incompletely dried solvent, forming 11. We
have seen no evidence in the NMR spectra, recorded
while reactions are occurring in CD3CN, that can be tied
to the presence of 11 in solution. Consequently, it appears
that once formed, 11 quickly cyclizes into 6-H+, a reaction
(Scheme 3) that displaces (and thus reduces) the thian-
threnium group. Subsequently, 6-H+ reacts slowly with
residual water in solution to give 7-H+ (Scheme 3).
We do not know if the bond opening that gives 9
(Scheme 2) is reversible. That would be an interesting
development in our work, because we have stressed in
earlier reports that the configuration of alkenes is
retained when monoadducts are formed.1-3 Bond opening
(6) Gabriel, S.; Heymann, Th. Chem. Ber. 1890, 23, 2493-2502.
(7) Phillips, A. P.; Baltzly, R. J. Am. Chem. Soc. 1947, 69, 200-
204.
(8) Porter, G. R.; Rydon, H. N.; Schofield, J. A. J. Chem. Soc. 1960,
2686-2690.
(9) Meyers, A. I.; Temple, D. L., Jr. J. Am. Chem. Soc. 1970, 92,
6646-6647.
(10) Sylvestre, J.; Papantoniou, C. Compt. Rend. 1965, 260, 1440-
1441.
(11) Nishiwaki, N.; Nishida, D.; Ohnishi, T.; Hidaka, F.; Satoru, S.;
Tamura, M.; Hori, K.; Tohda, Y.; Ariga, M. J. Org. Chem. 2003, 68,
8650-8656.
9258 J. Org. Chem., Vol. 69, No. 26, 2004

Formation of Alkyl-2-oxazolines
SCHEME 4
In 5a-h, the methylene protons on C-1 and the methyl
groups on C-2 of the alkyl chain are singlets. In 5i-n,
the methylene protons on C-1 are no longer equivalent,
as reflected in two 1H d with J ) 14-15 Hz. Similarly,
the methylene protons on C-3 show inequivalence in the
two sets of 1H dq, with J ) 14.5-15 and 7.0-7.5 Hz.
The two methyl groups on C-3 of 5o-t appear as separate
singlets. Inequivalence is also revealed within the
(alkylidene)ammonio groups of 5i-u, where, for example,
the -CH2O proton signals appear as two dq or two dt,
depending on the alkyl group attached to the CH2.
Finally, the yields of 5 (Table 1) are quite small. It is
probable that formation of 5 competes poorly with the
other routes of decomposition of 4. We have made no
efforts to optimize yields of 5.
The preparation and isolation of 7-HCl have been
described in detail,5 however, and NMR results in D2O
were given. Our data for 7-HClO4, recovered from
CD3CN and placed in D2O, are in perfect agreement with
those for 7-HCl. Furthermore, the NMR data for
7-HClO4, obtained by conversion of 6 in D2O, agree with
these results. Isomerization of 7 into 8 apparently
occurred when we attempted to neutralize 7-HClO4.
C. Role of 8. At one time, we considered also that
2-acetylamino-2-methylpropanol (8), possibly derived
from 11 (as 8-H+) by reaction with water in the solvent
(Scheme 4), may have been the source of 6-H+ in the
decomposition of 4a in MeCN. We found, indeed, that 8
was converted into 6-H+, but only very slowly, when
HClO4 was added to its solution in CD3CN. Over a period
of 10 days, the signals from 8-H+ decreased until they
were no longer measurable. The solution then contained
6-H+ and a smaller amount of 7-H+. However, in none of
the experiments in which we followed the decomposition
of 4a in CD3CN with NMR spectroscopy were we able to
detect peaks attributable to 8-H+. Had 8-H+ been formed
from 11 (Scheme 4), its slow conversion into 6-H+ and
7-H+ should have made it detectable. Instead, the first
signals to appear in the decomposition of 4a were those
of 6-H+. Consequently, 8 was not a participant in the
decomposition of 4a.
Structures of 5. The Ortep diagrams (Figures S1-
S15, Supporting Information) leave no question as to the
structures of these new compounds. Further, in each of
these diagrams, it can be seen that the H atom attached
to N and the adjacent R′O group (attached to C) have
the anti configuration on the CdN bond. That configu-
ration diagnoses the trans addition of R′OH to the C-N
triple bond of 10 (Scheme 2).
The NMR spectra (Supporting Information) reveal
patterns of structure among the three major groups of
5, even in solution. The three major groups are 5a-h
(from isobutene), 5i-n (from 2-methylbutene), and 5o-t
(from 2-methyl-2-butene). The aromatic proton signals
in 5a-h are typical of a symmetrically placed thianthe-
nium (Th+) group,3 consisting of two dd (the 1,9- and 4,6-
protons) and two td (the 2, 8- and 3, 7-protons), each
multiplet representing 2H with J values of about 8.0 and
1.5 Hz. The aromatic 13C signals complement this indica-
tion of symmetry, there being mainly six peaks per
spectrum. In contrast, the aromatic proton spectra of
most of 5i-n and, more markedly, 5o-t, show signals
from eight individual H atoms in four sets of dd and four
sets of td. That is, the 1,9- and 4,6-protons, etc., are no
longer equivalent. Correspondingly, the aromatic 13C
spectra of these compounds show mainly 12 peaks.
The spectral characteristics of the alkyl portions of the
three groups of 5 also reflect differences in symmetry.
Experimental Section
Thianthrene cation radical perchlorate (1a) was used for
almost all of the present work. Therefore, all of the new
compounds 5 that are reported are diperchlorates. 1a is the
easiest thianthrenium salt to prepare in reproducible yields,
but it is temperamental toward explosion.12 We have used it
for many years without trouble, only to have it explode
occasionally without apparent reason. It has been prepared
also by other workers many years ago and none of them has
reported having had trouble with it. We have now abandoned
-
its use in favor of Th•+PF6 (1a′).
Preparation of 1a′. To get reliable yields of 1a′ in reaction
of Th with NOPF6, it was found necessary to remove NO as it
was formed. Th (2.1 g, 9.7 mmol) and NOPF6 (1.9 g, 10.6 mmol)
were placed side by side under argon in a 500 mL flask capped
with a septum, through which 60 mL of dry MeCN was
injected. Argon was bubbled through the solution, while it was
stirred for 2 h. The solution was then cooled in ice, and 250
mL of dry ether was added in portions. The dark blue
precipitate was removed, washed with dry ether and dried
under vacuum to give 2.7 g (7.5 mmol, 76%) of 1a′.
2-Acetylamino-2-methylpropanol (8). Prepared as de-
scribed, mp 87-87.5 °C; lit. mp 87.5-88 °C.13 NMR (CD3CN),
1
δ (J), H: 6.64, br s, 1H; 4.52 (6.0), t, 1H; 3.45 (5.5), d, 2H;
1.85, s, 3H; 1.21, s, 6H. 13C: 172.5 (-CdO), 71.0 (CH2), 56.9
(quat), 25.0 (2 CH3), 24.4 (CH3). 1H NMR (D2O), δ: 3.47, s,
2H; 1.78, s, 3H; 1.08, s, 6H.
Preparations of 4: A. 4a. 1a (319 mg, 1.01 mmol) and 4
mL of MeCN were placed in a septum-capped flask that had
been flushed with argon. The flask was cooled in ice, and into
it was injected a cold solution of 343 mg (6.1 mmol) of isobutene
in 4 mL of MeCN. After the mixture was stirred for 40 min,
the color of 1a had faded. Dry ether (60 mL) was added
dropwise, causing precipitation of a white solid. Filtration and
washing with ether gave 151 mg (0.32 mmol, 63%) of product,
shown with NMR spectroscopy to be 4a, mp 118-118.5 °C
(dec). GC of the filtrate gave 0.616 mmol (61%) of Th. NMR
(CD3CN), δ (J), 1H: 8.59, m, 4H; 8.17 (7.6, 1.7), td, 2H
overlapping 8.15 (7.6, 1.7), td, 2H; 4.01, s, 2H; 1.63, s, 6H.
13C: 137.0, 136.9, 136.7, 136.4, 124.7, 123.4, 65.1, 48.0, 26.7.
4a′. A similar procedure with 704 mg (1.95 mmol) of 1a′
and 1.5 g (27 mmol) of isobutene gave 315 mg (0.560 mmol,
58%) of 4a′.
B. 4b (129 mg, 0.27 mmol, 40%), mp 88-89 °C (dec), was
obtained from reaction of 358 mg (1.14 mmol) of 1a with 0.7
mL (6.5 mmol) of 2-methylbutene. Attempts to purify 4b by
1
reprecipitation caused its decomposition. H NMR (CD3CN),
300 MHz, δ (J): 8.61-8.56, m, 4H; 8.19-8.14, m, 4H; 3.96
(1.5), d, 2H; 1.87-1.63, m, 2H; 1.54, s, 3H; 1.12 (7.4), t, 3H.
(12) Murata, Y.; Shine, H. J. J. Org. Chem. 1969, 34, 3368-3372.
(13) Handrick, G. R.; Atkinson, E. R.; Granchelli, F. E.; Bruni, R.
J. J. Med. Chem. 1965, 8, 762-766.
J. Org. Chem, Vol. 69, No. 26, 2004 9259

Shine et al.
C. 4c. To a suspension of 416 mg (1.32 mmol) of 1a in 5 mL
of MeCN cooled in ice was added 4 mL of a 2 M solution of
2-methy-2-butene in THF. Reaction was fast. Addition of 80
mL of ether and washing of the filtered product with ether
gave 174 mg (0.358 mmol, 54%) of 4c, mp 103-105 °C (dec).
Although quite unstable in MeCN,3 4c was able to be used to
prepare 5o-t. We were also able to record its 1H NMR
(CD3CN) spectrum, the aromatic portion of which, however,
was poorly resolved; δ (J): 8.67-8.65, m, 1H; 8.63-8.57, m,
3H; 8.21-8.17, m, 4H; 4.20 (7.0), q, 1H; 1.68, s, 3H; 1.58 (7.5),
d, 3H; 1.47, s, 3H.
ether to remove Th, leaving a sticky solid whose NMR
spectrum consisted of four major peaks, divisible with integra-
tion into two sets of two peaks, namely, δ: 4.67 and 1.50 ppm
and 4.02 and 1.46 ppm. The solid was placed on a column of
silica gel, which was eluted with petroleum ether/dichlo-
romethane to remove remaining Th and next with ethyl
acetate to give a sticky solid whose NMR spectrum was
consistent with the formation of 2-(d3-acetylamino)-2-methyl-
1
propanol, namely: δ H 6.41, br s, 1H; 4.53, br s, 1H; 3.43, s,
2H; 1.18, s, 6H and δ 13C 172.5 (-CdO), 70.2 (CH2), 56.3
(quat), 24.3 (2 CH3) ppm.
Preparation of 5 (Method 2). An example is given with
5a, 5-[2-[(1-methoxyethylidene)ammonio]-2-methylpropyl]-
thianthrenium diperchlorate. 4a (89 mg, 0.19 mmol) was
placed in a three-necked, septum-capped flask that had been
flushed with argon. Dried MeCN (10 mL) was injected through
the septum, followed by 0.10 mL (2.5 mmol) of MeOH. The
mixture was stirred at room temperature for 24 h, and the
solvent was removed with a current of air. The residue was
shown with NMR spectroscopy not to contain 4a. The residue
was dissolved in MeCN, and ether was added to precipitate
30 mg (0.055 mmol, 30%) of 5a. Reprecipitation and drying
gave 5a, mp 164-165 °C (dec). Anal. Calcd for C19H23NO9-
Cl2S2: C, 41.9; H, 4.23; N, 2.57; Cl, 13.1; S, 11.8. Found: C,
42.2; H, 4.35; N, 2.62; Cl, 13.7; S, 11.6. NMR (CD3CN), δ (J),
1H: 9.33, br s, 1H; 8.25 (8.0, 1.5), dd, 2H; 8.06 (8.0, 1.0), dd,
2H; 7.90 (7.6, 1.2), td, 2H; 7.80 (7.8, 1.2), td, 2H; 4.22, s, 2H;
4.12, s, 3H; 2.23, S, 3H; 1.59, S, 6H. 13C: 181.6, 137.5, 136.2,
135.0, 131.3, 131.2, 118.2, 63.1, 59.0, 48.1, 26.4, 18.9.
Preparation of 5a (Method 1). A suspension of 406 mg
(1.28 mmol) of 1a in 5 mL of MeCN was cooled in ice. A cold
solution of 1.04 g (18.6 mmol) of isobutene and 0.15 mL(3.7
mmol) of MeOH in 5 mL of MeCN was added to the suspension
of 1a. The mixture was stirred for 1 h at 0 °C and at room
temperature overnight. Addition of 60 mL of dry ether gave
80 mg (0.147 mmol, 23%) of a white solid, shown with NMR
spectroscopy to be 5a.
Preparation of 5g (Method 1). A similar experiment with
378 mg (1.20 mmol) of 1a in EtCN and with stirring only at 0
°C for 1 h gave a mixture of 4a and 5g in a 4/1 ratio. This
mixture was redissolved in MeCN, to which ether was added
dropwise to precipitate first 115 mg of 4a and then 22 mg
(0.039 mmol, 7%) of 5g, mp 148-149 °C (dec). Anal. Calcd for
C20H25NO9Cl2S2: C, 43.0; H, 4.48; N, 2.51; Cl, 12.7; S, 11.5.
Found: C, 42.8; H, 4.53; N, 2.37; Cl, 13.1; S, 11.1. NMR
(CD3CN), δ (J), 1H: 8.94, br s, 1H; 8.19 (8.0, 1.5), dd, 2H; 8.02
(8.0, 1.0), dd, 2H; 7.86 (7.8, 1.0), td, 2H; 7.75 (7.6, 1.2), td, 2H;
4.18, s, 2H; 4.14, s, 3H; 2.51 (7.5), q, 2H; 1.55, s, 6H; 1.17 (7.5),
t, 3H. 13C: 184.9, 137.5, 136.2, 135.0, 131.8, 131.3, 62.9, 59.4,
48.6, 26.5, 25.6, 9.75.
All other 5 products were prepared by one of these methods.
Each of the products 5i-n from 2-methylbutene, when first
precipitated, was found with NMR spectroscopy to contain a
small amount of the corresponding product (5o-t), from
2-methyl-2-butene. For example, 5i contained some 5o, and
5j contained some 5p. Each of 5i-n was freed of its contami-
nant by reprecipitation and crystallization. The cause of the
contamination of series 5i-n by series 5o-t was traced to
isomerization of 2-methybutene to 2-methyl-2-butene during
reaction by method 1, and not, as was first feared, from
contamination of our 2-methylbutene by 2-methyl-2-butene.
Isomerization of the former alkene into the latter by HClO4
in MeCN was shown to occur independently. NMR data and
melting points of 5 are listed in Supporting Information.
B. 4a′ in MeCN. A solution of 315 mg (0.560 mmol) of 4a′
in 25 mL of MeCN was kept for 25 days at room temperature.
The solvent was removed with a current of air, and the residue
was washed with ether to remove Th, leaving a sticky solid
whose 1H and 13C NMR spectra were divisible into two sets of
peaks consistent with the presence of 6-H+ and 7-H+. That is,
for 6-H+: δ 1H 4.64, 2.34, 1.49 and δ 13C 177.9, 85.0, 64.2, 26.4,
14.4 ppm. For 7-H+: δ 1H 4.03, 2.08, 1.35 and δ 13C 171.3,
68.6, 56.3, 22.8, 20.8 ppm. The 1H NMR spectra now show the
presence of the methyl group from solvent MeCN, differing
from spectra of reaction in CD3CN.
Reaction of 6 in CD3CN/HClO4. The NMR spectra of a
solution of 6 in CD3CN were recorded at 500 MHz. δ 1H: 3.85,
s, 2H; 1.83, s, 3H; 1.16, s, 6H. δ 13C: 162.9, 79.6, 68.0, 28.6,
14.0. After addition of an equimolar amount of HClO4, the
spectra were recorded again, including DEPT, HQMC, and
HMBC. Two groups of peaks were discernible. The larger
group (6-H+) had δ 1H 4.64, s, 2H; 2.33, s, 3H; 1.48, s, 6H and
δ
13C 177.6, 84.9, 64.3, 26.5, 15.0 ppm. The smaller group (7-
H+) had δ 1H 4.03, s, 0.26H; 2.08, s, 0.28H; 1.36, s, 0.55H and
δ 13C 171.2, 68.5, 56.6, 22.8, and 20.8 ppm. The NMR spectra
were then recorded at 300 MHz over a period of 16 days,
during which time the ratio of peaks 7-H+/6-H+ increased as
follows: 0.1 (1 day), 1.0 (5 days), 2.0 (9 days), 3.3 (12 days),
and 5.5 (16 days).
Preparation of 2,4,4-Trimethyloxazolinium Perchlo-
rate (6-HClO4). A solution of 0.25 mL (2.0 mmol) of 6 in 0.17
mL (2.0 mmol) of 70% HClO4 was placed on a column of silica
gel. Elution with ethyl acetate gave first 134 mg of a sticky
1
solid, shown with H NMR to be a mixture of 6-H+ and 7-H+
in a 3/4 ratio. Continued elution and evaporation of the solvent
gave 275 mg (1.29 mmol) of crystalline 6-HClO4, mp 118-
121 °C. NMR (CD3CN), δ 1H: 4.67, s, 2H; 2.35, s, 3H; 1.50, s,
6H. 13C: 178.2 (-CdO), 85.2 (CH2), 64.3 (quat), 26.4 (2 CH3),
1
14.6 (CH3) ppm. NMR (D2O), δ H: 4.53, s, 2H; 2.20, s, 3H;
1.36, s, 6H.
Preparation of 7-HClO4. A solution was made of 2 mL
(0.016 mmol) of 6 in 1.4 mL (0.016 mmol) of HClO4 in 10 mL
of D2O. One drop of this solution was dissolved in D2O, and
the 1H NMR spectrum was recorded at 300 MHz at timed
intervals. In 20 h, the initial spectrum of δ 4.56, s, 2H; 2.22,
s, 3H; 1.35, s, 6H had changed almost completely into δ 4.00,
s, 2H; 2.02, s, 3H; 1.25, s, 6H. The original peaks were visible
but too small to be integrated. After 66 h, only peaks at 3.99,
2.01, and 1.24 ppm were visible. At 500 MHz, the 13C NMR
(DEPT) spectrum was 173.0 (-CdO), 68.1 (CH2), 53.0 (quat),
21.3 (2 CH3), and 19.5 (CH3). Neutralization of a sample of
this solution with solid NaOH resulted in the formation of 8,
1
as shown by NMR spectra δ H 3.46, s, 2H; 1.78, s, 3H; 1.08,
s, 6H and δ 13C 173.4 (-CdO), 66.6 (CH2), 54.3 (quat), 22.5 (2
CH3), 22.4 (CH3).
D2O was removed from the bulk of the solution under
reduced pressure. The viscous residue was triturated with
ether, and the ether was evaporated with a current of air to
leave 3.6 g (0.016 mmol, 100%) of white solid, 7-HClO4, mp
117-118 °C. NMR (CD3CN), δ, 1H: 6.5, br s; 4.03, s, 2H; 2.09,
s, 3H; 1.36, s, 6H. 13C (DEPT): 171.1, 68.4 (CH2), 56.8 (quat),
22.7 (2 CH3), 20.8 (CH3).
Decomposition of 4a and 4a′: A. 4a in CD3CN. A
solution of 4a was kept in a foil-wrapped NMR tube for 5 days.
The NMR spectra then were δ 1H 4.67, s, 2H; 1.50, s, 6H and
δ
13C 182.0 (-CdO), 85.2 (CH2), 64.2 (quat), 26.4 (CH3) ppm.
On a larger scale, a solution of 174 mg (0.369 mmol) of 4a
in 8 g of CD3CN was monitored with NMR spectroscopy until
the signals from 4a were no longer visible. The solvent was
removed under vacuum, and the residue was washed with
Reaction of 8 in CD3CN/HClO4. The NMR spectra of a
solution containing equimolar amounts of 8 and HClO4 were
recorded and consisted of three sets of peaks attributable to
9260 J. Org. Chem., Vol. 69, No. 26, 2004

Formation of Alkyl-2-oxazolines
8-H+, 6-H+, and 7-H+ as follows. 8-H+, δ 1H: 3.67, s, 2H; 2.28,
s, 3H; 1.35, s, 6H. 13C: 177.6 (-CdO), 68.2 (CH2), 61.3 (quat),
°C. An aliquot was taken periodically and diluted with CDCl3
for 300 MHz 1H NMR spectroscopy. Peaks attributable to tert-
butylacetamide appeared slowly at δ 1.91, s, 3H; 1.32, s, 9H.15
After 7 days, 50% of 12 had reacted.
Ethyl 2-(2,4-Dinitrophenyl)acetoacetate (12) was pre-
pared as described,11 mp 93.5-95 °C; lit. mp 93-94 °C.14 Its
NMR spectra (Supporting Information) were recorded for use
in following its reactions with 2-amino-2-methylpropanol.
1
23.3 (2 CH3), 21.1 (CH3). 6-H+, δ H: 4.66, s, 0.12H, 2.33, s,
0.19H; 1.49, s, 0.37H. 7-H+, δ 1H: 4.03, s, 0.03H, 2.08, s, 0.05H;
1.35 overlap with the peak from 8-H+. The 1H NMR spectrum
was recorded at 300 MHz over a period of 10 days. Overlap of
the peaks from 7-H+ and 8-H+ at 1.35 ppm prevented their
diagnostic use. Integrations of the remaining peaks showed
the decrease in intensity of those from 8-H+ and increase
mainly of those from 6-H+. After 10 days, the peaks from 8-H+
were too small to integrate. The ratio of 6-H+/7-H+ was 5/1.
Attempted Preparation of 7: A. In CHCl3. A solution of
936 mg (3.16 mmol) of 12 and 0.3 mL (3.14 mmol) of 2-amino-
2-methylpropanol was heated at 80 °C in a sealed vessel for 7
days.11 The solvent was distilled off, and the residue was placed
under high vacuum to give 83 mg (0.736 mmol, 23%) of 6, as
shown by its 1H NMR spectrum. The remainder of the residue
was placed on a column of silica gel, 60-200 mesh. Elution
with dichloromethane gave 740 mg (2.91 mmol, 92%) of ethyl
(2, 4-dinitrophenyl) acetate as a red oil. Continued elution with
ethyl acetate gave 239 mg (2.01 mmol, 64%) of 8, as shown by
its 1H NMR spectrum. When 8 was heated in CDCl3 at 80 °C,
its 1H NMR spectrum changed slowly into that of 6. The ratio
of 6/8 was 15/85 (1 day), 30/70 (3 days) and 65/35 (7 days).
B. In CDCl3. A similar solution in CDCl3 was heated for 3
days. A drop of the solution was diluted with CDCl3 for NMR
X-ray Crystallography. Details are given in Supporting
Information.
Acknowledgment. H. J. S. thanks the Welch Foun-
dation for support (Grant D-0028). K. H. W. thanks the
Welch Foundation for support (Grant C-0976) and for
the purchase of the CCD, and the National Science
Foundation for support (Grant CHE-9983352). We
thank Mr. David W. Purkiss for the 500-MHz NMR
spectroscopy.
Supporting Information Available: General experimen-
tal procedures, 1H and 13C NMR data for compounds 5b-f,
5h-u, 6-8, 12, Figures S1-S15 (Ortep diagrams), and tables
giving X-ray crystallographic data for compounds 5a-c, 5e-
g, 5i-l, 5n-r. This material is available free of charge via
the Internet at http://pubs.acs.org.
1
spectroscopy. The complex H spectrum showed the presence
of 12 and ethyl (2,4-dinitrophenyl) acetate in a 25/75 ratio.
Despite the complexity of the spectrum, it was possible with
the use of data from authentic compounds to detect the signals
from 2-amino-2-methylpropanol, 6, and 8. The dominant
component was 8.
JO0402125
(14) Hall, G. E.; Hughes, D.; Rae, D.; Rhodes, A. P. Tetrahedron Lett.
1967, 241-246.
(15) Newcomb, M.; Varick, T. R.; Goh, S.-H. J. Am. Chem. Soc. 1990,
112, 5186-5193.
A solution of 592 mg (2.0 mmol) of 12 and 0.21 mL (2.0
mmol) of tert-butylamine in 20 mL of CHCl3 was heated at 80
J. Org. Chem, Vol. 69, No. 26, 2004 9261