Structural analyses of borane and chloroborane adducts of 1,3,5- dithiaza-, -dioxaza-, -thiadiaza-, and -triazacyclohexanes and their rearrangement products, boracyclohexanes

Article abstract of DOI:10.1002/(sici)1099-0682(199911)1999:11<2063::aid-ejic2063>3.0.co;2-a

Structural and conformational studies performed by ¹H-, ¹¹B-, ¹³C-, two-dimensional, and variable-temperature NMR spectroscopy of borane and chloroborane adducts of 1,3,5-heterocyclohexanes and their rearrangement products

Full text of DOI:10.1002/(sici)1099-0682(199911)1999:11<2063::aid-ejic2063>3.0.co;2-a

FULL PAPER
Structural Analyses of Borane and Chloroborane Adducts of 1,3,5-Dithiaza-,
-Dioxaza-, -Thiadiaza-, and -Triazacyclohexanes and Their Rearrangement
Products, Boracyclohexanes
[a]
[a]
[a]
´
´
´
Angelina Flores-Parra,* Sonia A. Sanchez-Ruız, and Carlos Guadarrama-Perez
Keywords: Borane adducts / Triazacyclohexanes / Thiadiazacyclohexanes / Dioxazacyclohexanes / Boracyclohexanes /
Rearrangements
Structural and conformational studies performed by 1H-, 11B-,
13C-, two-dimensional, and variable-temperature NMR Rearrangement reactions of the adducts gave the first
spectroscopy of borane and chloroborane adducts of 1,3,5- examples of chloroboracyclohexanes bearing boron and
heterocyclohexanes and their rearrangement products, nitrogen atoms as stable stereogenic centers. BClH2 and
derivatives produced the axial borane compounds.
boracyclohexanes, are reported. N-Methyl derivatives gave
equatorial N-borane adducts whereas the N-isopropyl
BCl2H adducts were found to be more stable towards ring
rearrangement than the corresponding N-BH3 analogs.
Introduction
We have been systematically studying the synthesis and
particularly the coordination behavior of 1,3,5-heterocy-
clohexanes bearing heteroatoms such as O, S, and N, which
are rich in lone pairs and good ligands for Lewis acids.[1]
Reactions with boron[1a,1b,1eϪ1f] and lithium[1g] compounds
were investigated because these reagents function as coordi-
nation probes conveniently studied by NMR techniques.
Herein, we report extended studies of chloroboranes,
which are more acidic reagents which could give stronger
coordination bonds and more stable adducts, and of new
families of heterocycles: 1,3,5-thiadiazacyclohexanes and
1,3,5-dioxazacyclohexanes. Because these heterocycles are
difficult to prepare, few examples of them were known,[2]
but fortunately we have recently established suitable reac-
tion conditions for their preparation.[1h]
Figure 1
we were interested to find out if coordination would freeze
the conformations of the heterocycles. NMR studies of het-
erocycles 1؊7 and 9 showed that they are in ring- and nitro-
gen-conformational equilibrium at room temp. (400-MHz
1H NMR), whereas compound 8 has a preferred chair con-
formation with the 2-methyl group in the equatorial and
the N-methyl group in the axial position.[1g]
When heated, N-BH3 adducts of 1,3,5-dithiazacyclohex-
anes rearrange into boracyclohexanes by exchange of boron
and carbon atoms[1b] (Scheme 1). The stability of these
boraheterocycles depends on the size of the N-alkyl group:
Those with bulky groups are rapidly converted into N-
(BH3)-dimethylalkylamine complexes.[1b] This rearrange-
ment was not found for 1,3,5-triazacyclohexanes. Therefore,
we wanted to investigate if these rearrangements occur for
other heterocyclohexanes or with the more reactive chloro-
boranes, if the more acidic boron atom in the resulting chlo-
roborate allows better coordination and a more stable ring,
if the chlorine atom could have a preferred position in a
frozen ring and thus result, stereoselectively, in a stereo-
genic boron atom. In addition, we wanted to study the in-
fluence of the chlorine atom on the reactivity and NMR
data and on the conformational behavior.
Results and Discussion
Herein, we present the study of the reactions of
BH3·THF and various chloroborane·DMS with the hetero-
cycles 3,5-dialkyl-1,3,5-thiadiazacyclohexane (1, 2,[1h,2] and
3
[1h]), 5-alkyl-1,3,5-dioxazacyclohexane (4 and 5[1h]), 5-
alkyl-1,3,5-dithiazacyclohexane (6, 7,[1d] and 8[1g]), and
1,3,5-trimethyl-1,3,5-triazacyclohexane[1f] (9) (Figure 1).
AcidϪbase studies with BH3 as the Lewis acid partner,
showed that the potential basicity decreases in the order N
> S > O. Therefore, we would expect mono(N-BX3) deriva-
tives to form from the reactions of 1Ϫ9 with BH3 or chloro-
borane compounds, and that two or even three borane mol-
ecules would coordinate to heterocycles 1؊3 and 9. Also,
[a]
´
Chemistry Department, Centro de Investigacion y de Estudios
Avanzados del I.P.N.
´
´
A. P. 14-740, C. P. 07000, Mexico D.F., Mexico
Fax: (internat.) ϩ 52-5/747-7113
E-mail: aflores@mail.cinvestav.mx
Eur. J. Inorg. Chem. 1999, 2063Ϫ2068
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
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A. Flores-Parra, S. A. Sanchez-Ruiz, C. Guadarrama-Perez
FULL PAPER
with the bulky isopropyl groups in equatorial positions, as
shown by the 13C-δ values for CH (δ ഠ 54; for the axial
position δ ഠ 46).[1e] These heterocycles provide examples of
axial BH3 groups. The frozen conformation of 13 that re-
sults from BH3 addition makes the N atoms stereogenic
centers and the CϪCH3 groups diasterotopic. The signal of
CH3 groups of the isopropyl group attached to the coordi-
nated nitrogen atom appear at δ ϭ 15.9 and 15.7, whereas
those of the ones attached to the free nitrogen atom appear
at δ ϭ 18.8 and 18.4. In the free ligand 2 the signals of all
the CH3 groups appear at δ ϭ 20.1.
Scheme 1. Rearrangement of the BH3 adducts
Borane Adducts
Chloroborane Adducts
NMR spectroscopy showed that the equimolar reaction
of thiadiazacyclohexane 1 with BH3·THF resulted in
monoadduct 10, whereas an excess of borane led to bis(bor-
ane) 11 (Figure 2). The 13C-NMR spectrum of compound
1, at Ϫ90°C in [D8]THF (100.53 MHz), did not indicate a
preferred conformation, as the CH3 and SCH2N resonances
were averaged, indicating that ∆G° for the ring inversion
is very low. In contrast, 10 and 11 are present in frozen
conformations, because the CH2 groups have geminal coup-
ling patterns. Their N-BH3 groups are in equatorial posi-
tions as shown by the position of the N-CH3 group in the
13C spectrum at δ ഠ 45;[1e] this conformation is also sup-
ported by an X-ray diffraction structure.[1i] The bis(borane)
11 is an analog of the reported compound 12.[1f] In solu-
tion, adduct 10 is slowly transformed into 11 and the free
We prepared the chloroborane adducts of 1,3,5-heterocy-
clohexanes 18Ϫ22 and 24Ϫ29. The reaction of a commer-
cial mixture of BH2Cl, BHCl2, and BH3 (in the ratio 90:8:2,
respectively), in DMS, with compounds 6 and 8 produced,
in the same ratio, the corresponding adducts 18Ϫ21 (Figure
4). Upon coordination, the ring of adducts 18؊21 adopted
a preferred conformation with the N-methyl group in the
axial position as indicated by their 13C-δ values in the range
δ ϭ 37.7Ϫ40.2 (Table 2). To analyze the trends in the NMR
spectra, the data of compounds 18Ϫ21 were compared to
those of the BCl3 (22) and BH3 (23[1b]) adducts of 6. In the
1H as well as the 11B spectra, the resonances of the CH2
groups close to the NϪB bond are systematically shifted to
higher frequencies with an increasing number of chlorine
atoms. The coupling constants 1J(BϪH) increase in the
same order.
1
heterocycle. H-NMR data are summarized in Table 1.
We found that chloroborane adducts are more stable to
ring rearrangement than the corresponding N-BH3 analogs,
making them useful for the observation and study of coor-
dination compounds of heterocycles with bulky groups. For
example, we obtained adduct 24, derived from 3-isopropyl-
1,3,5-dioxazacyclohexane (Table 1, Figure 5). It is moder-
ately stable and could be observed by NMR, but we were
not able to detect the corresponding BCl2H adduct. The N-
BH3 adducts of 3 and 5 could not be observed because they
are rapidly reduced to the corresponding dimethyl-
amineborane.
Figure 2. 11B- and 13C-NMR chemical shifts of 10Ϫ12
Heterocycle 1 has two N sites for borane coordination
The reaction of equimolar amounts of BH3·THF and and readily formed monoadduct 25 and bis(monochloro-
3,5-diisopropyl-1,3,5-thiadiazacyclohexane (2) afforded the borane) adduct 26. Both are stable compounds with the N-
stable N-borane 13 with the two isopropyl groups in equa- chloroborane group in the equatorial position as the pre-
torial positions and the BH3 group in the axial position ferred conformation. In contrast, only one example of an
(Figure 3). Compound 13 is more stable than 14,[1b] which N-BCl3 adduct of a 1,3,5-thiadiazacyclohexane was pre-
could be observed only at low temperature. In the presence pared, 27, which is a weak complex that decomposes on
of an excess of BH3·THF, 13 rapidly rearranged into 31 vacuum evaporation of the solvent. According to its
(vide infra, Figure 8), whereas the triisopropyltriazacy- 13C-NMR spectrum, the BCl3 adopts an axial position
clohexane 15[1f] gave a small amount of the bisadduct 16.[1f] (Figure 5). An interesting observation was that BCl3 ad-
The reaction of BH3·THF with the dioxazacyclohexane 4 ducts of the studied heterocycles are less stable than adducts
also yielded an N-borane, 17, as shown by NMR spec- with at least one BϪH bond. This can be explained by the
troscopy at room temp. The stability of the borane adducts stabilization resulting from interaction between the hydrides
is shown by the order of the ease of rearrangemen: 14 > 17 on B and the protons on C, as discussed in the next
> 13 > 15.
paper.[1i]
The N-BH2Cl monoadduct 28 and bisadduct 29 of 1,3,5-
The room-temp. NMR spectra of 13؊17 (Figure 3) show
that the ring conformation is preferentially that of a chair triazacyclohexane (9) were obtained. The BH2Cl groups oc-
2064
Eur. J. Inorg. Chem. 1999, 2063Ϫ2068

Borane and Chloroborane Adducts of 1,3,5-Dithiaza-, -Dioxaza-, -Thiadiaza-, and -Triazacyclohexanes
FULL PAPER
1
Table 1. H-NMR data (400 MHz in CDCl3 at 25°C or in [D8]THF at low temperature; for atomic numbering see Figure 1)
Compd.
R2 or 2-Heq/2-Hax
4-Heq/4-Hax
6-Heq/6-Hax
N1Ϫ
R
N3-R
N5-R
1 (Ϫ90°C)
2 (Ϫ95°C)
3
3.82/4.57
3.92/4.15
4.20/4.58
5.12/5.04
5.11/5.16
3.56/4.60
3.68/4.65
1.46/4.24
3.86/3.18
3.60/4.14
3.54/3.85
3.69/2.59
4.14
3.75/3.07
4.25/3.64
5.16/4.88
4.93
3.66/4.22
2.90/2.76
3.65/3.36
1.39/4.41
1.40/4.22
2.65/4.05
3.53/3.93
4.76/4.24
4.21/4.04
4.68
3.82/4.57
3.92/4.15
4.20/4.58
4.68
2.56
3.13
3.73
2.56
3.13
3.73
3.42
4.63
2.59
3.73
2.56
2.83
2.61
2.47
2.79
4.33
4.19
3.89
4.06
4.37
2.73
2.92
2.47
4 (Ϫ80°C)
5 (Ϫ60°C)
6 (Ϫ80°C)
7 (Ϫ90°C)
8 (27°C)
9 (Ϫ90°C)
10
4.13/4.59
3.93/4.95
4.29/4.80
4.09/4.67
3.86/3.18
3.55/4.23
3.97/3.71
3.54/3.12
4.08/3.51
4.02/3.16
4.43/4.08
4.80/4.44
4.53/4.28
3.34/4.32
3.74/3.33
3.73/4.03
3.45/4.94
3.73/5.12
3.93/4.30
4.98/4.83
3.93/4.95
4.29/4.80
4.09/4.67
3.86/3.18
3.66/3.81
3.54/3.85
3.54/3.12
3.82/3.96
4.02/3.16
4.43/4.08
4.80/4.44
4.53/4.28
3.73/4.00
3.74/3.33
3.65/3.36
2.83
2.30
2.83
2.65
2.47
2.79
2.99
2.81
3.89
11
12[1f]
13
15[1f]
2.81
3.02
16[1f]
17
24
25
2.61
2.37
2.30
2.72
2.95
28
2.37
2.30
2.79
3.10
2.80
30[1f]
33
34
38 (25°C)
2.71
Table 2. 13C-NMR data (100.5 MHz, in CDCl3 at 25°C or
[D8]THF at low temperature; for atomic numbering see Figure
1; * ϭ quaternary nitrogen atom)
Compd.
C-2
C-4
C-6
N*ϪR
1 (Ϫ90°C)
58.1
54.1
59.2
95.4
95.2
34.3
34.3
44.3
80.7
30.9
30.7
42.5
42.0
30.3
30.2
30.2
75.7
69.3
70.1
81.3
80.2
59.9
56.9
60.3
75.9
60.0
59.1
61.0
59.7
58.9
62.2
62.2
63.9
64.6
58.1
54.1
59.6
81.3
81.3
59.9
56.9
60.3
75.9
60.0
59.1
61.0
59.7
58.9
62.2
41.4
2 (Ϫ95°C)
50.3
3
54.6
4 (Ϫ20°C)
50.5
5 (Ϫ60°C)
56.0
6 (Ϫ90°C)
37.5
7 (Ϫ80°C)
45.8
8
37.0
9 (Ϫ100°C)
39.7,[b] 41.4[a]
40.2
18
19
38.3
20
39.5
21
37.7
Figure 3. Borane adducts of N-isopropyl heterocycles; 11B-NMR
data are shown, the boron signal of 16 is masked by that of 15
22
38.6
23
42.9
32eq (Ϫ65°C)
44.5*,[a] 47.7*[b]
43.8*,[a] 52.6*[b]
44.3*,[a] 53.1*[b]
32ax (Ϫ65°C) 29.9
37 (Ϫ55°C)
32.0
[a]
[b]
Axial position. Ϫ Equatorial position.
Figure 5. 11B- and 13C-NMR chemical shifts and the preferred con-
formations of 24, 25, 26, and 27
1
Figure 4. 11B- and H-NMR data of 18Ϫ23
Eur. J. Inorg. Chem. 1999, 2063Ϫ2068
2065

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A. Flores-Parra, S. A. Sanchez-Ruiz, C. Guadarrama-Perez
FULL PAPER
cupy equatorial positions and the ring is not fluxional. The
13C chemical shifts of 28 and 30[1f] were similar, and those
of 29 and 12 were also similar[1f] (Figures 2, 6).
1
Figure 8. H- and 11B-NMR data of 32 and 37
Figure 6. 11B- and 13C-NMR data and the preferred conformations
of 28, 29, and 30
and 13C-NMR data indicate that the chair conformation is
the preferred one for both molecules at room temp., and
the CϪCH3 group anchors the molecule. Here, the boron
atom and C-2 are stereogenic centers.
1,3,5,6-Thiadiazaboracyclohexane (31)
Herein, we report the first example of a 1,3,5,6-thiadiaza-
boracyclohexane (31), quantitatively formed by reaction of
1,3,5-thiadiazacyclohexane (2) and an excess of BH3·THF
in CHCl3 at room temp. The 11B-NMR spectrum of 31
shows a triplet at δ ϭ Ϫ5.3, characteristic of an SϪBH2ǟN
group. The ring appears nondynamic on the time scale of
1
the H-NMR spectrum at room temp (Figure 7).
Figure 9. 13C-NMR data of 33, 34, and 38 at 25°C
1
Figure 7. 13C-, 11B-, and H-NMR chemical shifts of 31 at 25°C
To see if a more bulky N-substituent will also function
as an anchor for ring inversion, we treated the 1,3,5-dithiaz-
acyclohexane 7 in equimolar amounts with the mixture of
chloroboranes for 5 h at room temp. The reaction products
were the cyclohexanes 35 (60%) and 36 (40%) (Figure 10).
1,3,5,6-Dithiazaboracyclohexanes 32؊36
2-Chlorobora-1,3,5-dithiazacyclohexanes 32؊36 were
formed by allowing the 1,3,5-dithiazacyclohexanes 6؊8 to
react with excess BH2Cl·DMS in CHCl3. The resulting
structures were assigned by HETCOR, COSY, and APT
NMR experiments. The positions of the chlorine atoms
were determined by their effects on the 1H resonances of the
neighboring protons and by comparison with the analogous
BH2 compounds. The boron atom becomes a stereogenic
center and two isomers were indeed observed. At room
temp. compound 32 is an equilibrium mixture of the two
conformers shown in Figure 8. At Ϫ65°C, both conformers
were observed in the 13C- (Table 2) and 11B-NMR spectra,
for assignment a comparison with 37 was helpful. The con-
1
Both compounds were shown by their H-NMR spectra to
be nonfluxional, and their boron and nitrogen atoms are
stereogenic centers. The equatorial position of the isopropyl
groups was found by 13C-NMR spectroscopy (CH at δ ϭ
59.4 and 54.7 in 35 and 36, respectively). An anomeric ef-
fect produced by the axial chlorine atom on the axial N-
methyl group (which is deshielded) was observed for 33
and 35.
Conclusions
The 1,3,5-heterocyclohexanes and borane or chlorobor-
former with the Cl atom in axial position was present in ane form stable adducts which have frozen conformations
1
70% abundance. At this temperature the J(BϪH) values as shown by the geminal coupling pattern of the CH2
of the two isomers differed significantly, with 161 Hz for groups. The values of the coupling constants in the frozen
equatorial BϪH and 127 Hz for axial BϪH, indicating free heterocycles vary according to the nature of the het-
frozen conformations.
eroatom (OCH2O: 5.9; SCH2S: ca. 13.3; NCH2N: 8.0;
Compound 8 with an excess of BH2Cl produced the two SCH2N: 10.5Ϫ13.5). The corresponding values in the ad-
1
diasteromers 33 and 34 in a 1:1 ratio (Figure 9). The H- ducts do not show systematic trends except for the triazacy-
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Eur. J. Inorg. Chem. 1999, 2063Ϫ2068

Borane and Chloroborane Adducts of 1,3,5-Dithiaza-, -Dioxaza-, -Thiadiaza-, and -Triazacyclohexanes
FULL PAPER
Experimental Section
1H-, 13C-, and 11B-NMR spectra were recorded with Jeol spec-
trometers at frequencies of 270 and 400 MHz for protons; δ values
are referenced to TMS, and to BF3·OEt2 for 11B-NMR spectra.
Ϫ BH3·THF was prepared as described.[3] The BH3ϪnCln·S(CH3)2
mixture was purchased from Aldrich Co. Anhydrous solvents were
prepared according to usual laboratory methods. Ϫ All reactions
were carried out in inert atmosphere with oven-dried glassware. Ϫ
Adducts 10, 11, 13, 17؊21, 24؊29, and boracyclohexanes 31؊36
were analyzed only by variable-temperature, and two-dimensional
1H-, 13C-, 11B-NMR spectroscopy. Our attempts to isolate them
from the mixture of adducts were unsuccessful because they are
unstable. Therefore, we could not perform elemental analyses.
However, their structures were derived by comparison to fully
characterized similar compounds.[1]
1
Figure 10. 13C-, 11B-, and H-NMR chemical shifts of 35 and 36
Preparation of Mono-N-BH3 Adducts 10, 13, and 17. ؊ General
Procedure: To a solution of the corresponding heterocyclohexane
(0.25 g) in 20 mL of dry THF, was added a solution of BH3·THF
(1.2 mmol) at Ϫ78°C. The mixture was stirred for 5 min, and then
the solvent was removed under vacuum leaving behind a mixture
of adducts as white solids which were analyzed by NMR spec-
troscopy (10, 80%; 13, 85% and 17, 80%).
clohexanes and dithiazacyclohexanes where these values in-
crease upon coordination [e.g., in 9 it increases from 8 Hz
to 9.1 and 11.7 Hz, and in 6 (SCH2N) it increases from 12.6
to 13.9Ϫ14.3 Hz, Table 3]. The frozen conformations are
also deduced from the 4Jw couplings between the equatorial
protons, the values of which vary between 1.2 to 2.6 Hz. In
37 this coupling occurs between the equatorial CϪH and
BϪH, with J ϭ 2.0 Hz.
Preparation
of
3,5-Bis(borane)-3,5-dimethyl-1,3,5-thiadiazacy-
clohexane (11): To a stirred solution of 1 (0.25 g, 1.9 mmol) in
20 mL of dry THF, was added a solution of BH3·THF (2.0 mmol)
at 25°C. After 10 min, more BH3·THF (4.1 mmol) was added and
the reaction mixture was kept for 30 min at 50°C. The solvent was
then removed under vacuum to give the adduct as a white solid.
Compound 11 (80%, 0.24 g) was crystallized from CHCl3. m.p.
40°C. Ϫ C5H18B2N2S (132.23): calcd. C 37.56, H 11.34, N 17.52;
found C 37.51, H 11.46, N 17.36.
The configuration of the nitrogen atoms in borane and
chloroborane adducts of triaza-, thiadiaza-, dithiaza-, and
dioxazacyclohexanes is determined by the size of the N-sub-
stituents. The bulky isopropyl groups direct the borane
units into the axial positions, while the methyl groups direct
1
the boranes to the equatorial positions. J(BϪH) constants
for axial BH3 are smaller that the corresponding values for
equatorial BH3, which could be attributed to a weaker co-
ordination of axial borane.
That the formation of adducts resulted in frozen ring
conformations indicate that there is a hydrideϪproton in-
teraction.[1i] This is supported by the result that BCl3 did
not give stable adducts. The use of excess borane and chlo-
roboranes led to new boracyclohexanes. The chloroborata
compounds are more stable because SBHCl is more acidic
than the SBH2 group.
Preparation of N-BHCl2 and N-BH2Cl Adducts 18؊21, 24؊26, 28,
and 29. ؊ General Procedure: To a stirred solution of the corre-
sponding heterocyclohexane (1, 5, 6, 8, or 9) (0.25 g) in 20 mL of
dry CHCl3, was added at Ϫ60°C a solution of 1 or 2 equiv. of
BH3ϪnCln SMe2. The reaction mixture was stirred for 5 min. The
solvents were then removed under vacuum to afford the N-BHCl2
and N-BH2Cl adducts: 19 and 21 (8%); 24 (50%); 25 (95%); 26
(85%); 28 (40%), and 29 (95%). Ϫ Adduct 18 was crystallized from
CHCl3 and obtained in 80% yield (0.27 g). Ϫ C4H11BClNS2
(183.53): calcd. C 26.18, H 6.04, Cl 34.94, N 7.63; found C 26.69,
2
4
Table 3. J(HϪH) geminal coupling constants for CH2 and Jw(HϪH) for equatorial CH groups; for atomic numbering see Figure 1
Compd.
2-H
4-H
6-H
4Jw(HϪH)
Compd.
2-H
4-H
6-H
4Jw(HϪH)
1 (Ϫ90°C)
2 (Ϫ95°C)
3
12.4
10.5
13.5
5.9
13.5
13.5
12.1
12.4
10.5
13.5
20
12.1
14.1
14.3
13.9
11.0
13.2
10.8
13.8
7.0
12.8
12.1
12.8
13.1
13.2
12.4
12.5
12.7
12.1
14.1
14.3
13.9
11.0
13.2
10.8
13.8
21
22
14.0
13.9
4 (Ϫ80°C)
5 (Ϫ60°C)
6 (Ϫ80°C)
7 (Ϫ90°C)
8 (27°C)
9 (Ϫ90°C)
10
23
2.0
2.6
1.8
5.9
10.6
12.7
13.2
12.6
8.0
13.3
13.6
11.0
12.5
11.0
14.7
10.6
14.0
14.0
11.4
12.7
13.2
12.6
8.0
12.6
14.1
11.0
11.5
11.0
14.7
10.6
14.0
14.0
24
13.3
13.2
2.6
25
13.2
9.8
11.6
28
30[1f]
8.0
31 (25°C)
32eq (Ϫ65°C)
32ax (Ϫ65°C)
33
12.6
14.1
9.1
2.5
1.7
13.2
13.5
11
12[1f]
13
34
15[1f]
7.8
1.7
1.6
1.2
2.1
2.1
35
13.1
13.0
12.9
16[1f]
12.8
5.9
36
17
37 (Ϫ55°C)
38 (25°C)
2.0
18
14.0
14.0
19
Eur. J. Inorg. Chem. 1999, 2063Ϫ2068
2067

´
´
A. Flores-Parra, S. A. Sanchez-Ruiz, C. Guadarrama-Perez
FULL PAPER
[1] [1a]
´
A. Flores-Parra, N. Farfan, A. I. Hernadez-Bautista, L Fer-
H 6.09, Cl 34.83, N 6.62. Ϫ Adduct 20 was obtained in 85% yield
(0.28 g). Ϫ C5H13BClNS2·CH2Cl2 (282.49): calcd. C 25.51, H 5.35,
N 4.96; found C 25.05, H 5.47, N 5.11.
´
´
nandez-Sanchez, R. Contreras, Tetrahedron 1991, 47,
[1b]
6903Ϫ6914. Ϫ
A. Flores-Parra, G. Cadenas-Pliego, L. M.
´
´
R. Martınez-Aguilera, M. L. Garcıa-Nares, R. Contreras,
[1c]
Chem. Ber. 1993, 126, 863Ϫ867. Ϫ
G. Cardenas-Pliego, R.
Preparation of 3,5-Diisopropyl-1,3,5,6-thiadiazaboracyclohexane
(31): To a solution of 1 (0.25 g, 1.33 mmol) in 20 mL of dry THF,
was added a solution of BH3·THF (1.2 mmol) at Ϫ78°C; the result-
ant mixture was stirred for 5 min. It was then warmed to 25°C,
stirred for 5 min, and the solvent was removed under vacuum. The
adduct was obtained as a white solid (70%, 0.19 g). Ϫ 15N NMR
(CDCl3, 25°C, 270 MHz): δ ϭ Ϫ238.
Contreras, J. C. Daran, S. Halut, A. Flores-Parra, Phosphorus
[1d]
Sulfur Silicon 1993, 84, 9Ϫ15. Ϫ
G. Cadenas-Pliego, L. M.
´
´
R. Martınez-Aguilera, A. M. Bello-Ramırez, M.-J. Rosales-
Hoz, R. Contreras, J. C. Daran, S. Halut, A. Flores-Parra,
Phosphorus Sulfur Silicon 1993, 81, 111Ϫ123. Ϫ [1e] G. Cadenas-
Pliego, M.-J. Rosales-Hoz, R. Contreras A. Flores-Parra, Tetra-
hedron: Asymmetry 1994, 5, 633Ϫ640. Ϫ [1f] L. M. R. Martınez-
´
Aguilera, G. Cadenas-Pliego, R. Contreras, A. Flores-Parra,
[1g]
Tetrahedron Asymmetry 1995, 6, 1585Ϫ1592. Ϫ
C. Guadar-
Preparation of 6-Chloro-5-methyl-1,3,5,6-dithiazaboracyclohexanes
32؊36. ؊ General Procedure: To a solution of the corresponding
heterocyclohexane (0.25 g) in 20 mL of dry CH2Cl2, was added 3
equiv. of a mixture of BHCl2, BH2Cl, and BH3 in S(CH3)2 (90:8:2).
The reaction mixture was stirred at 40°C for 8 h, and the solvents
were subsequently removed by evaporation to afford the dithiaza-
boracyclohexane 32؊36 which were characterized by NMR spec-
troscopy.
´
´
rama-Perez, G. Cadenas-Pliego, L. M. R. Martınez-Aguilera,
[1h]
A. Flores-Parra, Chem. Ber. 1997, 130, 813Ϫ817. Ϫ
Flores-Parra, S. A. Sanchez-Ruiz, Heterocycles, in press. Ϫ
A.
[1i]
´
´
A. Flores-Parra, S. A. Sanchez-Ruiz, C. Guadarrama-Perez, H.
Nöth, R. Contreras, Eur. J. Inorg. Chem. 1999, 2069Ϫ2073, fol-
lowing paper.
[2] [2a]
L. Angiolini, R. P. Duke, R. A. Jones, A. R. Katritzky, J.
[2b]
Chem. Soc., Perkin Trans. 2 1972, 674Ϫ680. Ϫ
E. R.
[2c]
Braithwaite, J. Graymore, J. Chem. Soc. 1953, 143Ϫ145. Ϫ
E. R. Braithwaite, J. Graymore, J. Chem. Soc. 1950, 208Ϫ210.
[3]
H. C. Brown, C. W. Kramer, A. B. Levy, M. M. Midland, Or-
ganic Syntheses via Boranes, John Wiley and Sons, New York,
1975, p. 18Ϫ25.
Acknowledgments
Received December 14, 1999
We thank Conacyt-Mexico and TWAS (grant 97Ϫ337 RG/CHE/
LA) for financial support. C. G.-P. is grateful to Conacyt-Mexico
for a scholarship and Professor H. Nöth for helpful discussions.
[I98427]
2068
Eur. J. Inorg. Chem. 1999, 2063Ϫ2068