Diversity-oriented four-component synthesis of solid state luminescent difluoro oxazaborinines

Article abstract of DOI:10.1016/j.dyepig.2018.05.001

(Hetero)aroyl chlorides, alkynes, anilines, and BF₃ diethyl etherate are reacted in an alkynylation-amination-cyclization one-pot process to give trisubstituted difluoro oxazaborinines in moderate to very good yield in the sense of a consecutiv

Full text of DOI:10.1016/j.dyepig.2018.05.001

Accepted Manuscript
Diversity-oriented four-component synthesis of solid state luminescent difluoro
oxazaborinines
Janis Dohe, Janina Koßmann, Thomas J.J. Müller
PII:
S0143-7208(18)30670-3
10.1016/j.dyepig.2018.05.001
DYPI 6730
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 26 March 2018
Revised Date: 30 April 2018
Accepted Date: 1 May 2018
Please cite this article as: Dohe J, Koßmann J, Müller TJJ, Diversity-oriented four-component
synthesis of solid state luminescent difluoro oxazaborinines, Dyes and Pigments (2018), doi: 10.1016/
j.dyepig.2018.05.001.
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ACCEPTED MANUSCRIPT

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Diversity-oriented Four-component Synthesis of Solid State Luminescent Difluoro
Oxazaborinines
Janis Dohe,a Janina Koßmann,a and Thomas J. J. Müller*,a
aInstitut für Organische Chemie und Makromolekulare Chemie, Heinrich-Heine-Universität
Düsseldorf, Universitätsstrasse 1, D-40225 Düsseldorf, Germany
Email: ThomasJJ.Mueller@hhu.de
Keywords: Absorption; Boron; Copper; Cross-coupling; DFT-calculations; Fluorescence;
Heterocycles; Multi-component reactions; Palladium.
ABSTRACT
(Hetero)aroyl chlorides, alkynes, anilines, and BF3 diethyl etherate are reacted in an alkynylation-
amination-cyclization one-pot process to give trisubstituted difluoro oxazaborinines in moderate to
very good yield in the sense of a consecutive four-component synthesis. The obtained title compounds
are intensely fluorescent with bluish to yellow color, however, only in the solid state. Photophysical
measurements, physical organic correlation studies, and DFT and TD DFT calculations are employed
to rationalize the substituent effects on the dominant chromophores, which is oriented along the dipole
axis spanning from the (hetero)aroyl substituent to the aniline moiety.
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1.
Introduction
Difluoro oxazaborinines A, i.e. BF2-ketoimino complexes, can formally be considered as
borondifluoride-enaminone complexes, which are in a line with BF2-diketo (B) and BF2-diimino
complexes (C), the alternate complexes of 1,3-dicarbonyl synthetic equivalents (Figure 1) [1].
Figure 1. Structurally related BF2-ketoimino (A), BF2-diketo (B), and BF2-diimino (C) complexes.
Although already structurally characterized some decades ago [2,3] and employed in [2+2]
photodimerizations [4], difluoro oxazaborinines A as polar heterocyclic π-systems have gained
considerable interest as a consequence of their electronic ground and excited state properties [1].
According to cyclic voltammetry the chelating enaminone can be regarded as a weak electron
acceptor. Its LUMO can be stabilized by extending the π-conjugation with suitable aromatic
substituents, and thereby the reduction is facilitated. More recently, the observation of pronounced
solid state fluorescence has led to closer inspection of the induction of luminescence by aggregation
induced emission (AIE) [5] of the difluoro oxazaborinines with extended π-conjugation [6], displaying
mechanoluminescence and even heat-resistant mechanoluminescent chromism of oligomeric
silsesquioxane boron ketoiminate hybrids [7]. In comparison to the diketo analogue B the B-N bond in
the heterocycle A is considerably longer than the B-O bonds in structure B and therefore essential for
the occurrence of AIE.
Classical syntheses of difluoro oxazaborinines A are stepwise, starting from 1,3-dicarbonyl
compounds and require isolation of the enaminone or the BF2-diketo complexes B [6]. A major
drawback of this approach clearly is the inherent lack of control of the enaminone's regioselectivity.
Alternative routes to enaminones are either long linear stepwise processes [8] or only deliver very
specific substitution patterns [9]. For overcoming this shortcoming we reasoned that a diversity-
oriented synthesis [10] obtained by the same reaction principle through variation of suitable starting
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materials could be favorable. In particular, multicomponent reactions (MCR) [11] most beneficially
combine economic and ecological aspects for reaching this challenging goal. In the sense of a
chromophore concept, a chromogenic application of the MCR concept, functional chromophores have
become accessible more easily and more generally [12], an approach that has now been systematically
extended to a powerful tool in fluorophore design [13].
In the course of our program to devise multicomponent syntheses of heterocycles initiated by
transition metal catalyzed alkynylation [14], we also disclosed a straightforward, highly
stereoselective consecutive three-component synthesis of Z-configured enaminones 4 with perfect
regiospecificity from acid chlorides 1, alkynes 2, and primary amines 3 via the intermediacy of
alkynones 5 (Scheme 1) [15], which was later on expanded to four-component syntheses of
tetrahydro-β-carbolines [16], pyridones [17], and pyrroles [18].
R3
2 mol% Pd(PPh3)2Cl2, 4 mol% CuI
O
HN
O
1 equiv NEt3, THF, rt
R1
R2
+
R1
R2
then: R3NH2 3, MeOH,
Cl
O
4 (3 examples, 78-97%)
2
1
R2
via
R1
5
Scheme 1. Consecutive three-component synthesis of enaminones Z-4.
Herein, inspired by the interesting solid state luminescence of difluoro oxazaborinines A with
extended π-conjugation [6,7] we report a novel consecutive four-component synthesis of difluoro
oxazaborinines with perfect regioselectivity and their photophysical properties.
2.
Results and discussion
Synthesis and structure
2.1.
Initiated by our catalytic synthesis of alkynones 5 [14a,b,15] and a detailed optimization of the amine
addition in the presence of boron trifluoride as an activating Lewis acid and the remaining fourth
component (for details see Supp Inf) we identified optimal conditions for a diversity-oriented one-pot
approach to difluoro oxazaborinines 6. Upon subsequently reacting of acid chloride 1, alkyne 2, boron
trifluoride, and amine 3 in the sense of a consecutive four-component process the title compounds 6
were obtained in modest to good yield as yellow solids in most cases (Scheme 2, Table 1), which are
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nonemissive in solution but display pronounced solid state emission under UV light. A practical aspect
is the isolation of the products 6, which can often be obtained analytically pure by simple precipitation
into cold methanol. Thereby, a facile scale-up to 10 mmol was readily achieved (Table 1, entries 2, 5,
8-11, 14, and 16-29). Although the substrate scope is broad with respect to the alkynylation
substitution pattern, a special attention has to be paid to electron rich amines in the latter part of the
sequence. The domino formation of the difluoro oxazaborinines is considerably hampered in these
cases by formation of Lewis acid-base adducts between boron trifluoride and the amine nucleophiles.
To some extent this problem could be circumvented by first performing the enaminone generation
after the alkynylation, i. e. prior to the addition of the boron trifluoride as a cyclizing component.
Scheme 2. Consecutive four-component synthesis of 2,2-difluoro-2H-1,3λ4,2λ4-oxazaborinines 6.
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Table 1. Experimental details of the four-component synthesis of 2,2-difluoro-2H-1,3λ4,2λ4-
oxazaborinines 6.
2,2-difluoro-2H-1,3λ4,2λ4-
oxazaborinines 6 (yield)
entry acid chloride
1
1
alkyne 2
primary
amine 3
R1 = Ph (1a)
R2 = Ph (2a)
R3 = Ph (3a)
6a (73%)
2a
R1 = p-
MeOC6H4
(1b)
2a
2a
3a
3a
6b (64%)
3
R1 = p-
MeC6H4 (1c)
6c (62%)
6d (74%)
4
R1 = 2-thienyl
2a
2a
3a
3a
(1d)
5a
R1 = p-
NCC6H4 (1e)
6e (26%)
6
R1 = p-
O2NC6H4 (1f)
2a
2a
3a
6f (52%)
6g (74%)
7
R1 = o-FC6H4
(1g)
3a
3a
8a
R2 = p-
MeOC6H4
(2b)
1a
1a
1a
6h (46%)
9a
R2 = p-
MeC6H4 (2c)
3a
3a
6i (50%)
6j (56%)
10a
R2 = 2-thienyl
(2d)
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11a
R2 = p-
1a
3a
NCC6H4 (2e)
6k (48%)
12
13
R2 = n-Bu (2f)
1a
1c
3a
3a
6l (40%)
2f
6m (44%)
6n (5%)
14a
15
R3 = p-
Me2NC6H4
(3b)
1a
1a
1a
1a
2a
2a
2a
2a
R3 = p-
MeOC6H4 (3c)
6o (61%)
6p (71%)
16a
17a
R3 = p-ClC6H4
(3d)
R3 = p-IC6H4
(3e)
6q (73%)
6r (27%)
18a
19a
R3 = m-
O2NC6H4 (3f)
1a
1a
2a
2a
R3 = p-NCC6H4
(3g)
6s (36%)
20a
R3 = 2,6-
1a
2a
Me2C6H3 (3h)
6t (51%)
6u (73%)
21a
22a
R3 = 1-
naphthyl (3i)
1a
1b
2a
2a
3c
6v
(69%)
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23a
24a
1d
1e
2a
3c
6w (47%)
2a
3c
6x
(46%)
25a
26a
1a
1d
2b
2d
3c
3c
6y (84%)
6z (66%)
27b
28b
R3 = CH2Ph
1a
1a
2a
2a
(3j)
6aa (73%)
R3 = i-Pr (3k)
6ab (36%)
29b
1c
2a
3j
6ac (74%)
aPerformed on 10 mmol scale with the alkynylation step at room temp for 2 d and the amination-cyclization step
b
at 65 °C for 3 h. Performed on 10 mmol scale with the alkynylation step at room temp for 2 d, the amination
step at 65 °C for 3 h and the cyclization step at 65 °C for 3 h.
1
The structures of the difluoro oxazaborinines 6 were unambiguously assigned by comprehensive H
13
and C NMR spectroscopy and mass spectrometry. Most characteristically the proton resonances for
the central CH appear between
cone of the neighboring (hetero)aryl substituents. The corresponding methine carbon nuclei resonate
in range from 93.7 to 101.9, but mostly in a very narrow window between 95 to 98. In addition,
heteronuclear NMR spectra were recorded. The BF2-unit gives rise to coupling between the boron and
δ 6.0 and 7.0, depending of on shielding or deshielding by anisotropy
δ
δ
the fluorine nuclei that can be found in the 11B ( 0.86-1.56; t, 1JB-F = 14.1.-17.1 Hz) and 19F (
δ δ -132.3
1
to -138.7; q, JF-B = 13.7-19.7 Hz) NMR spectra. Due to the steric hindrance of the 1-naphthyl
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substitution compound 6u displays atropisomerism, which can be detected at room temp in both the
19
11B and the F NMR spectra by the occurrence of diastereotopic fluorine nuclei (Figure 2). While in
the 11B NMR spectrum the signal at
δ 1.5 splits into a doublet of doublets with direct coupling
1
constants of J of 12.4 and 17.1 Hz, the two diastereotopic fluorine nuclei give two doublets of
quartets at
δ
-133.09 (dq, 2JF-F = 89.3 Hz, 1JF-B = 16.6 Hz) and -138.43 (dq, 2JF-F = 91.4 Hz, 1JF-B = 11.5
1
Hz), with direct coupling constants at JF-B = 11.5 and 16.6 Hz, respectively, and large geminal
2
coupling constants at JF-F = 89.3 and 91.4 Hz. This sterically hindered rotation of the R3 substituent
can be additionally supported by inspection of the variable temperature (VT) 19F NMR spectra of
compound 6r (Figure 3), where the broad signal at
δ -133.37 for a coalescence temperature Tc = 258 K
can be used to estimate the rotational barrier ∆G≠ = 11.35 ± 0.23 kcal/mol (∆G≠ = 4.575 ·10-3 · Tc
[9.972 + log10(Tc/∆ν)]. But it has to be mentioned that in the measuring range the signals are broad and
do not resolve to quartets by coupling to the boron nucleus.
In all EI mass spectra of the compounds 6, with exception of difluoro oxazaborinine 6k, the molecular
peak can be detected, which undergoes extrusion of BF2 to give the corresponding enaminoyl radical
cations. This intermediate fragments into three dominant units, i.e. the fragments R1+, R1CO+, and
R2CN+R3, which appear in most cases and can be rationalized by α-cleavages.
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Figure 2. a) 11B NMR spectrum of compound 6u (recorded in CDCl3, 96 MHz, T = 298 K). b) 19F
NMR spectrum of compound 6u (recorded in CDCl3, 282 MHz, T = 298 K).
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Figure 3. VT 19F NMR spectra of compound 6r (recorded in CDCl3, 565 MHz, T = 268, 258, 248, and
243 K).
2.2.
Photophysical properties
Most remarkably difluoro oxazaborinines 6 are nonluminescent in solution, but the vast majority
distinctly fluoresces in the solid state upon excitation of the solid materials with a handheld UV lamp
and aroused our interest to study their photophysical properties by solid state absorption and emission
spectroscopy (Table 3). Only exemplarily, three representative difluoro oxazaborinines (6a, 6c, and
6o) were characterized by the solution absorption spectra (Table 1, entries 1, 3, and 12) showing broad
longest wave length absorption bands at 360 to 367 nm with decadic molar extinction coefficients
ε
between 23000 and 34500 L·mol-1·cm-1. In the solid state the excitation maxima of the N-aryl
substituted difluoro oxazaborinines 6a-z, which correspond to the longest absorption bands are
considerably red shifted and appear between 389 and 448 nm. The N-alkyl substituted derivatives 6ab
and 6ac absorb in the solid state with a maxima at 384 and 360 nm, respectively. This already
indicates that that the nature of N-substituent R3 is of prominent importance for the absorption
behavior as a consequence of extending the π-conjugation for N-aryl substituents. With exception of
compounds 6f, 6l, 6n, and 6aa, which did not fluoresce in the solid state, all other compounds were
studied in the emission behavior with an integrated sphere (Ulbricht sphere). Thereby, the emission
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maxima
λ
max,em, the fluorescence quantum yields
Φ
f, the excitation maxima
λ
max,abs (determined from
the fluorescence excitation spectra) (Figure 3), and the huge Stokes shifts ∆ν̃ in a range from 2400 to
6500 cm–1 were determined.
Table 3. Selected photophysical data (solid state absorption and emission, Stokes shifts) of difluoro
oxazaborinines 6 (recorded at T = 293 K).
entry compound
solution
solid state
absorption
absorption emission
Stokes shift
∆ν̃
[cm-1]b
λ
max,abs [nm] (
ε
λ
exc [nm]
λ
max,em [nm]
[L·mol-1·cm-1])a
253 (6100)
(
Φf [%])
360 (23200)
1
2
425
444
523 (18)
497 (34)
4400
6a
-
2400
6b
367 (34500)
3
4
5
430
448
423
500 (39)
525 (16)
563 (2)
3300
4900
5900
6c
-
-
6d
6e
-
-
6
7
8
406
443
422
512 (13)
533 (12)
526 (10)
5100
3800
4700
6g
6h
-
6i
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-
9
446
539 (4)
3900
5100
6j
-
10
429
549 (12)
6k
-
11
389
520 (6)
6500
6m
6o
255 (10000)
345 (23000)
363 (24000)
12
13
435
420
551 (12)
533 (9)
4800
5000
-
6p
-
14
15
16
414
423
422
526 (6)
488 (3)
497 (14)
5100
3100
3600
6q
-
-
6r
6s
-
17
18
441
429
503 (1)
563 (3)
2800
5500
6t
-
-
6u
19
441
524 (26)
3600
6v
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-
20
21
448
573 (6)
588 (2)
4900
5400
6w
-
446
6x
-
22
23
443
582 (3)
578 (3)
5400
5000
6y
-
448
6z
-
-
24
25
384
360
477 (5)
5100
5800
6ab
455 (14)
6ac
aRecorded in CH2Cl2, c(6) = 10-5
M ν̃ = 1/λexc – 1/λ
at T = 293 K. b∆ max,em [cm-1].
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Figure 3. a) Normalized solid state excitation (solid line) and fluorescence spectra (dashed line) of
compound 6v (recorded at T = 293 K). b) Normalized solid state excitation (solid line) and
fluorescence spectra (dashed line) of compound 6x (recorded at T = 293 K).
The physical organic treatment of the substituent effects on difluoro oxazaborinines 6 was performed
by screening for possible linear structure-property relationships based upon Hammett-Taft correlations
for the three points of diversity represented by the para-phenyl substituents R1, R2, and R3. The
photophysical data
λ
exc (excitation maximum),
λ
max,em (emission maximum),
14
Φf (fluorescence quantum

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yield), and ∆
ν
̃
(Stokes shift) of three consanguineous series, where one substituent was varied while
the other two substituents were held constant (as phenyl substituents), were plotted against the
Hammett-Taft parameters [19] σp, σI, σR, σp+, and σp- (for details, see Supp Inf).
The excitation spectra which were determined from the emission maxima did not reveal any
correlation in either substituent position. While substituent R1, introduced by the acid chloride 1, is not
affected by steric interactions with the neighboring substituents as for R2 and R3 stemming from the
alkyne 2 and the aniline 3, respectively, the electronic ground state properties, represented by the
excitation maxima
λ
exc, are obviously affected by the presence of different conformers, which are in a
f do not give systematic linear
thermodynamic equilibrium. Also the fluorescence quantum yields
Φ
free energy relationships. This is partly reflected by the fact that fluorescence quantum yield are far
from unity in all cases and, therefore, nonradiative deactivation dominates all excited stated processes
in all three series. Most interestingly, best correlations are found for the emission maxima
in the series of the variation of substituent R1.
λmax,em, and
for the Stokes shifts ∆ν̃
The series of R1 consists of compounds 6a-e, where the variation proceeds from electron releasing
(6b) over electro neutral (6a) to electron deficient (6e). The emission maxima λmax,em give a good
linear correlation with the substituent parameter σp (λ
max,em = -2558.5 · σP + 19348 [cm-1]; r² = 0.9593)
indicating that the substituent effect is transmitted both by resonance and inductive pathways in the
excited state. The negative reaction parameter accounts for a lowering of the energy of the emission by
electron withdrawing substituents. Most remarkably the Stokes shifts ∆ν̃ of this first series correlates
excellently with the substituent parameter (∆ν̃
= 2459.6 · σp+ + 4266.9 [cm-1]; r² = 0.9876), which
accounts for a significant charge transfer character in the vibrationally relaxed excited singlet state
from an electron releasing substituent capable of stabilizing positive charge to the nitrogen atom of the
difluoro oxazaborinine.
The second series of R2 consists of compounds 6a,h-k, where the variation proceeds from electron
releasing (6h) over electro neutral (6a) to electron deficient (6k). The only good linear correlation that
could be established occurs with the inductive parameter σI (λ
max,em = -1710.5 · σI + 19003 [cm-1], r² =
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0.9335). This indicates that in the vibrationally relaxed excited singlet state the aromatic substituent is
distorted considerably out of coplanarity with the major chromophore.
The last series of R3 encompasses the compounds 6a,o-q,s, where the variation proceeds from electron
releasing (6o) over electro neutral (6a) to electron deficient (6s). The best linear correlation can be
established with the resonance parameter σR (λmax,em = 3091.6 · σR + 19360 [cm-1], r² = 0.9393),
indicating that delocalization with substituents in the para-position stabilize the formally electron
deficient difluoro oxazaborinine nitrogen. This is further supported by the positive slope of the
reaction parameter.
This physical organic analysis of the difluoro oxazaborinine fluorophore suggests R1 adopts the
function as an acceptor moiety, whereas R3 acts as the donor counterpart (Figure 4). Substituent R2 is
obviously distorted out of coplanarity in the excited state and only can operate by its inductive effect.
Figure 4. Electronic substituent design of difluoro oxazaborinine fluorophores.
The interaction between substituents can be nicely demonstrated for variation of substituents R1 and
R3 compared to the mother system 6a (R1 = R2 = R3 = Ph). Donor (p-anisyl) and acceptor substituents
(p-cyanophenyl) were placed at positions R1 and R3 and for the compounds 6a (R1 = Ph, R3 = Ph), 6b
(R1 = p-anisyl, R3 = Ph), 6e (R1 = p-NCC6H4, R3 = Ph), 6o (R1 = Ph, R3 = p-anisyl), 6s (R1 = Ph, R3 =
p-NCC6H4), 6v (R1 = p-anisyl, R3 = p-anisyl), and 6x (R1 = p-NCC6H4, R3 = p-anisyl) the Stokes shifts
∆ν̃ and the fluorescence quantum yields Φf, were compared (Figure 5). While the placement of p-
anisyl donors at the positions R1 and/or R3 in tendency leads to smaller Stokes shifts, the placement of
p-cyanophenyl acceptors leads to an increase in the Stokes shifts compared to the all phenyl-
substituted reference chromophore 6a (Figure 5a). Interestingly the fluorescence quantum yields
Φf are
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consistently higher for the donor systems in comparison to the acceptor chromophores, while the
electroneutral reference chromophore 6a adopts the intermediate position (Figure 5b).
Figure 5. Qualitative comparison of a) Stokes shifts ∆ν̃ and b) fluorescence quantum yields Φf of
compounds 6a (R1 = Ph, R3 = Ph), 6b (R1 = p-anisyl, R3 = Ph), 6e (R1 = p-NCC6H4, R3 = Ph), 6o (R1 =
Ph, R3 = p-anisyl), 6s (R1 = Ph, R3 = p-NCC6H4), 6v (R1 = p-anisyl, R3 = p-anisyl), and 6x (R1 = p-
NCC6H4, R3 = p-anisyl) with donor (p-anisyl) and/or acceptor substituents (p-cyanophenyl) (the data
were taken from Table 3).
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Therefore, it was reasoned that the fluorescence quantum yield
Φ
f might correlate with the Stokes shift
∆ν
̃
Φ
ν
̃
* + 54.858 [%]; R² = 0.84311; *
ν̃
is normalized to a dimensionless value), indicating that increased changes in the electronic structure,
reflected by the considerable charge transfer in the vibrationally relaxed excited singlet state with
increased polarity by enhanced donor-acceptor substitution, causes a decrease in the fluorescence
quantum yield (Figure 6). This finding is in agreement with the energy gap law [20], i. e. the
nonradiative decay of the excited state with increasing redshift of the emission bands.
Figure 6. Linear correlation plot of the fluorescence quantum yields Φf against the Stokes shifts ∆
ν̃
(normalized) of compounds 6a (R1 = Ph, R3 = Ph), 6b (R1 = p-anisyl, R3 = Ph), 6e (R1 = p-NCC6H4, R3
= Ph), 6o (R1 = Ph, R3 = p-anisyl), 6s (R1 = Ph, R3 = p-NCC6H4), 6v (R1 = p-anisyl, R3 = p-anisyl), and
6x (R1 = p-NCC6H4, R3 = p-anisyl).
2.3.
Calculated electronic structure
Since computations of solid state absorption properties are particularly difficult due to the combination
of intermolecular interaction, crystal packing and ultimately aggregation, a qualitative understanding
of the photophysical behavior of difluoro oxazaborinines in solution was sought in elucidating the
electronic structure by calculating UV/vis absorption spectra at the TD DFT level of theory employing
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Gaussian09 [21] (B3LYP functional [22] and Pople 6-311+G(d,p) basis set [23]). The computations
were performed on the DFT optimized structures of compounds 6a (R1 = R2 = R3 = Ph), 6c (R1 = p-
tolyl, R2 = R3 = Ph), and 6o (R1 = R2 = Ph, R3 = p-anisyl,) where experimental absorption spectra were
recorded, in the electronic ground state applying the PCM model [24] with dichloromethane as a
dielectric to model the solvent influence (Table 4).
Table 4. Experimental and TD-DFT calculated (B3LYP/6-311+G(d,p)) UV/Vis absorption maxima of
the structures 6a, 6c, and 6o, applying PCM with dichloromethane as a solvent.
Most dominant contributions Oscillator strength
λ
max,abs [nm]
λmax,calcd [nm]
(
ε
[L mol-1 cm-1])[a]
253
6a
360
367
368
371
0.6336
0.8009
HOMO → LUMO (97 %)
HOMO → LUMO (98 %)
6c
6o
255 (10000)
345 (23000)
363 (24000)
336
413
0.6219
0.3723
HOMO-1 → LUMO (96 %)
HOMO → LUMO (99 %)
[a] Recorded in dichloromethane, T = 293 K, c(6) = 10-5
M
.
The calculated spectra qualitatively reproduce the experimental data and as can be seen the longest
wavelength absorption maxima are represented by HOMO-LUMO transitions, with the exception of
structure 6o, where the experimentally determined longest wavelength band consists of a HOMO-1 to
LUMO transition. The calculated longest wavelength maximum is found at 413 as a HOMO-LUMO
transition. A closer inspection of the frontier molecular orbitals of structure 6a reveals that the
coefficient density in the HOMO is aligned the heuristically assigned chromophore axis (vide supra),
i.e. including on the R1 and R3 substituents (Figure 7). Interestingly, the substituent R2 does not bear
coefficient density in the HOMO, but in the LUMO. Therefore, a Franck-Condon transition can be
assumed that leads to the S1 state after relaxation the HOMO-LUMO transition in this mother system
accounts for a partial charge transfer proceeding into this appending substituent.
19

ACCEPTED MANUSCRIPT
Figure 7. DFT calculated HOMO (bottom) and LUMO (top) of structure 6a.
The qualitative substituent effect on the FMO energies of the selected difluoro oxazaborinines 6 was
determined computationally by considering the HOMO-LUMO gap ∆EHOMO-LUMO and the differences
of the HOMO ∆EHOMO(6a – 6) and LUMO energies ∆ELUMO(6a – 6) to the mother chromophore 6a. In
detail the FMO energies of the p-anisyl donors 6b (R1 = p-anisyl, R2 = R3 = Ph), 6h (R1 = R3 = Ph, R2
= p-anisyl) and 6o (R1 = R2 = Ph, R3 = p-anisyl), of the reference 6a (R1 = R2 = R3 = Ph), of the p-
cyanophenyl acceptors 6e (R1 = p-NCC6H4, R2 = R3 = Ph), 6k (R1 = R3 = Ph, R2 = p-NCC6H4), and 6s
(R1 = R2 = Ph, R3 = p-NCC6H4), as well as the donor-acceptor chromophore 6x (R1 = p-NCC6H4, R2 =
Ph, R3 = p-anisyl) were calculated (Table 5, Supp Inf Figure S1).
As can be seen by comparing the FMOs of the three p-anisyl donor chromophores 6b (R1 = p-anisyl),
6h (R2 = p-anisyl) and 6o (R3 = p-anisyl) with the mother system 6a the donor rises the HOMO most
when positioned at R3, followed by R1 and only to a minor extend when positioned at R2 (Table 5,
entries 1-3). The LUMO is risen most when the donor is positioned at R1 and only slightly at the two
other positions.
20

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Table 5. DFT calculated HOMO and LUMO energies, HOMO-LUMO gap ∆EHOMO-LUMO and
differences of the HOMO ∆EHOMO(6a – 6) and LUMO energies ∆ELUMO(6a – 6) of the difluoro
oxazaborinines 6b, 6h, 6o, 6a, 6e, 6k, 6s, and 6x.
entry structure
EHOMO
[eV]
ELUMO
[eV]
∆EHOMO-LUMO ∆EHOMO(6a – 6) ∆ELUMO(6a – 6)
[eV]
3.739
3.855
3.494
3.840
3.651
3.699
4.081
3.211
[eV]
+ 0.265
+ 0.083
+ 0.423
0
- 0.321
- 0.259
- 0.335
+ 0.188
[eV]
+ 0.164
+ 0.098
+ 0.077
0
- 0.510
- 0.400
- 0.364
- 0.441
1
2
3
4
5
6
7
8
6b (R1 = p-anisyl)
-6.067
-6.249
-5.909
-6.332
-6.653
-6.591
-6.667
-6.144
-2.328
-2.394
-2.415
-2.492
-3.002
-2.892
-2.856
-2.933
6h (R2 = p-anisyl)
6o (R3 = p-anisyl)
6a (R1 = R2 = R3 = Ph)
6e (R1 = p-NCC6H4),
6k (R2 = p-NCC6H4)
6s (R3 = p-NCC6H4)
6x (R1 = p-NCC6H4, R3
= p-anisyl)
The HOMO-LUMO gap ∆EHOMO-LUMO largely affected by the positioning of the HOMO, and,
therefore, in this consanguineous series the donor placed at R3 in structure 6o gives with 3.494 eV the
smallest HOMO-LUMO gap. For the p-cyano phenyl acceptor the chromophores 6e (R1 = p-NCC6H4),
6k (R1 = R3 = Ph, R2 = p-NCC6H4), and 6s (R3 = p-NCC6H4) the HOMO is lowered by 0.26 and 0.34
eV, i.e. in a narrow range (Table 5, entries 5-7). However, the effect on the LUMO spans a range from
-0.36 to -0.51 eV upon variation the substituent position from R1 over R2 to R3. In this consanguineous
series the LUMO energy determines the ∆EHOMO-LUMO and here positioning at R1 in structure 6e causes
the most redshifted gap. Hence, the positioning of the donor at R3 and the acceptor at R1 in structure
6x consequently leads to the lowest ∆EHOMO-LUMO with 3.211eV (Table 5, entry 8). The considerable
charge transfer character along the chromophore main axis of this computationally modelled HOMO-
LUMO transition is additionally underlined by the electronic structure, where the coefficient density in
the HOMO is localized in the central difluoro oxazaborinine core and the p-anisyl substituent at R3. In
contrast, the LUMO bears the coefficient density in the central difluoro oxazaborinine core and the p-
cyanophenyl moiety at R1 (Figure 8). In essence the increase in polarity upon HOMO-LUMO
excitation, representing the S1 state, is also supported by the solid state emission spectrum, where
compound 6x displays the most redshifted emission maximum of all synthesized compounds 6.
Therefore, this semiempirical computational approach allows qualitatively predicting the photonic
properties of trisubstituted difluoro oxazaborinines 6.
21

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Figure 8. DFT calculated HOMO (bottom) and LUMO (top) of structure 6x.
Indeed, expanding the π-conjugation of the difluoro oxazaborinine can be easily accomplished by
Sonogashira coupling of the iodide 6q with phenylacetylene (2a) to give π-expanded difluoro
oxazaborinine 6ad in 92% yield (Scheme 3). The solid state fluorescence spectrum of compound 6ad
shows a maximum 595 nm with a solid state fluorescence quantum yield Φf of 3% with an excitation
maximum of 433 nm. This allows now for redshifting the emission maximum even to orange and red
solid state luminescence without further decreasing the solid state fluorescence quantum yield.
Ph
I
F
F
F
F
0.1 mol% Pd(PPh3)2Cl2
0.2 mol% CuI
B
B
O
N
O
N
Ph
+
NEt3 (3.0 equiv), THF, RT, 24 h
Ph
Ph
Ph
Ph
6ad (92%)
6q
2a
Scheme 3. Sonogashira coupling of 2,2-difluoro-3-(4-iodophenyl)-4,6-diphenyl-2H-1,3λ4,2λ4-
oxazaborinine (6q) with phenylacetylene (2a) furnishing the π-expanded difluoro oxazaborinine 6ad.
22

ACCEPTED MANUSCRIPT
3.
In summary we have developed a novel diversity-oriented one-pot approach to trisubstituted difluoro
oxazaborinines in the sense of consecutive four-component synthesis starting from
Conclusion
a
(hetero)aroylchlorides, terminal alkynes, anilines, and boron trifluoride etherate. In contrast to 1,3-
dicarbonyl based syntheses of difluoro oxazaborinines this alkynylation-amination-cyclization is
completely regioselective and allows the preparation of unsymmetrically decorated difluoro
oxazaborinines. All representatives show only luminescence in the solid state, but not in solution.
Therefore, photophysical and physical organic investigations were elaborated to give a general
rationale of relevant transitions in the absorption spectra and the polar nature of the difluoro
oxazaborinine core was correlated with the substitution pattern. In addition first DFT and TD DFT
calculations guide the way to lower the HOMO-LUMO gap and thereby also the emission
characteristics. Further studies to redshift the solid state emissions of these unusual solid state emitters
by expanding the methodology are currently underway.
4.
Experimental
4.1.
General considerations
Reagents, catalysts, and solvents were purchased in reagent grade and used without further
purification. Anhydrous 1,4-dioxane was obtained from a drying system (MBraun system MB-SPS-
800). The reaction progress and the purification process were observed qualitatively by using TLC
silica gel 60 F254 sheets obtained by Merck KGaA. The spots were detected with UV light at 254 and
365 nm and with aqueous potassium permanganate solution. Chemical shifts
δ
in the 1H NMR and 13C
NMR spectra are reported relative to CDCl3 or d6-DMSO. The assignments of quaternary C, CH, CH2,
and CH3 signals were made by using DEPT-135 spectra. IR spectra were recorded with neat
compounds under attenuated total reflection (ATR) and the intensities were characterized as strong (s),
middle (m), and weak (w).
23

ACCEPTED MANUSCRIPT
4.2.
General procedure (GP) for the Four-component Synthesis of 2,2-Difluoro-2H-1,3λ4,2λ4-
oxazaborinines 6.
PdCl2 (2.0 mg, 10 µmol) were placed in an oven-dried Schlenk tube with a magnetic stir bar under
nitrogen, and 1,4-dioxane (2mL), acid chloride 1 (1.00 mmol), terminal alkyne 2 (1.00 mmol) and
triethylamine (0.14 mL, 1.00 mmol) were successively added (for experimental details, see Table 6).
The reaction mixture was stirred at room temp under nitrogen until complete conversion (monitored
by TLC). Then, BF3·OEt2 (0.26 mL, 2.00 mmol) and primary amine 3 (2.00 mmol) was added to the
reaction mixture, which was then stirred under nitrogen at 100 °C for 3 h. After cooling to room temp
the mixture was poured into cold methanol (150 mL, cooled by an external NaCl/ice bath) and stirred
for 15 min. If no precipitate was formed ice water was added to the solution until no further precipitate
formed. The solid was collected by filtration and dried in vacuo overnight to give analytical pure 2,2-
difluoro-2H-1,3λ4,2λ4-oxazaborinines 6 as yellow to brown solids.
Table 6. Experimental details of the four-component synthesis of 2,2-difluoro-2H-1,3λ4,2λ4-
oxazaborinines 6.
entry
acid chloride 1
alkyne 2
primary amine 3
2,2-difluoro-2H-
1,3λ4,2λ4-
oxazaborinines 5
(yield)
1
2a
3
253 mg (73%) of 6a
115 µL (1.00 mmol) 112 µL (1.00 mmol) 183 µL (2.00 mmol)
of benzoyl chloride
(1a)
of phenylacetylene
(2a)
of aniline (3a)
1.35 mL (10.0 mmol)
of p-methoxybenzoyl
chloride (1b)
1.12 mL (10.0
mmol) of
phenylacetylene (2a)
1.83 mL (20.0 mmol) 2.42 g (64%) of 6b
of aniline (3a)
224 mg (62%) of 6c
132 µL (1.00 mmol) 112 µL (1.00 mmol) 183 µL (2.00 mmol)
of p-toluoyl chloride
(1c)
of phenylacetylene
of aniline (3a)
(2a)
4
261 mg (74%) of 6d
110 µL (1.00 mmol) 112 µL (1.00 mmol) 183 µL (2.00 mmol)
of 2-thienoyl chloride
(1d)
1.66 g (10.0 mmol)
of p-cyanobenzoyl
chloride (1e)
186 mg (1.00 mmol)
of p-nitrobenzoyl
chloride (1f)
of phenylacetylene
of aniline (3a)
(2a)
1.12 mL (10.0
mmol) of
phenylacetylene (2a)
112 µL (1.00 mmol) 183 µL (2.00 mmol)
of phenylacetylene
5a
6
1.83 mL (20.0 mmol) 0.98 g (26%) of 6e
of aniline (3a)
204 mg (52%) of 6f
of aniline (3a)
(2a)
7
270 mg (74%) of 6g
119 µL (1.00 mmol) 112 µL (1.00 mmol) 183 µL (2.00 mmol)
of o-fluorobenzoyl
chloride (1g)
of phenylacetylene
of aniline (3a)
(2a)
8a
1.15 mL (10.0 mmol) 1.32 g (10.0 mmol) 1.83 mL (20.0 mmol) 1.75 g (46%) of 6h
of benzoyl chloride of p-methoxy- of aniline (3a)
24

ACCEPTED MANUSCRIPT
(1a)
phenylacetylene (2b)
9a
1.15 mL (10.0 mmol)
of benzoyl chloride
(1a)
1.15 mL (10.0 mmol)
of benzoyl chloride
(1a)
1.27 mL (10.0
mmol) of p-
tolylacetylene (2c)
0.95 mL (10.0
mmol) of 2-
1.83 mL (20.0 mmol)
1.82 g (50%) of 6i
1.98 g (56%) of 6j
of aniline (3a)
10a
1.83 mL (20.0 mmol)
of aniline (3a)
thiophenyl-acetylene
(2d)
11a
12
1.15 mL (10.0 mmol) 1.27 g (10.0 mmol) 1.83 mL (20.0 mmol) 1.80 g (48%) of 6k
of benzoyl chloride
of p-cyano-
phenylacetylene (2e)
of aniline (3a)
(1a)
131 mg (40%) of 6l
115 µL (1.00 mmol) 115 µL (1.00 mmol) 183 µL (2.00 mmol)
of benzoyl chloride
of hex-1-yne (2f)
of aniline (3a)
(1a)
13
150 mg (44%) of
132 µL (1.00 mmol) 115 µL (1.00 mmol) 183 µL (2.00 mmol)
6m
of p-toluoyl chloride
(1c)
of hex-1-yne (2f)
of aniline (3a)
14a
1.15 mL (10.0 mmol)
of benzoyl chloride
(1a)
1.12 mL (10.0
mmol) of
phenylacetylene (2a)
2.72 g (20.0 mmol)
of p-N,N-dimethyl
phenylene diamine
(3b)
195 mg (5%) of 6n
15
246 mg (2.00 mmol) 230 mg (61%) of 6o
115 µL (1.00 mmol) 112 µL (1.00 mmol)
of p-methoxyaniline
(3c)
2.55 g (20.0 mmol)
of p-chloroaniline
(3d)
of benzoyl chloride
(1a)
1.15 mL (10.0 mmol)
of benzoyl chloride
(1a)
1.15 mL (10.0 mmol)
of benzoyl chloride
(1a)
1.15 mL (10.0 mmol)
of benzoyl chloride
(1a)
1.15 mL (10.0 mmol)
of benzoyl chloride
(1a)
1.15 mL (10.0 mmol)
of benzoyl chloride
(1a)
1.15 mL (10.0 mmol)
of benzoyl chloride
(1a)
1.35 mL (10.0 mmol)
of p-methoxybenzoyl
chloride (1b)
of phenylacetylene
(2a)
16a
17a
18a
19a
20a
21a
22a
23a
24a
25a
1.12 mL (10.0
mmol) of
phenylacetylene (2a)
1.12 mL (10.0
mmol) of
phenylacetylene (2a)
1.12 mL (10.0
mmol) of
phenylacetylene (2a)
1.12 mL (10.0
mmol) of
2.71 g (71%) of 6p
3.47 g (73%) of 6q
1.07 g (27%) of 6r
1.35 g (36%) of 6s
1.92 g (51%) of 6t
2.88 g (73%) of 6u
2.82 g (69%) of 6v
1.80 g (47%) of 6w
1.85 g (46%) of 6x
3.41 g (84%) of 6y
4.38 g (20.0 mmol)
of p-iodoaniline (3e)
2.76 g (20.0 mmol)
of m-nitroaniline (3f)
2.36 g (20.0 mmol)
of p-cyanoaniline
(3g)
2.46 mL (20.0 mmol)
of 2,6-
phenylacetylene (2a)
1.12 mL (10.0
mmol) of
phenylacetylene (2a) dimethylaniline (3h)
1.12 mL (10.0
mmol) of
phenylacetylene (2a)
1.12 mL (10.0
mmol) of
phenylacetylene (2a)
1.12 mL (10.0
mmol) of
phenylacetylene (2a)
1.12 mL (10.0
mmol) of
2.86 g (20.0 mmol)
of 1-naphthylamine
(3i)
2.46 g (20.0 mmol)
of p-methoxyaniline
(3c)
2.46 g (20.0 mmol)
of p-methoxyaniline
(3c)
2.46 g (20.0 mmol)
of p-methoxyaniline
(3c)
1.10 mL (10.0 mmol)
of 2-thienoyl chloride
(1d)
1.66 g (10.0 mmol)
of p-cyanobenzoyl
chloride (1e)
phenylacetylene (2a)
1.15 mL (10.0 mmol) 1.32 g (10.0 mmol)
of benzoyl chloride
2.46 g (20.0 mmol)
of p-methoxyaniline
(3c)
of p-methoxy-
phenylacetylene (2b)
(1a)
25

ACCEPTED MANUSCRIPT
26a
27b
28b
29b
1.10 mL (10.0 mmol)
of 2-thienoyl chloride
(1d)
1.15 mL (10.0 mmol)
of benzoyl chloride
(1a)
1.15 mL (10.0 mmol)
of benzoyl chloride
(1a)
1.32 mL (10.0 mmol)
of p-toluoyl chloride
(1c)
0.95 mL (10.0
mmol) of 2-thio-
phenylacetylene (2d)
1.12 mL (10.0
mmol) of
phenylacetylene (2a)
1.12 mL (10.0
mmol) of
phenylacetylene (2a)
1.12 mL (10.0
mmol) of
phenylacetylene (2a)
2.46 g (20.0 mmol)
of p-methoxyaniline
(3c)
2.18 mL (20.0 mmol) 2.65 g (73%) of 6aa
of benzylamine (3j)
2.39 g (66%) of 6z
1.64 mL (20.0 mmol) 1.12 g (36%) of 6ab
of i-propylamine (3k)
2.18 mL (20.0 mmol) 2.79 g (74%) of 6ac
of benzylamine (3j)
aPerformed on 10 mmol scale with Pd(PPh3)2Cl2 (14 mg, 20 µmol), CuI (7.0 mg, 40 µmol), THF (7
mL), triethylamine (1.40 mL, 10.0 mmol) (alkynylation step: room temp, 2 d); BF3·OEt2 (2.56 mL,
20.0 mmol) (amination-cyclization step: 65 °C, 3 h). bPerformed on 10 mmol scale with Pd(PPh3)2Cl2
(14 mg, 20 µmol), CuI (7.0 mg, 40 µmol), THF (7 mL), triethylamine (1.40 mL, 10.0 mmol)
(alkynylation step: room temp, 2 d); amination step: 65 °C, 3 h; BF3·OEt2 (2.56 mL, 20.0 mmol)
(cyclization step: 65 °C, 3 h).
4.2.1. 2,2-Difluoro-3,4,6-triphenyl-2H-1,3λ4,2λ4-oxazaborinine (6a)
1
According to the GP compound 6a (253 mg, 73%) was obtained as a yellow solid, Mp 195 °C. H
NMR (CDCl3, 300 MHz):
δ
6.39 (s, 1 H), 7.11-7.22 (m, 5 H), 7.22-7.36 (m, 5 H), 7.43-7.60 (m, 3 H),
96.8 (CH), 126.9 (CH), 127.3 (CH), 127.7 (CH),
13
8.01-8.06 (m, 2 H). C NMR (CDCl3, 75 MHz):
δ
128.4 (CH), 128.6 (CH), 128.7, (CH), 128.7 (CH), 130.4 (CH), 132.8 (CH), 133.1 (Cquat), 134.9 (Cquat),
19
140.5 (Cquat), 170.6 (Cquat), 172.2 (Cquat). F NMR (CDCl3, 282 MHz):
δ
-134.15 (q, 1JF-B = 14.2 Hz).
1
11B NMR (CDCl3, 96 MHz):
δ
1.46 (t, JB-F = 15.1 Hz). EI MS (m/z (%)): 347 ((M)+, 44), 180
((C13H10N)+, 5), 105 ((C7H5O)+, 21), 77 ((C6H5)+, 28), 51 ((C3H2N)+, 8). IR: [cm-1] = 1595 (w), 1568
ν̃
(m), 1558 (m), 1476 (s), 1454 (m), 1443 (m), 1402 (m), 1358 (m),1312 (w), 1287 (w), 1233 (w), 1153
(w), 1109 (s), 1076 (w), 1057 (m), 1022 (s), 997 (s), 976 (m), 930 (w), 912 (w), 868 (w), 839 (w), 806
(w), 779 (s), 762 (s), 727 (w), 691 (s), 658 (w), 631 (m), 619 (w). Anal. calcd. for C21H16BF2NO
(347.2): C 72.65, H 4.65, N 4.03; Found: C 72.68, H 4.76, N 3.90.
4.2.2. 2,2-Difluoro-6-(4-methoxyphenyl)-3,4-diphenyl-2H-1,3λ4,2λ4-oxazaborinine (6b)
1
According to the GP compound 6b (2.42 g, 64%) was obtained as a yellow solid, Mp 191 °C. H
NMR (CDCl3, 300 MHz):
δ 3.89 (s, 3 H), 6.31 (s, 1 H), 6.94-7.00 (m, 2 H), 7.11-7.22 (m, 5 H), 7.22-
7.37 (m, 5 H), 7.99-8.06 (m, 2 H). 13C NMR (CDCl3, 75 MHz):
δ
55.2 (CH3), 95.8 (CH), 114.1 (CH),
125.4 (Cquat), 127.0 (CH), 127.1 (CH), 128.4 (CH), 128.6 (CH), 128.6 (CH), 129.9 (CH), 130.2 (CH),
19
135.2 (Cquat), 140.7 (Cquat), 163.6 (Cquat), 170.1 (Cquat), 172.0 (Cquat). F NMR (CDCl3, 282 MHz):
26
δ -

ACCEPTED MANUSCRIPT
134.66 (q, 1JF-B = 15.2 Hz). 11B NMR (CDCl3, 96 MHz):
δ
1.43 (t, 1JB-F = 15.4 Hz). EI MS (m/z (%)):
377 ((M)+, 51), 362 ((M-CH3)+, 6), 333 (6), 312 ((M-BF2O)+, 5), 135 ((C8H7O2)+, 28), 107 ((C7H7O)+,
5), 77 ((C6H5)+, 16). IR: [cm-1] = 2995 (w), 2961 (w), 2945 (w), 2914 (w), 2849 (w), 1603 (m), 1393
ν̃
(s), 1362 (m), 1308 (m), 1265 (s), 1234 (s), 1175 (s), 1152 (m), 1136 (m), 1117 (s), 1101 (s), 1072
(m), 1051 (m), 1018 (s), 997 (s), 974 (m), 947 (m), 928 (m), 912 (w), 858 (s), 841 (m), 822 (m), 798
(s), 764 (s), 723 (m), 721 (m), 692 (s), 675 (m), 637 (m), 617 (m). Anal. calcd. C22H18BF2NO2 (377.2):
C 70.05, H 4.81, N 3.71; Found: C 69.96, H 4.84, N 3.64.
4.2.3. 2,2-Difluoro-3,4-diphenyl-6-(p-tolyl)-2H-1,3λ4,2λ4-oxazaborinine (6c)
1
According to the GP compound 6c (224 mg, 62%) was obtained as a yellow solid, Mp 214 °C. H
NMR (CDCl3, 600 MHz):
δ
2.42 (s, 3 H), 6.36 (s, 1 H), 7.12-7.18 (m, 3 H), 7.18-7.21 (m, 2 H), 7.21-
13
7.23 (m, 1 H), 7.24 (m, 2 H), 7.25-7.29 (m, 3 H), 7.30-7.33 (m, 1 H), 7.92-7.95 (m, 2 H). C NMR
(CDCl3, 75 MHz):
δ 21.8 (CH3), 96.6 (CH), 127.1 (CH), 127.3 (CH), 127.9 (CH), 128.6 (CH), 128.7
(CH), 128.8 (CH), 129.7 (CH), 130.5 (CH), 130.5 (Cquat), 135.2 (Cquat), 140.8 (Cquat), 143.9 (Cquat),
1
170.6 (Cquat), 172.5 (Cquat). 19F NMR (CDCl3, 565 MHz):
δ
-134.26 (q, JF-B = 14.7 Hz). 11B NMR
(CDCl3, 193 MHz):
δ
1.46 (t, 1JB-F = 15.2 Hz). EI MS (m/z (%)): 361 ((M)+, 55), 119 ((C8H7O)+, 10),
[cm-1] = 1603 (w), 1589 (w), 1491 (s), 1452 (m),
91 ((C7H7)+, 5), 77 ((C6H5)+, 5), 40 ((C3H4)+, 5). IR:
ν
̃
1425 (m), 1391 (m), 1364 (m), 1315 (w), 1296 (w), 1248 (w), 1231 (w), 1215 (w), 1192 (m), 1152
(w), 1099 (m), 1074 (w), 1057 (m), 1018 (s), 970 (m), 957 (w), 916 (w), 887 (w), 862 (w), 835 (m),
795 (s), 764 (s), 731 (w), 694 (s), 665 (w). Calcd. for C22H18BF2NO (361.2): C 73.16, H 5.02, N 3.88;
Found: C 72.98, H 5.01, N 3.73.
4.2.4. 2,2-Difluoro-3,4-diphenyl-6-(thiophen-2-yl)-2H-1,3λ4,2λ4-oxazaborinine (6d)
According to the GP and after recrystallization compound 6d (261 mg, 74%) was obtained as a yellow
1
solid, Mp 268 °C. H NMR (CDCl3, 300 MHz):
δ 6.23 (s, 1 H), 7.09-7.13 (m, 1 H), 7.14 (s, 1 H),
7.15-7.18 (m, 1 H), 7.18-7.20 (m, 1 H), 7.20-7.36 (m, 7 H), 7.64 (dd, J = 5.0 Hz, J = 1.2 Hz, 1 H), 7.86
(dd, J = 3.8 Hz, J = 1.2 Hz, 1 H). 13C NMR (CDCl3, 75 MHz):
δ
96.2 (CH), 127.0 (CH), 127.2 (CH),
128.4 (CH), 128.6 (CH), 128.6 (CH), 128.7 (CH), 130.4 (CH), 131.4 (CH), 132.8 (CH), 137.9 (Cquat),
140.6 (Cquat), 154.6 (Cquat), 166.9 (Cquat), 170.2 (Cquat). 19F NMR (CDCl3, 282 MHz): -134.96 (q, 1JF-B
δ
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ACCEPTED MANUSCRIPT
= 15.2 Hz). 11B NMR (CDCl3, 96 MHz):
δ
1.23 (t, 1JB-F = 15.1 Hz). EI MS (m/z (%)): 353 ((M)+, 47),
288 ((M-BF2O)+, 100), 180 ((C13H10N)+, 6), 111 ((C5H3OS)+, 46), 97 (12), 83 ((C4H3S)+, 11), 77
((C6H5)+, 23), 71 ((C3H3S)+, 10), 57 (13), 55 (8). IR: [cm-1] = 3109 (w), 3096 (w), 2990 (w), 2963
ν̃
(w), 2901 (w), 1601 (w), 1543 (w), 1526 (m), 1491 (s), 1477 (m), 1443 (m), 1412 (m), 1377 (m), 1329
(m), 1314 (m), 1285 (m), 1261 (w), 1229 (m), 1153 (m), 1136 (m), 1121 (m), 1074 (s), 1055 (s), 1015
(s), 998 (s), 978 (m), 916 (m), 903 (w), 880 (w), 862 (m), 851 (m), 841 (m), 797 (s), 785 (m), 762 (s),
748 (m), 726 (s), 696 (s), 681 (m), 654 (m), 619 (w). Anal. calcd. for C19H14BF2NOS (353.2): C 64.61,
H 4.00, N 3.97, S 9.08; Found: C 64.32, H 4.08, N 3.86, S 8.92.
4.2.5. 4-(2,2-Difluoro-3,4-diphenyl-2H-1,3λ4,2λ4-oxazaborinin-6-yl)benzonitrile (6e)
According to the GP and after recrystallization compound 6e (1.06 g, 34%) was obtained as a yellow
solid, Mp 244 °C. 1H NMR (CDCl3, 300 MHz):
H), 8.07-8.20 (m, 2 H). 13C NMR (CDCl3, 75 MHz):
δ 6.44 (s, 1 H), 7.06-7.44 (m, 10 H), 7.72-7.84 (m, 2
δ
98.2 (CH), 115.7 (Cquat), 118.0 (Cquat), 126.7
(CH), 127.7 (CH), 127.9 (CH), 128.5 (CH), 128.6 (CH), 128.8 (CH), 130.9 (CH), 132.4 (CH), 134.3
(Cquat), 137.2 (Cquat), 140.1 (Cquat), 169.0 (Cquat), 171.1 (Cquat). 19F NMR (CDCl3, 282 MHz):
δ
-133.71
1
1
(q, JF-B = 13.9 Hz). 11B NMR (CDCl3, 96 MHz):
δ
1.37 (t, JB-F = 14.4 Hz). EI MS (m/z (%)): 372
((M)+, 50), 130 ((C8H4NO)+, 22), 77 ((C6H5)+, 14). IR:
ν
̃
[cm-1] = 3127 (w), 3065 (w), 2230 (m), 1601
(m), 1578 (m), 1558 (m), 1487 (s), 1476 (s), 1435 (m), 1393 (m), 1373 (w), 1352 (m), 1323 (m), 1308
(w), 1290 (w), 1236 (m), 1221 (w), 1179 (m), 1140 (m), 1101 (m), 1063 (m), 1026 (s), 1015 (m), 997
(m), 972 (m), 957 (w), 937 (w), 918 (w), 907 (w), 868 (w), 853 (m), 810 (s), 768 (s), 756 (s), 741 (m),
723 (m), 696 (s), 667 (m), 646 (m), 615 (m). Anal. calcd. for C22H15BF2N2O (372.2): C 71.00, H 4.06,
N 7.53; Found: C 71.18, H 4.03, N 7.54.
4.2.6. 2,2-Difluoro-6-(4-nitrophenyl)-3,4-diphenyl-2H-1,3λ4,2λ4-oxazaborinine (6f)
According to the GP and after recrystallization compound 6f (204 mg, 52%) was obtained as a brown
solid, Mp 247 °C. 1H NMR (CDCl3, 300 MHz):
δ 6.47 (s, 1 H), 7.15 (dd, J = 7.7 Hz, J = 2.1 Hz, 2 H),
7.19-7.28 (m, 6 H), 7.28-7.33 (m, 1 H), 7.33-7.40 (m, 1 H), 8.15-8.23 (m, 2 H), 8.29-8.36 (m, 2 H).
13C NMR (CDCl3, 75 MHz):
δ
98.6 (CH), 123.9 (CH), 126.7 (CH), 127.8 (CH), 128.5 (CH), 128.5
(CH), 128.7 (CH), 128.9 (CH), 130.9 (CH), 134.3 (Cquat), 138.9 (Cquat), 140.1 (Cquat), 150.0 (Cquat),
28