Synthesis, structure and spectroscopic characteristics of 2′-boryl-4′-dimethylaminochalcones. Effect of an intramolecular boron-oxygen coordinate bond to the conjugated system

Article abstract of DOI:10.3987/COM-00-S(I)94

2′-Diethylboryl-4″-dimethylaminochalcone (1) and the related compounds (4)-(7) bearing a dioxyboryl group in the 2′-position were synthesized, and the effect of the intramolecular boron-oxygen coordinate bond on the spectroscopic characteristics of 4″-dimethylaminochalcone chromophore was examined by comparison with 4″-dimethylaminochalcone (2) using UV/VIS and fluorescence spectra.

Full text of DOI:10.3987/COM-00-S(I)94

HETEROCYCLES, Vol. 54, No. 2, pp. 929-942, Received, 22nd September, 2000
SYNTHESIS,
STRUCTURE
AND
SPECTROSCOPIC
CHARACTERISTICS
OF 2’-BORYL-4’’-DIMETHYLAMINO-
CHALCONES. EFFECT OF AN INTRAMOLECULAR BORON-
OXYGEN COORDINATE BOND TO THE CONJUGATED SYSTEM
Toshihiro Murafuji, * Kenji Sugimoto, Sachiko Yanagimoto,
Tomokazu Moriya, Yoshikazu Sugihara,* Yuji Mikata, † Masako
Kato,†† and Shigenobu Yano†
Department of Chemistry, Faculty of Science, Yamaguchi University, Yamaguchi
753-8512, Japan
†Department of Chemistry, Faculty of Science, Nara Women’s University, Nara
630-8506, Japan
††Divison of Material Science, Graduate School of Human Culture, Nara
Women’s University, Nara 630-8506, Japan
Abs tract – 2’-Diethylboryl-4’’-dimethylaminochalcone (1) and the related
compounds (4 )–(7 ) bearing a dioxyboryl group in the 2’-position were
synthesized, and the effect of the intramolecular boron–oxygen coordinate bond
on the spectroscopic characteristics of 4’’-dimethylaminochalcone chromophore
was examined by comparison with 4’’-dimethylaminochalcone (2) using UV/VIS
and fluorescence spectra.
INTRODUCTION
Construction of organometallics based on the coordinate bond between the metal center and the ligands is
an area of research that has grown tremendously in recent years. It is an important issue for us to
examine how coordination affects molecular structure and properties.1 Recently, we have reported the
structure and spectroscopic characteristics of 2’-diethylboryl-4’’-dimethylaminochalcone (1 ) bearing an
intramolecular boron–oxygen coordinate bond in comparison with 4’’-dimethylaminochalcone (2 ).2 It
has been found that, when compared with the respective ground states, the polarity of the exited state of 2
is greater than that of 1 due to the more polarized ground state of 1 , which is brought about by the
formation of the coordinate bond. In order to examine the effect of the coordinate bond to the properties

2 (1650 cm–1), which suggests the presence of the intramolecular coordinate bond between the boron and
carbonyl oxygen atoms. Hydrolysis of this salt under acidic conditions followed by neutralization
afforded 4. Compound (4) underwent transacetalization with some diols (1 equiv) in dichloromethane at
room temperature to give the corresponding cyclic boronic esters (5)–(7 ). These reactions proceeded
almost completely and did not give a mixture containing the starting boronic esters, which is suggestive of
the stability of 5–7 in preference to 4. The main reason in the respective reactions may be the electronic
factor at the boron center and/or the steric one around the boron atom, that is, the higher Lewis acidity of
the boron center of 4 than that of 5,3 the rigid conformation and lowered Lewis acidity of the boron center
in 6 by the tridentate ligand through an transannular boron–nitrogen coordinate bond, 4a and the steric
blocking around the boron center of 7 by the four methyl groups which suppress the reverse reaction.
Although a large excess (10 equiv) of ethanediol or N-methyldiethanolamine was allowed to react with 7 ,
each reaction proceeded scarcely.
While 1, 4, 5 and 7 are reddish-violet crystals, 6 is yellow crystals similar to 2, indicating the absence of
11
the intramolecular boron–oxygen coordinate bond. The measurement of B NMR spectra revealed the
respective chemical shifts (δ) of the boron atoms in 1(14.8), 4 (23. 0), 5(25.2), 6(12.1) and 7(25.5),
which appear at the upfield region compared with that in phenylboronic acid ethanediol ester (31. 2). 3
The signal of the boron atom of 6 was observed at the most upfield region among 4–7: the chemical shift
of 6 is comparable to that of 1.4b These observations suggest the formation of an intramolecular boron–
oxygen coordinate bond in 1, 4, 5 and 7 and an intramolecular boron–nitrogen coordinate bond in 6.
The UV/VIS spectra of 1, 2 and 4 –6 in chloroform are summarized in Figure 1. While 1 and 2 show
only one band in the longest wavelength region (486 and 414 nm for 1 and 2, respectively), 4–7 show
two bands in the longest wavelength absorption regions of 1 and 2. The relative intensity between these
bands in 4–7 is lower in the longer wavelength band. Such the difference in shape of the UV/VIS
spectra seems to be due to the lowered Lewis acidity of the dioxyboryl groups in 4–7 compared with that
of the diethylboryl group in 1. Addition of amine to a solution of 1, 4 , 5 or 7 in chloroform turns an
orange color of the respective solution into yellow one. For example, when an excess (15 equiv.) of
n-hexyldimethylamine is added, the absorbance of longest wavelength band of 1 is lowered and the new
absorption band appears at the corresponding region to the longest wavelength band of 2 . Furthermore,
when larger excess of the amine is used, the shape of the longest wavelength absorption band of 1 turns
similar to that of 4. In the 1H NMR spectrum of 1 in CDCl3, the proton signals of chalcone skeleton was
observed to shift to upfield region (0.2 ppm) on addition of the amine (15 equiv. ). These observations
suggest that the dissociation of the intramolecular boron–ox ygen coo rdinate b ond takes
place by the coordination of n-hexyldimethylamine to the boron atom. In contrast, an addition
of n-hexylamine caused the Michael addition followed by retro aldol-type reaction to give n-hexylimines of

1
dioxaborolane using variable temperature H NMR spectra in various solvents reported by Oki, 8 it is
revealed that ether, THF and acetone which have affinity toward boron atom promote the dissociation of
the intramolecular boron–nitrogen coordinate bond by the solvent assistance and that the dissociation is
also promoted in non-polar solvent than in polar solvent since the polarized structure brought about by the
intramolecular coordination can not be stabilized in the non-polar solvent. Thus, ether, THF, acetone,
ethyl acetate, carbon tetrachloride and cyclohexane promote to shift the equilibrium to the structure without
the intramolecular coordination in 7 . In acetonitrile, dichloromethane and chloroform which are polar
and possess weak or no coordination ability, the dissociation is somewhat restricted. In contrast,
methanol strengthens the intramolecular coordinate bond to promote the polarization of the 4’’-
dimethylaminochalcone chromophore to shift the equilibrium to the structure bearing the coordination.
Compounds ( 1 ) and (2 ) are moderately fluor escent and the fluorescence spectra display
solvatochromism.9 Compound (7) shows two emission maxima depending on the excitation wavelength,
each approximately corresponding to those of 1 and 2,10 which supports the presence of the equilibrium
derived from the UV/VIS spectral study. For example, when the solvent is changed from ethyl acetate to
methanol, bathochromic shifts of 52 and 28 nm are obtained for the shorter and the longer wavelength
emission maximum, respectively. In methanol only one emission maximum is observed, which is
considered to be the result that the equilibrium is shifted completely to the structure bearing the
intramolecular coordinate bond. Compounds (1) and (2) show good relationships in the Lippert–Mataga
equation11 (Y = 1.7168 + 3.6745X and Y = 2.8469 + 8.9390X where n = 10, R = 0.963 and σ = 0.0994
kK or n = 10, R = 0.950 and σ = 0.282 kK, respectively), where the difference between the absorption
and emission maxima in various solvents are plotted against a measure for solvent polarity defined as (ε –
1)/(2ε + 1) – (n2 – 1)/(2n2 – 1). Application of this equation to 7 gives a good relationship for the shifts
of the shorter wavelength emission maxima (Y = 1.1677 + 13.280X where n = 6, R = 0. 934 and σ =
0.914 kK). Similar treatment of 7 for the longer wavelength emission maxima, however, was not
successful since the absorption band corresponding to the species bearing the intramolecular boron–
oxygen coordinate bond is not assigned in the UV/VIS spectra measured in some solvents, which limits
the data needed for the plot of the equation. The shifts of the longer wavelength emission maxima of 7 in
various solvents show a good linear relationship with the measure for solvent polarity [ν(7) = 18.712 –
3.839X where n = 7, R = 0.798 and σ = 0.321 kK] as well as those of the shorter wavelength emission
maxima [ν(7) = 22.348 – 11.883X where n = 6, R = 0.868 and σ = 0.880 kK]. This indicates a more
pronounced polarity in the exited state than in the ground state in both cases. Furthermore, as is revealed
by the greater value of X coefficient of the latter than that of the former, the intramolecular coordinate bond
promotes the polarization of the ground state to reduce the difference of the polarity between the ground
state and the exited state.

A single-crystal X-Ray crystallographic study at –120 °C reveals the enhanced coplanarity of the skeletal
atoms, all the skeletal atoms of 1 being coplanar with a maximum deviation of only 3°(Figure 3), which is
different from the structure of 2 where the phenyl group is not coplanar within the molecule (Figure 4).
The intramolecular coordinate bond between the boron and oxygen atoms, together with the charge
transfer from the dimethylamino group to the carbonyl group, seems to be responsible for the coplanarity.
For the comparison of 1 and 2, the X-Ray structure analysis of 7 was carried out. As shown in Figure 5,
the presence of the intramolecular boron–oxygen coordinate bond was confirmed in crystalline state. The
intramolecular B1–O1 distance [1.817(5) Å] is, however, longer than that of 1 [1.608(2) Å], which
suggests the weakened intramolecular coordinate bond of 7 (Table 1). Furthermore, the THC
(tetrahedral character) values of the boron atom1 2 in 1 and 7 are estimated to be 52. 1 and 36.8%,
respectively, which supports the longer B1–O1 distance of 7. These findings are consistent with the
presence of the equilibrium in 7 based on the dissociation of the coordinate bond. The B1 atom is
deviated from the plane of the chalcone skeleton [C7–C6–C1–B1 = 5.7(4)°], which reflect the lowered
Lewis acidity of the dioxyboryl group. By using the Lippert–Mataga equation and taking the Onsager
effective radii estimated from the volume obtained by the X-Ray structure analysis13 of 2 into account, the
difference between the dipole moment vector of the exited state and that of the ground state, µe–µg, are
calculated to be 5.48 and 8.55 D for 1 and 2, respectively. Similarly, the values of µe–µg for 7 without
the intramolecular coordination is calculated to be 12.8 D if the volume of the molecule is assumed to be
constant regardless of dissociation of the coordinate bond. The large value of 7 comparable to that of 2
is consistent with the conclusion deduced from the studies of 1 and 2, which makes the presence of the
equilibrium in 7 more reliable.
EXPERIMENTAL
All reactions were carried out under argon unless otherwise noted. THF, ether, dichloromethane and
hexane were distilled from calcium hydride under nitrogen before use. Mps were measured using
Yanagimoto micro-melting apparatus and uncorrected. 1 H and 1 3C NMR spectra were recorded on a
Hitachi R–250 (250 MHz) or Bruker AVANCE 400S (400 MHz) using deuteriochloroform as a solvent
with tetramethylsilane as an internal standard unless otherwise stated; J values are recorded in Hz. 11 B
NMR spectra were recorded on a Varian GEMINI 2000 (96.3 MHz) using deuteriochloroform as a solvent
with boron trifluoride etherate as an internal standard. Electronic spectra were taken with Shimadzu UV–
1600PC spectrophotometer. Fluorescence spectra were obtained on a Hitachi 650–60 spectrophotometer.
IR spectra were recorded for KBr pellets on a Nicolet FT-IR Impact 410. MS spectra were determined
on a Waters LC–MS Integrity System at an ionization potential 70 eV.

Synthesis of 2’-Diethylborylacetophenone
Synthesis of acetophenone trimethylsilyl enol ether and its lithiation were carried out according to the
reported procedure.14 To a solution of tetramethylethylenediamine (1.35 mL, 9 mmol) in hexane (10 mL)
was added dropwise at ice bath temperature butyllithium (9 mmol) in hexane (5. 6 mL) followed by an
addition of acetophenone trimethylsilyl enol ether (576 mg, 3 mmol), and the mixture was stirred for 24 h
at rt. To a suspension of the lithium compound thus obtained was added at rt a 1. 0 M solution of
diethylmethoxyborane (6 mmol) in THF (6 mL), and the resulting mixture was stirred for 30 min. The
mixture was quenched with brine (10 mL) and the insoluble substances were removed by filtration. The
organic layer was separated and concentrated to leave the desired product as a yellow oil (421 mg, 75%),
which was used without further purification, δH 0.24–0.30 (10H, m), 2.42 (3H, s), 6.91 (1H, t, J 7.3),
7.16 (1H, t, J 7.3), 7.28 (1H, d, J 7.3) and 7.51 (1H, d, J 7.3); νmax / cm-1 1600, 1581, 1534, 1455,
1441, 1380 and 1335.
Synthesis of 2’-diethylboryl-4’’-dimethylaminochalcone (1)
To a mixture of 2’-diethylborylacetophenone (2.48 g, 13.2 mmol) and 4’’ -dimethylaminobenzaldehyde
(1.97 g, 13.2 mmol) in ether (10 mL) was added at ice bath temperature a solution of LDA (14. 5 mmol)
prepared from diisopropylamine (1.47 g, 14.5 mmol) and 1.6 M hexane solution of butyllithium (14. 5
mmol) in the same solvent (10 mL) and the resulting mixture was stirred for 45 min. The reaction was
quenched with brine (10 mL) and the insoluble substances were removed by filtration. The organic layer
was separated and concentrated to leave a reddish oily residue, which was purified by chromatography on
alumina (benzene as the eluent) followed by crystallization from hexane to give 1 (1.66 g, 39%), mp 84–
87 °C; δH 0.65–0.69 (10H, m), 3.11 (6H, s), 6.72 (2H, d, JA B 9.2), 7.30 (1H, t, J 7.9), 7.39 (1H, d,
JA B15.3), 7.51 (1H, t, J 7.9), 7.66 (2H, d, J A B9.2), 7.68 (1H, d, J 7.3 ), 8.00 (1H, d, J7.9) and 8.28
(1H, d, JA B15.3); δC 10.1, 14.8, 40.1, 108.6, 111.9, 122.2, 125.1, 125.7, 128.9, 131.9, 132.4, 132.8,
137.9, 150.5, 153.3 and 192.5; δB 14.8; νmax / cm-1 1598, 1587, 1558, 1373 and 1173; λmax / nm (log ε)
(CHCl3) 288 (4.00) and 486 (4.51); m/z 290 (M+ – Et, 100), 262 (M+ – 2Et + 1), 162 (51), 131(44) and
98 (67).
Formation of 3
To a mixture of 2’ -diethylborylacetophenone (695 mg, 3.7 mmol) and 4’’-dimethylaminobenzaldehyde
(551 mg g, 3.7 mmol) in benzene and tert-butyl alcohol (1:1, 6 mL) was added potassium tert-butoxide
(457 mg, 4.1 mmol) and the resulting solution was stirred for 3 h. The reaction was quenched with brine
(10 mL) and the organic layer was separated and concentrated to leave a reddish oily residue, which was
purified by chromatography on alumina (benzene as the eluent) followed by crystallization from benzene to

give 3 (561 mg, 30%), mp 137–138 °C; δH 0.50–0.54 (20H, m), 3.03 (6H, s), 5.30 (2H, s), 6.68 (2H, d,
JA B8.6), 7.25–7.38 (3H, m), 7.49 (1H, t, J 6.7), 7.58 (1H, s), 7.54–7.61 (2H, m), 7.64 (2H, d, JA B8.6),
8.02 (1H, d, JA B7.9) and 8. 16 (1H, d, J 7.9 ); νmax / cm-1 1613, 1567, 1576, 1553, 1533, 1488, 1375,
1167 and 1156; Anal. Calcd for C33H41NO2B2: C, 78.44; H, 8.18; N, 2.77. Found: C, 78.49; H, 8.16; N,
2.74.
Synthesis of 2-[(1’,1’-ethylenedioxy)ethyl]benzeneboronic acid
2-[(1’, 1’-Ethylenedioxy)ethyl]bromobenzene was prepared from the acetalization of 2’-bromo-
acetophenone with ethylene glycol in the presence of p-toluenesulfonic acid in refluxing benzene. To a
solution of the acetal (2. 43 g, 10 mmol) in THF (40 mL) was added butyllithium (10 mmol) in hexane
(6.3 mL) at –78 °C followed by, after 20 min, an addition of triisopropoxyborane (1.88 g, 10 mmol) at
this temperature. The reaction mixture was stirred for 1 h, during which time the temperature was raised
ambient. The reaction was quenched with brine and the organic layer was separated and concentrated to
leave an oily residue. Crystallization from hexane–ethyl acetate (3:1) gave the desired product (1.73 g,
83%), mp 213–215 °C; δH 1.74 (3H, s), 3.86–3.92 (2H, m), 4.05–4.15 (2H, s), 6.37 (2H, br), 7.34 (1H,
t, J 7.3), 7.41 (1H, t, J 7. 6), 7.60 (1H, d, J 7.9) and 7.91 (1H, J 7. 3); νmax / cm- 1 1600, 1485, 1483,
1354 and 1100; m/z 193 (M+ – Me, 78), 149 (42), 121 (38), 98 (34), 87 (100) and 77 (36).
Synthesis of 2’-ethylenedioxyboryl-4’’-dimethylaminochalcone (4)
2-[(1’,1’-Ethylenedioxy)ethyl]benzeneboronic acid (624 mg, 3 mmol) was dissolved in acetone (10 mL)
and p-toluenesulfonic acid (5.7 mg, 0.03 mmol) was added to the solution. After stirring for 30 min at rt,
the solvent was evaporated to leave an oily residue, which was dried under vacuum. The residue was
dissolved in THF–tert-butyl alcohol (1:1, 4 mL) and 4’’-dimethylaminobenzaldehyde (448 mg, 3 mmol)
followed by potassium tert-butoxide (1.01 g, 9 mmol) were added at 0 °C. The resulting solution was
stirred for 15 min and the reaction was quenched with brine (4 mL). Yellow precipitate gradually formed
and was filtered off and collected (500 mg). The substance was dissolved in methanol (10 mL) and
concentrated HCl (5 mL) was added. The resulting violet solution was stirred for 24 h at rt and
neutralized with sodium hydrogencarbonate until the evolution of gas ceased. After insoluble substances
were filtered off, the filtrate was concentrated to leave a reddish oily residue, which was crystallized from
hexane to give 4 (266 mg, 28%), mp 164–165 °C; δH 3.10 (6H, s), 4.34 (4H, s), 6.71 (2H, d, J 8.6),
7.33 (1H, d, JA B15.3), 7.44 (1H, t, J 7.3), 7,58 (1H, t, J 7.3), 7.62 (2H, d, JA B8.6), 7.90 (1H, d, J 7.3),
7.93 (1H, d, J 7.9) and 8.18 (1H, d, JA B15.3); δB 23. 0; νmax / cm-1 1590, 1436, 1375, 1171 and 1050;
λmax nm (log ε) (CHCl3) 264 (4. 08), 431 (3.94) and 500 (4.12, sh); m/z 321 (M+ , 100), 234 (51), 149
(49), 134 (50) and 77 (47).

Synthesis of 2’-propanedioxyboryl-4’’-dimethylaminochalcone (5)
To a solution of 4 (80 mg, 0.25 mmol) in dichloromethane (5 mL) was added 1,3-propanediol (19 mg,
0.25 mmol) and the mixture was stirred for 12 h. The solvent was removed to leave a reddish oily
residue, which was dissolved with benzene (3 mL) and washed with brine (3 mL). The organic layer
was separated and concentrated to leave an oily residue, which was crystallized from hexane to give 5 (65
mg, 77%), mp 123–125 °C; δH 2.14 (4H, m), 3. 06 (3H, s), 4.18 (4H, t, J 5.5), 6.69 (2H, d, JA B8.6),
7.33 (1H, d, JA B15.3), 7,41 (1H, t, J 7.3), 7.51 (1H, t, J 7.6), 7.56 (2H, d, JA B8.6), 7.59 (1H, d, J 7.6),
7.83 (1H, d, JA B15.3) and 7.87 (1H, d, J 7. 6)δB 25.2; νmax / cm-1 1607, 1593, 1569, 1522, 1435, 1371,
1305, 1259, 1150 and 1125; λmax nm (log ε) (CHCl3 ) 261 (4.16), 423 (4. 19) and 500 (3.49, sh). Anal.
Calcd for C20H22NO3B: C, 71.66; H, 6.62; N, 4.18. Found; C, 71.20; H, 6.62; N, 3.80.
Synthesis of 6
To a solution of 4 (80 mg, 0.25 mmol) in dichloromethane (5 mL) was added N-methydiethanolamine (30
mg, 0.25 mmol) and the mixture was stirred for 12 h. The solvent was removed to leave a reddish oily
residue which was dissolved in benzene (5 mL) and washed with brine. The organic layer was separated
and concentrated to leave an oily residue which was crystallized from benzene–hexane (1:1) to give crude
6. Recrystallization from hexane–2-propanol (10:1) afforded pure 6 (67 mg, 71%); δH 2.59 (3H, s),
2.99 (6H, s), 3.16 (4H, br t), 4.03 (4H, br t), 6.62 (2H, d, J 8.6), 6.80 (1H, d, JA B15.3), 7.15–7.20 (2H,
m), 7,26–7.34 (2H, m), 7. 37 (2H, d, JA B8.6) and 7. 80 (1H, d, J 7.3); δB 12. 1; νmax / cm-1 1632, 1595,
1525, 1368, 1184, 1171 and 1115; λmax nm (log ε) (CHCl3) 275 (4.12), 429 (4. 42) and 500 (3. 78, sh);
m/z 378 (M+, 2), 278 (35), 262 (27), 247 (48) and 88 (100).
Synthesis of 7
To a solution of 4 (80 mg, 0.25 mmol) in dichloromethane (5 mL) was added pinacol (30 mg, 0.25 mmol)
and the mixture was stirred for 12 h. The solvent was removed to leave a reddish oily residue which was
crystallized from hexane–ethyl acetate (3:1) to give 7 (68 mg, 72%), mp 175–176 °C;δH 1. 42 (12H, s),
3.05 (6H, s), 6.69 (2H, d, J 8.6), 7.28 (1H, d, JA B15.3), 7.41 (1H, t, J 7.6), 7.53 (1H, t, J 7.6), 7.56
(2H, d, JA B8.6), 7.63 (1H, d, J 7.6 ), 7.86 (1H, d, J 7.6) and 7.93 (1H, d, JA B15.3); δB 25.5; νmax / cm- 1
1603, 1591, 1569, 1526, 1505, 1437, 1299, 1184, 1167, 1123 and 1032 ; λmax nm (log ε) (CHCl3) 273
(4. 09), 428 (4. 33) and 486 (4. 22, sh). Anal. Calcd for C2 3H28NO3 B: C, 73.22; H, 7.48; N, 3. 71.
Found: C, 73.02; H, 7.48; N, 3.63.
Reaction of 1 with n-hexylamine
To a solution of 1 (80 mg, 0.25 mmol) in dichloromethane (5 mL) was added n-hexylamine (101 mg, 1

mmol) and the mixture was stirred for 12 h. The solvent was removed to to leave an oily residue whose
1H NMR spectrum showed the presence of n-hexylimines of 4-dimethylaminobenzaldehyde and 2’-
diethylborylacetophenone. Purification by column chromatography on silica gel (hexane–ethyl acetate;
5:1) afforded 4-dimethylaminobenzaldehyde and n-hexylimine of 2’-diethylborylacetophenone in 75 and
70 % yields, respectively, imine: oil (47 mg),δH 0.41–0.47 (8H, m), 0.70–0.72 (2H, m), 0.91–0.94 (3H,
m), 1.34–1.41 (6H, m), 1.54–1. 67 (2H, m), 2.51 (3H, s), 3.54–3.58 (2H, m), 7.22 (1H. dt, J 7.5 and
1.1), 7.39 (1H, dt, J 7.2 and 1.0), 7.59 (1H, d, J 7.5) and 7.61 (1H, d, J 7.7).
X-Ray structure analysis of 1, 2 and 7
Data were collected on a Rigaku AFC7R diffractometer with graphite-monochromated Mo–Kα radiation
(λ = 0.71069 Å) and a rotating anode generator. The structure was solved by direct methods. The non-
hydrogen atoms were refined anisotropically. Crystal data for 1: C21H26NOB•1.5C6H6, M = 436.42, red,
prismatic crystal (0.20 × 0.40 × 0. 80 mm), triclinic, P1 (#2), a = 9. 622(4), b = 15.155(5), c = 9.522(3)
Å, α = 101.21(3), β = 95. 90(4), γ = 108.32(3)°, U = 1272.9(9) Å3, Z = 2, Dc = 1.139 gcm–3, µ = 0.67
cm–1, F(000) = 470, T = 153 K The final cycle of full-matrix least squares refinement was based on
3338 observed reflections [I > 3.00 σ(I)] and 438 variable parameters and converged with unweighted and
weighted agreement factors of R = 0.040 and Rw = 0.046. Crystal data for 2: C17H17NO, M = 251.33,
yellow, prismatic crystal (0.20 × 0.40 × 0.60 mm), monoclinic, P21/a (#14), a = 9.491(4), b = 11.884(3),
c = 12.912(3) Å, β = 108.35(2)°, U = 1382.3(7) Å3 , Z = 4, Dc = 1.208 gcm–3, µ = 0.75 cm–1 , F(000) =
536, T = 153 K The final cycle of full-matrix least squares refinement was based on 1347 observed
reflections [I > 3.00 σ(I)] and 241 variable parameters and converged with unweighted and weighted
agreement factors of R = 0.051 and Rw = 0.065. Crystal data for 7: C2 3H28BNO3, M = 377.29, red,
prismatic crystal (0. 42 × 0.20 × 0.14 mm), monoclinic, P21 /c (#14), a = 9.886(5), b = 18. 978(7), c =
11.735(6) Å, β = 108.56(4)°, U = 2086(1) Å3, Z = 4, Dc = 1.201 gcm–3, µ = 0.78 cm–1, F(000) = 808, T
= 295 K The final cycle of full-matrix least squares refinement was based on 1807 observed reflections
[I > 3. 00 σ(I)] and 254 variable parameters and converged with unweighted and weighted agreement
factors of R = 0.058 and Rw = 0.077.
ACKNOWLEDGEMENTS
Support from the Ministry of Education, Science, Sports and Culture, Japan (Grant-in-Aid for Exploratory
Research, No. 09874134 and for Scientific Research on Priority Area (A), Nos. 10146235, 11133241
and 12020239) is gratefully acknowledged.

REFERENCES AND NOTES
1 Y. Sugihara, T. Murafuji, N. Abe, M. Takada, and A. Kakehi, New. J. Chem., 1998, 2 2, 1031.
2 T. Murafuji, Y. Sugihara, T. Moriya, Y. Mikata, and S. Yano, New. J. Chem., 1999, 2 3, 683.
3 The chemical shift values of the boron atom (δ 11B) in cyclic esters of ethylboronic acid derived from
ethanediol and propanediol are reported to be 35.0 and 30.5, respectively, see B. Wrackmeyer, Annual
Reports on NMR Spectroscopy, Vol. 20, Academic Press Limited, 1988.
4 (a) S. J. Rettig, and J. Trotter, Can. J. Chem., 1975, 5 3, 1392.
11
(b) The chemical shift value of the boron atom (δ B) in cyclic ester of phenylboronic acid derived
from N-methyldiethanolamine is reported to be 12.2, see ref 3.
5 Solvatochromism in the longest wavelength absorption bands of 1 and 2 (nm): cyclohexane (464,
386), Et2O (478, 390), CCl4 (468, 394), PriOH (481, 416), EtOH (486, 418), AcOEt (486, 402),
THF (490, 405), MeOH (487, 419), MeCN (494, 408), CHCl3 (486, 414), CH2Cl2 (492, 414).
6 M. J. Kamlet, J.–L. M. Abboud, M. H. Abraham, and R. W. Taft, J. Org. Chem., 1983, 4 8, 2877.
6 Solvatochromism in the longest wavelength absorption band in 7 (nm): cyclohexane (395, 466sh),
CCl4 (399), Et2O (400), AcOEt (408), Me2CO (417), THF (421), MeCN (421, 504sh), CH2Cl2 (423,
498sh), CHCl3 (428, 486sh), MeOH (518).
8 S. Toyota and M. Oki, Bull. Chem. Soc. Jpn., 1990, 6 3, 1168.
9 Solvatochromism of the fluorescence of 1 and 2 (nm): cyclohexane (512, 449), Et2O (533, 465), CCl4
(512, 449), PriOH (559, 542), EtOH (562, 545), AcOEt (552, 493), THF (559, 485), MeOH (563,
546), MeCN (576, 530), CHCl3 (546, 505), CH2Cl2 (559, 520).
10 Solvatochromism of the fluorescence of 7 (nm): AcOEt (490, 560), Me2CO (518, 570), THF (498,
555), MeCN (542, 560), CH2Cl2 (521, 562), CHCl3 (490, 550), MeOH (578).
11 E. Lippert, Z. Naturforsch. A, 1955, 10, 541; N. Mataga, Y. Kaifu, and M. Koizumi, Bull. Chem.
Soc. Jpn., 1955, 2 8, 690; ibid., 1956, 2 9, 465.
12 S. Toyota and M. Oki, Bull. Chem. Soc. Jpn., 1992, 6 5, 1832.
13 C. A. van Walree, H. Kooijman, A. L. Spek, J. W. Zwikker, and L. W. Jenneskens, J. Chem. Soc. ,
Chem. Commun., 1995, 35.
14 J. Klein and A. Medlik-Balan, J. Org. Chem., 1976, 4 1, 3307.