5-(4-Substituted-phenyldiazenyl)-1,3,2λ4-oxazaborines
Organometallics, Vol. 25, No. 8, 2006 2029
data collected with θ e 28°, 5416 independent reflections measured,
4026 reflections observed (I > 2σ(I)), final R index 0.0481
(observed reflections), Rw ) 0.1250, and S ) 1.022. The asymmetric
unit is built up by the two independent molecules A and B.
Complete crystallographic data (excluding structural factors) for
the six structures in this paper have been deposited at the Cambridge
Crystallographic Data Centre and allocated the deposition numbers
CCDC 292282-292287. Copies of the data can be obtained free
of charge via WWW.ccdc.cam.ac.uk/conts/retrieving.html or on
application to the CCDC, 12 Union Road, Cambridge CB2 1EZ,
U.K. (fax, +44(0)-1223-336033; e-mail, deposit@ccdc.cam.ac.uk).
General Considerations. Melting points were determined with
a Kofler hot stage microscope and were not corrected. The elemental
analyses were carried out with a FISONS EA 1108 automatic
analyzer.
Dichloromethane was predried by treatment with anhydrous
calcium chloride and subsequent distillation with phosphorus
pentoxide. The anhydrous sodium acetate was fused on a porcelain
dish and left to cool in a desiccator.
4-(Methylamino)pent-3-en-2-one19 (1), 4-aminopent-3-en-2-one20
(2), 4-((2,4-dimethoxyphenyl)amino)pent-3-en-2-one7 (3), and
3-(methylamino)-1-phenylbut-2-en-1-one21 (4) were prepared ac-
cording to the literature procedures.
diisopropyl ether (30 mL) and the enaminone 1 (5 mmol). The
reaction mixture was stirred by means of a magnetic stirrer, and
remelted sodium acetate (1.23 g, 15 mmol) was added, followed
by 4-methylbenzenediazonium tetrafluoroborate4 (5 mmol). The
mixture was stirred at room temperature for 28 h and then filtered.
The filter cake was washed with diisopropyl ether, and the filtrate
was evaporated in a vacuum evaporator. After recrystallization from
cyclohexane, 7 was obtained: yield 68%; mp 113-115 °C. Anal.
Found: C, 67.73; H, 7.69; N, 18.45. Calcd for C13H17N3O: C,
67.51; H, 7.41; N, 18.17.
The substituted benzenediazonium chlorides were prepared by
a known way.4 The diazonium chlorides were transformed into the
corresponding diazonium tetraphenylborates by adding a saturated
aqueous solution of an equimolar amount of sodium tetraphenylbo-
rate. Because of their low stability, the diazonium tetraphenylborates
had to be prepared immediately before use.
General Procedure for the Synthesis of 5-Aryldiazenyl-
1,3,2λ4-oxazaborines. Remelted sodium acetate (1.23 g, 15 mmol)
and the respective benzenediazonium tetraphenylborate (5 mmol)
were added to a solution of enaminone (5 mmol) in dichloromethane
(30 mL) with stirring. The reaction mixture was stirred at room
temperature for 24 h, whereupon the solids were collected by
suction on a sintered-glass filter and the filter cake was washed
with dichloromethane. The filtrate was evaporated under vacuum,
and the evaporation residue was either recrystallized or submitted
to column chromatography. The following compounds were
prepared by the procedure described.
5-((4-Methoxyphenyl)diazenyl)-4,6-dimethyl-2,2-diphenyl-3H-
1,3,2λ4-oxazaborine (8). The title compound was obtained in 58%
yield (1.56 g) as yellow crystals after recrystallization in cyclo-
hexane-toluene: mp 160-163 °C. Anal. Found: C, 72.28; H, 5.88;
N, 10.59. Calcd for C24H24BN3O2: C, 72.56; H, 6.09; N, 10.58.
5-((4-Methoxyphenyl)diazenyl)-3,4,6-trimethyl-2,2-diphenyl-
1,3,2λ4-oxazaborine (9). The title compound was obtained in 50%
yield (0.89 g) as yellow crystals after recrystallization in cyclo-
hexane-toluene: mp 185-187 °C. Anal. Found: C, 72.96; H, 6.41;
N, 10.03. Calcd for C25H26BN3O2: C, 73.00; H, 6.37; N, 10.22.
3,4,6-Trimethyl-5-((4-methylphenyl)diazenyl)-2,2-diphenyl-
1,3,2λ4-oxazaborine (10). Method A (from the Diazonium Salt).
This compound was obtained as a yellow crystalline solid after
column chromatography (silica gel, chloroform-ethyl acetate
4:1): recrystallization from cyclohexane-toluene; yield 60% (0.94
g); mp 179-182 °C. Anal. Found: C, 76.14; H, 6.71; N, 10.64.
Calcd for C25H26BN3O: C, 75.96; H, 6.63; N, 10.63.
Method B (from Triphenylborane). A flask equipped with a
calcium chloride drying tube and a dropping funnel was used to
dissolve 4-(methylamino)-3-((4-methylphenyl)diazenyl)pent-3-en-
2-one (7; 0.19 g, 0.82 mmol) in dichloromethane (10 mL) at room
temperature. The solution obtained was treated with a solution of
triphenylborane (0.2 g, 0.82 mmol) in dichloromethane (10 mL)
added from the dropping funnel. The solution was stirred for ca.
24 h, whereupon the solvent was evaporated under vacuum. The
crude evaporation residue was recrystallized from ethanol: yield
25% (0.08 g); mp 179-182.5 °C.
3-(2,4-Dimethoxyphenyl)-5-((4-methoxyphenyl)diazenyl)-4,6-
dimethyl-2,2-diphenyl-1,3,2λ4-oxazaborine (11). This compound
was obtained as a yellow crystalline solid after column chroma-
tography (silica gel, chloroform) and recrystallization from cyclo-
hexane: yield 32%; mp 151-154 °C. Anal. Found: C, 71.78; H,
5.85; N, 8.18. Calcd for C32H32BN3O4: C, 72.05; H, 6.05; N, 7.88.
5-((4-Methoxyphenyl)diazenyl)-3,4-dimethyl-2,2,6-triphenyl-
1,3,2λ4-oxazaborine (12). The title compound was obtained in 27%
yield (0.74 g) as orange crystals after recrystallization (cyclohex-
ane-toluene): mp 211-213 °C. Anal. Found: C, 76.02; H, 5.98;
N, 8.80. Calcd for C30H28BN3O2: C, 76.12; H, 5.96; N, 8.88.
3,4-Dimethyl-5-(4-((dimethylamino)phenyl)diazenyl)-2,2,6-tri-
phenyl-1,3,2λ4-oxazaborine (13). This compound was obtained as
3-(Methylamino)-1,4-diphenylbut-2-en-1-one (5). 1,4-Diphen-
ylbutane-1,3-dione (6.5 g, 28 mmol) and a 33% solution of
methylamine in absolute ethanol (50 mL) was refluxed for 10 h
and cooled, and the separated product was collected by suction.
After recrystallization from cyclohexane, 5 was obtained: yield
3.74 g (49%); mp 51-55 °C. Anal. Found: C, 81.26; H, 7.08; N,
5.74. Calcd for C17H17NO: C, 81.21; H, 6.82; N, 5.57.
1,4-Diphenylbutane-1,3-dione. A 500 mL three-necked flask
equipped with a dropping funnel, thermometer, and condenser with
calcium chloride drying tube was charged with dry ether (70 mL)
and sodium amide (11.7 g, 0.3 mol). The suspension was stirred
and, within 10 min, treated with acetophenone (18 g, 0.15 mol) in
dry ether (25 mL), added drop by drop. After 5 min, methyl
phenylacetate (45 g, 0.3 mol) was added. The reaction mixture was
stirred and refluxed on a water bath for another 2 h. The jellylike
reaction mixture was poured onto crushed ice (150 g) with
concentrated hydrochloric acid (30 mL). The ether phase was
separated and extracted first with sodium carbonate solution (3 ×
100 mL) and then with water (3 × 100 mL). The organic phase
was dried with anhydrous sodium sulfate, and the ether was distilled
off. The evaporation residue was dissolved in methanol (60 mL),
and a hot solution of copper(II) acetate hydrate (30 g, 0.15 mol) in
water (175 mL) was added into it through a filter. After the mixture
was cooled to room temperature, the copper(II) salt of the
â-diketone was collected by suction, washed with petroleum ether,
and dried. The salt was placed in a 500 mL Erlenmeyer flask
together with 30% sulfuric acid (250 mL) and ether (100 mL). The
mixture was stirred by means of a magnetic stirrer until the salt
dissolved. The ether was separated, and the aqueous phase was
extracted again with ether (3 × 50 mL). The combined ether phases
were shaken with sodium carbonate solution (3 × 50 mL) and dried
with anhydrous sodium sulfate. The ether was evaporated, and the
separated crystals were recrystallized from ethanol: yield 9.73 g
(24%) of â-diketone; mp 48-50 °C (lit.22 mp 50-51 °C).
4-Amino-4-phenylbut-3-en-2-one (6) was prepared by a known
procedure.3
4-(Methylamino)-3-((4-methylphenyl)diazenyl)pent-3-en-2-
one (7). A 100 mL Erlenmeyer flask was charged with dry
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