Zaidi et al.
for C39H39BN2O2: C, 80.96; H, 6.79; N, 4.84. Found: C, 80.81;
H, 7.00; N, 4.73.
reaction mixture was quenched by addition of a half-saturated
aqueous solution of NH4Cl (200 mL). Et2O (150 mL) was added.
The organic layer was separated and washed with saturated
aqueous NaHCO3 (2 × 150 mL) followed by brine (200 mL).
The organic layer was dried (Na2SO4). Some precipitation was
observed. The resulting suspension was filtered on Buchner
funnel. The filtrate (#1) was set aside. The combined precipi-
tate-Na2SO4 material was washed with Et2O (50 mL) to
remove impurities (filtrate #2). The combined precipitate-Na2-
SO4 material was extracted with CH2Cl2 to dissolve the
product. Concentration of the CH2Cl2 solution afforded a yellow
powder (6.70 g, 28%). Filtrates #1 and #2 were combined and
concentrated to dryness under vacuum. The resulting brown
residue was treated with Et2O (20 mL), affording a suspension
consisting of a brown solution and a bright yellow powder. The
resulting mixture was filtered on a Buchner funnel and
washed with hexanes (80 mL) to afford a yellow powder (14.9
g, 63%). The combined yield (21.6 g) is 91% (TLC and 1H NMR
spectroscopic analysis indicated the presence of a trace (<2%)
of the decomplexed title compound; no further purification was
performed): mp 190 °C dec; 1H NMR δ 0.68-0.74 (m, 2H),
1.68-2.24 (m, 12H), 2.48 (s, 3H), 3.87 (s, 3H), 6.00-6.02 (m,
1H), 6.10 (s, 1H), 6.45 (d, J ) 4.4 Hz, 1H), 6.80-6.82 (m, 1H),
6.96 (d, J ) 8.0 Hz, 2H), 7.18 (d, J ) 8.0 Hz, 2H), 7.26-7.38
(m, 6H), 7.89 (d, J ) 8.0 Hz, 2H), 8.13 (d, J ) 8.0 Hz, 2H),
9.08-9.14 (br, 1H); 13C NMR δ 22.2, 23.9, 25.2, 26.3, 26.4, 30.7,
31.0, 34.6, 34.7, 45.1, 55.7, 111.3, 113.8, 118.5, 119.5, 120.8,
127.6, 128.2, 128.5, 129.0, 130.0, 130.1, 131.2, 131.3, 131.3,
135.2, 140.1, 141.1, 145.4, 150.2, 162.8, 175.2, 183.4; FABMS
obsd 595.3150, calcd 595.3132 [(M + H)+] (M ) C39H39BN2O3).
Anal. Calcd for C39H39BN2O3: C, 78.79; H, 6.61; N, 4.71.
Found: C, 78.78; H, 6.63; N, 4.69. Notes 1-3 (vide supra) also
apply to this procedure.
Decomplexation of a 1,9-Diacyldipyrromethane-BR2
Complex: 5-Phenyl-1,9-di-p-toluoyldipyrromethane (4a).
A solution of 7a (0.29 g, 0.50 mmol) in THF (0.8 mL) was
treated with 1-pentanol (0.2 mL). The reaction mixture was
heated at reflux. After 1 h, TLC [silica, ethyl acetate/hexanes
(1:4)] examination showed complete consumption of boron
complex 7a. The mixture was concentrated to dryness and the
resulting oily residue was treated with 5 mL of hexanes to
afford a light pink solid residue. The mixture was heated
gently under reflux for 5 min (the solid dissolved completely).
The mixture was cooled affording a precipitate upon standing
for a few minutes. The solvent was decanted. The solid was
dissolved in a minimal amount of CH2Cl2 (∼0.2 mL). Hexanes
was added, causing precipitation. The resulting mixture was
filtered on a Buchner funnel. The precipitate was collected and
dried in vacuo to afford a light pink powder (0.075 g, 33%).
The filtrate was concentrated by 4-fold. The resulting precipi-
tate was filtered, dissolved in a minimal volume of CH2Cl2,
and precipitated upon addition of hexanes, affording an
additional 0.13 g of the title compound. The combined yield
(0.206 g) is 90%: mp 110-112 °C (lit.20 mp 75-76 °C); 1H NMR
δ 2.38 (s, 6H), 5.65 (s, 1H), 5.97-5.98 (m, 2H), 6.58-6.59 (m,
2H), 7.20 (d, J ) 8.0 Hz, 4H), 7.31-7.33 (m, 1H), 7.34-7.42
(m, 2H), 7.48-7.50 (m, 2H), 7.70 (d, J ) 8.0 Hz, 4H), 11.03-
11.05 (br, 2H); FABMS obsd 458.1994, calcd 458.1969 [(M +
H)+] (M ) C31H26N2O2).
Note 1: The highly crystalline nature of the 1,9-diacyl-
dipyrromethane-BR2 complex in diethyl ether often resulted
in crystallization during the organic-aqueous partition in the
separatory funnel. In such cases, the workup was performed
with additional THF, or alternatively, by using CH2Cl2. In the
latter case the organic layer should be washed twice with
saturated aqueous NaHCO3 to remove the 2-mercaptopyridine.
Note 2: Any 2-mercaptopyridine remaining after the Et2O/
hexanes wash can be removed by washing with a minimum
amount of cold methanol on a Buchner funnel.
Note 3: In a number of cases, analysis of the product at
this stage showed inclusion of ether or THF in the crystal
lattice, and traces of 1-acyldipyrromethane-BR2 complex and
uncomplexed species (1-acyldipyrromethane, 1,9-diacyldipyr-
romethane). When no such trace species were present, the
purification could be stopped at this stage, whereupon the
product was isolated as a neat solid or as a solid containing
the solvent inclusion. When the remaining purification steps
were performed, the product was often isolated containing
other included molecules (e.g., water, CH2Cl2, hexane).
9-Acylation of a 1-Acyldipyrromethane-BR2 Complex
(Method B, Acid Chloride): 10-(9-Borabicyclo[3.3.1]non-
9-yl)-5-phenyl-1,9-di-p-toluoyldipyrromethane (7a). A sus-
pension of 6a (0.921 g, 2.00 mmol) in THF (2 mL) under argon
was treated with MesMgBr (4.0 mL, 4.0 mmol, 1 M solution
in THF). The mixture was stirred at room temperature for 5
min. Then a solution of p-toluoyl chloride (0.294 mL, 2.20
mmol) in THF (2.2 mL) was added. The mixture was stirred
at room temperature for 10 min under argon. The mixture was
quenched by addition of a half-saturated aqueous solution of
NH4Cl (10 mL). Et2O (20 mL) was added. The organic layer
was separated and washed with saturated aqueous NaHCO3
(20 mL) followed by brine (10 mL). The organic layer was dried
(Na2SO4) and concentrated to dryness under vacuum. The
resulting yellow residue was treated with a small amount of
Et2O (∼2-4 mL), affording a suspension consisting of a
brownish yellow solution and a bright yellow powder. The
resulting mixture was filtered on a Buchner funnel and
washed with a small amount of hexanes (∼5-10 mL) to afford
the yellow powder (1.11 g, 96%, some decomplexed 1,9-
1
diacyldipyrromethane was present; ∼2% as estimated by H
NMR spectroscopy). The yellow powder was treated with CH2-
Cl2/hexanes (15 mL, 1:2) affording a suspension. The suspen-
sion was concentrated to one-fifth of the starting volume. The
resulting mixture was filtered on a Buchner funnel. The
precipitate was washed with hexanes to afford the title
compound (1.04 g, 90%): mp 190-192 °C dec; 1H NMR δ 0.67-
0.73 (m, 2H), 1.66-2.27 (m, 12H), 2.42 (s, 3H), 2.48 (s, 3H),
6.00-6.01 (m, 1H), 6.10 (s, 1H), 6.45 (d, J ) 4.4 Hz, 1H), 6.80-
6.82 (m, 1H), 7.18 (d, J ) 8.4 Hz, 2H), 7.25-7.38 (m, 8H), 7.77
(d, J ) 8.0 Hz, 2H), 8.13 (d, J ) 8.0 Hz, 2H), 9.07-9.11 (br,
1H); 13C NMR δ 21.8, 22.2, 23.9, 25.2, 26.2, 26.3, 30.8, 31.0,
34.6, 34.7, 45.1, 127.6, 128.2, 128.5, 129.1, 129.18, 129.24,
130.0, 130.1, 131.1, 135.3, 135.9, 140.5, 141.0, 142.5, 145.4,
150.0, 175.2, 184.3; FABMS obsd 579.3216, calcd 579.3183 [(M
+ H)+] (M ) C39H39BN2O2). The elemental analysis calcd for
the sample assuming 0.5 mol equiv of water (Anal. Calcd for
C39H40BN2O2.5: C, 79.72; H, 6.86; N, 4.77. Found: C, 80.13;
H, 6.75; N, 4.85) is in good agreement with the observed data.
Notes 1 and 3 (vide supra) also apply to this procedure.
9-Acylation Followed by Tin Complexation for Isola-
tion of a 1,9-Diacyldipyrromethane: Dibutyl[5,10-dihy-
dro-5-phenyl-1,9-di-p-toluoyldipyrrinato]tin(IV) (5). A
solution of 6a (0.46 g, 1.0 mmol) in THF (1 mL) was treated
with MesMgBr (2.00 mL, 2.00 mmol, 1 M solution in THF).
The mixture was stirred at room temperature for 5 min. Then
a solution of 2a (0.25 g, 1.1 mmol) in THF (1 mL) was added.
The mixture was stirred at room temperature for 10 min. The
mixture was quenched by addition of a half-saturated aqueous
solution of NH4Cl (10 mL). Et2O (50 mL) was added. The
Large-Scale Procedure for the 9-Acylation of a 1-Acyl-
dipyrromethane-BR2 Complex: 10-(9-Borabicyclo[3.3.1]-
non-9-yl)-9-(p-methoxybenzoyl)-5-phenyl-1-p-toluoyldipyr-
romethane (7b). A suspension of 6a (18.4 g, 40.0 mmol) in
THF (40 mL) under argon was treated with MesMgBr (80.0
mL, 80.0 mmol, 1 M solution in THF) via syringe, affording a
clear solution. The solution was stirred for 5 min at room
temperature under argon. A solution of 2b (10.79 g, 44.0 mmol)
in THF (44 mL) was added via cannula under argon. The
mixture was stirred at room temperature for 10 min. The
(20) Lee, C.-H.; Li, F.; Iwamoto, K.; Dadok, J.; Bothner-By, A. A.;
Lindsey, J. S. Tetrahedron 1995, 51, 11645-11672.
8364 J. Org. Chem., Vol. 69, No. 24, 2004