ACCEPTED MANUSCRIPT
4
.2.5 Synthesis of Bis(trimethylsilyl)bis(1,3 propanedi-
The methodology used to evaluate whether an or-
olatoboryl)methane (C(Si(CH (B(O(CH O)) ) (5):
3
)
3
)
2
2
)
3
2
ganolithium base can facilitate deborylative substitution in-
volved first reacting the disubstituted product with 2 eq of
base for 1hr followed by addition of 2 eq. of the electrophile.
For instance, (TMS) C(Bpg) (50mg, 0.15 mmol) was dis-
A solution of 4 (2.370 g, 6.97 mmol) in THF (100 mL) was
cooled to 0°C. 1.6M nBuLi solution in hexanes (7.62 mL, 12.2
mmol) was added dropwise over the course of 15 minutes via
syringe. The solution was allowed to stir for 1h at 0°C before
adding TMS-Cl (1.51 g, 13.94 mmol) dropwise over the
course of 5 minutes via syringe. The solution was stirred for
an additional hour at 0°C before removing the ice bath and
then for an additional 16 hours at room temperature. After
concentrating in vacuo, the crude product was extracted from
the LiCl byproduct with 25mL hexanes, filtered, and again
concentrated. The product was then purified via flash column
chromatography on silica gel using DCM as an eluent
2
2
solved in 10mL THF and cooled to -78°C. 1.6M nBuLi solu-
tion in hexanes (0.19 mL, 0.30 mmol) was added to the solu-
tion dropwise via syringe over the course of 5 minutes, and the
mixture was stirred for 1h before adding TMS-Cl (33 mg, 0.30
mmol) dropwise. After stirring an additional hour at -78°C,
the cold bath was removed, and the reaction was stirred 16
additional hours at room temperature. The solvent was re-
moved in vacuo, and the crude product was extracted with
10mL hexanes, filtered, concentrated again, and analyzed via
NMR. If no reaction was observed, the experiment was re-
peated using an addition temperature of 0°C for base systems
known to function at that temperature.
(
R =0.70). Yield: 1.398 g (61.1%)
f
1
H NMR (CDCl
3
, 400 MHz, ppm): 0.06 (s, 18H), 1.86 (p, J
13 1
=
5.5 Hz, 4H), 3.95 (t, J = 5.5 Hz, 8H). C[ H] NMR (CDCl ,
3
1
00MHz, ppm): 2.1, 27.5, 61.5. ESI-MS (m/z, MeOH, positive
Reactivity at the boronate B-O bonds of
(TMS) C(Bpg) and (TMG) C(Bpg) was observed when 4
+
ion mode): 351.22 found, 351.18 calcd for [M+Na] .
2
2
2
2
equivalents of organolithium reagents were reacted in diethyl
ether at room temperature. In an Ar-filled glovebox in a vial,
4
.2.6 Synthesis of Trimethylgermyltris(1,3 propanedi-
olatoboryl)methane (C(Ge(CH ) )(B(O(CH ) O)) ) (6):
A suspension of 2 (2.627 g, 7.46 mmol) in THF (100 mL) was
(TMS)
2
C(Bpg)
2
(25mg, 0.080 mmol) was dissolved in 3mL
O (0.19 mL, 0.30 mmol) was
3
3
2 3
3
2
Et O. 1.6M MeLi solution in Et
2
cooled to -78°C. 1.6M nBuLi solution in hexanes (8.17 mL,
added to the solution, and the mixture was stirred for 20
minutes, during which a white precipitate formed. TMS-Cl (33
mg, 0.30 mmol) was then added to the mixture, which was
stirred for 16 hours at room temperature. The solution was
then filtered, concentrated in vacuo, and analyzed via NMR.
1
3.1 mmol) was added dropwise over the course of 15 minutes
via syringe. The solution was allowed to stir for 15 additional
minutes at -78°C before removing the cold bath. Once the
solution reached 0°C, TMG-Br (2.95 g, 14.9 mmol) was added
dropwise via syringe. The solution was allowed to come to
room temperature and was stirred for 16 additional hours be-
fore removing the solvent and volatile byproducts in vacuo.
The resulting white solid was rinsed with 25mL hexanes, and
the product 5 was extracted from the residual LiBr via over-
night Soxhlet extraction using hexanes overnight. Yield: 2.587
1
The H NMR spectrum of the crude concentrate in
CDCl revealed a complex mixture of closely-related BCH
3 3
(0.34 ppm) ,SiCH (0.0-0.1 ppm) , and propanediolatoboryl –
3
OCH (3.90-4.05 ppm) and –OCH CH (1.85-1.95 ppm) pro-
2
2
2
11
tons. The B NMR spectrum showed a mixture of B(OR) (30
2
ppm region) and BR (50 ppm region) boron nuclei. In the
3
g (90.2%)
ESI-MS spectrum of this crude product, both
1
H NMR (CDCl , 600 MHz, ppm): 0.17 (s, 9H), 1.92 (p, J =
(TMS) C(BMe ) (m/z 279.17 found, 279.17 calcd for
3
2
2 2
13
1
+
5
1
.4 Hz, 6H), 4.09 (t, J = 5.4 Hz, 12H). C[ H] NMR (CDCl
51 MHz, ppm): 0.9, 26.8, 62.9. ESI-MS (MeOH, positive ion
3
,
[M+K] ) and (TMS)O(CH ) O(TMS) (m/z 221.14 found,
2 3
+
221.14 calcd for [M+H] ) peaks were detected. However, nei-
+
mode): 425.12 found, 425.09 calcd for [M+K] .
ther the trisilylated product (TMS) C(Bpg) nor the expected
3
byproduct B(pg)Me were apparent. This indicates that MeLi
4
.2.7
propanediolatoboryl)methane
C(Ge(CH ) ) (B(O(CH ) O)) ) (7):
Synthesis
of
Bis(trimethylgermyl)bis(1,3-
does not deborylate (TMS)
pg groups, replacing them with Me groups.
2 2
C(Bpg) , but instead removes both
(
3
3 2
2 3
2
4
2 2 2 2
.2.8 Screening (TMS) C(Bpg) and (TMG) C(Bpg) reac-
A solution of 6 (1.070 g, 2.78 mmol) in Et O (mL) was cooled
tivity with metal-alkoxide, and CsF bases for deborylation-
metalation
2
to -78°C. 1.6M nBuLi solution in hexanes (3.04 mL, 4.86
mmol) was added dropwise over the course of 15 minutes via
syringe. The solution was allowed to stir for 30 minutes at -
The methodology used to evaluate whether an alkali
metal alkoxide or CsF base can facilitate deborylative substi-
tution involved first reacting the disubstituted product with 2
eq of base for 30 min at room temperature followed by addi-
tion of 2 eq. of the electrophile. In an Ar-filled glovebox in a
vial, 50mg (TMS) C(Bpg) was dissolved in 3mL THF. In a
7
8°C before adding TMG-Br (1.10 g, 5.56 mmol) dropwise
via syringe over the course of 5 minutes. After stirring at -
8°C for 2 additional hours, the solution was allowed to come
7
to room temperature and stir 48 additional hours. After filtra-
tion, the solvent was removed in vacuo, and the product was
purified via flash column chromatography on silica gel using
2
2
second vial, KOtBu (34 mg, 0.30 mmol) was dissolved in 5mL
THF, and the contents of the second vial were added to the
first dropwise. The mixture was stirred for 30 minutes before
adding TMS-Cl (33 mg, 0.30 mmol) dropwise. The reaction
was then stirred for 16 hours at room temperature. The solvent
was removed in vacuo, and the crude product was extracted
with 10mL hexanes, filtered, concentrated again, and analyzed
via NMR. If no reaction was observed, the experiment was
repeated using a 30 minute reflux before adding TMS-Cl, re-
fluxing an additional 30 minutes, and stirring an additional
DCM as an eluent (R =0.75). Yield: 0.864 g (74.3%)
f
1
H NMR (CDCl , 600 MHz, ppm): 0.18 (s, 18H), 1.85 (p, J
5.5 Hz, 4H), 3.94 (t, J = 5.5 Hz, 8H). C[ H] NMR (CDCl ,
3
3
13 1
=
1
51 MHz, ppm): 1.6, 27.6, 61.6. ESI-MS (m/z, MeOH, posi-
+
tive ion mode): 441.11 found, 441.07 calcd for [M+Na] .
4
.2.7 Screening (TMS) C(Bpg) and (TMG) C(Bpg) reac-
2
2
2
2
tivity with organolithium bases for deborylation-
metalation
1
6h at room temperature. Protodeboronation of
6