The Journal of Organic Chemistry
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additional 30 min. The reaction mixtures given in Table 2, entries 4, 6,
7, and 8, were quenched with aqueous NH4Cl (2.5 mL, 0.16 M). The
reaction mixture was then transferred to a separatory funnel and
extracted with diethyl ether (3 × 15 mL). The combined organic layers
were dried over anhydrous MgSO4, filtered, and dried in vacuo (25 °C,
1 Torr) to afford m-tolyl pinacolborane as a pale yellow oil. The results
for the other pinacolborane esters prepared by this method are
summarized in Table 2. For the 1H, 13C, and 11B NMR spectra, see the
Supporting Information.
1019, 1056, 1146, 1211, 1302, 1377, 1463, 1522 cm−1. 1H NMR (500
MHz, CDCl3): δ 1.34 (s, 12H), 6.98 (d, J = 3.5 Hz, 1H), 7.41 (d, J = 4
Hz, 1H). 13C NMR (125.7 MHz, CDCl3): δ 24.7, 84.3, 127.7, 136.9.
11B NMR (160.4 MHz, CDCl3): δ +28.1 (s).
4,4,5,5-Tetramethyl-2-(1-phenylvinyl)-1,3,2-dioxaborolane
(Table 2, Entry 12).59 Clear oil; 75% yield (0.352 g). H NMR (500
1
MHz, CDCl3): δ 1.35 (s, 12H), 6.0 (d, J = 0.9 Hz, 1H), 6.11 (d, J = 0.8
Hz, 1H), 7.27 (dt, J = 1.5, 5.5 Hz, 1H), 7.34 (dt, J = 2, 5.5 Hz, 1H),
7.516 (m, 1H). 13C NMR (125.7 MHz, CDCl3): δ 24.8, 83.9, 127.1,
127.3, 128.3, 131.0, 141.5. 11B NMR (160.4 MHz, CDCl3): δ +29.9(s).
4.9. General Procedure for the Preparation of B-Allylpina-
colboronate and Subsequent Reaction with Benzaldehyde.
The following procedure for the preparation of B-allylpinacolboronate
is representative. A 25 mL round-bottom flask equipped with a
magnetic stir bar was charged with magnesium turnings (0.04 g, 1.65
mmol) and fitted with a rubber septum. The flask was purged with Ar
and charged with dry THF (2.3 mL) followed by PinBH (0.199 mL,
1.37 mmol). To the reaction mixture was added allyl bromide (0.116
mL, 1.37 mmol) dropwise with constant stirring over 5 min at 25 °C.
After 30 min of stirring at 25 °C, another 1 equiv of allyl bromide
(0.116 mL, 1.37 mmol) was added. After 90 min of stirring at 25 °C
the magnesium turnings were fully consumed and 11B NMR analysis
confirmed the complete formation of allylpinacolboronate. The
reaction was then diluted with hexanes (5 mL) and quenched with
aqueous 0.1 M HCl (10 mL) (Caution! hydrogen evolution). After 10
min of stirring the reaction mixture was transferred to a separatory
funnel and extracted with hexanes (3 × 15 mL). The combined
organic layers were dried over anhydrous MgSO4, filtered, and dried in
vacuo (25 °C, 1 Torr) to afford 2-allyl-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane as a clear oil. The results for the other substituted B-
allylpinacolboronic esters prepared by this method are summarized in
2-(4-Ethylphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (Table
2, Entry 1).53 Clear oil; 99% yield (0.483 g). H NMR (500 MHz,
1
CDCl3): δ 1.24 (t, J = 6 Hz, 3H), 1.34 (s, 12H), 2.67 (q, J = 7.5 Hz,
2H) 7.23 (d, J = 8 Hz, 1H), 7.75 (d, J = 8 Hz, 1H). 13C NMR (125.7
MHz, CDCl3): δ 15.4, 24.8, 29.1, 83.7, 127.4, 135.0. 11B NMR (160.4
MHz, CDCl3): δ +30.8 (s).
4,4,5,5-Tetramethyl-2-m-tolyl-1,3,2-dioxaborolane (Table 2,
Entry 2).26 Clear oil; 99% yield (0.436 g). 1H NMR (500 MHz,
CDCl3): δ 1.36 (s, 12H), 2.37 (s, 3H), 7.26−7.29 (m, 2H), 7.63 (t,
1H), 7.65 (s, 1H), 7.54 (m, 1H). 13C NMR (125.7 MHz, CDCl3): δ
21.3, 24.9, 83.7, 127.8, 131.9, 132.0, 132.2, 135.5, 137.2. 11B NMR
(160.4 MHz, CDCl3): δ +30.6 (s).
4,4,5,5-Tetramethyl-2-(pyren-2-yl)-1,3,2-dioxaborolane (Table 2,
Entry 3).34 Deep red oil; 78% yield (0.511 g). H NMR (500 MHz,
1
CDCl3): δ 1.51 (s, 12H), 8.12 (m, 7H), 8.57 (d, J = 7.5 Hz, 1H), 9.11
(d, J = 9.5 Hz, 1H). 13C NMR (125.7 MHz, CDCl3): δ 25.1, 84.0,
124.2, 125.0, 125.3, 125.4, 125.8, 125.9, 127.5, 127.6, 127.9, 128.2,
128.6, 130.9, 131.3, 133.6, 134.0, 136.6. 11B NMR (160.4 MHz,
CDCl3): δ +22.50 (s), +31.9 (s).
2-(Biphenyl-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (Table
2, Entry 4).54 Clear oil; 88% yield (0.351 g). H NMR (500 MHz,
1
CDCl3): δ 1.24 (s, 12H), 7.35−7.49 (m, 8H); 7.76 (d, J = 7.5 Hz,
1H). 13C NMR (125.7 MHz, CDCl3): δ 24.6, 83.8, 126.4, 126.9, 127.9,
129.1, 129.3, 130.2, 134.6, 143.4, 147.7. 11B NMR (160.4 MHz,
CDCl3): δ +30.7 (s).
1
Table 3. For the H, 13C, and 11B NMR spectra, see the Supporting
Information.
2-(4-Methoxy-2-methylphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxa-
borolane (Table 2, Entry 5). Clear oil; 97% yield (0.483 g). 1H NMR
(500 MHz, CDCl3): δ 1.29 (s, 12H), 2.56 (s, 3H), 3.82 (s, 3H), 6.74
(m, 2H), 7.77 (d, J = 7 Hz, 1H). 13C NMR (125.7 MHz, CDCl3): δ
22.4, 24.9, 54.9, 83.1, 110.1, 115.5, 137.8. 11B NMR (160.4 MHz,
CDCl3): δ +30.7 (s).
2-(4-(Dimethoxymethyl)phenyl)-4,4,5,5-tetramethyl-1,3,2-dioxa-
borolane (Table 2, Entry 6). Clear oil; 81% yield (0.450 g). 1H NMR
(500 MHz, CDCl3): δ 1.29 (s, 12H), 3.35 (s, 6H), 5.38 (s, 1H), 7.41
(d, J = 7.5 Hz, 2H), 7.78 (d, J = 8.5 Hz, 2H). 13C NMR (125.7 MHz,
CDCl3): δ 24.7, 24.8, 52.4, 52.6, 83.8, 102.8, 10.1, 126.1, 134.7, 141.0.
11B NMR (160.4 MHz, CDCl3): δ +30.4 (s).
2-Allyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (Table 3, Entry
1).60 Clear oil; 90% yield (0.207 g). H NMR (500 MHz, CDCl3): δ
1
1.25 (s, 12H), 1.72 (d, J = 6.5 Hz, 2H), 4.93 (d, J = 10 Hz, 1H), 5.0 (d,
J = 17 Hz, 1H), 5.83−5.89 (m, 1H); 11B NMR (160.4 Hz, CDCl3): δ
+33.0 (s).
3-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolane-2-yl)-but-1-ene
(Table 3, Entry 3).61,62 An isomeric mixture of crotyl bromide was
used (E/Z ratio 90/10). Clear oil; 90% yield (0.224 g). 1H NMR (500
MHz, CDCl3): δ 1.09 (d, J = 7.5 Hz, 3H), 1.23 (s, 12H), 1.89 (quint, J
= 7.5 Hz, 1H), 4.92 (app dt, J = 10 Hz, 2H), 4.97 (app dt, J = 17.5 Hz,
2H), 5.90−5.97 (m, 1H). 13C NMR (125.7 MHz, CDCl3): δ 14.1,
24.6, 25.5, 83.2, 112.0, 141.0. 11B NMR (160.4 MHz, CDCl3): δ +33.1
(s).
4,4,5,5-Tetramethyl-2-(2-methylallyl)-1,3,2-dioxaborolane (Table
3, Entry 4).63 Clear/light yellow oil; 90% yield (0.222). 1H NMR (500
MHz, CDCl3): δ 1.25 (s, 12H), 1.72 (s, 2H), 1.77 (s, 3H), 4.66−4.69
(m, 2H). 13C NMR (125.7 MHz, CDCl3): δ 24.4, 24.7, 83.3, 110.2,
142.9. 11B NMR (160.4 MHz, CDCl3): δ +33.1 (s).
4,4,5,5-Tetramethyl-2-octyl-1,3,2-dioxaborolane (Table 2, Entry
7).55 Clear oil; 86% yield (0.411 g). H NMR (500 MHz, CDCl3): δ
1
0.76 (t, J = 7.5 Hz, 2H), 0.86 (t, J = 7 Hz, 3H), 1.23 (s, 12H), 1.25 (s,
8H), 1.38 (m, 4H). 13C NMR (125.7 MHz, CDCl3): δ 14.1, 22.7, 24.0,
24.8, 29.2, 29.4, 31.9, 32.4, 82.5. 11B NMR (160.4 MHz, CDCl3): δ
+33.7 (s).
1,4-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene
(Table 2, Entry 8).56 A 2.2 equiv amount of Mg0 and 2.5 equiv of
PinBH were used. Clear oil; 61% yield (0.404 g). 1H NMR (500 MHz,
CDCl3): δ 1.34 (s, 24H), 7.81 (s, 4H). 13C NMR (125.7 MHz,
CDCl3): δ 24.9, 134.0. 11B NMR (160.4 MHz, CDCl3): δ +30.7(s).
4,4,5,5-Tetramethyl-2-(1-phenylethyl)-1,3,2-dioxaborolane
3-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolane-2-yl)-3-methylbut-1-
ene (Table 3, Entry 5).61 The starting halide was 1-bromo-3-
methylbut-2-ene. Clear oil; 95% yield (0.242 g). 1H NMR (500
MHz, CDCl3): δ 1.07 (s, 6H), 1.22 (s, 12H), 4.90 (dd, J = 0.5, 0.5 Hz,
1H), 4.93 (dd, J = 0.3, 0.6 Hz, 1H), 5.96 (dd, J = 5.7, 3.3 Hz, 1H). 13
C
NMR (125.7 MHz, CDCl3): δ 23.4, 24.5, 83.2, 110.0, 146.7. 11B NMR
(160.4 MHz, CDCl3): δ +33.9 (s).
(Table 2, Entry 9).57 Clear oil; 75% yield (0.351 g). H NMR (500
1
MHz, CDCl3): δ 1.25 (s, 6H), 1.275 (s, 6H), 1.40 (d, J = 7.5 Hz, 3H),
2.50 (q, J = 7.5 Hz, 1H), 7.30 (m, 5H). 13C NMR (125.7 MHz,
CDCl3): δ 17.1, 24.6, 47.5, 83.3, 125.1, 127.8, 128.3, 144.9. 11B NMR
(160.4 MHz, CDCl3): δ +33.2 (s).
1-Phenyl-3-buten-1-ol (Table 3, Entry 1).64 As an alternative to
the aqueous quench, benzaldehyde (0.138 mL, 1.37 mmol) was then
added and the reaction mixture was stirred for an additional 12 h at 25
°C. The reaction mixture was then diluted with hexane (5 mL),
quenched with aqueous 1 M HCl (5 mL), and transferred to a
separatory funnel. The organic layer was washed with aqueous 1 M
NaOH (2 × 5 mL) and DI water (2 × 3 mL). The combined organic
layers were dried over anhydrous MgSO4, filtered, and dried in vacuo
(25 °C, 1 Torr) to afford 1-phenyl-3-buten-1-ol as a clear/light yellow
4,4,5,5-Tetramethyl-2-(thiophen-2-yl)-1,3,2-dioxaborolane
(Table 2, Entry 10).21 White solid; 92% yield (0.193 g). H NMR
1
(500 MHz, CDCl3): δ 1.36 (s, 12H), 7.21−7.19 (m, 1H), 7.27 (d, J =
4.5 Hz, 1H), 7.64−7.67 (m, 1H). 13C NMR (125.7 MHz, CDCl3): δ
24.7, 84.1, 128.3, 132.5, 137.3. 11B NMR (160.4 MHz, CDCl3): δ
+29.4 (s).
1
oil; 94% yield (0.190 g). H NMR (500 MHz, CDCl3): δ 2.50−2.57
2-(5-Chlorothiophen-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lane (Table 2, Entry 11).58 Clear oil; 75% yield (0.360 g). IR (Nujol):
(m, 2H), 4.75 (dd, J = 5, 7.5 Hz, 1H), 5.15−5.20 (m, 2H), 5.79−5.87
9608
dx.doi.org/10.1021/jo201093u|J. Org. Chem. 2011, 76, 9602−9610