Organometallics
Article
Preparation of 2-(3-Methylbenzyl)-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane (2a) and 2,2′-(m-Tolylmethylene)bis-
(4,4,5,5-tetramethyl-1,3,2 dioxaborolane) (2b).11 The general
borylation procedure was carried out on m-xylene using 1.0 mL of
HBpin (6.7 equiv). This modified procedure afforded 0.248 g of the
products (2a:2b = 1:1.9) in 78% yield. SiO2 column chromatography,
with hexane/EtOAc (5/1) as eluent, afforded 0.136 g of the
diborylated product (2b) as a white sticky solid in 38% yield. Data
for 2b: 1H NMR (500 MHz, CDCl3, ppm) δ 7.13−7.09 (m, 2 H),7.05
(s, 1 H), 6.89 (d, J = 6.5 Hz, 1 H), 2.29 (s, 3 H), 2.26 (s, 1 H), 1.23 (s,
12 H), 1.22 (s, 12 H); 13C NMR (125 MHz, CDCl3, ppm) δ 139.26,
137.26, 129.94, 127.78, 126.23, 125.01, 83.30, 24.69, 24.60; 11B NMR
(160 MHz, CDCl3, ppm) δ 32.9. Data for 2a:8g 1H NMR (500 MHz,
CDCl3, ppm) δ 7.13 (t, J = 7.5 Hz, 1 H), 7.00 (s, 1 H), 6.98 (s, 1 H),
6.94 (d, J = 7.5 Hz, 1 H), 2.31 (s, 3 H), 2.26 (s, 2 H), 1.24 (s, 12 H);
13C NMR (125 MHz, CDCl3, ppm) δ 138.46, 137.72, 129.86, 128.13,
(125 MHz, CDCl3, ppm) δ 128.2, 121.8, 108.3, 83.0, 36.6, 24.8; 11B
NMR (160 MHz, CDCl3, ppm) δ 28.9. Data for diborylated product
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(8b): H NMR (500 MHz, CDCl3, ppm) δ 6.77 (s, 2 H), 4.01 (s, 3
H), 1.30 (s, 24 H); 13C NMR (125 MHz, CDCl3, ppm) δ 121.6, 108.1,
83.1, 24.5; 11B NMR (160 MHz, CDCl3, ppm) δ 28.9; HRMS (EI+)
m/z 334.2349 [(M + H+) calcd for C17H30B2NO4 334.2360].
Preparation of 1-Methyl-5-(4,4,5,5-tetramethyl-1,3,2-dioxa-
borolan-2-yl)-1H-pyrazole (9a).37 The general borylation proce-
dure was carried out on N-methylpyrazole with 2 mol % of Co
precatalyst (10.2 mg, 0.02 mmol). This modified procedure afforded
0.185 g of the product as a white solid (mp 59−60 °C; lit.19 mp 74−75
°C38) in 90% yield: 1H NMR (500 MHz, CDCl3, ppm) δ 7.49 (d, J =
2.0 Hz, 1 H), 6.71 (d, J = 2.0 Hz, 1 H), 4.09 (s, 3 H), 1.34 (s, 12 H);
13C NMR (125 MHz, CDCl3, ppm) δ 138.3, 115.8, 84.1, 39.3, 24.8;
11B NMR (160 MHz, CDCl3, ppm) δ 27.7.
Preparation of 1-Methyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxa-
borolan-2-yl)-1H-indole (10a).5a The general borylation procedure
was carried out on N-methylindole and afforded 0.227 g of a mixture
of products. SiO2 column chromatography, with hexane/CH2Cl2 (3/
1) as eluent, afforded 0.133 g of the 2-borylated product, which was
isolated as a white solid (mp 82−84 °C) in 53% yield. Over time in a
125.96, 125.60, 83.37, 24.72, 21.52; 11B NMR (160 MHz, CDCl3,
ppm) δ 33.1.
Preparation of 2-(4-Methylbenzyl)-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane (3a)34 and 2,2′-(p-Tolylmethylene)bis-
(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) (3b). The general
borylation procedure was carried out on p-xylene using 1.0 mL of
HBpin (6.7 equiv). This modified procedure afforded 0.098 g of the
products as an oil (3a:3b = 1:1) in 33% yield. Data for diborylated
product (3b):11 1H NMR (500 MHz, CDCl3, ppm) δ 7.15 (d, J = 7.5
Hz, 2 H), 7.02 (d, J = 7.5 Hz, 2 H), 2.28 (s, 3 H), 2.25 (s, 1 H), 1.23−
1.22 (overlapping peaks, 24 H); 11B NMR (160 MHz, CDCl3, ppm) δ
33.0. Data for monoborylated product (3a):35 1H NMR (500 MHz,
CDCl3, ppm) δ 7.07 (m, 4 H), 2.29 (s, 3 H), 2.25 (s, 2 H), 1.21 (s, 12
H).
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refrigerator 10a developed a brownish color. Data for 10a: H NMR
(500 MHz, CDCl3, ppm) δ 7.65 (d, J = 8.0 Hz, 1 H), 7.35 (d, J = 8.0
Hz, 1 H), 7.28−7.25 (m, 1 H), 7.13 (s, 1 H), 7.09 (t, J = 7.5 Hz, 1 H),
3.98 (s, 3 H), 1.37 (s, 12 H); 13C NMR (125 MHz, CDCl3, ppm) δ
140.1,127.8, 123.2, 121.6, 119.3, 114.2, 109.7, 83.7, 32.2, 24.8; 11B
NMR (160 MHz, CDCl3, ppm) δ 28.4.
Preparation of 1-Benzyl-2,5-bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)-1H-pyrrole (12b). The general borylation
procedure was carried out on 1-benzyl-1H-pyrrole, and after 48 h
another 3 mol % of Co precatalyst and HBpin (0.4 mL) were added;
this mixture was heated at 80 °C for another 48 h. This modified
procedure afforded 0.207 g of the product as a white solid (mp 107−
108 °C) in 51% yield: 1H NMR (500 MHz, CDCl3, ppm) δ 7.23−7.16
(m, 2H), 7.16−7.11 (m, 1H), 7.04−6.99 (m, 2H), 6.85 (s, 2H), 5.73
(s, 2H), 1.22 (s, 24H); 13C NMR (126 MHz, CDCl3, ppm) δ 141.2,
127.8, 126.5, 126.3, 121.9, 83.3, 51.7, 24.6; 11B NMR (160 MHz,
CDCl3, ppm) δ 27.8; HRMS (EI+) m/z 410.2708 [(M + H+) calcd for
C23H34B2NO4 410.2674].
Preparation of 2-(4-Isopropylbenzyl)-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane (4a) and 2,2′-((4-Isopropylphenyl)-
methylene)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane)
(4b).11,8g The general borylation procedure was carried out on
cymene and afforded 0.091 g of the products as an oil mixture (4a:4b
1
= 1:1) in 21% yield. Data for monoborylated product (4a): H NMR
(500 MHz, CDCl3, ppm) δ 7.11 (s, 4 H), 2.85 (m, 1 H), 2.27 (s, 2 H),
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1.21 (s, 12 H). Data for diborylated product (4b): H NMR (500
MHz, CDCl3, ppm) δ 7.19 (d, J = 8.5 Hz, 2 H), 7.07 (d, J = 8.5 Hz, 2
H), 2.85 (m, 1 H), 2.29 (s, 1 H), 1.24 (s, 12 H), 1.23 (s, 12 H).
Preparation of 2-(1-Phenylethyl)-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane (6a).36 The general borylation procedure was carried
out on ethylbenzene with 2 mol % of Co precatalyst (10.2 mg, 0.02
mmol) and HBpin (0.4 mL, 2.6 mmol). This modified procedure
afforded 0.106 g of the product, was isolated as a colorless oil in 49%
Preparation of 1,2-Dimethyl-3-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)-1H-indole (13a).39 The general borylation
procedure was carried out on 1,2-dimethylindole and afforded 0.016
1
g of product as a sticky white solid in 6% yield: H NMR (500 MHz,
CDCl3) δ 8.03−7.97 (m, 1H), 7.25 (dt, J = 8.0, 0.9 Hz, 1H), 7.18−
7.04 (m, 2H), 3.67 (s, 3H), 2.64 (s, 3H), 1.36 (s, 12H); 13C NMR
(126 MHz, chloroform-d) δ 147.5, 137.9, 132.4, 121.8, 120.8, 120.1,
108.5, 82.3, 24.9.
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yield: H NMR (500 MHz, CDCl3, ppm) δ 7.27−7.21 (m, 4 H),
7.14−7.12 (m, 1 H), 2.43 (q, J = 7.5 Hz, 1 H), 1.33 (d, J = 7.5 Hz, 3
H), 1.21 (s, 6 H), 1.20 (s, 6 H); 13C NMR (125 MHz, CDCl3, ppm) δ
144.95, 128.29, 127.78, 125.08, 83.27, 24.62, 24.58, 17.06; 11B NMR
(160 MHz, CDCl3, ppm) δ 33.3.
ASSOCIATED CONTENT
* Supporting Information
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Preparation of 2-(3-Methyl-1-phenylbutyl)-4,4,5,5-tetra-
methyl-1,3,2-dioxaborolane (7a).34 The general borylation
procedure was carried out on isopentylbenzene with 2 mol % of Co
precatalyst (10.2 mg, 0.02 mmol). After workup 0.097 g of the product
The Supporting Information is available free of charge on the
1
was isolated as a colorless oil in 35% yield: H NMR (500 MHz,
Experimental details and product characterization data
CDCl3, ppm) δ 7.27−7.21 (m, 4 H), 7.14−7.12 (m, 1 H), 2.43 (t, J =
8.0 Hz, 1 H), 1.72−1.58 (m, 2 H), 1.52−1.45 (m, 1 H), 1.20 (s, 6 H),
1.18 (s, 6 H), 0.90 (d, J = 7.0 Hz, 3 H), 0.88 (d, J = 6.5 Hz, 3 H); 13C
NMR (125 MHz, CDCl3, ppm) δ 143.45, 128.34, 128.23, 125.02,
83.19, 41.46, 29.72 (C−B), 26.87, 24.57, 22.99, 22.17; 11B NMR (160
MHz, CDCl3, ppm) δ 33.2.
Preparation of 1-Methyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxa-
borolan-2-yl)-1H-pyrrole (8a)5a and 1-Methyl-2,5-bis(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrrole (8b). The gen-
eral borylation procedure was carried out on N-methylpyrrole with 2
mol % of Co precatalyst (10.2 mg, 0.02 mmol). This modified
procedure afforded 0.211 g of the products as a solid mixture (8a:8b =
2:1) in 88% yield. 2-Borylated N-methylpyrrole is not stable and
deboronates back to starting material. Data for monoborylated product
(8a): 1H NMR (500 MHz, CDCl3, ppm) δ 6.81−6.80 (m, 2 H), 6.15
(dd, J = 2.5, 3.5 Hz, 1 H), 3.85 (s, 3 H), 1.27 (s, 12 H); 13C NMR
Accession Codes
supplementary crystallographic data for this paper. These data
uk, or by contacting The Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44
1223 336033.
AUTHOR INFORMATION
Corresponding Authors
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Organometallics XXXX, XXX, XXX−XXX