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CHEMISTRY
B. M. MIKHAILOV, L. S. VASIL'EV, E. N. SAFONOVA
TRANSFORMATIONS OF CYCLIC BORON COMPOUNDS UNDER THE ACTION OF METHYL BORATE
(Presented by Academician B. A. Kazanskii, 17 VII 1962)
Earlier we showed (\(^1,^2\)) that borotrialkyls and orthoborates, depending on their ratio, are smoothly converted under the influence of tetraalkyldiboranes into esters of alkyl- or dialkylboronic acids. In continuation of this work we studied the interaction of di-(boracycloalkyl)alkanes and 1-methoxyboracycloalkanes with methyl borate in the presence of tetraalkyldiboranes. It was found that di-1,4-(1-boracyclopentyl)butane (I), on moderate heating with an equimolecular amount of methyl borate, is converted into 1-methoxyboracyclopentane (II) in 80% yield, calculated according to the following equation:
\[ \begin{gathered} \text{(I)} \qquad \begin{array}{c} \mathrm{CH_2-CH_2}\\[-2pt] | \qquad \backslash\\[-2pt] \mathrm{CH_2-CH_2}\ \ \mathrm{B-(CH_2)_4-B}\ \ \begin{matrix} \mathrm{CH_2-CH_2}\\[-2pt] / \qquad |\\[-2pt] \mathrm{CH_2-CH_2} \end{matrix} \end{array} \;+\;\mathrm{B(OCH_3)_3} \;\xrightarrow[\ ]{\mathrm{B-H}}\; 3\, \begin{array}{c} \mathrm{CH_2-CH_2}\\[-2pt] | \qquad \backslash\\[-2pt] \mathrm{CH_2-CH_2}\ \ \mathrm{BOCH_3} \end{array} \\ \text{(II)} \end{gathered} \]
As a by-product of the reaction, a compound of composition \(\mathrm{C_{10}H_{22}B_2O_2}\) is obtained, probably representing 1,6-dimethoxy-1,6-diboracyclodecane (III)
\[ \begin{gathered} \mathrm{CH_3O-B} \begin{matrix} / \ \mathrm{CH_2-CH_2-CH_2-CH_2}\ \backslash\\ \backslash\ \mathrm{CH_2-CH_2-CH_2-CH_2}\ / \end{matrix} \mathrm{B-OCH_3}. \\ \text{(III)} \end{gathered} \]
1-Methoxyboracyclopentane (II) also reacts with methyl borate, giving the tetramethyl ester of butane-1,4-diboronic acid (IV) and, in small amount, a triboron compound—the methyl ester of di-(4-dimethoxyborylbutyl)boronic acid (V):
\[ \begin{gathered} \text{(II)} \qquad \begin{array}{c} \text{cyclic } \mathrm{B-OCH_3} \end{array} + \mathrm{B(OCH_3)_3} \xrightarrow[\ ]{\mathrm{B-H}} \mathrm{(CH_3O)_2B-(CH_2)_4-B(OCH_3)_2}. \\ \text{(IV)} \end{gathered} \]
\[ \begin{gathered} \mathrm{(CH_3O)_2B-(CH_2)_4-B-(CH_2)_4-B(OCH_3)_2} \\[-2pt] \qquad\qquad\qquad\qquad\quad | \\[-2pt] \qquad\qquad\qquad\qquad\quad \mathrm{OCH_3} \\ \text{(V)} \end{gathered} \]
Substances (IV) and (V) can be obtained directly from di-1,4-(1-boracyclopentyl)butane (I), if it is heated with 5 moles of methyl borate:
\[ \mathrm{I + 4B(OCH_3)_3} \xrightarrow[\ ]{\mathrm{B-H}} 3\,\mathrm{(CH_3O)_2B-(CH_2)_4-B(OCH_3)_2}. \]
\[ \text{(IV)} \]
By transesterification of the tetramethyl ester of butane-1,4-diboronic acid (IV) with n-hexyl alcohol, the tetra-n-hexyl ester of butane-1,4-diboronic acid (VI) was obtained in 98% yield; at \(\sim 300^\circ\) it decomposes into 1-hexoxyboracyclopentane (VII) and hexyl borate:
\[ (\mathrm{C_6H_{13}O})_2\mathrm{B}-(\mathrm{CH_2})_4-\mathrm{B}(\mathrm{OC_6H_{13}})_2 \xrightarrow{\sim 300^\circ} \mathrm{\left(\begin{matrix} & \mathrm{B}-\mathrm{OC_6H_{13}} \end{matrix}\right)} +\mathrm{B}(\mathrm{OC_6H_{13}})_3. \]
\[ \tag{VI} \qquad\qquad\qquad\qquad \tag{VII} \]
1-Alkoxyboracyclopentanes (II) and (VII) polymerize on standing. The polymer, however, is unstable and depolymerizes on heating.
The second object of the investigation was di-1,4-(1-boracyclopentyl)hexane (VIII), formed as the sole product in the interaction of diborane and diallyl in a ratio of \(2:3\) \((^3)\).
We found that if the reaction between diborane and diallyl is carried out in a ratio of \(1:4\), then the dicyclic compound (VIII) and 6-(1-boracyclopentyl)hexene-1 (IX) are obtained in almost equimolecular amounts
\[ \begin{aligned} &\mathrm{CH_2-CH_2-CH_2}\qquad\qquad\qquad\mathrm{CH_2-CH_2-CH_2}\\ &\left|\qquad\qquad\right.\mathrm{B}-(\mathrm{CH_2})_6-\mathrm{B}\left.\qquad\qquad\right|\\ &\mathrm{CH_2-CH_2-CH_2}\qquad\qquad\qquad\mathrm{CH_2-CH_2-CH_2} \end{aligned} \]
\[ \tag{VIII} \]
\[ \begin{aligned} &\mathrm{CH_2-CH_2-CH_2}\\ &\left|\qquad\qquad\right.\mathrm{B}-(\mathrm{CH_2})_4\mathrm{CH}=\mathrm{CH_2}.\\ &\mathrm{CH_2-CH_2-CH_2} \end{aligned} \]
\[ \tag{IX} \]
On heating (VIII) with one mole of methyl borate in the presence of tetrapropyldiborane, 1-methoxyboracyclopentane (X) is obtained in 81% yield
\[ \mathrm{VIII}+\mathrm{B}(\mathrm{OCH_3})_3 \xrightarrow[\ ]{\mathrm{B-H}} \begin{aligned} &\mathrm{CH_2-CH_2-CH_2}\\ &\left|\qquad\qquad\right.\mathrm{B}-\mathrm{OCH_3}.\\ &\mathrm{CH_2-CH_2-CH_2} \end{aligned} \]
\[ \tag{X} \]
With 5 moles of methyl borate in the presence of tetra-n-propyldiborane, (VIII) gives equimolecular amounts of 1-methoxyboracyclopentane (X) and the tetramethyl ester of hexane-1,6-diboronic acid (XI)
\[ (\mathrm{CH_3O})_2\mathrm{B}-(\mathrm{CH_2})_6-\mathrm{B}(\mathrm{OCH_3})_2 \tag{XI}. \]
1-Methoxyboracyclopentane also reacts with methyl borate, being converted into the tetramethyl ester of hexane-1,6-diboronic acid.
Experimental Part
All operations with organoboron compounds were carried out in an atmosphere of dry nitrogen. Di-1,4-(1-boracyclopentyl)butane was obtained by the interaction of butadiene and diborane in ether medium at \(-20 \div (-30^\circ)\) \((^4)\). Tetraalkyldiboranes were obtained by the methods proposed by us earlier \((^5)\).
Interaction of di-1,4-(1-boracyclopentyl)butane and methyl borate. a) In a ratio of 1:1. Into a three-necked flask equipped with a thermometer, a nitrogen inlet, and a reflux condenser connected to a Tishchenko bottle with acetone, were placed 93.8 g (0.494 mole) of di-1,4-(1-boracyclopentyl)butane, 54.0 g (0.519 mole)
methyl borate and 2.0 g (0.0102 mole) of tetra-n-propyldiborane. The reaction mixture is boiled for 1.5 hours (the b.p. thereby rises from 84 to 130°), then kept for another 1.5 hours at 130–135° and subjected to fractional distillation on a Hempel column. Obtained:
1) 116.7 g (yield 80.5%) of 1-methoxiboracyclopentane with b.p. 42–43°/87 mm. After redistillation the substance had b.p. 40.5–41.0°/83 mm; $d_4^{20}$ 0.8421; $n_D^{20}$ 1.4172.
\[ \begin{aligned} &\text{Found, \%: } &&\mathrm{C}\ 61.27;\ 61.14;\ \mathrm{H}\ 11.27;\ 11.39;\ \mathrm{B}\ 11.15;\ 11.29\\ &\mathrm{C_5H_{11}BO}.\ \text{Calculated, \%: } &&\mathrm{C}\ 61.35;\ \mathrm{H}\ 11.32;\ \mathrm{B}\ 11.05 \end{aligned} \]
Molecular weight found 100.6, 101.2, calculated 97.96.
2) 22.3 g of 1,6-dimethoxy-1,6-diboracyclodecane with b.p. 77–79°/3 mm. After redistillation the ether had b.p. 69.5–70.0°/2.5 mm; $d_4^{20}$ 0.9055; $n_D^{20}$ 1.4538.
\[ \begin{aligned} &\text{Found, \%: } &&\mathrm{C}\ 61.16;\ 61.00;\ \mathrm{H}\ 11.25;\ 11.57;\ \mathrm{B}\ 10.91;\ 10.81\\ &\mathrm{C_{10}H_{22}B_2O_2}.\ \text{Calculated, \%: } &&\mathrm{C}\ 61.35;\ \mathrm{H}\ 11.32;\ \mathrm{B}\ 11.05 \end{aligned} \]
Molecular weight found 183.4, 184.3, calculated 195.9.
b) In a ratio of 1:5. 15.2 g (0.08 mole) of di-1,4-(1-boracyclopentyl)butane, 42.6 g (0.41 mole) of methyl borate, and 2.3 g (0.0068 mole) of tetraisoamyldiborane are boiled for 7 hours; the b.p. of the reaction mass thereby gradually rises from 73 to 104°. After addition of 2.5 ml of methanol to the reaction mass and fractional distillation on a Hempel column, the following were obtained:
1) 36.4 g (yield 75.2%) of the tetramethyl ester of butane-1,4-diboronic acid with b.p. 57–60°/2.5 mm; $n_D^{20}$ 1.4170. After redistillation the ether had b.p. 53.0–53.5°/2 mm; $d_4^{20}$ 0.9441; $n_D^{20}$ 1.4185.
\[ \begin{aligned} &\text{Found, \%: } &&\mathrm{C}\ 48.27;\ 48.33;\ \mathrm{H}\ 9.99;\ 10.10;\ \mathrm{B}\ 10.58;\ 10.75\\ &\mathrm{C_8H_{20}B_2O_4}.\ \text{Calculated, \%: } &&\mathrm{C}\ 47.59;\ \mathrm{H}\ 9.98;\ \mathrm{B}\ 10.71 \end{aligned} \]
2) 3.6 g of the methyl ester of di-(4-dimethoxiborylbutyl)boric acid with b.p. 116–120°/2 mm; $n_D^{20}$ 1.4370. After redistillation the ether had b.p. 115–116°/1.5 mm; $d_4^{20}$ 0.9428; $n_D^{20}$ 1.4358.
\[ \begin{aligned} &\text{Found, \%: } &&\mathrm{C}\ 52.17;\ 52.44;\ \mathrm{H}\ 10.02;\ 10.12;\ \mathrm{B}\ 11.17;\ 11.02\\ &\mathrm{C_{13}H_{31}B_3O_5}.\ \text{Calculated, \%: } &&\mathrm{C}\ 52.08;\ \mathrm{H}\ 10.41;\ \mathrm{B}\ 10.82 \end{aligned} \]
Molecular weight found 291.7, 298.2, calculated 299.84.
By transesterification of the tetramethyl ester of butane-1,4-diboronic acid with n-hexyl alcohol, the tetra-n-hexyl ester of butane-1,4-diboronic acid was obtained in 98.5% yield, with b.p. 198–200°/1.5 mm, $d_4^{20}$ 0.8667; $n_D^{20}$ 1.4402.
\[ \begin{aligned} &\text{Found, \%: } &&\mathrm{C}\ 69.40;\ 69.33;\ \mathrm{H}\ 12.32;\ 12.40;\ \mathrm{B}\ 4.55;\ 4.84\\ &\mathrm{C_{28}H_{60}B_2O_4}.\ \text{Calculated, \%: } &&\mathrm{C}\ 69.70;\ \mathrm{H}\ 12.53;\ \mathrm{B}\ 4.48 \end{aligned} \]
Reaction of 1-methoxiboracyclopentane and methyl borate. 20.6 g (0.210 mole) of 1-methoxiboracyclopentane, 27.9 g (0.268 mole) of methyl borate, and 1.3 g (0.0066 mole) of tetra-n-propyldiborane are boiled for 3.5 hours; during this time the boiling temperature of the reaction mass rises from 76 to 102°. After addition of 1.5 ml of abs. methanol and fractional distillation on a Hempel column, the following were obtained:
1) 30.4 g (yield 71.5%) of the tetramethyl ester of butane-1,4-diboronic acid with b.p. 54–56°/2.5 mm, $n_D^{20}$ 1.4175.
2) 2.8 g of the methyl ester of di-(4-dimethoxiborylbutyl)boric acid with b.p. 116–120°/2 mm, $n_D^{20}$ 1.4360.
Pyrolysis of the tetrahexyl ester of butane-1,4-diboronic acid. 121.8 g (0.253 mo-
of tetra-n-hexyl ester of butane-1,4-diboronic acid and heated at 270–310°; over 1.5 hours 1-n-hexoxyboracyclopentane distilled off, while tri-n-hexyl borate remained in the flask. Fractional distillation gave:
1) 30.7 g (yield 72.4%) of 1-hexoxyboracyclopentane, b.p. 44–45°/2 mm; \(d_4^{20}\) 0.8386; \(n_D^{20}\) 1.4382.
\[ \begin{aligned} &\text{Found, \%: } &&\mathrm{C}\ 71.22;\ 71.08;\quad \mathrm{H}\ 12.46;\ 12.43;\quad \mathrm{B}\ 6.56;\ 6.24\\ &\mathrm{C}_{10}\mathrm{H}_{21}\mathrm{BO}.\ \text{Calculated, \%: } &&\mathrm{C}\ 71.44;\quad \mathrm{H}\ 12.59;\quad \mathrm{B}\ 6.43 \end{aligned} \]
2) 71.1 g (yield 89.5%) of tri-n-hexyl borate, b.p. 129–133°/2.5 mm; \(n_D^{20}\) 1.4270.
3) 7.3 g of the starting tetra-n-hexyl ester of butane-1,4-diboronic acid, b.p. 195–203°/2.5 mm; \(n_D^{20}\) 1.4415.
Reaction of diborane and diallyl. Diborane (0.25 mole), prepared from 13.5 g of lithium hydride, 80 g of aluminum bromide, and 79 g of boron trifluoride etherate in 430 ml of ether, was passed into a solution of 82 g (1 mole) of diallyl in 250 ml of ether with water cooling. On the next day the solvent was distilled off, and the residue was fractionated in vacuo. Obtained: 1) 26.2 g (0.146 mole) of 6-(1-boracycloheptyl)-hexene-1, b.p. 57–59°/3 mm; \(d_4^{20}\) 0.8214; \(n_D^{20}\) 1.4630.
\[ \begin{aligned} &\text{Found, \%: } &&\mathrm{C}\ 81.19;\ 80.78;\quad \mathrm{H}\ 12.66;\ 12.87;\quad \mathrm{B}\ 6.07;\ 6.57\\ &\mathrm{C}_{12}\mathrm{H}_{23}\mathrm{B}.\ \text{Calculated, \%: } &&\mathrm{C}\ 80.91;\quad \mathrm{H}\ 13.01;\quad \mathrm{B}\ 6.07 \end{aligned} \]
Molecular weight found 175, calculated 178.12. 2) 44.4 g (0.16 mole) of di-1,6-(1-boracycloheptyl)-hexane, b.p. 141–142°/2 mm; \(n_D^{20}\) 1.4818 (literature data: b.p. 131–132°/1 mm \(^{(3)}\)).
Reaction of di-1,6-(1-boracycloheptyl)hexane and methyl borate. a) In a ratio of 1 : 1. A mixture of 15.1 g (0.055 mole) of di-1,6-(1-boracycloheptyl)-hexane, 5.7 g (0.055 mole) of methyl borate, and 0.7 g (0.0036 mole) of tetrapropyldiborane was heated for 2 hours at 120–130°. Obtained: 1) 17.0 g (yield 81%) of 1-methoxyboracycloheptane, b.p. 42–43°/15 mm; \(d_4^{20}\) 0.864; \(n_D^{20}\) 1.4391.
\[ \begin{aligned} &\text{Found, \%: } &&\mathrm{C}\ 67.01;\ 66.53;\quad \mathrm{H}\ 12.04;\ 12.20;\quad \mathrm{B}\ 9.06;\ 9.02\\ &\mathrm{C}_{7}\mathrm{H}_{15}\mathrm{BO}.\ \text{Calculated, \%: } &&\mathrm{C}\ 66.72;\quad \mathrm{H}\ 12.00;\quad \mathrm{B}\ 8.59 \end{aligned} \]
2) 3.3 g of polymer.
b) In a ratio of 1 : 5. To a mixture of 13.9 g (0.051 mole) of di-1,6-(1-boracycloheptyl)-hexane and 2.2 g (0.011 mole) of tetrapropyldiborane, heated to 130°, 26.4 g (0.254 mole) of methyl borate was added over 2 hours. By the end of the addition the boiling temperature had dropped to 94°. The mixture was then boiled for 2 hours, during which the temperature rose to 102°. Distillation gave: 1) 8.9 g (0.07 mole) of 1-methoxyboracycloheptane, b.p. 42–43°/15 mm; \(n_D^{20}\) 1.4391. 2) 16.2 g (0.071 mole) of tetramethyl ester of hexane-1,6-diboronic acid, b.p. 82–84°/1.5 mm; \(d_4^{20}\) 0.9325; \(n_D^{20}\) 1.4252.
\[ \begin{aligned} &\text{Found, \%: } &&\mathrm{C}\ 52.29;\ 52.51;\quad \mathrm{H}\ 10.41;\ 10.13;\quad \mathrm{B}\ 9.57;\ 9.71\\ &\mathrm{C}_{10}\mathrm{H}_{24}\mathrm{B}_{2}\mathrm{O}_{4}.\ \text{Calculated, \%: } &&\mathrm{C}\ 52.23;\quad \mathrm{H}\ 10.52;\quad \mathrm{B}\ 9.41 \end{aligned} \]
Received
12 VII 1962
REFERENCES CITED
- B. M. Mikhailov, L. S. Vasil’ev, Izv. AN SSSR, OKhN, 1961, 531.
- B. M. Mikhailov, L. S. Vasil’ev, DAN, 139, 385 (1961).
- K. Saegebarth, J. Am. Chem. Soc., 82, 2082 (1960).
- R. Köster, Angew. Chem., 71, 520 (1959).
- B. M. Mikhailov, A. A. Akhnazaryan, L. S. Vasil’ev, DAN, 136, 828 (1961).