RU2129557C1 - Method of preparing 1-ethyl-trans-3,4- dialkylborocyclopentanes - Google Patents

Abstract

FIELD: fine organic and organometal synthesis. SUBSTANCE: method comprises reacting alpha-olefins with ethyl aluminium dichloride and magnesium in the presence of two-component catalyst consisting of zirconacene dichloride and diisobutyl aluminium hydride in argon atmosphere under normal conditions for 8 h and subsequently adding boron trifluoride and stirring for 2-6 h. Solvent is tetrahydrofuran. Yield of desired products is 64-79%. EFFECT: new method of regio- and stereo-selective synthesis. 1 tbl

Description

Предлагаемые бороорганические соединения могут найти применение в синтезе трео-2,3-диалкил-1,4-бутадиолов, замещенных циклических кетонов, спиртов, эфиров и других практически важных соединений, используемых в тонком органическом и металлоорганическом синтезе [Б. М. Михайлов, Ю.Н. Бубнов, "Борорганические соединения в органическом синтезе", М., "Наука", 1977, с. 331].The invention relates to methods for producing cyclic organoboron compounds, in particular, to a method for producing 1-ethyl-trans-3,4-dialkylborocyclopentanes of the general formula (1):

The proposed organoboron compounds can be used in the synthesis of threo-2,3-dialkyl-1,4-butadiols, substituted cyclic ketones, alcohols, esters and other practically important compounds used in fine organic and organometallic synthesis [B. M. Mikhailov, Yu.N. Bubnov, "Organoboron compounds in organic synthesis", M., "Science", 1977, p. 331].

По известному способу не могут быть получены 1-этил-транс-3,4-диалкилборациклопентаны (1).The known method [B. M. Mikhailov, V. A. Dorokhov, DAN USSR, 133, 119, (1960)] for the preparation of 1-ethyl-3-methylborocyclopentane by reaction of isoprene with 1,2-diarylborane in ether according to the scheme

According to the known method, 1-ethyl-trans-3,4-dialkylborocyclopentanes (1) cannot be obtained.

Известный способ не позволяет получать 1-этил-транс-3,4-диалкилборациклопентаны (1).The known method [R. Koster, G. Schomburg, Angew. Chem., 72. 567 (I960)] for the preparation of 1-ethyl-3-methylborocyclopentanes by reaction of isoprene with trialkylaminoborane in the presence of trialkylboranes at a temperature of 140 ^o C according to the scheme

The known method does not allow to obtain 1-ethyl-trans-3,4-dialkylborocyclopentanes (1).

 Thus, in the literature there is no information on the regio- and stereoselective synthesis of 1-ethyl-trans-3,4-dialkyl - boracyclopentanes.

 A new method for the regio- and stereoselective synthesis of 1-ethyl-trans-3,4-dialkylborocyclopentanes is proposed.

например, 1-гексена, 1-октена, 1-децена с этилалюминийдихлоридом (Et-AlCl₂) и металлическим магнием (порошок), взятыми в мольном соотношении

: Mg : Et - AlCl₂ = (20-22) : 10 : (10-14), предпочтительно 21:10:12, в присутствии двухкомпонентного катализатора, состоящего из цирконацендихлорида (Cp₂ZrCl₂) в количестве 2-5 мол.% по отношению к магнию, предпочтительно 3 мол. %, и диизобутилалюминийгидрида (i - Bu₂AlH), взятых в мольном соотношении Cp₂ZrCl₂ : Bu $\genfrac{}{}{0ex}{}{\text{i}}{\text{2}}$ AlH = 1 : (1-3), предпочтительно 1:2, в атмосфере аргона при комнатной температуре (22-23^oC) и нормальном давлении в течение 8 часов, в тетрагидрофуране в качестве растворителя, с последующим добавлением эфирата трехфтористого бора (BF₃ • Et₂O) в эквимольном количестве по отношению к Et - AlCl₂ и перемешивании в течение 2-6 часов, предпочтительно 4 часов. Выход целевых продуктов 64-79%. Реакция протекает по схеме

Реакция сопровождается выделением MgCl₂ и AlF₃ в качестве побочных продуктов.The essence of the method is the interaction of α-olefins

for example, 1-hexene, 1-octene, 1-decene with ethyl aluminum dichloride (Et-AlCl ₂ ) and magnesium metal (powder), taken in a molar ratio

: Mg: Et - AlCl ₂ = (20-22): 10: (10-14), preferably 21:10:12, in the presence of a two-component catalyst consisting of zirconacenedichloride (Cp ₂ ZrCl ₂ ) in an amount of 2-5 mol. % in relation to magnesium, preferably 3 mol. %, and diisobutylaluminum hydride (i - Bu ₂ AlH) taken in a molar ratio of Cp ₂ ZrCl ₂ : Bu $\genfrac{}{}{0ex}{}{\text{i}}{}$$\genfrac{}{}{0ex}{}{}{\text{2}}$ AlH = 1: (1-3), preferably 1: 2, in an argon atmosphere at room temperature (22-23 ^o C) and normal pressure for 8 hours, in tetrahydrofuran as a solvent, followed by the addition of boron trifluoride etherate (BF ₃ • Et ₂ O) in an equimolar amount with respect to Et - AlCl ₂ and stirring for 2-6 hours, preferably 4 hours. The yield of target products 64-79%. The reaction proceeds according to the scheme.

The reaction is accompanied by the release of MgCl ₂ and AlF ₃ as by-products.

1-ethyl-trans-3,4-dialkylborocyclopentanes are formed only with the participation of Et - AlCl ₂ and the catalytic system (Cp ₂ ZrCl ₂ + i - Bu ₂ AlH). In the presence of other aluminum compounds (e.g. i - Bu ₃ Al, Et ₃ Al, AlH ₃ , i - Bu ₂ AlCl) or another catalyst (e.g. TiCl ₄ , Zr (OB $\genfrac{}{}{0ex}{}{\text{n}}{\text{u}}$ ) ₄ , Zr (ACAC) ₄ , Zr (OP $\genfrac{}{}{0ex}{}{\text{i}}{\text{r}}$ ) ₄ , Ti (OB $\genfrac{}{}{0ex}{}{\text{n}}{\text{u}}$ ) ₄ ) target products (1) are not formed.

Carrying out the specified reaction in the presence of a catalyst of more than 5 mol.% With respect to magnesium does not lead to a significant increase in the yield of the target product. The use of a catalyst of less than 2 mol.% Reduces the yield of 1-ethyl-trans-3,4-dialkylborocyclopentanes, which is associated with a decrease in catalytically active centers in the reaction mass. The experiments were carried out at room temperature (22-23 ^o C). At a higher temperature (for example, 60 ^o C), the content of the seal products increases, at a lower temperature (for example, 0 ^o C) the reaction rate decreases. Changing the ratio of the starting reagents in the direction of increasing the content of α - olefin or EtAlCl ₂ with respect to magnesium does not lead to a significant increase in the yield of the target product. A decrease in the amount of α-olefin or Et-AlCl ₂ with respect to magnesium reduces the yield of the target products.

Significant differences of the proposed method:
1. The proposed method is based on the use of α - olefins, magnesium metal, Et - AlCl ₂ and BF ₃ • OEt ₂ in the presence of a zirconium-containing catalyst. The reaction proceeds at room temperature (22-23 ^o C). In the known method, trialkylamine borane, isoprene and trialkylborane are used. The reaction proceeds at 140 ^o C.

 The proposed method allows to obtain with high regio- and stereoselectivity individual 1-ethyl-trans-3,4-dialkylborocyclopentanes under mild conditions from the available starting reagents.

Спектр ЯМР ¹³C ( δ , м.д.) трео-2,3-ди(н-бутил)-1,4-бутандиола (2): 60.86т (C¹), 42.52д (C²), 29.39т (C³), 30.08т (C⁴), 23.10т (C₅), 14.17к (C⁶).The method is illustrated by the following examples:
Example 1. In a 50 ml glass reactor mounted on a magnetic stirrer in an argon atmosphere, 10 mmol of magnesium (powder), 20 ml of dry THF, 21 mmol of 1-hexene, 12 mmol Et - AlCl ₂ and a catalyst consisting of 0.3 were placed mmol Cp ₂ ZrCl ₂ and 0.6 mmol i-Bu ₂ AlH in 2 ml of dry THF, stirred for 8 hours at room temperature (22-23 ^o C), add 12 mmol of BF ₃ • Et ₂ O, stirred for 4 hours . Get individual 1-ethyl-trans-3,4-dialkylborocyclopentane. The yield of the target product was determined by oxidation (1) by the known method [I] using alkaline hydrogen peroxide. The oxidation of 1-ethyl-trans-3,4-dialkylborocyclopentane produces threo-2,3-di (n-butyl) -1,4-butanediol (2) according to the scheme:

¹³ C NMR spectrum (δ, ppm) of threo-2,3-di (n-butyl) -1,4-butanediol (2): 60.86 t (C ¹ ), 42.52 d (C ² ), 29.39 t (C ³ ), 30.08t (C ⁴ ), 23.10t (C ₅ ), 14.17k (C ⁶ ).

 Other examples confirming the method are given in the table.

The reaction was carried out at room temperature (22-23 ^o C) in THF. In other solvents (ether, dioxane), the yield of the target products and the selectivity of the reaction drop sharply. In aromatic (benzene, toluene) and aliphatic (hexane, cyclohexane) solvents, the reaction does not proceed. The temperature increase is impractical, because there is no increase in the yield of the target products. At lower temperatures, the reaction rate decreases.

Claims (1)

The method of obtaining 1-ethyl-trans-3,4-dialkylborocyclopentanes, characterized in that α-olefins

interact with ethylaluminium dichloride (Et-AlCl ₂ ) and metallic magnesium, taken in a molar ratio

: Mg: Et - AlCl ₂ = (20 - 22): 10: (10 - 14), in the presence of a two-component catalyst consisting of zirconacene dichloride (Cp ₂ ZrCl ₂ ), in an amount of 2 - 5 mol. % with respect to magnesium and diisobutylaluminium hydride (i-Bu ₂ AlH), taken in a molar ratio of Cp ₂ ZrCl ₂ : i-Bu ₂ AlH = 1: (1 - 3), in an argon atmosphere under normal conditions in the presence of tetrahydrofuran as solvent, followed by the addition of boron trifluoride etherate (BF ₃ • Et ₂ O) in an equimolar amount with Et-AlCl ₂ and stirred for 2 to 6 hours

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