Boron trifluoride ethyl acetate complex

Method A A solution of 0.5 mmol of (2/ /S ,3R/S )-2,3-dialkyl-1,4-diarylbutane and 0.125 mL (1.0 mmol) of boron trifluoride-diethyl ether complex in 2 mL of trifluoroacctic acid is added to a suspension of 0.12 g (0.26 mmol) of thallium(III) oxide in 2 mL of trifluoroacetic acid at — 40°C to +25CC under an argon atmosphere. The dark colored solution is stirred until the reaction is complete, diluted with ethyl acetate, then washed successively with water (twice) and sat. aq NaCl. Evaporation of the dried extract gives the crude product. In a variant of this method the boron trifluoride-diethyl ether complex can be omitted. 

A solution of 3 g of the nitrile, water (5 moles per mole of nitrile), and 20 g of boron trifluoride-acetic acid complex is heated (mantle or oil bath) at 115-120° for 10 minutes. The solution is cooled in an ice bath with stirring and is carefully made alkaline by the slow addition of 6 A sodium hydroxide (about 100 ml). The mixture is then extracted three times with 100-ml portions of 1 1 ether-ethyl acetate, the extracts are dried over anhydrous sodium sulfate, and the solvent is evaporated on a rotary evaporator to yield the desired amide. The product may be recrystallized from water or aqueous methanol. Examples are given in Table 7.1. 

Ethylenedioxy-3(5,1 la.-dihydroxy-5a-pregnan-20-one.2 A solution of 3/ , 17a-dihydroxy-5a-pregnane-12,20-dione (8.75 g) dissolved in ethylene glycol (90 ml) containing boron trifluoride-ether complex (14 ml) is kept for 16 hr at room temperature. The solution is diluted with chloroform and washed to neutrality with water. The solution is evaporated to yield a crude ketal which is purified by crystallization from chloroform-ethyl acetate or methanol mp 255-259° (softens 252°) [a]D 74° (CHC13). 

Tetrahydrofuran (350 cm3), sodium borohydride (14.1 g) and (la,5a,6a)-3-N-benzyl-6-nitro-2,4-dioxo-3-azabicyclo[3.1.0]hexane (35.0 g, mmol) obtained above were stirred under nitrogen for 0.25 h and then treated dropwise with boron trifluoride-THF complex containing 21.5% BF3 (44.9 cm3) so that the exotherm was controlled to <40°C. After addition was completed, the reaction mixture was stirred for 3 h at 40°C, quenched slowly with water/THF 1 1 (70 cm3) to avoid excessive foaming, and stirred for 0.5 h at 50°C to ensure that the quench of unreacted diborane generated in situ was completed. The quench formed a salt slurry which was filtered and washed with THF (140 cm3) the combined filtrate was partially concentrated, diluted with water (350 cm3) and further concentrated to remove most of the THF, and extracted with ethyl acetate (140 cm3). The resulting ethyl acetate solution was concentrated to afford the (la,5a,6a)-3-N-benzyl-6-nitro-3-azabicyclo[3.1.0]hexane as a clear oil (30.6 g, 97%). 

The nature of donor-acceptor complexes has been the subject of various NMR studies conducted as early as the 1960s. Early calorimetric studies showed that boron trihalides are capable of forming donor-acceptor complexes with a number of Lewis bases and the heats of adduct formation for some of these complexes were determined. Gaseous boron trifluoride, for example, was shown to form a ctxnplex with ethyl acetate in a highly exothermic reaction (-A// = 32.9 0.2 kcal mol ). IR and UV analysis of BF3 complexes of aromatic aldehydes indicated a o-complex with a lengthened CVO bond and a highly delocalized ir-system. More detailed structural information, however, was acquired only after closer inspection by low temperature H, B, C and F NMR studies. ... 

The telomerization of a mixture of isoprene and prenyl acetate in ethyl acetate, catalysed by boron trifluoride, gives the usual complex mixture of acetates this includes geranyl and a-terpinyl acetates. Isoprene dimerizes in the presence of certain titanium or zirconium catalysts, e.g. ZrBusCl -f AlClEt2 + Ph3P, giving 70% of the hydrocarbon (8), 8% of (9), and 22% of trimers. Heggie and... 

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