Boron trifluoride-diethyl ether adduct

In addition to the boron trifluoride-diethyl ether complex, chlorotrimcthylsilanc also shows a rate accelerating effect on cuprate addition reactions this effect emerges only if tetrahydrofuran is used as the reaction solvent. No significant difference in rate and diastereoselectivity is observed in diethyl ether as reaction solvent when addition of the cuprate, prepared from butyllithium and copper(I) bromide-dimethylsulfide complex, is performed in the presence or absence of chlorotrimethylsilane17. If, however, the reaction is performed in tetrahydrofuran, the reaction rate is accelerated in the presence of chlorotrimethylsilane and the diastereofacial selectivity increases to a ratio of 88 12 17. In contrast to the reaction in diethyl ether, the O-silylated product is predominantly formed in tetrahydrofuran. The alcohol product is only formed to a low extent and showed a diastereomeric ratio of 55 45, which is similar to the result obtained in the absence of chlorotrimethylsilane. This discrepancy indicates that the selective pathway leading to the O-silylated product is totally different and several times faster than the unselective pathway" which leads to the unsilylated alcohol adduct. A slight further increase in the Cram selectivity was achieved when 18-crown-6 was used in order to increase the steric bulk of the reagent. 

Diethyl phosphorocyanidate adds to a,/J-unsaturated aldehydes or ketones in the presence of lithium cyanide in a 1,2-fashion28. Boron trifluoride-diethyl ether complex catalyzed rearrangement of these allylic phosphates shows high E selectivity (>85 15) for the adducts derived from aldehydes and Z selectivity (>90 10) for ketone adducts. The selectivity of the rearrangement can be explained by assuming a chairlike transition state, in which the sterically more demanding x-substituent occupies the quasi-equatorial position. The steric requirement decreases in the order of R1 > CN > H. Thus, the cyano substituent occupies the quasi-equatorial position in the aldehyde-derived adduct (R1 = H), but the quasi-axial position in the ketone-derived adduct (R1 = CH3, C6H5). 

Adducts of cyclic enones (n = 1, 2 R = H or CH3) and diethyl phosphorocyanidate rearrange in a suprafacial fashion to give (3-cyano-2-cycloalkenyl) diethyl phosphates 1 under boron trifluoride-diethyl ether complex catalysis26,27. 

Addition of. Sh-phenyl 4-methylphenylselenosulfonate to alkenes can be performed in the presence of boron trifluoride-diethyl ether complex or, alternatively, can be thermally induced (Table 11)69. The boron trifluoride-diethyl ether procedure affords tram-l-arylsulfonyl-2-(phenylseleno)alkanes stereoselectively, however, the thermally induced procedure, when applied to ( )- and (Z)-l-phenyl-l-propene, is a nonstereoselective process when indene is used as the alkene it gives the tram-adduct as the major product. 

Similar reactions of norbornadiene with substituted buta-1,3-dienes in the presence of cobalt catalysts lead to the corresponding 1,4-adducts in 92-96% yield.In the presence of chiral phosphane ligands, this reaction has been brought about with up to 79% enantiomeric excess. The head-to-head dimer of norbornadiene, 1,2,4 5,6,8-dimethano-5-indacene (3, Binor-S ) was formed in quantitative yield on dimerizing norbornadiene with catalysts such as co-balt(II) bromide/triphenylphosphane, cobalt(ll) iodide/triphenylphosphane, or (triphenylphos-phanejrhodium chloride, in the presence of boron trifluoride-diethyl ether complex. ... 

Aldehydes obtained by oxidation of the C-6 position of carbohydrates are highly diastereose-lective dienophiles. Addition of diene 10b to the galactose derived aldehyde 9 in the presence of boron trifluoride - diethyl ether complex leads to a single adduct 11, while the addition to the ribose derived aldehyde 12 produces adduct 13 with a d.r. [(25,35 )/(21 ,31 )] 94 69. Eu(fod)3 catalyzed addition of 12 to ( )-l-methoxy-3-trimethylsilyloxy-l,3-butadiene (14) produces adduct 1543. 

Excellent results are achieved for aldehydes with an elongated side chain. Aldehyde 16 gives adduct 17 and aldehyde 18 gives the adduct 19 (boron trifluoride-diethyl ether complex catalysis) as single products35,44. 

The 1-phenylethylimine of methyl glyoxylatc 6 is activated by trifluoroacetic acid and boron trifluoride diethyl ether complex. The resulting complex 7 reacts with cyclopentadiene (8) to give adducts 9 and 10 with complete facial selectivity and an endojexo ratio of 98 272. 

Monoisopinocampheylborane of essentially 100% ee is best prepared from diisopinocampheylborane84. Treatment of one equivalent of diisopinocampheylborane with TMEDA provides a diamine/monoisopinocampheylborane (1/2) adduct with the liberation of one equivalent of a-pinene. The adduct crystallizes in enantiomerically pure form. Free monoisopinocampheylborane is liberated by treatment with a boron trifluoride-diethyl ether complex. The di-amine/boranc (1/2) adduct is highly insoluble and precipitates quantitatively. 

Michael adducts 58 and 2-ethoxy-3,4-bis(methoxycarbonyl-3//-benzo-djazepine (59). The latter product was obtained in 20% yield. 2-Ethoxy-1-methyl-1//-indole (57, R = CH3) yielded exclusively the corresponding 1//-benzo[ ]azepine (60), in a much higher yield (72%). The (2 + 2)-cycloadduct (61) was proposed to be the unstable intermediate in both reactions. 1,3-Dimethyl-1//-indole (62a) was reported to react with dimethyl acetylenedicarboxylate only in the presence of boron trifluoride diethyl etherate as a catalyst.65 In the reaction mixture, two isomeric Michael adducts and a thermally unstable product were... 

Boron trifluoride is one of the most avid acceptors—that is, strongest Lewis acids-—known, and readily unites with water, ethers, alcohols, amines, phosphines, etc., to form adducts. BF3 is commonly available as its diethyl etherate, (C2H5)26bf3. Because of its potency as a Lewis acid and its greater resistance to hydrolysis compared with BC13 and BBr3, BF3 is widely used to... 

Organoboranes are obtained by addition of borane or alkyl boranes to alkenes (or alkynes). Borane itself can be prepared by reaction of boron trifluoride ether-ate with sodium borohydride. Borane exists as a dimer, but solutions containing an electron donor, such as an ether, amine or sulfide, allow adduct formation. The complexes BHa-THF and the borane-dimethyl sulfide complex BH3 SMc2 are commercially available and provide a convenient source of borane. The dimethyl sulfide complex is more stable than BHa-THF and has the additional advantage that it is soluble in a variety of organic solvents, such as diethyl ether and hexane. 

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