Boron trifluoride benzaldehyde complex

The structure of the complex (96) between benzaldehyde (95) and boron trifluoride (equation 15) was investigated by X-ray crystallography169. In 96, BF3 is in the anti position to the phenyl ring and this geometry remains also in solutions, as tested by the 19F-NMR spectrum in CD2CI2. An ab-initio study170 on interactions between formaldehyde and boron trihalides showed that these complexes (mainly donor-acceptor complexes) affect spectroscopic properties and the reactivity of the carbonyl group the polarization of the C=0 bond favours the attack of nucleophiles. 

While aromatic aldimines of amino acid esters are readily accessible from benzaldehyde or related derivatives and amino acid esters with concomitant removal of water,the corresponding ketimines require harsher reaction conditions, e.g. the benzophenone imine of glycine methyl ester is formed in boiling xylene in the presence of boron trifluoride-diethyl ether complex as a Lewis acid in 82% yield.P l These or similar reaction conditions lead also to piperazine-2,5-dione (DKP) formation therefore milder reaction conditions have been developed such as the transimination with benzophenone imine in dichloromethane, which occurs at room temperature overnight in 80-95% yield (Scheme The N -diphen-... 

Arylcarbenes are formed from benzaldehyde and some of its derivatives if the Clemmensen reduction is performed using boron trifluoride or another Lewis acid instead of hydrochloric acid. If the reaction is carried out in the presence of an alkene, which is often used as solvent, addition to the C-C double bond takes place and cyclopropane formation results in low to fair yields. The arylcyclopropanes are always formed as mixtures of stereoisomers and, in all cases but two, the endo-isomcr is significantly predominant. Thus, when a mixture of 4-methoxybenzaldehyde, boron trifluoride-diethyl ether complex and a considerable excess of cyclohexene was allowed to react with amalgamated zinc, 7-(4-methoxyphenyl)bicy-clo[4.1.0]heptane (1) was obtained in 60% yield. 

Christie and Jones first demonstrated in 2004 that appropriately substituted cyclopropanes adjacent to cobalt-alkyne complexes react with Lewis acids to yield 1,3-dipoles that are poised to participate in dipolar cycloadditions. Reaction of cyclopropane 21 with benzaldehyde and boron trifluoride provides tetrahydrofuran 22 in 83% yield. Kerr subsequently applied this strategy to the synthesis of tetrahydro-l,2-oxazines upon combination of cyclopranes like 21 with a variety of nitrones. ... 

A freshly prepared solution of (ii -ailyl)dicarbonyl(ii -cyclopentadienyl)iron(II) (0.71 g, 3.25 mmol) in diethyl ether (20 mL) is added dropwise to a stirred solution of benzaldehyde (1.24 g, 8.8 mmol) and boron trifluoride etherate (0.41 mL, 3.25 mmol) in diethyl ether (20 mL) at 0 °C under argon. The mixture is stirred at 0 °C for 4 h and the yellow precipitate is collected, washed with dry diethyl ether (75 mL), and dried under vacuum to give the product complex as a 1 1 mixture of the two diastereoisomers 1.00 g (80%). 

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