Boron trifluoridc

Conducting the aldol reaction at temperatures below —78 "C increases the diastereoselectivity, but at the cost of reduced yields45. Transmetalation of the lithium enolate 2 a by treatment with diethylaluminum chloride generated an enolate species that provided high yields of aldol products, however, the diastereoselectivity was as low as that of the lithium species45. Pre treatment of the lithium enolate 2a with tin(II) chloride, zinc(II) chloride, or boron trifluoridc suppressed the aldol reaction and the starting iron-acyl complex was recovered. 

Thiazolinc 2 proves to be inert to organometallic attack. However, addition of organolithium and Grignard reagents to the C —N double bond of 2 can easily be achieved by previous activation with boron trifluoridc, providing /r[Pg.696]

Only one example, showing high stereoselectivity, is known in this class of reactions. On treatment of the acyclic glycine cation equivalent 1 (see Appendix), containing the ( + )-cam-phor-10-sulfonamide ester as a chiral auxiliary, with boron trifluoridc and anisole at 0"C a mixture of aromatic substitution products is obtained in essentially quantitative yield 55. Besides 11 % of cuV/io-substitution product, the mixture contains (R,S)-2 and its (/ ,/ )-epimer in a ratio >96 4 (NMR). The same stereoisomer 2 predominates when the reaction is conducted in sulfuric acid/acetic acid 1 9, although the selectivity is slightly lower (91 9 besides 25% of ortho substitution). 

Mesitylene, condensation with dichioro-methyl methyl ether, 47, 1 oxidation with peroxytrifluoroacetic acid and boron trifluoridc, 48, 90... 

Method B A solution of 0.5 mmol of (2/ /.S,3/t/5 )-2,3-dialkyl-l,4-diarylbutane and 0.125 mL (1.0 mmol) of boron trifluoridc-dicthyl ether complex in 2 mL of CH2C12 is added to a stirred suspension of 0.12 g (0.26 mmol) of thallium(III) oxide in 10 mL of CH2C12 containing 0.4 mL of trifluoroacetic acid and 0.2 mL of trifluoroacetic anhydride at the stated temperature under argon. The mixture is stirred until the end of the reaction and then diluted with ethyl acetate and worked up as in method A. 

Hydroxymelhyl)cyc opropan-l-ol (11), readily obtained by hydrogen peroxide oxidation of methylenecyclopropane, was rearranged to cyclobutanone (12) either directly, or via an intermediate l-(tosyloxymethyl)cyclopropan-l-ol.114 115 Competitive ring opening to 1-hydroxy-butan-2-one (13) was observed in the boron trifluoridc catalyzed process. 

Substitution of hydrogen by fluorine in compounds with acidic a-hydrogens can be achieved with xenon difluoride and some catalysts. Thus, room-temperature fluorination of 1,3-diketones, e g. 20, with xenon difluoride in the presence of the insoluble cross-linked polysty-rene-4-vinylpyridine, either complexed with boron trifluoridc or Nafion-H, as catalyst, gives mono and difluoro products.27-28... 

A significant change in the fluoro halide to methoxy halide ratio does not occur with large changes in the boron trifluoride to hypohalite ratio. For example, experiments with hex-1-ene (13) and methyl hypochlorite (Table 7) have shown that variation of the boron trifluoridc methyl hypochlorite ratio from 10 1 to 1 10 does not produce large changes in the proportion of fluoride incorporation. These experiments also have shown that boron trifluoride is consumed in stoichiometric amounts in the formation of fluoro halide from methyl hypochlorite and that all three of the fluorine atoms of boron trifluoride are about equally effective. 

Similarly, dehydrofluorination of ester 13 by the triethylamine-boron trifluoridc complex gives the product 14.94... 

The examples given demonstrate that l,3,5-trichloro-2.4,6-trifluorobenzene can be dispropor-tionated either with or without an additive. Aluminum trifluoride and chromium(III) fluoride act as catalysts and enhance the reaction boron trifluoridc, however, seems to act as an inhibitor. 

Further examples of fluorinating ring-opening reactions of epoxides with the boron trifluoridc-diethyl ether complex are given by the formation of 6. 7, 8, 9. and 10. ... 

Substituted HeptafluorocycIohexa-l,4-dienes7by Boron Trifluoridc Catalyzed Fluorinationof 1-Substituted Pentafluorobenzenes 6 with Xenon Difluoride General Procedure ... 

Table 14. Ring Opening of 1,2-Epoxyeyelohexaneearbonitriles with Hydrogen Fluoride/Boron Trifluoridc-Diethyl Ether Complex...

Esterification. Boron thfluoride etherale in combination with a large excess of an alcohol is an elTeclive reagent for the esterification of 4-aminobenzoic acid. The combination is particularly useful for esterification of unsaturated carboxylic acids. The boron trifluoridc etherate alcohol reaction is particularly useful for esterification of heterocyclic carboxylic adds. ... 

Enol acetylation (I, 1174 1178). As a Grst step in the synthesis of 3-n-butyl-2,4-pentanedione, a mixture of 28.6 g. (0.25 mole) of 2-heptanone, 51.0 g. (0.50 mole) of acetic anhydride, and 1.9 g. (0.01 mole) of p-toluenesulfonic acid monohydrate contained in a stoppered 500-ml. round-bottomed flask equipped with a magnetic stirrer is stirred at room temperature for 30 min. Then 55 g. (0.43 mole) of the I 1 boron trifluoridc-acetic acid complex [Reagents, I, 69 (1967)] is added some heat is evolved... 

Funaoka M, Abe I (1978b) The reaction of lignin under he-presence of phenol and boron trifluoridc. II. The effect of methoxyl group and ethylene double bond on the formation of catechol. Mokuzai Gakkaishi 24 892-897... 

S. Geller and J. L. Hoard. Acta Cryst, 4, 399-405 (1951). Crystal structure tri-methylamine-boron trifluoridc. 

Transannular cyclization can be induced by acid-mediated activation of a,/J-unsaturated carbonyl groups. Treatment of an a./J-unsaturated ketone with formic acid/boron trifluoridc-di-ethyl ether complex produces the tricycle 1423. Ketone 14 is a precursor in the pentalene 8 synthesis (Prins reaction analog). Transannular Prins cyclizations are described in Section 1.5.5.2.2.2.26-27. 

Bi l,5-cycloocttHlicnc)nickcl(0). 35 By Diels-Atdcr reaction Boron trifluoridc ethcrate. 43... 

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