Showing papers on "Boron trifluoride published in 1986"

Structure and electronic nature of the benzaldehyde/boron trifluoride adduct.

Abstract: The structure of the benzaldehyde/boron trifluoride adduct (6) has been determined by X-ray crystallography. Accordingly, the Lewis acid BF3 is complexed anti to the phenyl group in benzaldehyde. The B-OC-C fragment lies essentially in a common plane. Anti complexation also pertains in solution, as shown by a heteronuclear Overhauser experiment. MNDO calculations of the acetaldehyde/BF, adduct show that anti complexation does indeed lead to the lowest energy species. However, the syn adduct lies only 1.8 kcal/mol higher in energy. The linear form does not represent a minimum on the energy surface but rather the lowest energy transition state for intramolecular anti * syn isomerization. The calculations of CH,CHO/BF,, of 6, and of the free aldehydes clearly point to LUMO lowering and to an increased positive charge at the carbonyl carbon atom upon complexation. The results are discussed in light of Lewis acid mediated aldehyde additions involving allyl and enolsilanes, stannanes, and cyanotrimethylsilane as well as such processes as Diels-Alder, ene, and Grignard reactions. A wide variety of C-C bond-forming reactions of carbonyl compounds are mediated by Lewis acids such as BF3, AICI,, EtAlCI,, TiCI4, SnC1,. and ZnX,. They include carbonyl additions of allylsilanes, enosilanes, cyanotrimethylsilane, and other silyated' and stannylated* carbon nucleophiles, as well as ene reaction^,^ Diels-Alder addition^,^ and hetero-Diels-Alder cycloconden~at ions.~ It is generally accepted that the Lewis acid activates the carbonyl component by forming an adduct prior to C-C bond formation. Whereas X-ray crystallographic data of a TiCI4 adduct of a chiral acrylic acid ester has recently been reported and discussed with regard to stereoselective Diels-Alder reactions,6 precise structural information concerning complexes of aldehydes with the above-mentioned Lewis acid remains to be presented. N M R , UV, and I R data of common aldehyde/Lewis acid complexes are available, but they do not answer the question of anti vs. syn complexation (1 vs. 2; MX, = Lewis acid).' A great deal of experimental and theoretical work concerning the interaction of formaldehyde with Li+ and other Lewis acids has accumulated ' Philipps-Universitat. 'Universitat Essen. R H KMX"

From Penicillin to Penem and Carbapenem. VIII. Introduction of an Allyl Group at the C-4 Position of the Azetidinone Molecule, and the Synthesis of Dethiathienamycin

Abstract: A new C3-unit introduction reaction at the C-4 position of 4-acetoxy-2-azetidinone derivatives using tetraallyltin in the presence of 1/10 equiv of boron trifluoride etherate in dichloromethane is described. Dethiathienamycin was synthesized from (3S,4R)-4-allyl-3-[(R)-1-(t-butyldimethylsilyloxy)ethyl]-2-azetidinone via the ylide intermediate.

Production of oxymethylene copolymer

Abstract: PURPOSE: To readily obtain the titled copolymer having improved heat-resistant stability, by polymerizing trioxane with a cyclic ether in the presence of a boron trifluoride based polymerization catalyst, deactivating the catalyst with a specific compound and heating the reaction mixture together with a stabilizer CONSTITUTION: A blend of trioxane with a cyclic ether is subjected to bulk polymerization in the presence of a polymerization catalyst selected from boron trifluoride (hydrate) and coordination compounds of the boron trifluoride with organic compounds containing O or S atom After completing the polymerization reaction, a hindered amine expressed by the formula (R 1 is H or 1W30C monofunctional organic group; R 2 WR 5 are 1W5C alkyl; n is a positive integer; R 6 is n-valent organic residue) is added to the reaction system to deactivate the above-mentioned catalyst A stabilizer is then added thereto to heat the reaction mixture at 100W260°C Thereby the aimed copolymer containing oxymethylene units and other oxyalkylene units is obtained COPYRIGHT: (C)1988,JPO&Japio

Epoxy resin cure III: Boron trifluoride catalysts

Abstract: Boron trifluoride forms complexes with nitrogen-and oxygen-containing Lewis bases. These acid–base complexes are sometimes added to epoxy resins to accelerate their cure at elevated temperature (120°C–160°C). Several possible processing concerns with the use of boron trifluoride complexes have been investigated. It was shown that each complex can be readily identified by its distinct fluorine-19 NMR spectrum. All of the boron trifluoride complexes are converted to fluoroboric acid under normal epoxy resin cure conditions. The fluoroboric acid is the true catalyst for epoxy resins. Experimental results show that fluoroboric acid does not catalyze the polymerization of an epoxy resin at room temperature. Finally, it was shown that fluoroboric acid is not hydrolyzed to hydrofluoric acid.

Rearrangement approaches to cyclic skeletons. III. Practical route to cis-bicyclo(4.3.0)non-4-en-7-ones based on photochemical (1,3) acyl migration of bicyclo(3.2.2)non-6-en-2-ones.

Abstract: 1-Methoxybicyclo[3.2.2]non-6-en-2-ones and the related compounds were derived I) from the Diels-Alder type 1,4-addition products of tropones with ethylene by selective reduction of the α,β-unsaturated carbonyl part (hydrosilylation followed by hydrolysis) and/or II) from bicyclo[2.2.2]oct-5-en-2-ones a) by the ring-enlargement utilizing Tieffeneau-Demjanov type conditions (1, TMS–CN; 2, LiAlH4; 3, NaNO2–AcOH) and/or b) by the related ringexpansion using trimethylsilyldiazomethane and boron trifluoride etherate. These bridged compounds were transformed into the respective [1,3] acyl migration products, cis-bicyclo[4.3.0]non-4-en-7-ones, in practical yields by direct irradiation through a Pyrex filter.

Allylic Rearrangement of Cyanophosphates. III. : Reaction of Acyclic Enone Cyanophosphates

Abstract: Boron trifluoride-catalyzed allylic rearrangement of α, β-unsaturated ketone cyanophosphates (2, 6 and 12) gave (Z)-4-diethylphosphonooxy-2-butenenitriles (3, 8 and 13), while α, β-unsaturated aldehyde cyanophosphates (17a-c) afforded (E)-4-diethylphosphonooxy-2-butenenitriles (18a-c) stereoselectively. The stereo- and regioselective reaction of 2 with several kinds of aromatics in the presence of boron trifluoride etherate afforded (Z)-4-aryl-2-methyl-2-butenenitriles (20) via the SN2' reaction. On the other hand, treatment of 2 with 1-subsituted indoles in the presence of boron trifluoride etherate gave 1-amino-2-methylcarbazole derivatives (23a-c).

Manufacture of laminated sheet

Abstract: PURPOSE:To contrive to improve the heat resistance and plating property of a laminated sheet by a method wherein a prepreg is made by impregnating paper base material with varnish treated by organic solvent containing epoxy resin with epoxy equivalent of 500-1,500, specified amine compound and Lewis acid complex and, after that, drying the resultant base material. CONSTITUTION:Firstly, a paper base material is impregnated with varnish treated by organic solvent containing epoxy resin with epoxy equivalent of 500-1,500, amine compound represented by the formula (1) and Lewis acid complex and, after that, dried in order to make a prepreg. Secondly, a necessary number of the prepregs are heated under pressure in order to obtain the titled laminated sheet. The compound represented by the general formula (1) is employed as the amine compound, which acts as curing agent. Further, boron trifluoride complex is exampled the Lewis acid complex, which acts as curing promotor. Bisphenol A type epoxy resin, brominated bisphenol A type epoxy resin, phthalic acid type epoxy resin, polypropylene type epoxy resin or the like is employed as the epoxy resin. Common organic solvent such as methyl ethyl ketone, acetone, alcohol or the like is used as the organic solvent.

A NOVEL AND USEFUL SYNTHETIC WAY TO CHIRAL α-SULFINYL CYCLIC KETONES BY THE ACID-CATALYZED REACTION OF ENOL SILYL ETHERS OF CYCLIC KETONES WITH CHIRAL SULFINATES

Abstract: The acid-catalyzed reactions of enol silyl ethers of cyclic ketones with chiral sulfinic esters provided a new and general entry to optically active α-sulfinyl ketones. Reaction of the enol silyl ether of cyclohexanone with methyl (S)-p-toluenesulfinate in the presence of boron trifluoride etherate (2.0 equiv.) produced (Rs)-2-p-toluenesulfinylcyclohexanone with inversion of configuration in 98.3% stereospecificity at the sulfur atom. This method was applicable smoothly to enol silyl ethers of other cyclic ketones with high stereospecificity.

The first biomimetic conversion of a germacrolide-4-epoxide into a xanthanolide

Abstract: Boron trifluoride catalysed cyclization of the germacrolide-4-epoxide dihydroparthenolide (1) provided two known guaianolides and the xanthanolide (4), the latter transformation representing the first biomimetic conversion of a germacrolide into a xanthanolide.

The chemical and enzymatic oxidation of hematohemin IX

Abstract: Oxidative cleavage of hematohemin IX in pyridine solution in the presence of ascorbic acid (coupled oxidation), followed by esterification of the products with boron trifluoride/methanol produced the four possible hematobiliverdin dimethyl esters in 11.1% overall yield. Transetherifications took place simultaneously with the esterification reaction and resulted in the formation of the dimethyl ester of hematobiliverdin IX gamma 8a,13a-dimethyl ether (1.8%), the dimethyl ester of hematobiliverdin IX beta 13a,18a-dimethyl ether (1.9%), the dimethyl ester of hematobiliverdin IX delta 8a-monomethyl ether (1.4%), and the dimethyl ester of hematobiliverdin IX alpha 18a-monomethyl ether (0.4%). The latter was the sole product obtained after the enzymatic oxidation of hematohemin with heme oxygenase, after esterification of the reaction product with boron trifluoride/methanol. When the esterification step was omitted hematobiliverdin IX alpha was obtained from the enzymatic oxidation. The structures of the hematobiliverdin derivatives were secured by their NMR and mass spectra data. Saponification of the dimethyl esters afforded the hematobiliverdin methyl ethers, which were excellent substrates of biliverdin reductase and were readily reduced to the corresponding bilirubins. Hematobiliverdin IX alpha was also a good substrate of biliverdin reductase. It is concluded that the enzymatic oxidation of hematohemin IX by heme oxygenase is alpha-selective, while biliverdin reductase shows no selectivity in the reduction of the four hematobiliverdin isomers.

Regioselectively Modified Stereoregular Polysaccharides IX. A Synthetic Polysaccharide Having One Hydroxyl Group in Its Repeating Unit, 2,4-Dideoxy-(1→6)α- D - threo -hexopyranan

Abstract: A new synthetic linear dextran having one hydroxyl group in position 3 of each repeating unit, 2,4-dideoxy-(1→6)α-D-threo-hexopyranan (3), was prepared by the cationic ring-opening polymerization of 1,6-anhydro-3-O-benzyl-2,4-dideoxy-β-D-threo-hexopyranose (1), followed by debenzylation. The 1 ,6-anhydro dideoxy compound 1 was obtained from microcrystalline cellulose via four step reactions. The polymerization of 1 was carried out using phosphorus pentafluoride and boron trifluoride diethyl etherate at temperatures ranging from −90 to 0°C. The stereoregular polymer with α-anomeric configuration, 3-O-benzyl-2,4-dideoxy-(1→6)-α-D-threo-hexopyranan (2), was obtained at lower temperature in high yield. Disordering of the stereoreg-ularity depending upon polymerization conditions was estimated by the 13C NMR spectrum and specific optical rotation. The high reactivity of 1 in polymerization, copolymerization, and acid-catalyzed solvolysis is discussed on the basis of the electronic and steric effects for the deoxygenated structure of 1. Debenzylation of 2 with sodium metal in liquid ammonia afforded a white powdery polymer identified as 3 by the 13C NMR spectroscopy.

Doping of a-Si:H using BF3

Abstract: P-type dc-glow-discharge a-Si films have been prepared using boron trifluoride as the doping agent. Film growth on various cathodic substrates is examined. The effect of BF 3 -doping on hydrogen incorporation into the a-Si network is investigated using the 15 N profiling technique and FIR measurements of Si-H vibrational modes. The concentration of boron and fluorine that is incorporated into BF 3 -doped films is profiled using SIMS. Data on the dark conductivity of BF 3 -doped films is presented.