Tetrafluoboric acid

However, the electronic spectrum of dark green bi(cyclohepta)pyr-role 262 dissolved in tetrafluoboric acid shifts hypsochromically to become, ultimately, identical with the spectrum of tropylium salt 263 (75TL1849). A strong shift in the same direction is observed with acidified... 

Other amidoselenenylation reactions have been described. Salazar [50] reported that the carbamatoselenenylation of alkenes can be effected using hT-(phenylseleno)phthalimide, in the presence of tetrafluoboric acid, and ethyl carbamate as the nucleophile. The reaction is a stereospecific anti addition and works well with monosubstituted and 1,2-disubstituted alkenes. In the case of monosubstituted alkenes mixtures of regioisomers were obtained. 

Based on these early studies, two current approaches have evolved for generating ozone electrolytically. One of them, shown in Fig. 13, uses glassy carbon anodes, a specialized electrolyte, tetrafluoboric acid (HBF4), and an air cathode [66]. At a current density of 400 mA/cm, 35 vol Vo of ozone was obtained from 48 wt.% HBF4 maintained at -5 to 0°C, with a cell potential of 3.2-3.4 V vs. NHE. The ozone gas formed within the cell was immediately diluted with air to lower the ozone concentration to 15 wt.%, a value below explosion limits. The electrodes were not attacked at these current densities and in the presence of this electrolyte. 

The esters derived from acetylacetic acid have been realised either from ethy-lacetoacetate by transesterification with l-(2-hydroxyethyl)-3-methylimidazolium tetrafluoborate under MW irradiation [35] or by reaction of hydroxyalkyltrimethy-lammonium salts with a ketene dimer (Scheme 5.5-18) [36]. 

Coupling reactions are an excellent field for testing new soluble supports. For example, a small hbrary of stilbenes was easily obtained by the reaction of a supported styrene on a functionahzed trimethylammonium tetrafluoborate with a mixture of 7 aryl iodides in DMF at 100 °C for 2 h. The reaction was monitored by HPLC and, after completion, the DMF was evaporated under vacuum and the residue vrashed several times vyith ether and water. Transesterification of this mixture vyith acidic methanol led, after evaporation and extraction with ether, to a hbrary of 7 stilbenes in an excellent state of purity as determined by GC/MS. No impurity and particularly no starting styrene could be detected, showing that the reaction vyas complete (Scheme 5.5-40) [21,51]. 

Alternative methodologies for the indirect reduction of carboxylic derivatives employ as intermediates 2-substituted 1,3-benzoxathiolium tetrafluoborates (prepared from carboxylic acids, acyl chlorides, anhydrides, or esters) and dihydro-1,3-... 

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