Triethyloxonium fluoborate reactions

Furthermore, recent studies indicate that esterifications involving triethyloxonium fluoborate are often very rapid. For example, subsequent to the checking of this procedure the submitters ha ve found that the reaction time of Part A may be shortened from 16-24 hours to 0.5 hour with no decrease in yield. The longer reaction time is still recommended for esterifications involving the trimethyl salt, such as that of Part B, because of the heterogeneous nature of the reaction mixture in these cases. 

Hydroxypyridone 337 by triethyloxonium fluoborate was transformed to ether 338 that resisted nucleophilic reactions (76IJB400). Such reactions were possible, however, in the case of pyridone 192a through chloro compound 384. Nucleophilic displacement of triflate 28 resulted in the formation of iodide 29a as the major product (94TL393). 

Freshly prepared triethyloxonium fluoborate (170 g., 0,90 mole) is dissolved in 500 ml. of anhydrous methylene chloride in a 1-1. three-necked flask equipped with a stirrer, gas-inlet tube, and drying tube (Note 1). The reaction flask is immersed in an ice bath, the stirrer is started, and 138 g. (3.00 moles) of dry dimethyl ether is passed into the solution from a tared cylinder over a period of about 2 hours. The reaction mixture is allowed to stand overnight at room temperature. An hour after the addition of dimethyl ether is complete, trimethyloxonium fluo-borate begins to separate. The initially liquid product solidifies slowly. 

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