The triethyloxonium tetrafluoroborate/1,2-dimethoxyethane (TEO/DME) mixture is a versatile and cheap substitute for trimethyloxonium tetrafluoroborate in O-methylations of pyrrolin-2-ones, quinolones, acridones, and 1-oxo-β -carbolines. Undesired O-ethylation can be avoided by preincubation of triethyloxonium tetrafluoroborate and 1,2-dimethoxyethane for 1 h, prior to addition of the substrate. In the course of these investigations it was found that the structures assigned to the alkaloids taraxacine A and B are erroneous.

Etherification O 0328Triethyloxonium Tetrafluoroborate/1,2-Dimethoxyethane -A Versatile Substitute for Trimethyloxonium Tetrafluoroborate in O-Methylation Reactions. -Et3O + BF4/DME mixture is a versatile and cheap substitute for Me3O + in O-methylations of pyrrolin-2-ones, quinolones, acridones, and 1-oxo-β-carbolines. Undesired O-ethylation as observed in reactions of carbolines (VIII) can be avoided by preincubation of Et3O + and DME for 1 h followed by addition of the substrate. The structures (Xa) and (XII) assigned to the alkaloids taraxacine A and B, resp., are found to be erroneous. -(RITTER, A.; POSCHENRIEDER, H.; BRACHER