Grignard Reactions in Pyridinium and Phosphonium Ionic Liquids

Alkylpyridinium (10a, R = Me and 10b, R = Et) and tetraalkylphosphonium (19) ionic liquids which possess ether functionality were prepared and evaluated as solvents and co‐solvents for Grignard reactions. Interestingly, reduction of the starting aldehydes to the corresponding primary alcohol was the favored pathway when reactions were conducted in pyridinium ILs 10a, b in the absence an ethereal co‐solvent. However, the same reactions in the phosphonium IL 19 afforded the expected Grignard products in good yield in cases where diethyl ether was present as a co‐solvent. Grignard reactions conducted in pyridinium ionic liquids bearing an ether moiety were found to unexpected afford reduction products. In contrast, Grignard reactionsconducted in phosphonium ionic liquids bearing an ether moiety gave the expected Grignard products.