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Ionic reactions with polarized transition states are favored by the solvent system LiClO 4 /Et 2 O (3–5 M ). This is demonstrated by (hetero) Diels–Alder reactions and by the sigmatropic rearrangement of ally1 vinyl ethers in this medium. The former react even faster and with higher endo selectivity than in water; the latter are not 3,3 but 1,3 sigmatropic rearrangements, which yield aldehydes. An important advantage of the LiClO 4 /Et 2 O system is it that may also be used for acceleration of reactions sensitive to hydrolysis.
Herbert Waldmann (1991) studied this question.