The reactivity of methyl 4, 5-epoxy-(2E)-pentenoate (2) toward various aromatic nucleophiles in the presence of boron trifluoride etherate was examined. When benzene derivatives possessing an electron-donating substituent were employed, meta-substituted benzenes attacked only the 4-position of 2, while ortho- or para-substituted benzenes simultaneously attacked the 4- and 2-positions of 2.
Intramolecular Reaction of a Phenonium Ion. Novel Lactonization of 4-Aryl-5-tosyloxypentanoates and 4-Aryl-5-tosyloxyhexanoates Concomitant with a Phenyl Rearrangement<sup>1</sup>
of the aromatic ring on the reactivity, it was found that the reaction proceeded via a phenonium ion. This finding was supported by the stereochemical results for the lactonization of opticalactive 1. Silica gel-promoted lactonization of 1 gave only gamma-lactone 2, whereas that of 3 afforded gamma-lactone 4 and delta-lactone 5. These lactonizations proved to be kineticallycontrolled. On the other
Silica gel promotes the lactonization and the concomitant aryl rearrangement of 4-aryl-5-tosyloxy pentanoates (3c-j) to give γ-lactones along with complete inversion in high yields.