Efficient formation of a spirotetrahydrofuran ring by the ionic cyclization of bishomoallyl tertiary alcohols via their hypoiodites

Abstract

Spirotetrahydrofuran derivatives are produced in high yields by an intramolecular cyclization of several steroidal bishomoallyl tertiary alcohols in benzene containing mercury(II) oxide and iodine at room temperature in the dark. 2-Hydroxy-2-(but-3-enyl)tetrahydrofuran thus cyclizes to give a mixture of the corresponding diastereoisomeric spirotetrahydrofurans in the dark.

An ionic mechanism for the formation of the tetrahydrofuran ring, which involves the formation of the hypoiodite followed by the cyclization of its iodonium ion, is proposed based on studies concerning several model substrates.