Tetrahalogenated Spiroketals

Tetrahalogenated Spiroketals

Author: Asian Journal of Organic Chemistry

The spiroketal skeleton is important in numerous biologically significant natural products, and its synthesis is a research hotspot. However, no successful example of the preparation of the spiroketals by an electrophile-promoted cyclization has been reported until now.

Yong-Min Liang and co-workers from Lanzhou University, China, developed the synthesis of tetrahalogenated spiroketals through an iodocyclization. Reactions of symmetrical tertiary α,β-diynyl ketodiols produce tetrahalogenated spiroketals in the presence of electrophiles, such as I2, ICl, or IBr, and the same is true for tetraiodospiroketals when symmetrical primary α,β-diynyl ketodiols are used. Reactions with substrates bearing primary and tertiary hydroxy groups on both ends of α,β-diynyl ketodiols also afford the desired spiroketal products.
The team discovered that when the reactions of chiral secondary α,β-diynyl keto diol derivatives with I2 were examined,

optically active spiroketals were obtained. This spiroketalization is a synergetic process and the chiral spiroketal center is induced by intramolecular chiral alkynols.

This method might be applied to synthesize chiral ligands in Pd-catalyzed coupling reactions.

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