Cyclic iodonium species

An interesting variant on this theme involves the cyclization of substituted 2-allylphenols by A-iodosuccinimide. The 3-iodochromans, which presumably arise via a cyclic iodonium species, are readily dehydrohalogenated by base. The overall yields are generally impressive, although ring iodination can compete (79TL2545). 

Reaction of trimethylsilylalkynes with 16 in dichloromethane in the presence of BF3 OEt2 at room temperature followed by heating in methanol at 60 °C results in the stable heterocyclic alkynyliodonium salts 17 [Eq. (9)] [31]. These species represent intramolecular iodonium salts where the counterion is a carboxylate. Unlike the acyclic alkynyl(phenyl)iodonium carbox-ylates 18, that are unstable to isolation and decompose to the corresponding alkynyl benzoates 19 [Eq. (10)] [32], the cyclic analogs 17 are readily isolable. 

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