Intramolecular heterocyclic alkynyliodonium salts

Likewise, interaction of terminal alkynes with 20 in refluxing acetonitrile in the presence of toluenesulfonic acid gives the intramolecular heterocyclic alkynyliodonium salts 21 [Eq. (11)] [33]. A wide range of the alkyl- and phenyl-substituted congeners 21 of these intramolecular analogs of the acyclic iodonium tosylates, 9, are obtained in 26-70% isolated yields. 

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. 

A variety of five-membered nitrogen heterocycles can be prepared efficiently by inter- or intramolecular addition/cyclizations of sulfonamide anions with alkynyliodonium salts. The intermolecular variant employs the combination of the amides 172 or anilides 174 with propynyl(phenyl)iodonium triflate (Scheme 65) [131,132]. The yield of dihydropyrroles 173 in this cyclization is extremely sensitive to the nature of the protective group P the tosyl group in 172 proved... 

Various flve-membered heterocycles can be prepared by inter- or intramolecular addition/cyclizations of appropriate nucleophiles with alkynyliodonium salts via alkylidene carbene intermediates [856, 978, 979]. The intermolecular variant of this cyclization has been employed in the synthesis of 3-substituted-5,6-dihydroimidazo[2,l-( ]thiazoles [997], 2-substituted imidazo[l,2-a]pyrimidines [998] and 2-substituted-imidazo[l,2-fl]pyridines [999]. In a representative example, 2-substituted imidazo[l,2-fl]pyridines 744 were synthesized in good yield by cyclocondensation of 2-aminopyridine (742) with alkynyl(phenyl)iodonium tosylates 743 under mild conditions (Scheme 3.293) [999]. The mechanism of this cyclization involves... 

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See also in sourсe #XX -- [ ]

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