Alkynyl iodonium tetrafluoroborates, preparation

Using this method, several mesogen diacetylenes were obtained [49]. Palladium-catalysed coupling of an allylic cyclic carbonate with 1-pentynyl phenyliodonium tetrafluoroborate to give an enyne was highly successful [50]. Alkynyl iodonium triflates and lithium salts of diethyl 2-[(diphenylmethylene)amino]malonate were used for the preparation of alkynyl-a-amino acid derivatives, e.g. [51] ... 

The present procedure, similar to that of Fujita for the preparation of alkynyl(phenyl)iodonlum tetrafluoroborates, RC5CIPh BF4, is simpler, much more general and in most cases gives significantly better yields. Table I gives yields of alkynyl(phenyl)iodonium sulfonates prepared by this procedure. 

Alkynyl(aryl)iodonium salts can serve as precursors to some alkenyl(aryl)iodonium salts [453 55], For example, ( )-(3-fluoroalkenyl(phenyl)iodonium tetrafluoroborates 316 can be stereoselectively prepared by... 

A common method for preparing alkynyl(phenyl)iodonium tetrafluoroborates involves the reaction of iodosylbenzene in the presence of triethyloxonium tetrafluoroborate or boron trifluoride etherate with alkynyl-silanes. For example, the complex of iodosylbenzene with triethyloxonium tetrafluoroborate (362) reacts with alkynylsilanes in dichloromethane at room temperature to afford alkynyl(phenyl)iodonium tetrafluoroborates 363 in good yield [496]. A variation of this procedure employs the complex of iodosylbenzene with boron trifluoride etherate (364) followed by treatment with aqueous NaBp4 [493,497] or sodium arylsulfonates to furnish, respectively, the appropriate alkynyl(phenyl)iodonium tetrafluoroborates 363 [483,487] or organosul-fonates 365 [488,489] (Scheme2.102) [498,499],... 

Alkynyl(phenyl)iodonium salts can be used for the preparation of substituted alkynes by the reaction with carbon nucleophiles. The parent ethynyliodonium tetrafluoroborate 124 reacts with various enolates of /J-dicarbonyl compounds 123 to give the respective alkynylated products 125 in a high yield (Scheme 51) [109]. The anion of nitrocyclohexane can also be ethynylated under these conditions. A similar alkynylation of 2-methyl-1,3-cyclopentanedione by ethynyliodonium salt 124 was applied in the key step of the synthesis of chiral methylene lactones [110]. 

Alkynyliodonium ions, 1 and 2, are hypervalent iodine species in which one or two alkynyl ligands are bound to a positively charged iodine(III) atom. They are sensitive to nucleophiles, especially at the /1-carbon atom(s) of the alkynyl ligand(s), and for that reason, the isolation of stable alkynyliodonium salts generally requires the incorporation of nucleofugic anions. A list of known alkynyliodonium compounds (i.e. as of 4/1/94), containing 134 iodonium salts derived from 103 iodonium ions, and references (5-45) to their preparation and characterization are presented in Table 1. Among these compounds, alkynyl(phenyl)iodonium sulfonates and tetrafluoroborates are the most common, while alkynyl(alkyl)iodonium salts of any kind are unknown. 

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