Alkynyliodonium tosylates, coupling

Alkynyl(phenyl)iodonium salts can be efficiently coupled with various organo-copper reagents. Direct coupling of alkynyliodonium tosylates 132 with vinyl-... 

A similar coupling of alkynyliodonium tosylates 132 with dialkynylcuprates 134 leads to conjugated diynes 135 (Scheme 55) [114,115]. This method can be used for the preparation of unsymmetrical diynes in moderate yield. Recently, this coupling was employed in the synthesis of various liquid-crystalline diaryl-diacetylenes [115]. 

Likewise, alkynyliodonium tosylates can be coupled with dialkyl- and diphenyl cuprates 136 to afford the respective alkyl- and phenyl-substituted alkynes 137 (Scheme 56) [114]. An interesting example of this reaction involves the coupling of (trimethylsilyl)ethynyl iodonium triflate with cubyl cuprate generated in situ from iodocubane 138 [116]. 

Reaction of vinylcopper reagents, 62, with alkynyliodonium tosylates results in conjugated enyne 63, [53] [Eq. (24)]. The reaction is stereospecific with retention of olefin geometry. By appropriate order of addition, either of the two possible isomeric trisubstituted olefin isomers, 63, can be obtained in good isolated yields and excellent (>99%) stereoselectivity. Likewise, conjugated diynes, 65, are obtained [54] in the reaction of dialkynylcuprates, 64, with alkynyliodonium tosylates [Eq. (25)]. This method may be used for the preparation of unsym-metrical diynes. The mechanism of these coupling reactions is not understood at present. 

Copper-catalyzed carbonylative coupling of ( )-a-(ethylsdanyl)-vinyl zircono-cene chloride derivatives with alkynyliodonium tosylates has been reported to be a mild method for the preparation of vinyl alkynyl ketones in good yields (Scheme 12.30) [39]. 

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