Ethynyl iodonium triflates

Under similar conditions, (2-oxoazetidinyl)malonates 129 can be alkynylated by (trimethylsilyl)ethynyl iodonium triflate (Scheme 53). In contrast to the previous reaction (Scheme 52), this alkynylation directly affords the desilylated terminal alkynes 130 as the final isolated products [112]. This reaction (Scheme 53) allows ethynylation of malonates under milder conditions compared to the reaction shown in Scheme 51. 

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]. 

TABLE 5. Cyclopentenyl sulfones and sulfonyl lactams from (ketoethynyl)iodonium and (amido ethynyl)iodonium triflates 17 and 18 with sodium / -toluenesulfinate in dichloromethane"... 

Phenyl[(trimethylsilyl)ethynyl]iodonium triflate has also been employed for alkynylations of diethyl 2-phthalimidomalonate and the (2-oxoazetidinyl)malonates shown in equation 126. However, unlike the result with the [(diphenyl)amino]malonate system (equation 125), the trimethylsilyl group is lost, and the ethynyl group is ultimately introduced. 

A Simple and Convenient Method for the Preparation of p-Functionalized Alkynyl(phenyl)iodonium Triflates Phenyl[p-toluenesulfonyl)ethynyl]iodonium Triflate. 

This approach to N-alkynylsulfonamides has been applied to the synthesis of enantiomerically pure derivatives 27 of N-(ethynyl)allylglycine (Scheme 52) [152]. In this case, deprotonated sulfonamide derivatives of (S)-allylglycine were treated with ethynyl(phenyl)iodonium triflate (28), since the trimethylsi-lylethynyl salt 26 was not very effective for this purpose. 

Certainly one of the most unusual nucleophiles to be treated with alkynyliodonium salts is the tetra-ter -butyltetraphosphacubane shown in equation 7791. However, despite its unique structure, this compound reacts with ethynyl(phenyl)- and l-propynyl(phenyl)-iodonium triflates in the now expected way to give good yields of alkynylphosphonium salts91. 

A more general, simpler procedure [20] takes advantage of the in situ formation of the p-oxo-bis-triflate (6 R=CF3) and its interaction with a sila- or tin-acetylene [Eq. (2)]. This methodology affords a wide variety of stable, alkynyl(phenyl)iodonium triflates 10 in good to excellent yields and is applicable to the synthesis of the parent [21] ethynyl(phenyl)iodonium triflate (10 R=H) from n-Bu3SnC=CH. 

Scheme 3-1 Preparation and yield of various p-substituted ethynyl(phenyI)iodonium triflates, 11, via PhKCNlOSOjCFj.

The deprotonation of N—H bonds in diverse oxazoUdin-2-ones with KHMDS as the base followed by tbe treatment of tbe crade reaction mixtures with trimethylsilylethynyl iodonium triflate electrophiles afforded trimethylsilyl-terminated IV-ethynyl oxa-zolidinones in 50-60% yields (eq 74). Desilylation could be realized on the purified products or the crude reaction mixtures, and the alk)myl oxazolidinones were elaborated into novel stannyl enamines in the subsequent steps. In contrast, protocols employing -BuLi in toluene, or CS2CO3 in DMF gave yields lower than 20%. The procedure could be successfully applied to chiral oxazolidinones, since substitution at the C4 position of the oxazolidinones did not have a detrimental effect on reactivity. 

An alternative, less general procedure for the preparation of alkynyl(phenyl)iodonium triflates in moderate yields employs the reaction of alkynylsilanes [493], alkynylstannanes [494], or alkynylboronates [297] with Zefirov s reagent, 2PhI0-Tf20. This method is also applicable to the synthesis of the parent ethynyl(phenyl)iodonium triflate [495]. 

Single-crystal X-ray structural data have been reported for the following alkynyliodonium compounds the parent ethynyl(phenyl)iodonium triflate (368) [495], phenylethynyl(phenyl)iodonium tosylate (369) [477], cyanoethynyl(phenyl)iodonium triflate (370) [458], propynyl(phenyl)iodonium periodate (371) [502], trimethylsilylethynyl(phenyl)iodonium triflate (372) [503], 3,3,3-trifluoropropynyl(phenyl)iodonium triflate (373) [504], bis(alkynyl)iodonium triflate 374 [505] and complexes of ethynyl(phenyl)iodonium [506] and l-decynyl(phenyl)iodonium [507] tetrafluoroborates with 18-crown-6 (Figure 2.13). 

The reactions of the lithium enolate of diethyl 2-[(diphenylmethylene)amino]malonate with several alkynyliodonium triflates are rare examples of enolate alkynylations with iodonium species other than the ethynyl(phenyl)- and (phenylethynyl)phenyliodonium ions (equation 125)16. Two experimental protocols were followed, i.e. addition of the enolates to the iodonium salts and vice versa, the former procedure giving higher yields of alkynylmalonates. As with other enolate alkynylations, these reactions are thought to involve alkylidenecarbene intermediates. It has been proposed, however, that the carbenes rearrange with migration of the diethyl 2-[(diphenyl) amino] malonate anion 16. 

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