Alkynyl iodonium triflates, preparation

Alkynyl iodonium triflates prepared by the above reactions (equations 70,72, and 73) have become valuable reagents m organic chemistry, serving as premier... 

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] ... 

Fluoroalkyl(alkynyl)iodonium triflates 388 can be prepared by the reaction of triflates 387 and (trimethylsi-lyl)acetylenes (Scheme 2.112) [176],... 

Instead of silyl-, stannylalkenes are also suitable precursors [4] cyano phenyliodonium triflate (Section 9.1.4) was here the reagent of choice. This variation enabled the preparation of the parent ethenyl and several trisubstituted alkenyl phenyliodonium triflates [5], More elaborate members were obtained through additions to the triple bond of alkynyl iodonium salts, notably Diels-Alder adducts. 

The iodonium triflate (460 mg, 1 mmol) was added to a stirred slurry of anhydrous sodium p-toluene sulphinate (180 mg, 1.01 mmol) in dichloromethane (15 ml) at 20°C under nitrogen. After 15 min water (10 ml) was added and the phases were separated the aqueous layer was extracted with additional dichloromethane (2 x 5 ml), and the combined organic extracts were dried. The filtered solution was treated with hexanes (30 ml) and concentrated. The solid residue was purified by radial chromatography (silica gel, 200-400 mesh, dichloromethane-hexanes) to afford 3-tosyl-bicyclo[3.2.0]-3-heptene-2-one (197 mg, 75%), m.p. 164-165°C. The method is general for the preparation of sulphones with a cyclopentenone moiety other alkenyl iodonium salts gave alkynyl sulphones with sulphinates (Section 9.4.4). 

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

The best and most versatile contemporary method [22] of preparation of alkynyl(aryl)io-donium salts employs readily available alkynylstannanes [23], and the easily prepared [24] cyano(phenyl)iodonium triflate 7 as an iodonium transfer agent in dichloromethane at low temperatures [Eq. (3)]. This procedure provides excellent yields of iodonium triflates 10 and is applicable to a very broad range of alkynylstannanes, including those with strongly electron-withdrawing groups as summarized in Scheme 3-1. Particularly noteworthy and valuable are the P-keto- and P-amido-substituted species 11 and the cyano-functionalized molecule 11 (Y=CN) [25, 26]. 

A similar approach to aryl- and heteroaryl(phenyl)iodonium triflates 285 involves the ligand-transfer reaction between vinyliodonium salt 284 with aryllithiums (Scheme 2.83) [405]. Likewise, the reaction of ( )-[(3-(trifluoromethanesulfonyloxy)ethenyl](aryl)iodonium triflates 286 with aryllithiums or alkynyllithiums can be used for a selective preparation of the respective diaryl- or alkynyl(aryl)iodonium triflates in high yields [406]. 

The most versatile method for preparing alkynyl(phenyl)iodonium triflates employs the iodonium transfer reaction between cyano(phenyl)iodonium triflate (348) and alkynylstannanes. The interaction of a large variety of readily available p-functionalized alkynylstannanes 349 with reagent 348 under very mild conditions provides ready access to diverse p-functionalized alkynyliodonium salts 350 in excellent yields (Scheme 2.100) [458,482,483]. This procedure is particularly useful for the preparation of various complex. 

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]. 

Alkynyl(phenyl)iodonium salts have found synthetic application for the preparation of various substituted alkynes by the reaction with appropriate nucleophiles, such as enolate anions [980,981], selenide and telluride anions [982-984], dialkylphosphonate anions [985], benzotriazolate anion [986], imidazolate anion [987], N-functionalized amide anions [988-990] and transition metal complexes [991-993]. Scheme 3.291 shows several representative reactions the preparation of Ai-alkynyl carbamates 733 by alkynylation of carbamates 732 using alkynyliodonium triflates 731 [989], synthesis of ynamides 735 by the alkyny-lation/desilylation of tosylanilides 734 using trimethylsilylethynyl(phenyl)iodonium triflate [990] and the preparation of Ir(III) a-acetylide complex 737 by the alkynylation of Vaska s complex 736 [991]. 

The intramolecular variant of the alkylidene carbene cyclization is achieved by treating functionalized alkynyliodonium salts with a suitable nucleophile. These cyclizations are exemplified by the following works the preparation of various functionalized 2,5-dihydrofurans by treatment of 3-alkoxy-l-alkynyl-(phenyl)iodonium triflates with sodium benzenesulfinate [1002], employment of the alkylidene carbene cyclization in the total syntheses of natural products agelastatin A and agelastatin B [1003] and preparation of the tricyclic core of ( )-halichlorine through the use of an alkynyliodonium salt/alkylidenecarbene/1,5 C—H insertion sequence [1004]. In particular, Wardrop and Fritz have employed the sodium benzenesulfinate-induced cyclization of alkynyliodonium triflate 751 for the preparation of dihydrofuran 752 (Scheme 3.295), which is a key intermediate product in the total synthesis of ( )-magnofargesin [1002]. 

The most versatile method of preparation uses the readily available alkynylstannanes (21) and the mixed phenyliodonium triflate (22) as the iodonium transfer agent (equation 7). This procedure works very well for the synthesis of a wide variety of hydrocarbon as well as jS-functionalized alkynyl(phenyl)iodonium trifiates [23 Y=CN, Cl, RC(0), (CH3)2NC(0), ArSOi, etc.]. 

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