Iodonium ylides preparation

CuCl-catalyzed decomposition of iodonium ylides prepared from /3-keto esters and diacetoxyiodobenzene, has been developed (equation 151)331. 1-Methylbenzvalene is obtained in a good yield by treating a mixture of lithium cyclopentadienide and 1,1-dichloroethane with butyllithium332. The tandem cyclization substitution in l-selenyl-5-hexenyllithiums derived from corresponding selenacetals via selenium/lithium exchange produces bicyclo[3.1.0]hexane derivatives333. 

Diazocarbonyl compounds are optimum for these transformations, and they may be readily prepared by a variety of methods. The use of iodonium ylides (17) has also been developed, " but they exhibit no obvious advantage for selectivity in carbene-transfer reactions. Enantioselection is much higher with diazoacetates than with diazoacetoacetates (18). 

Carbenoid sources other than those derived from diazo precursors for catalytic cyclopropanation reactions are currently limited. Inter- and intramolecular catalytic cyclopropanation using iodonium ylide have been reported. Simple olefins react with iodonium ylides of the type shown in equations 83 and 84, catalysed by copper catalysts, to give cyclopropane adducts in moderate yield127 128. In contrast to the intermolecular cyclopropanation, intramolecular cyclopropanation using iodonium ylides affords high yields of products (equations 85 and 86). The key intermediate 88 for the 3,5-cyclovitamin D ring A synthon 89 was prepared in 80% yield as a diastereomeric mixture (70 30) via intramolecular cyclopropanation from iodonium ylide 87 (equation 87)1 0. 

The standard method for the preparation of many phenyliodonium ylides is reaction of compounds having an active methylene group with an iodine(III) species, usually in aqueous alkali, to give iodonium ylides (Scheme 50) [151]. 

The catalytical decomposition of iodonium ylides is especially useful as a method of cyclization via intramolecular cycloaddition or bond insertion [146 -148]. Several representative examples of these cyclizations are shown in Scheme 73. Specifically, the intramolecular cyclopropanation of ylide 203 leading to product 204 was used in the synthesis of the 3,5-cyclovitamin D ring A synthon [146]. The copper(I) catalyzed decomposition of phenyliodonium ylides 205 affords the corresponding substituted tetralones 206 in good preparative yields [147]. Under similar conditions,iodonium ylides 207 undergo regio-and stereoselective intramolecular cyclopropanation to form the key bicy-clo[3.1.0]hexane intermediates 208 for prostaglandin synthesis [148]. 

An efficient construction of the 1 / -methylcarbapenam nucleus (87) was established by Kume and co-workers utilizing acid- or rhodium (II)-catalyzed cyclization of the iodonium ylide derivatives (174), which were easily prepared from the corresponding jS-ketoester derivatives (173) with PIDA [133] (Scheme 41). 

Oxidative methanolysis of azetidinone 176 followed by hydrogenolysis of compound 177 afforded /3-lactam 178, which was protected to obtain the protected amine 179. The best conditions for rearrangement of 179 were found using TFA. Conversion of compound 180 to carbacephem 183 was accomplished by ketone reduction, alcohol protection, and elimination of methanol. Synthesis of carbacephem derivative 186 has been performed by rhodium(n)-catalyzed cycliza-tion of iodonium ylide 185 <1997TL6981> (Scheme 33). The iodonium ylide 185 was easily prepared from the corresponding /3-keto ester 184 and [(diacetoxy)iodo]benzene in good yield. 

Several iodonium ylides, thermally or photochemically, transferred their carbene moiety to alkenes which were converted into cyclopropane derivatives. The thermal decomposition of ylides was usually catalysed by copper or rhodium salts and was most efficient in intramolecular cyclopropanation. Reactions of PhI=C(C02Me)2 with styrenes, allylbenzene and phenylacetylene have established the intermediacy of carbenes in the presence of a chiral catalyst, intramolecular cyclopropanation resulted in the preparation of a product in 67% enantiomeric excess [12]. 

Iodonium ylides of type 6 cannot be isolated, unless the carbanion center is substantially stabilized (83MI1, 92MI1, 97MI1, 02MI1). For example, although iodonium enolates 22 can be prepared by base-catalyzed condensations of DAIB or iodosylbenzene with /J-dicarbonyl compounds, they are not similarly available from unactivated ketones and esters. Indeed, cyclic and acyclic mono-ketones are converted to a-hydroxy dimethylketals 23 with DAIB (or 13) in KOH/MeOH (86ACR244, 99QR273). Other... 

The azetidinonyl iodonium ylide 290 is a safe and convenient alternative to the related diazo compound for synthesis of the carbacephalosporin precursor 291 (Scheme 82) (97TL6981). The ylide was prepared in 88% yield from the corresponding /3-ketoester and was cyclized to 291 with a Rh(II)-catalyst, presumably via a Rh-carbenoid intermediate. 

Other new oxathiolane syntheses include reaction of an epoxide with a stable thioketone <01HCA3319>. Rhodium catalysed reaction of dimethyl diazomalonate with a thioketone has been used to prepare oxathiole 92 <02PJC551> and the iodonium ylide 8 reacts with thioketones or carbon disulfide to form oxathioles <02TL5997>. 

A series of mixed phosphonium-iodonium ylides (26) and (27), compounds that contain both phosphoranyl and hypervalent iodine (X, -iodanes), have been prepared and characterised (Scheme 5). These compounds might prove to be synthetically valuable reagents. ... 

The most versatile carbene precursors are a-diazocarbonyl compounds such as diazoacetic acid esters because they are readily prepared, easy to handle and much more stable than ordinary diazoalkanes [10,38]. Nevertheless, one should always be aware of the potential hazards of diazo compounds in general [39],but if the necessary precautions are taken, they can be safely handled even on an industrial scale [18]. The most frequently used reagent is commercially available ethyl diazoacetate. Besides a-diazocarbonyl reagents, diazomethane [40,41 ] and a y-diazoacrylate derivative [42] have been used in enantioselective Cu-cata-lyzed cyclopropanations but the scope of these reactions has not been studied systematically. It has been shown in certain cases that diazo compounds can be replaced by other carbene precursors such as iodonium ylides, sulfonium yUdes, or lithiated sulfones [8,43],but successful applications of these reagents in enantioselective Cu-catalyzed reactions have not been reported yet. 

In this case the ylide was not isolated but allowed to react with benzophenone to give, after hydrolysis with hydrochloric acid, 1,1-diphenylethylene, diphenylacetaldehyde, and triphenylarsine (160). An excellent method for preparing arsonium ylides involves the reaction between a stable diazo compound and triphenylarsine in the presence of a copper catalyst such as bis(acetylacetonato)copper(II) (161). Rather than a diazo compound, an iodonium ylide can be used again a copper catalyst is necessary for an optimum yield of product. An example of the use of a diazo compound is shown in the formulation of tfiphenylarsonium 2,3,4-triphenylcydopentadienylide [29629-32-1], C41H31As ... 

The iodonium ylide (309) has been prepared from 3-oxobenzo[Z>]thiophene-1,1-dioxide by treatment with phenyl iodosyl bis(trifluoroacetate). This reacts with nucleophiles to produce various novel molecules (Scheme 58) <89TL6673>. 

Most iodonium ylides have low thermal stability and can be handled only at low temperature or generated and used in situ. The relatively stable and practically important iodonium ylides, the dicarbonyl derivatives PhIC(COR)2 [535,540-543] andbis(organosulfonyl)(phenyliodonium)methanides, PhIC(S02R)2 [544-547], are prepared by the reaction of (diacetoxyiodo)benzene with the appropriate dicarbonyl compound or disulfone under basic conditions. A general procedure for the synthesis of phenyliodonium ylides 397 from malonate esters 396 is based on the treatment of esters 396 with (diacetoxyiodo)benzene in dichloromethane in the presence of potassium hydroxide (Scheme 2.115) [542]. An optimized method for preparing bis(methoxycarbonyl)(phenyliodonium)methanide (399) by using reaction of dimethyl malonate... 

The preparation of iodonium phenolates 410 was first reported in 1977 via a reaction of phenols 409 with (diacetoxyiodo)benzene followed by treatment with pyridine (Scheme 2.119) [553]. The system of an iodonium phenolate is stabilized by the presence of at least one electron-withdrawing substituent on the aromatic ring. Monosubstituted iodonium phenolates 410 are relatively unstable and easily rearrange to iodo ethers 411 under heating. Such a 1,4 aryl migration is a very common phenomenon for iodonium ylides of types 405-408 according to mechanistic and computational studies it is an intramolecular rearrangement via a concerted mechanism [554,555]. 

A relatively stable iodonium ylide (426) was prepared by the reaction of -ketosulfone 425 with [bis(trifluoroacetoxy)iodo]benzene (Scheme 2.124) [565]. Ylide 426 decomposes in a solution of dichloromethane/ethanol to form quantitatively, the trimer 427. 

Mixed phosphonium-iodonium ylides 432 represent a useful class of reagents that combine in one molecule the synthetic advantages of a phosphonium ylide and an iodonium salt. The preparation of the tetrafluoroborate derivatives 432 by the reaction of phosphonium ylides with (diacetoxyiodo)benzene in the presence of HBF4... 

The analogous mixed arsonium-iodonium ylides (see structure 442 below in Figure 2.16) were synthesized using a similar procedure [574]. Preparation of hetaryl-substituted phosphonium-iodonium ylides was also reported [575]. 

Alternatively, most AD derivatives can be prepared with a Suzuki coupling reaction between iodonium-ylides 17 and phenylboronates 18 (Scheme 9.4). 

Preparation by hypervalent iodine oxidation of resacetophenone with iodosobenzene diacetate in the presence of potassium hydroxide in methanol via the rearrangement of iodonium ylide previously formed (20%) [3511]. 

The rhodium complex also catalyzed the cyclopropanation of iodonium ylides 159 that was prepared from malonic esters (Scheme 1.75) [120]. The treatment of a malonic ester with phenyhodonium diacetate gave corresponding iodonium ylides, which underwent smooth cyclopropanation with various alkenes. It was shown that these two steps... 

Among various modifications of the side chain of stabilized ylides [13,14] can be pointed out the preparation and transformation of the phenyliodonio a-substi-tuted phosphonium yhdes (Scheme 3) [15]. These compounds represent a potentially useful class of reagents, in which the iodonium group can be further substituted by nucleophiles such as PhSLi. 

Reactions of phosphines and phosphites have received some attention but their preparative value is limited. The zwitterion formed from diphenylmethylphosphine and benzyne rearranges to ylide (124) which can be captured by Wittig alkenation, with cyclohexanone, in about 20% yield.159 Some synthetically useful reactions of tellurium and selenium compounds with arynes have been reported. For example, heating diphenyl iodonium carboxylate and bis(p-ethoxyphenyl) ditelluride in dichlorobenzene affords the compound (125).160 The corresponding reactions with diphenyl selenide and diphenyl sulfide... 

Preparation Aryliodonium imides 463 are usually prepared by the reaction of (diace-toxyiodo)arenes with the respective amides under basic conditions (Scheme 2.133) [623]. Most iodonium imides are relatively unstable at room temperature and their storage under an inert atmosphere at low temperature is recommended. Exothermic decomposition frequently occurs at the melting point of ylides and some of them were even claimed to be explosive [623]. 

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