Ylides phenyliodonium

Muller et al. have also examined the enantioselectivity and the stereochemical course of copper-catalyzed intramolecular CH insertions of phenyl-iodonium ylides [34]. The decomposition of diazo compounds in the presence of transition metals leads to typical reactions for metal-carbenoid intermediates, such as cyclopropanations, insertions into X - H bonds, and formation of ylides with heteroatoms that have available lone pairs. Since diazo compounds are potentially explosive, toxic, and carcinogenic, the number of industrial applications is limited. Phenyliodonium ylides are potential substitutes for diazo compounds in metal-carbenoid reactions. Their photochemical, thermal, and transition-metal-catalyzed decompositions exhibit some similarities to those of diazo compounds. 

Alternative furan ring fusion involves the reactions of phenyliodonium ylides of cyclic seven-membered jS-diketones with alkynes. These processes lead under mild conditions to cyclization products 152. The high regioselectivity can be explained by the formation of dipolar intermediate 151 favored by the predominant enolization of the carbonyl adjacent to phenyl ring. Terminal alkynes react in the similar fashion, although, in this case, mixtures of regioisomers have been reported due to steric hindrance in the intermediate enol (Scheme 30 (1993JOC4885)). 

A variety of compounds belong to this category, in which are included some interesting phenyliodonium ylides and salts. 

This class, also described as phenyliodonium ylides, has several members, notably those coming from sulfonamides, of the general formula PhI = NS02R, where R is an aromatic, aliphatic or heterocyclic group. 

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]. 

Among some unstable phenyliodonium ylides the most interesting are those with a monocarbonyl carbanionic moiety which are formed from / -ace-toxyalkenyl(phenyl)iodonium precursors upon reaction with EtOLi (Scheme 52) [160]. These reagents are useful for the synthesis of a,/ -epoxy ketones and 2-acylaziridines. 

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]. 

The metal-catalyzed carbenoid decomposition of iodonium ylides can be applied in asymmetric reactions [149-152]. For example, the copper(II)-cat-alyzed intramolecular C-H insertion of phenyliodonium ylide 209 in the presence of several chiral ligands affords product 210 (Scheme 74) [151]. Enantiose-lectivities in this reaction vary in the range of 38-72% for different chiral... 

Phenyliodonium 4,4-dimethyl-2,6-dioxocyclohexylide [1] (phenyliodonium ylide of dimedone)... 

The rhodium catalysed decomposition of 2-diazo-1,3-diketones in iodobenzene produced phenyliodonium ylides in 37-71% yield [3] similarly, o-iodophenyl precursors were converted intramolecularly into cyclic ylides [4,5]. 

Thermal decomposition of phenyliodonium ylide of 2-hydroxy-l,4-naphthoquinone (lawsone) 403 in the presence of indole derivatives 402 (GH2CI2, reflux, 4-7 h) affords 3-acylated indoles existing in their enol forms 404, through a ring contraction and ot,ot -dioxoketene formation reaction (Scheme 87) <2005JOC8780>. 

Similarly, 3-oxospiro[benzo[it]thiophene-2(3//)-r-cyclopropane] S,5-dioxides 3 and 4 were synthesized starting from phenyliodonium ylide 2 and alkenes with catalysis by bis(acetyl-acetonato)copper(II). The ylide is easily obtained in 95% yield from 3-oxo-2,3-dihydro-benzo[h]thiophene 1,1-dioxide and bis(trifluoroacetoxy)iodobenzene. 

Bis(sulfonyl)carbene (carbenoid) is generated photolytically, thermally or catalytically from bis(sulfonyl)diazomethane or from the corresponding phenyliodonium ylide (Houben-Weyl, Vol. E19b, ppl735, 1739-1743). In the latter case only, the carbene reacts with an alkene to form l,l-bis(sulfonyl)cyclopropanes (Houben-Weyl, Vol. E19b, pl743). 

The starting phenyliodonium ylides 3 are prepared simply from the corresponding bis(sul-fonyl)methane and phenyliodonium diacetate. ... 

The photoreactions of diaryliodonium salts have been examined.The phenyliodonium ylide (120) is converted on irradiation in the presence of terminal alkenes (121) into the 4-substituted-2-acyl-l-naphthols (122) the probable pathway is outlined in Scheme 8. 

While this cyclopropanation strategy is usually limited to the use of diazo compounds there has been one recent report of the use of phenyliodonium ylides as the carbene source. In this example the ylide generated from methyl nitroacetate (9.13) and iodosobenzene reacts with styrenes and also 1,3-butadiene in the presence of the copper complex derived from bis-oxazoline (9.14). ... 

Diazomalonate esters are generally poor substrates for this reaction and only moderate ees have been obtained so far in the rhodium-catalysed addition to alkenes. Far better results have been obtained using the phenyliodonium ylide generated from dimethylmalonate and also Meldrum s acid (9.34) and iodosylben-zene in the presence of the rhodium catalyst bearing ligand (9.35). ... 

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... 

A particularly useful reagent in these carbenoid reactions is the highly soluble and reactive iodonium ylide 780 derived from malonate methyl ester and bearing an ortfw methoxy substituent on the phenyl ring [1059]. This reagent shows higher reactivity than common phenyliodonium ylides in the Rh-catalyzed cyclopropanation, C-H insertion and transylidation reactions under homogeneous conditions. Scheme 3.307 shows representative examples of the carbenoid reactions of ylide 780 [1059]. 

Another synthetically useful reagent of this type is 5,5-dimethyl-l,3-cyclohexanedione phenyliodonium ylide (781) (Scheme 3.308), a relatively stable iodonium ylide synthesized by condensation of PhI(OAc)2 with dimedone under basic condition [1060,1061]. Under catalytic, thermal, or photochemical conditions, ylide 781 serves as an excellent carbenoid precursor the transfer of such a carbenoid moiety to a suitable... 

---