Iodonium ylides, intramolecular cyclopropanations

Reactions with -Dicarbonyl Systems Formation of lodo-nium Ylides Intramolecular Cyclopropanation. -Dicarbo-nyl compounds upon reaction with PhI(OAc)2 and KOH/MeOH at 0 °C yield isolable iodonium ylides (eq 22). This is a general reaction which requires two stabilizing groups flanking the carbon of the C=I group, such as NO2 and S02Ph. Decomposition of unsaturated analogs in the presence of Copper(I) Chloride proceeds with intramolecular cyclopropanation (Table 1). ... 

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. 

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 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]. 

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]. 

Obtained from active methylene compounds, such as malonic esters, -0x0 esters and jS-oxo sulfones, iodonium ylides serve as precursors of the corresponding carbenes. Their decomposition by a catalytic amount of a copper salt in the presence of a C-C double bond has been used for inter- and intramolecular cyclopropanation reactions. Thus, reaction of cyclohexene with bis(methoxycarbonyl)methylene(phenyl)iodine(III) under the catalytic action of bis(acetylacetonato)copper(II) yielded dimethyl bicyclo[4.1.0]heptane-7,7-dicarboxylate (1) (38%, mp 91-93°C) in addition to tetrakis(methoxycarbonyl)ethene (41%). ... 

Intramolecular cyclopropanation was achieved when the iodonium ylides, that were obtained from 3-oxohept-6-enoic esters or 8-oxo(but-3-enyl) sulfones and bis(acetoxy)iodobenzene in... 

Table 2. Copper Salt Catalyzed Intramolecular Cyclopropanation Using Iodonium Ylides Derived from 3-Oxohept-6-enoic Esters or / -Oxobut-3-enyl Sulfones...

Intramolecular Cyclopropanation Using Iodonium Ylides Typical Procedure 50... 

Table 1 Intramolecular cyclopropanation of iodonium yUdes Reactants Iodonium ylide Product Yield (%)...

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