Iodocyclopropanation

Di-iodocyclopropanes are unstable and cannot be isolated readily [133]. Other dihalocyclopropanes rearrange thermally during work up, or in the presence of the base, to produce ring-opened allylic dihalides or vinyl halides [e.g. 15, 81, 87, 96, 100, 103, 152, 157] (Scheme 7.4). Thermal rearrangement of the dihalocarbene adducts from halocycloalkenes leads to ring expanded products or methylene derivatives [e.g. 87], whereas 1, l-dichlorocyclopent-3-enes produce halobenzenes in high yield [96]. 

Mann and Barnes [45] have discussed the mechanism of reduction of substituted and optically active 1-bromo-and 1-iodocyclopropanes, and Hazard and coworkers [46] have investigated the reduction of l-bromo-l-carboxy-2,2-diphenyl-cyclopropane. At mercury cathodes, electrolyses of 1-bromo- and 1-iodonorbornane proceed via two-electron cleavage of the carbon-halogen bond to give mainly nor-bomane, plus a small amount of bis(l-norbomyl)mercury [47]. 

Bromo- and iodocyclopropanes cannot be prepared by the direct halogenation of cyclopropanes. Substituted chloro- and bromocyclopropanes have been synthesized by the photochemical decomposition of a-halodiazomethanes in the presence of olefins iodocyclopropanes have been prepared from the reaction of an olefin, iodoform and potassium f-butoxide followed by the reduction of diiodocyclopropane formed with tri-w-butyl tin hydride. The method described employs a readily available light source and common laboratory equipment, and is relatively safe to carry out. The method is adaptable for the preparation of bromo- and chlorocyclopropanes as well by using bromodiiodomethane or chlorodiiodomethane instead of iodoform. If the olefin used will give two isomeric halocyclopropanes, the isomers are usually separable by chromatography. ... 

Alternatively, the use of the reagent prepared by mixing trifluoroethanol, diethylzinc and iodoform led to the formation of the corresponding iodocyclopropane with outstanding diastereocontrol (equation 62). 

Purify the crude residue by flash chromatography using hexanes ether (60 40). frans-1-ethyl-2-(hydroxymethyl)-1-iodocyclopropane (113 mg, 76%) is obtained as a colourless oil. Characterize the product by 1H NMR, 13C NMR, IR spectroscopy, high-resolution mass spectrometry, and elementary analysis. 

Charette synthesized polycyclopropane natural product by utilizing this approach, i.e. by coupling iodocyclopropanes to various boronic acids or esters. ... 

The reaction between CHCI3 and HO- is often carried out under phase transfer conditions. " It has been shown that the reaction between PhCHCl2 and t-BuOK produces a carbenoid, but when the reaction is run in the presence of a crown ether, the free Ph(Cl)C is formed instead. The reaction of iodoform and CrCl2 leads to iodocyclopropanes upon reaction with alkenes. Dihalocyclopropanes are very useful compounds that can be reduced to cyclopropanes, treated with magnesium or sodium to give allenes (18-3), or converted to a number of other products. 

A complete analysis of the H spectra of bromo- and iodocyclopropane was reported by Schrumpf and Liittke . ... 

For a detailed analysis of the H-NMR spectrum of iodocyclopropane see G. Schrumpf and W. Liittke, Tetrahedron Lett., 2635 (1969). 

The synthesis of substituted spiro[2.4]heptanes was also recently accomplished by treatment of functionalized iodocyclopropanes as described in Scheme 7-12 [16]. 

The reaction of the carbene with olefins yields 1-fluoro-l-iodocyclopropanes in 20-60% yield. 

Two methods for the preparation of iodocyclopropanes via cycloaddition of iodocarbene (or carbenoid) to alkenes are known ... 

The photolysis of iodoform presumably generates a free iodocarbene which reacts with an alkene in a stereospecific manner to form iodocyclopropanes" (see Table 3 and Houben-Weyl, Vol. E19b, pp 1623-1624). 

Under either conditions (hv or diethylzinc), nine- to twelve-membered cycloalkenes formed endo-adducts only, while cyclopentene gave the exo-iodocyclopropane, exclusively (independently synthesized exo-products do not izomerize to the endo-products, or undergo cleav-... 

The reaction of diiodomethane with a variety of bases (sodium hexamethyldisilazanide, lithium diisopropylamide, potassium triphenylmethanide, potassium iert-butoxide, potassium hydroxide under phase-transfer conditions, methyllithium) and alkenes does not afford iodocyclo-propanes. The thermal decomposition of diiodomethyl(phenyl)mercury in an alkene also does not result in the formation of iodocyclopropanes." ... 

Fluoro-l-iodocyclopropanes are prepared by addition of fluoroiodocarbene, generated from fluorodiiodomethane under phase-transfer catalysis conditions, to alkenes (see Houben-Weyl, Vol. El9b, pp 1504-1505). 

Chlorodiiodomethane, under phase-transfer catalysis conditions, generates chloroiodocarbene which undergoes addition to alkenes with the formation of 1-chloro-l-iodocyclopropanes P (Houben-Weyl, Vol.E19b, pp 1598-1600). 

A general procedure for the preparation of chlorodiiodomethaneand 1-chloro-l-iodocy-clopropanes, can be found in Houben-Weyl, Vol. E19b, pl599. Examples of the synthesis of 1-chloro-l-iodocyclopropanes are given by 2 and 3. ... 

There is a lack of convenient methodology for the preparation of 1 -bromo-1 -iodocyclopropanes via the addition of bromoiodocarbene to alkenes. The reaction of dibromoiodo- or bromo-diiodomethane and various alkenes in the presence of a concentrated aqueous solution of sodium hydroxide and catalytic amounts of benzyltriethylammonium chloride gives a mixture of dibromo-, bromoiodo- and diiodocyclopropanes. Due to the restricted stability of the last two cyclopropanes, the isolation of pure compounds presents serious preparative problems (Houben-Weyl, Vol. E19b, pp 1621-1622), e.g. formation of 1-3. ... 

Diiodocyclopropanes were also formed in a mixture with 1,1-dibromo- and 1-bromo-l-iodocyclopropanes when dibromoiodo- or bromodiiodomethane and an alkene were reacted under phase-transfer catalytic conditions (see Section 1.2.1.4.3.2.). ... 

Iodine has also been introduced by treating cyclopropyltrimethylsilane with iodine chloride at 90°C for 24 h iodocyclopropane (2) was isolated in 65% yield. 

Two iodocyclopropanes have been prepared by decarboxylation of the corresponding cyclo-propanecarboxylic acids with lead(IV) acetate in the presence of iodine and iodosobenzene diacetate in the presence of iodine. ... 

Perhaloalkanes readily undergo addition to the double bond of methylenecyclopropane. The addition of heptafluoropropyl iodide in the presence of 2,2 -azobisisobutyronitrile at elevated temperature gave l-(2,2,3,3,4,4,4-heptafluorobutyl)-l-iodocyclopropane (1) in excellent yield (96%). ... 

Thienylboronic acids are useful building blocks for preparing biaryls and heterobiaryls employing the Suzuki reaction. In one case, a Suzuki coupling between thiophene-3-boronic acid and iodocyclopropane 99 was promoted by cesium fluoride to furnish the adduct 100 with retention of configuration [74]. In another example, the union between thiophene-3-boronic acid and 5-bromo-2,2-dimethoxy-l,3-mdandione (101) provided ninhydrin derivative 102 [75]. 

Iodocyclopropanes by Reaction of Diethylzinc with Iodoform General Procedure 43... 

Table 3. Iodocyclopropanes from Iodoform, Alkenes and Photolysis or Diethylzinc...

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