Iodoalkylation

Fluorochloro, fluorobromo, and fluoroiodoalkanes react selectively with aromatics under boron trifluoride catalysis to provide chloro-, bromo- and iodoalkylated products (48). The higher reactivity of the C—F bond over C—Cl, C—Br, and C—I bonds under Lewis acid catalysis results in the observed products. 

Treatment of l-arylsulfonyl-2-(l-iodoalkyl)piperidines 48 (R = H) with 2.7 equiv. of BusSnH in the presence of azobisisobutyronitrile (ABIN) furnished a mixture of 7,8,9,10,10u,ll-hexahydropyrido[l,2-ft][l,2]ben-zothiazine 5,5-dioxides 50, 2-benzylpiperidines 51 and l-arylsulfonyl-2-alkylpiperidines 52 in a radical process (Scheme 6) (77TL631,78JCS(CC)166, 80JCS(CC)142). The yield of 7,8,9,10,10u,ll-hexahydropyrido[l,2-6][l,2]... 

Solns of I azide react readily with olefins to give 2-iodoalkyl azides which lose H iodide to form unsaturated azides (Ref 13)... 

No j3-bromo- or iodoalkyl complexes have yet been isolated. The reaction of vicinal dibromides or diiodides with [Co (CN)j] , [Co(CN)5H], or a Co(I)-DMG complex merely gives the olefin 32, 75,105,109,161), though kinetic evidence was obtained for the intermediate formation of the j8-bromo complex in the reaction of [Co"(CN)5] with a,j8-dibromopropionate and a,/3-dibromosuccinate (75). It is interesting that the pentacyanide produced is the bromo or iodo, and not the aquo, complex 32, 75), which suggests that the decomposition may involve a cis rather than a trans elimination of Co—X. The /3-chloroethyl complex can be prepared by tbe reaction of [Co(CN)5H]3- with CICH2CH2I 105). 

A convenient aziridine synthesis using 2-iodoalkyl azides and triphenyl-phosphine has been reported. The reaction is stereospecific and is thought to proceed by attack of the phosphine on azide ... 

Based on a transformation described by Catellani and coworkers [61], the Lautens group [62] developed a three-component domino reaction catalyzed by palladium for the synthesis of benzo annulated oxacycles 6/1-114 (Scheme 6/1.30). As substrates, these authors used a m-iodoaryl iodoalkyl ether 6/1-113, an alkene substi-... 

As shown in Eq. 9.48, optically active alkylidene lactones having an iodoalkyl substituent were prepared from the corresponding optically active epoxy alcohol by means of the Sharpless epoxidation. These represent precursors of optically active functionalized cyclopentanes and cyclohexanes, respectively, as shown in the equation [92]. 

Barbier-type cyclization of a-(>a-iodoalkyl)- -keto esters or amides. 

Radical cyclization to macrolides.111 Cyclization of iodoalkyl acrylates (1) by reaction with Bu3SnH (1 equiv.) in the presence of AIBN is useful for formation of macrolides (2) containing 11 or more members. Similar cyclization of iodoalkyl fumarates (3) results in two macrolides with the endo-product predominating except when n is 16 or higher. Tertiary iodides undergo this free radical cyclization more... 

As a unique [1,4]-Wittig rearrangement, the transformation of 3-iodoalkyl vinyl ether 107 to the 4-alken-l-ol 108 has been reported by Bailey s group (equation 61, Table 5) . The rearrangement is undoubtedly mediated by a regiospecific 5-cxo-trig ring closure. 

Enamine carbaldehyde 76 (Scheme 20) by sequential photochemical cycloaddition and iminium ion-propargylsilane cyclimtion furnishes allenes 77a-c in good yield and with high diastereoselectivity (92X2081). (Gas chromatographic fR values and thin-layer chromatographic Rp values have been reported.) Radical cyclization of ca-iodoalkyl isoquinolone 78a under... 

Free radical addition to oximes and oxime ethers emerged as a useful alternative to addition of organometallic reagents, particularly for intramolecular reactions. The most important advantage of free radical V5. organometallic addition is its tolerance for almost any functional group (with the exception of thiocarbonyl and iodoalkyl functions). 

IntramolecularBarbier-type cyclization (12,429-430).1 Cyclizations of 2-(co-iodoalkyl)cyclopentanones induced with Sml2 result almost entirely in cw-fused products (equation I). ds-Fused bicyclic alcohols are also formed selectively from 2-substituted 2-(co-iodoalkyl)cycloalkanones (equation II). 

Intermolecular free-radical addition of iodoalkyl sulfones to vinylsilanes yields regios-electively the adduct 146 which can be further transformed to cyclopropene derivatives (equation 122)214. 

Reactions of rhodium porphyrins with diazo esters - According to Callot et al., iodorhodium(III) porphyrins are efficient catalysts for the cyclopropanation of alkenes by diazo esters [320,321], The transfer of ethoxycarbonylcarbene to a variety of olefins was found to proceed with a large syn-selectivity as compared with other catalysts. In their study to further develop this reaction to a shape-selective and asymmetric process [322], Kodadek et al. [323] have delineated the reaction sequences (29, 30) and identified as the active catalyst the iodoalkyl-rhodium(III) complex resulting from attack of a metal carbene moiety Rh(CHCOOEt) by iodide. 

The product of reaction (30) is thought to coordinate a further molecule of ethyldiazoacetate trans to the iodoalkyl group which looses dinitrogen, yielding a hexacoordinate rhodium carbene complex according to Eq. (31) which transfers its carbene moiety to an attacking alkene molecule. 

Several ru-haloalkyllithiums and Grignard reagents have been described which are sufficiently stable to react intermolecularly with electrophiles before cyclizing (Scheme 5.62). Particularly stable are ei-chloroalkyl derivatives [475-477] whereas, not surprisingly, the ei-bromo- or oi-iodoalkyl carbanions are usually more difficult to prepare and handle (see below). Propargyl chloride has been lithiated at the alky-... 

Iodoalkylation of 1,2-allenyl sulfides or selenides, ArXCH=C=CH2 (X = S or Se), with I2 in MeCN-ROH (20 1) has been shown to afford (Z)-3-alkoxy-2-iodopropenyl (g) sulfides or selenides, ArXCH=C(I)-CH2OR, in high stereoselectivity and moderate to good yields.43... 

Ring expansion in conjunction with Tamao-type oxidation of carbon-silicon bonds provides access to 1,4-diols. The l-(l-iodoalkyl)-l-silacyclobutanes are available from 1-chlorosilacyclobutanes (addition of vinyl, Scheme 34) <1991TL6383>. The utility of silacyclopentanes formed by the ring expansion of SCB for the synthesis of diols has been reported <1992TL7031, 1995BCJ625>. 

Another way to activate l-(l-iodoalkyl)-l-silacyclobutanes toward ring expansion is to use silver acetate in acetic acid. In this case, the reaction is believed to proceed via formation of a carbocation a to the silicon. The acetate counterion acts as a nucleophile, attacking the activated SCB with C-Si bond migration (Scheme 35) <1991TL6383>. Silver tetrafluoroborate in dichloromethane induces ring enlargement as well, but shows much lower efficiency (30% yield upon treatment with MeLi) <1994BCJ1694>. 

When 2-iodoalkyl vinylsilyl ethers 231 (Z=Si) were reacted with 224 in the presence of the Co(dppb)Cl2 catalyst, silatetrahydrofurans 232a (Z=Si) were isolated [294], When substrates 231 with substituted allyl groups (R3 and/or R4=alkyl) were treated with catalytic amounts of Co(dppe)Cl2 and 224 or phenylmagnesium bromide, a 5-exo cyclization proceeded and tetrahydrofurans 232c with exocyclic alkenyl units were isolated in 58-89% yield. For substrates with disubstituted alkene acceptors (R3=alkyl, R4=H), the formation of 18% of reduced tetrahydrofuran 232b was also observed [280, 295],... 

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