Iodoalkenes reactions

The reaction of perfluoroalkyl iodides with alkenes affords the perfluoro-alkylated alkyl iodides 931. Q.a-Difluoro-functionalized phosphonates are prepared by the addition of the iododifluoromethylphosphonate (932) at room temperature[778], A one-electron transfer-initiated radical mechanism has been proposed for the addition reaction. Addition to alkynes affords 1-perfluoro-alkyl-2-iodoalkenes (933)[779-781]. The fluorine-containing oxirane 934 is obtained by the reaction of allyl aicohol[782]. Under a CO atmosphere, the carbocarbonylation of the alkenol 935 and the alkynol 937 takes place with perfluoroalkyl iodides to give the fluorine-containing lactones 936 and 938[783]. 

To date, only one example of a combination of a photochemically induced transformation with a transition metal-catalyzed reaction has been found in the literature. This hv/Pd°-promoted process allows the synthesis of five-membered cyclic y-keto esters 5-119 from 5-iodoalkenes 5-117 in the presence of CO and an alcohol 5-118 as a nucleophile (Scheme 5.24) [41]. The yields are high, and differently substituted iodoalkenes can be employed. 

The method enables conversion of substituted alkynes to (fc)-2-methyl-1 -alkenylalumi-num species, and, by subsequent iodinolysis, to the corresponding iodoalkenes with retention of the double-bond configuration. Depending on the substitution pattern of the starting alkyne, many useful products emerge from this reaction, which themselves can serve as building blocks for transition metal-mediated or -catalyzed coupling reactions [59—62]. 

A 1,2-metalate rearrangement of a higher order cuprate, known as a Kodenski rearrangement [64], was used as a key step in the synthesis of the marine antiinflammatory sesterterpenoid manoalide 95 (Scheme 9.20) [65]. Treatment of the alkenyl lithium 89 (prepared from the alkenylstannane 88 with s-BuLi in a diethyl ether-pentane mixture) with the homocuprate 91 (produced from iodoalkane 90) gave the iodoalkene 94 in 72% overall yield from 88. The reaction proceeds as fol-... 

Electrophiles also react at C-5 of 1,3-dioxin-4-ones. Two ways of activation have been reported (1) magnesiation of 5-iodo-l,3-dioxin-4-ones afforded the Grignard reagents which can be cross-coupled with allyl halides in the presence of copper cyanide <2001TL6847> or with iodoalkenes under Pd(0) catalysis <2002T4787> and (2) Sc(OTf)3-catalyzed reaction of a side-chain-hydroxylated l,3-dioxin-4-one with aldehydes provided the bicyclic dioxinone in 60-85% yield (Scheme 27) <20050L1113>. 

The equivalent intramolecular Heck-type vinylation of a a>-vinyl-(Z)-iodoalkene has been used as the key step in the synthesis of A-ring synthons for 1 at,25-di hydroxy vitamin D3 and its analogues403. The reaction takes place under reflux in acetonitrile in the presence of one equivalent of triethylamine404 and gives a 81% yield (equation 102). 

Lithium dimethylcuprate transfers a methyl group, which substitutes for iodine on the iodoalkene. Even halogens on. s/r-hybridized carbon are reactive in substitution reactions with lithium dialkylcuprates. 

Fig. 16.17. Mechanism of the carbocupration of acetylene (R = H) or terminal alkynes (R H) with a saturated Gilman cuprate. The unsaturated Gilman cuprate I is obtained via the cuprolithiation product E and the resulting carbolithiation product F in several steps—and stereoselectively. Iodolysis of I leads to the formation of the iodoalkenes J with complete retention of configuration. Note The last step but one in this figure does not only afford I, but again the initial Gilman cuprate A B, too. The latter reenters the reaction chain "at the top" so that in the end the entire saturated (and more reactive) initial cuprate is incorporated into the unsaturated (and less reactive) cuprate (I). - Caution The organometallic compounds depicted here contain two-electron, multi-center bonds. Other than in "normal" cases, i.e., those with two-electron, two-center bonds, the lines cannot be automatically equated with the number of electron pairs. This is why only three electron shift arrows can be used to illustrate the reaction process. The fourth red arrow—in boldface— is not an electron shift arrow, but only indicates the site where the lithium atom binds next.

Fig. 16.36. Stereoselectivity and stereospecificity of Heck coupling reactions with isomeric iodoalkenes.

A haloalkene that contains a stereogenic C=C double bond can usually be coupled with alkenes via the Heck reaction without isomerization. This is illustrated with the three reaction pairs in Figure 16.36. As can be seen, both the as- and the /raw-configured iodoalkenes react with acrolein or methyl vinyl ketone or acrylic acid methyl ester with complete retention of the C=C double bond configuration. These coupling reactions are thus stereoselective and— when considered as a pair—stereospecific. 

Arylalkenes are accessible not only by way of an arylation of alkenylboron compounds (example in Figure 13.14) but also via an alkenylation of arylboron compounds. Figure 13.15 exemplifies this for a Pd-catalyzed reaction of an arylboronic acid with iodoalkenes with widely variable substitution patterns. The addition of KOH increases the reactivity of the arylboronic acid in this coupling and in similar ones. The base converts the boronic acid into a negatively charged boronate ion A. This ion A is transmetallated faster than the neutral boronic acid by the Pd(II) intermediate the boronate ion is a superior nucleophile and replaces the iodide ion in the Pd(II) complex particularly fast. 

The reactions of Cu-acetylides with configurationally homogenous cts-iodoalkenes (accessible via the procedure in Figure 13.12) or with stereopure frans-iodoalkenes (e.g., preparation according to Figure 3.11), respectively, result in 1,3-enynes with retention of the respective double bond geometry (Figure 13.24). 

The coupling of an iodoalkene with a trimethylsilylacetylene and a subsequent desi-lylation result in the formation of 1,3-enynes with a terminal C=C triple bond. The parent acetylene usually does not react to give such an enyne under these reaction conditions, since Cu2C2 is formed. The solubility of this carbide is very low so that it precipitates. The very small amount of this copper species that remains in solution— if it couples at all—couples at both C atoms. Hence, the major coupling product then is the bis-coupling product of acetylene, a 3-ene-l,5-diyne, but in any case this product is formed only in small amounts because of the low solubility of Cu2C2. 

Indium-mediated radical cyclization reactions of aliphatic iodoalkynes proceeds with a catalytic amount of In and I2. Iodoalkyne 94 undergoes an atom-transfer 5-exo cyclization to give five-membered iodoalkene. In contrast, the reaction with In (200mol%) and I2 (100mol%) yields the reductive 5-m -cyclization product via the same 5-exo-cyclization (Scheme 116).387-389 The existence of a vinylindium intermediate formed via the radical 95 has been confirmed by a Pd-catalyzed cross-coupling reaction (Scheme 117).390... 

A Ni-catalyzed cyclization cross-coupling reaction of iodoalkenes with alkyl zinc halides has been employed for the synthesis of various tetrahydrofuran derivatives <2007AGE-ASAP>. The TiCU-catalyzed anti-Markovnikov hydration of alkynes has been applied to the synthesis of various benzo[3]furans <2007JOC6149>. 

The reactions of alkenyldialkylboranes with iodine lead to rearrangements rather than iodinolysis. However, alkenyldihydroxyboranes undergo iodinolysis with retention of configuration, in contrast to the corresponding reaction with bromine, to give high yields of the corresponding iodoalkenes (equation 61). ... 

The decarboxylation of the sodium salts of perfluorinated a. -unsaturated carboxylic acids gives perfluoroacetylenes and allcnes (3-10 %) when the thermal reaction is carried out without solvent, e.g. formation of 9 and 10. When the reaction is carried out in ethylene glycol, the alkene is formed in the presence of iodine, the corresponding iodoalkene can be obtained. ... 

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