Iodo, from alkenes

Before discussing examples of the reactions, it should be pointed out that most types of vinylic halides used in this reaction are easily available. The UV-catalyzed addition of HBr to terminal acetylenes forms the 1-bromo-l-alkenes. The cis isomer is formed almost exclusively if the addition is carried out at dry ice temperature. The 2-bromo or 2-iodo-l-alkenes are obtained from reacting aqueous hydrogen halides with alkynes. The 2-substituted-1-bromo-l-alkenes are available by the bromination-base dehydrobromination reactions. 

A similar reaction has been adopted for the preparation of amides from alkenes by the photoaddition of "CONH2 radicals generated from formamide by benzophe-none [7], or via a TBADT [25] photocatalyzed hydrogen abstraction. Solar light has been used in the first case. Furthermore, the introduction of an ester function has been accomplished by generating an alkoxycarbonyl radical by photolysis of [bis(alkoxyoxalyloxy)iodo]benzene at 0-5 °C and ensuing addition to vinyl sulfones in the presence of 1,4-cyclohexadiene [9]. 

Silver chromate, Ag2Cr04, a reddish-brown precipitate prepared by adding an aqueous solution of silver nitrate to an aqueous solution of potassium chromate, is used with iodine for the preparation of a-iodo-ketones from alkenes [616]. 

Fluoro-l-iodo-l-alkenes. These compounds are prepared from 1 -alkynes by the... 

Kadota, I. et ah, A simple and practical method for the stereoselective synthesis of (Z)-l-iodo-l-alkenes from 1,1-diiodo-l-alkenes, Tetrahedron Lett., 44, 8645, 2003. 

Treatment of terminal acetylenes with hydrogen iodide, generated in situ from TMSCl, sodium iodide, and water, provides a highly regioselective synthesis of 2-iodo-l-alkenes. Followed by addition of cuprous cyanide, the protocol offers a convenient one-pot preparation of 2-substituted acrylonitriles in fair to good yield (eq 90). In contrast, when the reaction with arylacetylene proceeds in DMSO and with catalytic amount of sodium iodide, the 3-arylpropynenitrile is obtained as the preferred product. 

In a reaction resembling halohydrin formation (Section 6.17), vicinal haloethers are prepared from alkenes by reaction with an alcohol in the presence of halogens— usually bromine or iodine. This haleotherification proceeds through a cyclic halonium ion, which reacts with the alcohol. 1-Methylcyclohexene undergoes iodoetherification with ethanol in the presence of iodine to give ran -l-ethoxy-2-iodo-l-methylcyclohexane. 

The Simmons-Smith reaction (Section 14.12) Methylene transfer from iodo-methylzinc iodide converts alkenes to cyclopropanes. The reaction is a stereospecific syn addition of a CH2 group to the double bond. 

The adjacent iodine and lactone groupings in 16 constitute the structural prerequisite, or retron, for the iodolactonization transform.15 It was anticipated that the action of iodine on unsaturated carboxylic acid 17 would induce iodolactonization16 to give iodo-lactone 16. The cis C20-C21 double bond in 17 provides a convenient opportunity for molecular simplification. In the synthetic direction, a Wittig reaction17 between the nonstabilized phosphorous ylide derived from 19 and aldehyde 18 could result in the formation of cis alkene 17. Enantiomerically pure (/ )-citronellic acid (20) and (+)-/ -hydroxyisobutyric acid (11) are readily available sources of chirality that could be converted in a straightforward manner into optically active building blocks 18 and 19, respectively. 

Allyltitanium complexes derived from a chiral acetal have been reacted with carbonyl compounds and imines [63], While the chiral induction proved to be low with carbonyl compounds, high induction was observed with imines. This complex represents the first chiral homoenolate equivalent that reacts efficiently with imines. Finally, the reactions with electrophiles other than carbonyl compounds and imines, namely a proton source, NCS, and I2, furnished the corresponding alkene, chloro, and iodo derivatives in good yields [64]. 

A more recent report describes the regio- and stereoselective addition of aryltellurenyl iodides (prepared in situ from the corresponding ditellurides and iodine) to alkynes to afford the ( )-l-iodo-2-aryltelluro-l-alkenes, which treated with bromine give the corresponding dibromides. ... 

Phenyliodonium sulfate 289, which is obtained from the reaction of iodo-sobenzene and sulfur trioxide at -50°C, behaves as a 1,4-dipole in the reactions with several alkenes (86ZOR450) to give intermediate [4 + 2] cycloadduct 290. Decomposition of this unstable adduct affords cyclic sulfates 291 (Scheme 73). Likewise, another 1,4-dipole 292 undergoes cycloaddition reaction to give cyclic sulfone 293 (88ZOR888). The 1,4-dipole 292 thermally decomposes to give 294 (86DOK1374) (Scheme 74). 

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