Iodides vinyl, preparation

A variety of fluorinated alkenyl zinc reagents such as CF2=CFZnCl, CF2=CHZnCl, E and Z-RCF = CFZnCl have been prepared by the first method (Scheme 54). In the presence of palladium catalyst, these fluorinated alkenyl zinc reagents undergo cross-coupling reactions with aryl iodides, vinyl iodides, acid chlorides and 1-iodo-l-alkynes to give the corresponding fluorinated alkenyl derivatives [127, 146-153], which have been utilized in the synthesis of fluorinated codlemones [154]. Typical examples are outlined below (Scheme 55). 

The next reaction accomplishes coupling of the building blocks 9 and 10 Fragment 10 is prepared through iterative use of (R)-pina-nediol, the enantiomer of 2. by an addition-functionalization sequence similar to that already presented. The vinylic iodide is prepared with a hikai reaction (see Chapter 13). 

Addition of zinc(II) chloride to the lithium compound 4 gave the zinc derivative 6, which is stable even at 50 °C in tetrahydrofuran. The palladium-catalyzed coupling reaction of the zinc salt with vinyl iodides, vinyl triflates and aryl iodides produced vinyl and aryl derivatives 7 and 8 (Table 1, entries 11-16). Cerium derivatives of cyclopropenone acetals were prepared by addition of the lithium salt 4 to a suspension of anhydrous cerium(III) chloride in tetrahydrofuran at — 70 C. The resulting organocerium reagent coupled with oc-aminoaldehydes (Table 1, entry 17). ° ... 

Many stannane reagents are commercially available, or they can be readily synthesized via reaction between a Grignard reagent and tri- -butyl tin chloride. The reactants that most commonly react with the transmetallated group are a vinyl triflate (C=C—OSO2CF3) and a vinyl iodide. Vinyl triflates are prepared from the reaction of an enolate with N-phenyl triflimide (PhNTfj, Tf = SOjCFj). 

Preparation of Vinyl Bromides and Iodides. Vinyl bromides can be prepared from ketones in moderate to excellent yield via the V-silyl hydrazone derivatives (eq 11). The reaction proceeds... 

The ( )-vinyl iodide 599 prepared this way, for instance, offers itself for a wide variety of coupling reactions. 

The coupling of alkenylboranes with alkenyl halides is particularly useful for the stereoselective synthesis of conjugated dienes of the four possible double bond isomers[499]. The E and Z forms of vinylboron compounds can be prepared by hydroboration of alkynes and haloalkynes, and their reaction with ( ) or (Z)-vinyl iodides or bromides proceeds without isomerization, and the conjugated dienes of four possible isomeric forms can be prepared in high purity. 

Reductive coupling reaction of fluonnated vinyl iodides or bromides has been used as a route to fluorinated dienes [246, 247, 248, 249, 250. Generally, the vinyl iodide is heated with copper metal in DMSO or DMF no 1 ntermediate perfluorovmy I-copper reagent is detected. Typical examples are shown m equations 163-165 [246, 247, 249. The X-ray crystal structure of perfluorotetracyclobutacyclooctatetraene, prepared via coupling of tetrafluoro-l,2-diiodocyclobutene with copper, is planar... 

Reactivity and yields are greatly enhanced by the presence of 0.5-1% Na in the Li. The reaction is also generally available for the preparation of metal alkyls of the heavier Group 1 metals. Lithium aryls are best prepared by metal-halogen exchange using LiBu" and an aryl iodide, and transmetalation is the most convenient route to vinyl, allyl and other unsaturated derivatives ... 

The original Sonogashira reaction uses copper(l) iodide as a co-catalyst, which converts the alkyne in situ into a copper acetylide. In a subsequent transmeta-lation reaction, the copper is replaced by the palladium complex. The reaction mechanism, with respect to the catalytic cycle, largely corresponds to the Heck reaction.Besides the usual aryl and vinyl halides, i.e. bromides and iodides, trifluoromethanesulfonates (triflates) may be employed. The Sonogashira reaction is well-suited for the synthesis of unsymmetrical bis-2xy ethynes, e.g. 23, which can be prepared as outlined in the following scheme, in a one-pot reaction by applying the so-called sila-Sonogashira reaction ... 

The synthesis of the key intermediate aldehyde 68 is outlined in Schemes 19-21. The two hydroxyls of butyne-l,4-diol (74, Scheme 19), a cheap intermediate in the industrial synthesis of THF, can be protected as 4-methoxybenzyl (PMB) ethers in 94% yield. The triple bond is then m-hydrostannylated with tri-n-butyl-tin hydride and a catalytic amount of Pd(PPh3)2Cl238 to give the vinylstannane 76 in 98 % yield. Note that the stereospecific nature of the m-hydrostannylation absolutely guarantees the correct relative stereochemistry of C-3 and C-4 in the natural product. The other partner for the Stille coupling, vinyl iodide 78, is prepared by... 

The C-Se and C-Te bonds are formed by an internal homolytic substitution of vinyl or aryl radicals at selenium or tellurium with the preparation of selenophenes and tellurophenes, respectively. An example is shown below, where (TMSIsSiH was used in the cyclization of vinyl iodide 65 that affords... 

Halide exchange, sometimes call the Finkelstein reaction, is an equilibrium process, but it is often possible to shift the equilibrium." The reaction is most often applied to the preparation of iodides and fluorides. Iodides can be prepared from chlorides or bromides by taking advantage of the fact that sodium iodide, but not the bromide or chloride, is soluble in acetone. When an alkyl chloride or bromide is treated with a solution of sodium iodide in acetone, the equilibrium is shifted by the precipitation of sodium chloride or bromide. Since the mechanism is Sn2, the reaction is much more successful for primary halides than for secondary or tertiary halides sodium iodide in acetone can be used as a test for primary bromides or chlorides. Tertiary chlorides can be converted to iodides by treatment with excess Nal in CS2, with ZnCl2 as catalyst. " Vinylic bromides give vinylic iodides with retention of configuration when treated with KI and a nickel bromide-zinc catalyst," or with KI and Cul in hot HMPA." ... 

The adducts derived from catechol borane are hydrolyzed by water to vinylboronic acids. These materials are useful intermediates for the preparation of terminal vinyl iodides. Since the hydroboration is a syn addition and the iodinolysis occurs with retention of the alkene geometry, the iodides have the -configuration.214... 

A portion of the side chain of calyculin was prepared by a tandem reaction sequence that combined an alkenylzinc reagent with 2-bromoethenylboronate, followed by Suzuki coupling with a vinyl iodide in the same pot.230... 

The C(9)-C(14) segment VI was prepared by Steps D-l to D-3. The formation of the vinyl iodide in Step D-3 was difficult and proceeded in only 25-30% yield. The C(15)-C(21) segment VII was synthesized from the common intermediate 17 by Steps E-l to E-6. A DDQ oxidation led to formation of a 1,3-dioxane ring in Step E-l. The A-methoxy amide was converted to an aldehyde by LiAlH4 reduction and the chain was extended to include C(14) and C(15) using a boron enolate of an oxazo-lidinone chiral auxiliary. After reductive removal of the chiral auxiliary, the primary alcohol group was converted to a primary iodide. The overall yield for these steps was about 25%. 

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