E-vinyl iodide

The dimethyl sulfide complex of dibromoborane 215 and pinacolborane216 are also useful for synthesis of E-vinyl iodides from terminal alkynes. 

The preparation of vinyl iodide 39 first required the transformation of (E,E)-farnesyl acetone (28), performed according to Negishi, to the terminal alkyne 27 with 75% yield [35]. The latter then gave (E)-vinyl iodide 39 in dia-stereomerically pure form and 74% yield by Zr-catalyzed carboalumination with trimethylaluminum and trapping of the intermediate vinylaluminum species with iodine [36]. The alkyl iodide rac-29 necessary to ensure the coupling with 39 was obtained by selective monofunctionalization of 3-methyl-pentane-1,5-diol (26) in a few steps [37]. 

Stereoselective conversion of an aldehyde to the corresponding E-vinyl iodide using CHI3 and CrCl2. 

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. 

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%. 

Enynes. In the presence of this Pd(II) catalyst, vinyl iodides couple with alkynyltrimethylstannanes with retention of the geometry of the vinyl iodide to provide 1,3-enynes in high yields.2 Since the conjugated triple bond can be reduced to a (Z)-double bond stereospecifically, the coupling also provides a route to (Z,E)-or(Z,Z)-l,3-dienes. An example is the synthesis of bombykol (1), the sex attractant of the silkworm moth. 

For alkenylation of silyl ligands with vinyl iodides see (a) B. H. Lipshutz, D. C. Reuter, E. L. Ellsworth,/. 

Other Pd cross-coupling reactions such as Heck [52] and Suzuki [53] reactions have also been used for macrocyclizations. The main drawback for Pd catalyzed macrocylization is the yield, that is often somewhat disappointing if compared with other established methods. Also, the introduction of the required coupling components (e.g., trialkyltin group, vinylic iodide) can be difficult in some compounds. In other cases, Pd-catalyzed side reactions such as double bond migration or allylic activation can occur. 

The stereospecific construction of the trisubstituted double bond of the side chain at C-1 of carbazomadurins A (253) and B (254) was achieved using Negishi s zirconium-catalyzed carboalumination of alkynes 758 and 763, respectively. Reaction of 5-methyl-l-hexyne (758) with trimethylalane in the presence of zirconocene dichloride, followed by the addition of iodine, afforded the vinyl iodide 759 with the desired E-configuration of the double bond. Halogen-metal exchange with ferf-butyllithium, and reaction of the intermediate vinyllithium compound with tributyltin chloride, provided the vinylstannane 751a (603) (Scheme 5.79). 

A Stille type coupling strategy has been utilised to complete a total synthesis of epothilone E. The vinyl iodide 30 and the thiazole stannane 31 were coupled to give the macrolactone 32 which is a precursor to natural epithilone E. The thiazole stannane 31 was prepared from 4-bromo-2-hydroxymethylthiazole via treatment of the lithiated protected 4-bromO 2-hydroxymethylthiazole with tributylstannyl chloride. This Stille coupling approach was also used to prepare a range of epothilone B analogues <99BMC665>,... 

HMDS is known as an ammonia substitute in the preparation of primary amides via ammonolysis since 1985. With the use of excess HMDS, the Pd-catalyzed aminocarbonylation of various aryl and vinyl iodides and triflates (e.g., 146, 148, and 150) has been successfully performed to give the corresponding vinyl and aryl amides (e.g., 147, 149, and 151, respectively) in good to excellent yields (Scheme 21). " ... 

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). 

Reactions which are apparently stereospecific occur in the nucleophilic displacement of vinylic iodide [31] in the electron-deficient alkenes E- and Z-24 shown in Scheme 9.14. With ethanolic toluenethiolate, the sole detectable product from the reaction of -24 is -25. However, -25 is also the sole detectable product from the reaction of Z-24. This stereoconvergence demands that the stereoisomers react through a common intermediate, and it was reasonably suggested that initial nucleophilic addition of the thiolate anion yields a resonance-stabilised carbanion (26) whose stereoisomerisation, again by rotation about a carbon-carbon single bond, is much faster than the loss of iodide to yield the substitution product ( fy). 

Removal of the tri-wo-propylsilyl (TIPS) and tm-butyldimethylsilyl (TBS) protecting groups could be accomplished concomitantly with TBAF in tetrahydrofuran at 0 °C, but here competing elimination of the secondary bromide was observed. Better overall yields and cleaner conversion was observed when TBS ether was cleaved with 5 % aqueous HF in acetonitrile at 0 °C followed by removal of the acetylenic TIPS with TBAF under milder conditions of -78 °C.10 The diastereomers are not separated before the desilylation process therefore even a 3 1 mixture of E- and Z-enyne is obtained. Prelaureatin 4 and its F-isomer 17 are likewise goals in natural product synthesis. Crimmins and co-workers developed an own synthetic route to 4. The reaction sequence is similar up to aldehyde 55. Afterwards a Z-vinyl-iodide is selectively formed and the alkyne is introduced via a Sonogashira reaction. 

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