Iodides, alkenyl, formation

In an efficient diastereo-differentiative assembly of three components of norbornene, tv. v-alkenyl iodide, and KCN, the isomerization of the cis to the trans double bond takes place to give the coupled product 224. The isomerization is explained by the formation of the cyclopropane 222. its rearrangement to give a irans double bond in 223, and trapping with CN anion to give 224[168],... 

A unique system for catalytic silaboration of allenes, in which a catalytic amount of organic halide is used as a crucial additive, has been reported (Equation (86)).232 In the presence of Pd2(dba)3 (5 mol%) with 3-iodo-2-methyl-2-cyclohexen-l-one (10mol%), reactions of terminal allenes with a silylborane afford /3-silylallylboranes in good yields with excellent regioselectivity. It is worth noting that the addition takes place at the terminal C=C bond in contrast to the above-mentioned palladium-catalyzed silaboration. The alkenyl iodide can be replaced with iodine or trimethylsilyl iodide. The key reaction intermediate seems to be silylpalladium(n) iodide, which promotes the insertion of allenes with Si-C bond formation at the central -carbon. 

Palladium-catalyzed arylation of olefins and the analogous alkenylation (Heck reaction) are the useful synthetic methods for carbon-carbon bond formation.60 Although these reactions have been known for over 20 years, it was only in 1989 that the asymmetric Heck reaction was pioneered in independent work by Sato et al.60d and Carpenter et al.61 These scientists demonstrated that intramolecular cyclization of an alkenyl iodide or triflate yielded chiral cyclic compounds with approximately 45% ee. The first example of the intermolecular asymmetric Heck reaction was reported by Ozawa et al.60c Under appropriate conditions, the major product was obtained in over 96% ee for a variety of aryl triflates.62... 

Addition of a catalytic amount of NiCfe to CrCl2 is essential for the formation of alkenylchromium reagents.4-6 However, a substantial amount of 1,3-diene, the coupling product of the alkenyl Iodide, is produced if a higher content of NiCfe is employed.8 9... 

Formation of aldehydes. Aldehydes can be prepared by the carbonylation of halides in the presence of various hydride sources. The carbonylation of aryl and alkenyl iodides and bromides with CO and H (1 1) in aprotic solvents in the presence of tertiary amines affords aldehydes[373,374]. Aryl chlorides, as tricarbonylchromium derivatives, are converted into aldehydes at 130 C[366], Sodium formate can be used as a hydride source to afford aldehydes. Chlorobenzene (514) was carbonylated at 150 °C to give benzaldehyde with CO and sodium formate by using dippp as a ligand[375,376]. 

The enantiomerically-pure intermediate 1 was prepared from the dioxolanone 4, available in three steps from L-malic acid. Lewis acid-mediated homologation converted 4, a 4 1 mixture of diastereomers, into 5 as a single diastereomer. After establishment of the alkenyl iodide, it necessary to maintain the lactone in its open form. A solution was found in the formation of the Weinreb amide. The final stereogenic center was established by Brown allylation of the derived aldehyde. The alkene metathesis to form 1 was carried out with the commercially-available Schrock Mo catalyst. The authors did not comment on the relative efficacy of alternative alkene metathesis catalysts. 

Wang et al. have discovered that ultrafme Ni powder in the presence of Cul, PPh3, and KOH promotes coupling of terminal alkynes with aryl and alkenyl iodides in high yields [65], Recent developments have shown, moreover, that the use of co-catalysts (Cu, Zn, Al, etc.) to facilitate the formation of the acetylides is not always required and that cross-coupling reactions of acetylenes and aryl halides can be performed successfully with Pd-based catalysts alone, even with difficult substrates [48, 66]... 

A BINAP-Pd complex catalyzes a highly enantioselective C-C bond formation between an aryl triflate and 2,3-dihydrofuran (eq 22). The intramolecular version of the reaction using an alkenyl iodide in the presence of PdCl2[(/J)-BINAP] and Silver(I) Phosphate allows enantioselective formation of a bicyclic ring system (eq 23). ... 

The scope of the reaction was extended somewhat by the use of the trisubstituted alkenyl iodide 15, which gave the decalin systems 16a and 16b in yields of 63% (83% ee) and 67% (87% ee), respectively (Scheme The deleterious effect of the acetate counterion on ee and favorable influence of the Ag3P04/CaC03 additive combination seen for the AHR conversion of 12 to 13 are reproduced here. Interestingly, 16a was accompanied by a minor amount (35%) of the desilylated alcohol 16c, which displayed a higher ee (92%)—control experiments indicated that desilylation was occurring via transmetalla-tion to Pd after completion of the ring closure. No such free hydroxyl formation was seen in the case of the acetate 15b. 

Sato, Y., Sodeoka, M. and Shibasaki, M. (1989) Catalytic asymmetric C—C bond formation asymmetric synthesis of cw-decalin derivatives by palladium-catalyzed cyclization of prochiral alkenyl iodides. J. Org. Chem., 54, 4738-9. 

The palladium-catalyzed domino assembly of norbornene (65), the ds-alkenyl iodide 66, and a terminal alkyne or cyanide reported by Torii, Okumoto et al. [315] provides an example for a sequence of oxidative addition, intermolecular double bond insertion, and interception of a copper acetylide or potassium cyanide. These reactions with acetylenes have been performed in good yields in the presence of diethylamine, tetra-n-butylammonium chloride, and catalytic amounts of palladium acetate, triphenylphosphine, and copper] I) iodide. Remarkably, they are characterized by complete inversion of the cis configuration of the alkenyl iodide and a high degree of discrimination for the enantiotopic ends of the double bond in norbornene. To account for that, intermediate formation of a cyclopropylcarbinyl-palladium species by a 3-exo-trig cyclization in 67 and subsequent cycloreversion to a new homoallylpalladium intermediate as the direct precursor to 68 and 69 has been assumed. Thus, the products 68 and 69 are formed virtually with complete stereoselectivity (Scheme 8.17). 

More recently, a cascade process that presumably consists of (i) oxidative addition of Pd to an alkenyl iodide, (ii) Pd-alkene 7r-complex formation, (iii) anti-attack by a carbon nucleophile, and (iv) reductive elimination has been devised. This cascade process has been used for the synthesis of ( )-A -capnellene (Scheme 22). 

Cowell and StiUe reported on the formation of butenohdes from alkenyl iodides (Scheme The most useful catalyst was Pd(PPh3)2Cl2 and the solvent was THF or... 

A similar synthesis of (Z)-a-alkylidene-y-lactones from alkenyl iodides was reported by Luo et al. In a related procedure,the presence of an acetyl group a to the hydroxyl group of the iodide led to the formation of a,/S-unsaturated butenolides. The presumed intermediate a-methylene lactone probably undergoes isomerization to the more stable butenolide under the reaction conditions, as shown in Scheme 8. 

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