Butadiyne addition

It was found [99JCS(PI )3713] that, in all cases, the formation of the deiodinated products 38 and 39 was accompanied by formation of the diynes 40 which were isolated in 60-90% yield. The authors believed that the mechanism of deiodination may be represented as an interaction ofbis(triphenylphosphine)phenylethynyl-palladium(II) hydride with the 4-iodopyrazole, giving rise to the bisftriphenylphos-phine)phenylethynyl palladium(II) iodide complex which, due to the reductive elimination of 1 -iodoalkyne and subsequent addition of alk-1 -yne, converts into the initial palladium complex. Furthermore, the interaction of 1-iodoalkynes with the initial alkyne in the presence of Cul and EtsN (the Cadiot-Chodkiewicz reaction) results in the formation of the observed disubstituted butadiynes 40 (Scheme 51). 

Palladium-catalyzed bis-silylation of l,4-bis(trimethylsilyl)butadiyne affords 1,2- and 1,4-addition products with varying ratios, depending on the disilanes and palladium catalysts used (Equation (28)).98... 

The first tt complexes of 1,3-diynes were reported by Greenfield. Shortly thereafter, Tilney-Bassett described the first heterometallic derivatives. This area has grown steadily since these initial reports and many complexes of this type are now known. Diyne complexes are often simply alkyne-substituted analogues of conventional jr-alkyne complexes. Indeed, transition metal compounds that form -complexes with mono-alkynes can be expected to form complexes with diynes. However, the thermal sensitivity of terminal diynes, especially 1,3-butadiyne, may limit the application of routine reaction conditions in some cases. Further coordination of the ynyl ligand by additional metal fragments is usually determined by the reagent stoichiometry and by steric effects. 

Nucleophilic additions of alcohols, amines, thiols, and selenols to Group 8 buta-trienylidene intermediates [M]=C=C=C=CR2 have also been used in the preparation of stable heteroatom-conjugated allenylidene complexes. Thus, activation of trimethylsilyl-l,3-butadiyne HC=C-C=CSiMe3 by the iron(II) complex [FeClCp (dppe)], in methanol and in the presence of NaBPh4, resulted in the high-yield formation of the methoxy-allenylidene [FeCp =C=C=C(OMe)Me ... 

Scheme 3.5 Generation of [Cp(PPh3)2Ru=(C)4H2] (4) by reaction of [RuCI(Cp)(PPh3)2] with butadiyne and addition of HNPh2 across the C3-C4 bond of the chain.

The interesting zwitterionic compound (39) with the cationic component a butadien-2-yl cation was obtained by reaction of l,4-di(t-butyl)butadiyne with 2 mol of di(r-butyl)aluminium hydride, with the structure being established by X-ray analysis.80 The reactions of the l,2-diferrocenyl-3-(methylthio)cyclopropenylium ion with carbanions derived from active methylene compounds were investigated.81 Products were derived by ring opening of the cyclopropene ring after the initial carbanion addition. The bis(ferrocenylethynyl)phenylmethylium cation (Fc-C=C-)2C+Ph (Fc = ferrocenyl) was prepared 82 This cation proved to be much less stable than its bis-ethenyl analogue (Fc-CH=CH-)2C+Ph. 

Tellurophene1 A 1 /, three-necked flask is fitted with a reflux condenser, a stirrer, an addition funnel, and a nitrogen inlet tube. 4.0 g (31 mmol) of tellurium, 28 g(200 mmol) of 85% sodium formaldehyde sulfoxylate, 17 g (425 mmol) of sodium hydroxide, and 150 ml of water are placed in the flask which is then purged with pure nitrogen. The stirred mixture is heated under reflux for 15 min and cooled to 20°. 8.2 g (42 mmol) of 1,4-bis[trimethylsilyl]-l,3-butadiyne dissolved in 100 m/ of ethanol are slowly added dropwise to the stirred sodium telluride solution, the mixture is heated under reflux for 15 min, then stirred at 20° for 3 h, extracted with diethyl ether, and the extract is dried with anhydrous sodium sulfate. The extract is filtered and 10 ml (200 mmol) of bromine are added dropwise to the filtrate until the bromine color persists. The solution is concentrated on a water bath at 40° under aspirator vacuum to a volume of 50 ml and the red precipitate of tellurophene. dibromide is collected yield 8.9 g (84%) m.p. 120° (dec.). 

This rarer, and rather surprising, approach to Z-alkenes sometimes gives excellent results particularly in the addition of nucleophiles to butadiyne. The base-catalysed addition of methanol gives an... 

The red R group may seem to get in the way of the reaction but, of course, the dienophile is not approaching in the plane of the diene but from underneath. Itis difficult to find a convincing example of this stereochemistry as there are so few known, partly because of the difficulty of making E,2-dienes. One good approach uses two reactions you met in Chapter 31 for the control of double bond geometry. The cis double bond is put in first by the addition of methanol to butadiyne and the trans double bond then comes from LIAIH4 reduction of the intermediate acetylenic alcohol. 

The first Group 9 C4 complex was reported by Marder and his colleagues in 1991. Facile oxidative addition of each C-H moiety in butadiyne... 

For crystals of l,4-bis(3-benzothienyl)butadiyne 34c, the distance between adjacent molecules in a stack as well as the angle between the molecular axis and the stack axis are not suitable for 1,4-addition reaction to occur. 

The production of acetylene as the major gaseous product in the reaction of butadiyne (equation 9) occurs in part via C2H radicals when short wavelength radiation is used , but with 254 nm radiation it is suggested that a molecular process occurs in a non-linear excited state. The evidence for this additional process is that no C2HD is formed when perdeuteriopropyne is present as a source of deuterium to trap the radicals. 

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