Copper chloride alkoxides

It is important to note that this new protocol operates under completely neutral conditions. Indeed, addition of BuOK to the copper chloride - Phen/alcohol mixture generates the corresponding copper alkoxide. Prom that point onward, the oxidation proceeds under neutral conditions since all the base has been consumed. It is noteworthy that sensitive substrates do not undergo epimerization or racemization. 

In addition to the methods described above, prenol (51) can be prepared from methyl-butynol (43) by rearrangement to prenal (52) using a titanium alkoxide/copper chloride catalyst [69, 70] followed by selective hydrogenation using a ruthenium rhodium tris( 7-sulfonatoyl)phosphine trisodium salt (TPPTS) catalyst [71, 72]. However, it is more usual to prepare the prenyl esters by nucleophilic substitution of a carboxylate anion on prenyl chloride [503-60-6] (56) which, in turn, is available through hydrochlorination of isoprene [78-79-5] (1). This hydrochlorination often employs copper ions as catalysts. These processes are shown in Fig. 8.14. 

Nucleophilic Reactions. Useful nucleophilic substitutions of halothiophenes are readily achieved in copper-mediated reactions. Of particular note is the ready conversion of 3-bromoderivatives to the corresponding 3-chloroderivatives with copper(I)chloride in hot /V, /V- dim ethyl form am i de (26). High yields of alkoxythiophenes are obtained from bromo- and iodothiophenes on reaction with sodium alkoxide in the appropriate alcohol, and catalyzed by copper(II) oxide, a trace of potassium iodide, and in more recent years a phase-transfer catalyst (27). 

Furthermore, the preparation and reactions of 2-methoxythiophene were studied by Sice (70). This compound was obtained by a copper catalysed Williamson synthesis. It was also found that iodothiophene reacted readily with sodium alkoxides, whereas bromothiophene reacted slowly and chlorothiophene did not react at all. Sodium iodide accelerated the reaction of bromothiophene. The ortho, para orienting alkoxy group on carbon atom 2 increased the directive influence of the sulphur atom to the 5 position but competed with it to induce some attack on the 3 position by electrophilic reagents (nitration, acylation). The acylation of 2-methoxythiophene with stannic chloride at low temperatures furnished a mixture of two isomers. The 5-methoxy-2-acetothienone was obtained in higher yield and was identified by its ultraviolet absorption spectrum. 

Arnold and co-workers also reported the deprotonation of alkoxy imi-dazolium iodides with -butyl lithium to yield lithium alkoxide carbenes (Scheme 3).14 Single crystals of one of the complexes were grown from a diethyl ether solution, and revealed a dimer of LiL with lithium iodide incorporated to form a tetramer of lithium cations (7). The lithium-NHC bond distance of 2.131(6) A is similar to that of the lithium amide carbene 4. Also as in 4 there is distortion of the lithium-NCN bond which has an angle of 152.3°. The C2 carbon resonates at 200 ppm in the 13C NMR spectrum which is a relatively high-frequency, possibly as a result of the incorporated lithium iodide. The lithium salts were able to act as ligand transfer reagents and react with copper (II) chloride or triflate to afford mono- or bis-substituted copper(II) alkoxy carbene complexes. 

Several methods have been recommended for the preparation of pure methylcopper, each having advantages over previously reported methods. Costa et al. consider the [Pb(CH3)4 + Cu(N03)2] method superior to the Grignard route, as reproducible analyses are obtained 82). However, Thiele and Kohler recommend the reaction of zinc dialkyls with cop-per(II) chloride in ether at — 78°C for the preparation of pure yellow methylcopper, red-brown ethylcopper, and orange propylcopper, uncontaminated by copper alkoxides (277). The mechanism was considered to be a reduction of copper(II) to copper(I) chloride, followed by the reaction of the latter with the zinc dialkyl. The results from the recent... 

Chelation of the C-2 alkoxide with copper(II) chloride leaves the C-3 alkoxide free to react with the alkylating agent. 

While ATRP of methyl acrylate was reported only for the copper catalyst system [290-292] methyl meth(acrylate) was also polymerized with copper [290,293 295], ruthenium/aluminum alkoxide [296,297], iron [298,299] and nickel [300 303] eatalyst systems (Table 9). Thereby, it must be noted that in principle, the ruthenium-based system proposed by Sawamoto et al. requires the addition of Lewis acids, e.g., Al(0- -Pr)3 [297]. Recent investigations showed, that the half-metallocene -type ruthenium(II) chloride Ru(Ind)Cl(PPh3)2 (Ind = indenyl) led to a fast and well controlled polymerization even without the addition of Al(0- -Pr)3, whereas in case of a polymerization with Ru(Cp)Cl(PPh3)2 (Cp = cyclopentadienyl), the addition of Al(0-z-Pr)3 is necessary. The activity of Ru(II)-catalysts decreases in the order Ru(Ind)Cl(PPh3)2 > RuCl2(PPh3)2 > Ru(Cp)Cl(PPh3)2 [304]. 

A formal [2+1+1] cycloaddition is achieved by reaction of alkynes with an iron carbonyl species that is prepared in situ from dodecacarbonyltriiron Fe3(CO)i2 in the presence of certain amines. This procedure provides cyclobutenediones in moderate to good yields after demetalation with copper(II) chloride (Scheme 4-14). Instead of amines and dodecacarbonyltriiron, alkoxides such as ter/-BuOK can be reacted with pentacarbonyliron to give reactive carbonyliron intermediates that undergo cyclization... 

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