Acetylene, cuprate

The mixed vinyl acetylene cuprate (435) has been developed as an ethyl acrylate synthon. Whereas (435) does not react with alkyl bromides and iodides, it is reactive towards allylic (and propargylic) bromides, as exemplified by its reaction with 3-bromo-... 

Thus, the reaction of mixed (phenylthio)alkylcuprates with 9-BBN overcomes the problem associated with (1) the thermal instability of phenoxy- and tert-bu-toxyalkylcuprates, (2) the low reactivity of mixed acetylenic cuprates, and (3) the wasting of one R group of the homocuprates. 

In a study of the reactivity of organocopper compounds with a,/3>unsaturated aldehydes, allylic and acetylenic cuprates have been found to give selective 1,2-addition to afford allylic alcohols, in contrast to the predominant 1,4-addition observed with homoallylic, phenyl, and vinyl cuprates secondary alkyl cuprates give both types of addition product. 

On treatment with organocopper(i) species, 1-iodo-l-methoxyallene (70) undergoes 1,3-substitution to give 1-methoxyacetylenes (e.g. Scheme 114). Acetylenic cuprates give 1,4-diynes. The choice of solvent for the reaction is critical if by-products are to be avoided. 

S. Pvepavation of a solution of lithium di(Z-hexenyl)auprate. A needle connected to an acetylene supply (Note 6) is introduced through the rubber septum of the flask, with its end at least 1 cm below the surface of the cuprate solution. The stopcock is fully opened towards the balloon, the... 

This reaction illustrates a stereoselective preparation of (Z)-vinylic cuprates, which are very useful synthetic intermediates. They react with a variety of electrophiles such as carbon dioxide, epoxides, aldehydes, allylic halides, alkyl halides, and acetylenic halides they undergo... 

A number of alternative multi-step procedures for the synthesis of a-tert-alkyl ketones are known, none of which possess wide generality. A previous synthesis of 2-tert-penty1cyclopentanone involved reaction of N-1-cyclopentenylpyrrol 1 dine with 3-chloro-3-methy1-l-butyne and reduction of the resulting acetylene (overall yield 46 ). However, all other enamines tested afford much lower yields. Cuprate addition to unsaturated ketones may be useful in certain cases. Other indirect methods have been briefly reviewed. ... 

The conversion of the dehydrotrimer 135 into the corresponding bis-cuprate followed by coupling with dibromide 131 (Cadiot-Chodkiewicz conditions) gave the expanded [5]pericycline 122 in 53% isolated yield (Scheme 28) [4]. The more versatile approach by simple oxidative cyclooligomerization of dehydrooligomers of type 135 under high dilution conditions as shown in Scheme 28 provided the acetylene-expanded [3]- 82, [5]- 122 and [6]pericyclines 163 in reasonable to excellent yields [4,7]. 

Z, 6Z- 10 COOMe was produced by a short and stereospecific one-pot synthesis (Scheme 17) [25], via sequential addition of dipropyllithium cuprate 115 to two equivalents of acetylene, followed by Michael addition of the resulting conjugated dienyl cuprate 116 with methyl propiolate 117. The only sig-... 

The initial reports in 1982-83 by Westmijze et. al. [25a] and Piers [25b] on the addition of stannylcopper and cuprate reagents to simple alkynes were followed by full studies [76] and reports from several laboratories [14b, 16b-e, 25c, 77-78]. In the earlier studies, the vinylcopper species could only be trapped with a proton. Marino achieved success in the addition to cyclohexenone of the vinyl cuprate generated by addition of BusSnCuCNLi to acetylene [79a-b], and Fleming [79c]... 

The carbocupration of acetylene has been studied systematically for five model species - MeCu, Me2Cu, Me2CuLi, Me2CuLi LiCl, and (Me2CuLi)2 [91] - all of which have been invoked once in a while in discussions of cuprate mechanisms. A few general conclusions have been made regarding the reactivities of these reagents with 71-acceptors ... 

Fig. 10.7. Orbital interactions between RzCu and substrates in (a) an early stage of interaction of the cuprate with methyl bromide, and (b) n-complexation to acetylene or olefin.

Conjugated acetylenic esters react readily with cuprate reagents, with syn addition being kinetically preferred.63 64 65 66 67... 

Cuprate, dibutyl-, lithium, reaction with acetylene, 66, 62 Cuprates, higher order, 66, 57... 

Pericas and Jeong demonstrated independently that sulfur-tethered substrates, when subjected to the PKR conditions, afforded the desired bicyclic products. The sulfur tether is removed cleanly by Pummerer reaction after oxidation of sulfur to sulfoxide or 1,4-addition of bisalkyl cuprate followed by hydrogenolysis of sulfide with Raney nickel. It is worth mentioning that the regioselectivity regarding the acetylene part is opposite to that of the intermolecular version (Equation (30)). 

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