Dimethyl zinc, reaction with

The dimer of 1-methyl- -pyrroline (39) was obtained by reduction of N-methylpyrrole with zinc and hydrochloric acid (132) and, together with the trimer, by mercuric acetate dehydrogenation of N-methylpyrrolidine (131). J -Pyrroline-N-oxides form dimers in a similar manner (302). Treatment of 1,2-dimethyl-zl -piperideine with formaldehyde, producing l-methyl-3-acetylpiperidine (603), serves as an example of a mixed aldol reaction (Scheme 18). 

The coupling reaction of zinc(II) (3- or)8-monobromodeuteroporphyrin dimethyl ester (ID with 1,4-divinylbenzene under the typical conditions of the Heck reaction results in the formation of dimeric porphyrin 12 linked via a divinylbenzene moiety. Use of 1,3,5-trivinyl-benzene in the same reaction makes the trisadduct available."5... 

The titanium(IV) chloride catalyzed addition of allylic silanes to (E)-(2-nitroethenyl)benzene affords y,<5-unsaturated nitronates which, on treatment with low valent titanium species [generated in situ from titanium(IV) and zinc], give y,<5-unsaturated nitriles. For example, [(Zs)-2-butenyl]-(dimethyl)phenylsilane underwent reaction with ( )-(2-nitroethenyl)benzene to give 3-methyl-2-phenyl-4-pentenenitrile in 65 % yield as a 3 1 mixture of diastereomers of unassigned configuration22. 

Further optimization of this reaction was carried out with TFE as an achiral adduct, since reaction with TFE is much faster than that with neopentyl alcohol. We found that dimethyl- and diethylzinc were equally effective, and the chiral zinc reagent could be prepared by mixing the chiral modifier, the achiral alcohol and dialkylzinc reagent in any order without affecting the conversion and selectivity of the reaction. However, the ratio of chiral to achiral modifier does affect the efficiency of the reaction. Less than 1 equiv of the chiral modifier lowered the ee %. For example with 0.8 equiv of 46 the enantiomeric excess of 53 was only 58.8% but with 1 equiv of 46 it was increased to 95.6%. Reaction temperature has a little effect on the enantiomeric excess. Reactions with zinc alkoxide derived for 46 and TFE gave 53 with 99.2% ee at 0°C and 94.0% ee at 40°C. 

A zinc-mediated carbon-carbon coupling reaction can be carried out on the metallated form of (t-butyldimethylsilyl)(2-pyridylmethyl)amine, formed in reaction with dimethylzinc. The isolated dimeric species can be reacted with further dimethyl zinc to give bis(methylzinc)-l,2-dipyridyl-l,2-bis(t-butyldimethylsilylamido)ethane, which contains two N3C coordinated zinc centers.89... 

The interactions of dimethyl- and diethylzinc with bulky tris(hydroxyphenyl)methanes, Scheme 86, yielded, depending on the reaction conditions, a variety of alkylzinc alkoxides, featuring two-, three-, and four-coordinate zinc centers. These polynuclear compounds (Figure 63 shows the trinuclear ethylzinc derivative 136) are relatively poor catalysts for the co-polymerization of cyclohexene oxide and carbon dioxide.197... 

The basic assumption is made in these calculations that the benzyl or phenyl radicals formed are removed in the hot zone only by recombination with methyl radicals. When dimethyl zinc is used, the apparent energy of activation for reaction (11) is negative indicating a loss of phenyl radicals in the hot zone by an additional process. The only species present which is absent when the mercury and cadmium alkyls are used is ZnCH3. The additional process by which phenyl radicals are lost is therefore probably... 

This reaction was therefore negligible when C6D12/Zn(CH3)2 = 13. The rates of reactions (1) and (14) are strongly dependent on the nature of the surface. In an ampoule coated with tar from decomposition of a large quantity of dimethyl zinc, the rate of both reactions is only J-i the rate observed in unconditioned vessels (tested at 348 °C with fraction Zn(CH3)2 reacted in conditioned vessel = 0.035). It has also been shown that in 90 min at 290 °C, the overall decomposition of dimethyl zinc in the absence of cyclohexane is 94 % complete if a zinc oxide surface is used, but only 4.5 % complete in a conditioned vessel. Decompositions carried out in conditioned vessels were assumed to be homogeneous. 

It is therefore possible that the initial fate of ZnCH3 in the static system work is dimerization. Under the conditions used diffusion to the surface can compete successfully with reaction (2) so formation of an intermediate dimer could be either a homogeneous or a heterogeneous process. By elimination, the two hydrogen atoms required to convert the dimer to 2 Zn+2 CH4 must come from dimethyl zinc itself and must leave a product that does not undergo subsequent decomposition. It is possible that this occurs via a cyclic intermediate, with adsorbed dimethyl zinc leaving surface-adsorbed radicals which may undergo polymerization, viz. 

The reaction of (3,5-di-tert-butylpyrazol-l-yl)(3, 5 -dimethylpyrazol-l-yl)acetic acid Hbpa (3d) with dimethyl zinc resulted in the chiral zinc methyl complex [Zn(bpa )(CH3)] (15) (Fig. 17) as racemic mixture (47). 

Mercury dimethyl undergoes single replacement reactions with several metals such as alkali and alkaline earth metals, zinc, aluminum, tin, lead and bismuth forming their corresponding dialkyls. 

Such reaction is a synthetic route to prepare many organometallic compounds. Thus, reaction with metallic zinc yields zinc dimethyl ... 

Homo-Reformatsky reaction.1 The reaction of 1-ethoxy-1-trimethylsilyloxy-cyclopropane (1) with an aldehyde in the presence of ZnCl2 results in y-silyloxy esters via a zinc homoenolate (a) of ethyl propionate (equation I). Znl2 is the preferred catalyst in the case of reactions with acetophenone and benzaldehyde dimethyl acetal and in reactions of l-isopropoxy-l-(t-butyldimethylsilyl-oxy)cyclopropane with aromatic aldehydes. 

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