Lithium dimethylamide

Preparation by reaction of tantalum pentachloride with pure lithium dimethylamide in pentane is unsafe. Initial non-reaction is followed by explosion during manipulation of the slurry. Presence of ether or dimethylamine gives smooth reaction. Stepwise displacement of chlorine, starting with the free amine, is also recommended. 

In Fallen, in denen es auf milde Reaktionsbedingungcn ankommt, kann man das Oxiran statt mit dem Amin selbst mit dessen Lithium-Derivat umsetzen und auf diese Weise bei tieferen als den sonst iiblichen Temperaturen arbeiten, wie hier am Beispiel der RingofF-nung von Ethyloxiran mit Lithium-dimethylamid beschrieben1. 

Lithium dialkylamide. Four catalysts, namely lithium dimethylamide, lithium diethylamide, lithium di-n-butylamide and lithium di-i-propylamide, have been prepared by the reaction of ji-butyllithium and the corresponding amines. Characterization of these amides was performed by G.C.-Mass Spectroscopy after D O quenching of the amides. Further analysis for the total alkalinity was performed by a titration... 

The copolymerizations of butadiene and styrene with these four amides were carried out in hexane with the insoluble initiators at several different temperatures. In general, the styrene content in the lithium diethylamide or lithium di-n-butylamide initiated butadiene-styrene polymerizations is higher than in the lithium dimethylamide or lithium di-i-propylamide system (Table VII). A high styrene content (23.4% to 25.3%) in the lithium diethylamide and the lithium di-n-butylamide systems was obtained at 50°C polymerization temperature. From this result, it appears that the best copolymerization temperature for these systems is 50 C. 

The metallation of 3-methyl-4//-5,6-dihydro-l,2-oxazine has been shown to take place at the methyl group with hindered bases and at the methylene group with unhindered bases (81JA5916). Deprotonation of (753) with lithium dimethylamide at -65 °C followed by reaction with benzyl bromide gave (754) in 85% yield. This product was converted to enone (755) by reaction first with triethyloxonium tetrafluoroborate to produce an oxoiminium salt. The salt was stirred with trimethylamine and the resulting a,/3-unsaturated imine hydrolyzed with wet silica gel to the enone (Scheme 174). The lithiated derivative of (753) serves as a synthon for the unknown a-anion of methyl vinyl ketone. 

Materials. The complex RhCl(ttp) was prepared as described previously (6). Cyclohexanone was obtained from Mallinkrodt cyclohexene and 1-pentene were obtained from MCB. All other olefins and 1-octyne were purchased from ChemSampCo. The aluminum alkyls were obtained from Aldrich as 25% w/w solutions in toluene. Neat liquids used in the H-l NMR work were obtained from these solutions by removing the toluene under vacuum. Lithium dimethylamide, LiN(CH3)2, was obtained from Alpha/Ventron as a 10% w/w slurry in hexane. Hydrogen was passed through an Englehard Deoxo purifier and activated alumina before use. 

DFT calculations have been performed to examine the possible formation of mixed aggregates between chloromethyllithium carbenoids and lithium dimethylamide (LiDMA).5 In the gas phase, the major species are mixed trimers and mixed tetramers. 

Another study employing the MPE model (at the SCF computational level) is the calculation of spin-spin coupling constants in methyllithium and lithium dimethylamide [82], In this case, modelling of the solvent as supermolecular aggregates leads to far better agreement with experimentally measured liquid-state spin-spin coupling constants than... 

It was soon realized that the far more readily available 1-chloro and bromo acetylenes w 16) could be used too and in fact phenylchloroacetylene gives with lithium dimethylamide in ether, 87 % of the corresponding ynamine 6). Similarly, N-lithium pyrroline affords 67% of the corresponding ynamine17. ... 

Unlike this reaction, the reaction of OFN with lithium dialkylamides easily proceeds at ambient temperature and results in the formation of hexa- 73-75 or heptaamines 76 and 77 in 41-46% yield63. The reaction occurs smoothly and selectively in dioxane or THF with two-fold excess of lithium dialkylamide per each fluorine atom. It is also recommended that UMPA be added to the reaction mixture (2 equivalents per 1 equivalent of the lithium amide), since cyclic ether solvents are prone to interact with non-solvated lithium amides and thus to form ring-opening products that then react with OFN. Lithium piperidide in either dioxane or THF gives exclusively the hexa-substituted derivative 75. Lithium dimethylamide produces hexaamine 73 in dioxane and heptaamine 76 in THF, whereas the most reactive lithium pyrrolidide forms in dioxane almost a 1 1 mixture of polyamines 74 and 77, and the only product in THF is 77. 

The reaction of tetraamines 71 and 72 with lithium dialkylamides has also been investigated. Under a wide range of conditions (dioxane or THF, heating up to 95 °C for 48 h) the pairs 72/lithium piperidide and 71/lithium dimethylamide remain intact in dioxane. However, using THF instead of dioxane in the last case enables one to introduce three... 

The reagent is prepared by the reaction of dimethylamine with n-butyllithium in n-hexane at 0°. An ethereal solution of nickel carbonyl is added to an ethereal suspension of lithium dimethylamide below 10° and the mixture is stirred for 1 hr. 

The only recorded nucleophilic substitutions of benzo[c]cinnoline are with lithium dialkylamides. The reaction with lithium dimethylamide in dimethylamine gives 4-dimethylaminobenzo[c]cinnoline, further at-... 

Reactions of the chloro compounds with lithium dimethylamide are complicated by the fact that nucleophilic displacement of hydrogen often precedes that of chlorine, giving complex mixtures of products. - The results obtained in reactions of potassium amide with chloro- and iodobenzo[ -]cin-nolines show that elimination-addition processes via arynes 93 and 94 are more important than direct nucleophilic displacement (addition-elimina-tion), Surprisingly, no l-aminobenzo[c]cinnoline is formed from the 1-and 2-halogeno compounds, while 4-chlorobenzo[c]dnnoline gives small amounts of 2-aminobenzo[c]cinnoline by a 1,3-displacement. 

Based on mechanistic considerations, 171 has been suggested as an intermediate in the base-induced transformation of 170 to benzocyclopropene (172) (150). On treatment of 173 with lithium dimethylamide at — 75°C, the fulvene derivative 175 could be isolated (151). The mechanism by which the fulvene arises was elucidated by several isotope labeling experiments. These results require the formation of triene 174 as an intermediate in the base-induced elimination reaction of 173 (151). 

Lithium dimethylamide was prepared from the reaction between butyllithium in hexane (commercially available from Alfa Ventron Co. as ca. 2.6 M LiBu in hexane) and dimethylamine according to the stoichiometric reaction ... 

The lithium dimethylamide can be used without further purification in this hexane solution, or it may be stored as a fine, powdery solid by merely stripping off the hexane in vacuo. 

Deprotonation of the chiral 1,2-oxazine (34) by n-butyllithium proceeds with a high degree of stereoselectivity cis to the C-6 substituent subsequent capture of this carbanion with carbonyl compounds also proceeds syn to the C-6 substituent, so that the overall process occurs with retention of configuration at C-4 (Scheme 16).40 Although the related 1,2-oxazine (35) has not been condensed with carbonyl compounds, it is useful to note that the regioselectivity of its deprotonation can be easily controlled by the size of the base employed. Bulky amide bases preferentially abstract the proton at the exocyclic methyl group, whereas small amide bases such as lithium dimethylamide preferentially abstract a proton at C-4.41... 

One problem in working with the lithiated tertiary diamines is that they will undergo further decomposition when overheated or on standing. For example lithiated TMEDA yields lithium dimethylamide, dimethyl-vinylamine, and lithium acetylide (I, 2, 5, 34). Lithiated TMEDA (I) in hexane decomposes at a rate of 0.52% of the initially contained material per day at 35 °C. Therefore solutions of the lithiated tertiary diamines and amines should be stored at 10°C or lower for long periods of storage. 

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