Organolithium reagents, addition salts

By the extension of the above-mentioned stereoselective asymmetric addition of alkylithiums to other organolithium reagents such as lithium salts of methyl phenyl sulfide, 2-methylthiazoline, trialkylsilylacetylene, N-nitroso-dimethylamine, and acetonitrile, chiral oxiranes (95) U1), thiiranes (96) nl), acetylenic alcohols (98) 112), and amino alcohols (97) U1) were readily obtained. 

The reacuons of electrophihc tnflyl sources with nucleophiles were investi gated The reaction of tnfhc anhydride with an organolithium reagent is not synthetically promising because of ditnflylation and other side reactions [20] When phenyllithium reacts with tnfhc anhydnde, dimerization products and acetylenic Michael diadducts are observed [20] (equation 17), but using the sodium salt of the alkynes instead of the lithium salt provides the alkynyl tnfluoromethyl sulfones [21] (equation 18) (Table 7) Alkynyl tnfluoromethyl sulfones are of synthetic interest, because they show a pronounced reactivity toward nucleophiles in addition reactions and cyclopentadiene in Diels-Alder reactions [21] (Table 7)... 

Solvent and temperature effects on the diastereoselective addition of n-BuLi to 2-phenylpropanal have been reassessed95 and the stereochemistry of addition of organolithium reagents to carbohydrate enones has been studied.96 No compelling evidence has been found to support the suggestion that addition of n-BuLi to benzoic acid might compete with formation of the lithium salt and thereby provide an alternative to the sequential route to PhCOBu".97... 

The addition compounds (I) are insoluble in diethyl ether, and the slurries obtained are quite stable. In more strongly solvating media, such as tetrahydrofuran or dimethoxyethane, the compounds are soluble but show rapid decomposition, with trimethylamine and polymethylene as the main products. These experiments indicate (9, 40) that when the lithium salt is trapped by donor solvent molecules, the free ylide quickly undergoes decomposition (40). No free trialkylammonium ylide has yet been prepared, even under very mild conditions (35). On the other hand, it has been shown, that the tetramethylammonium cation can even be metalated twice by organolithium reagents (102) to afford dimethyl-ammonium bismethylides ... 

The addition of zinc salts to a propargyl/allenyl organolithium reagent leads quantitatively to the allenylzinc bromide [60] and, considering that this latter reacts with the vinylmetal moiety, via an S 2 process [62, 107], the stereochemical result is thus explained... 

A(-(Arylthiomethyl)amines, which are easily prepared and reportedly have better shelf stability than the corresponding )V-(alkoxymethyl)amines, have also been utilized to prepare tertiary amines. Alkenyl cuprate addition to )V,A -diethylphenylthiomethylamine produces allylic amines in high yield (entry 1, Table 6). Both alkenyl groups of the cuprate react. 5-(Dialkylaminomethyl) dithiocarbamates (entry 2, Table 6), sulfonates (entry 3, Table 6) and amides also generate iminium salts in situ. Of a variety of amides examined, imides such as dialkylaminomethyl-succinimides (entry 4, Table 6) and -phthali-mides provide the best overall yields. Organolithium reagents are rarely utilized in aminomethylation reactions. However, )V-chloromethylamines condense readily with lithiated anisole derivatives (entry S, Table 6). ... 

Iminium salts bearing a labile trimethylsilyl group can be generated in situ and undergo nucleophilic addition (see Sections 1.12.4.2 and 1.12.7.3). Bis(trimethylsilyl)methoxymethylamine (75), for example, has been used as a formaldehyde equivalent for the preparation of primary amines. Cyclic imines, such as 3,4-dihydroquinolines, react with trimethylsilyl triflate (TMS-OTf) to provide reactive labile iminium salts (55), which condense with picoline anions. The addition of nonstabilized Grignard and organolithium reagents to acyclic aromatic ketimines and aldimines, however, is often not facilitated by the presence of TMS-OTf ... 

Addition of organolithium reagents to diphenylarsenoethene provides another route to a-arseno anions. This reaction is general to the second and third row elements (Si, P, S, Ge, As and Se) but does not occur with elements from the fourth and fifth rows (Sn, Sb, Te, Pb and Bi). Unlike their phosphorus analogs, triphenylarsonium salts cannot be prepared by reaction of triphenylarsine with an alkyl halide. Their preparation can be achieved by reaction of triphenylarsine with the more electrophilic alkyl tri-flates. It is also possible to alkylate arsonium ylides. ° ° ... 

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