Brom/Lithium‐Austausch an Vinylbromiden mit 2 Moläquivv. tert ‐Butyllithium. Umsetzungen von Vinyllithiumverbindungen mit Hetero‐ und Kohlenstoff‐Elektrophilen

Abstract

Alkylhalogenidfreie Ether-oder THF-Losungen von Vinyllithiumverbindungen 2 -unterhalb von -110°C auch endstandige -sind durch Umsetzung von Vinylbromiden 1 mit 2 Molaquivv. tert-Butyllithium nach Gleichung (1) leicht zuganglich. Die Grenzen der Methode werden diskutiert. Iodierungen, Silylierungen, Sulfenylierungen und Oxygenierungen zu 4, 5, 6 bzw. 8 werden beschrieben (Tab. 1). Die Bedeutung dieser Reaktionen fur die Herstellung von Carbonylverbindungen wird mit der alternativer Verfahren verglichen. Beispiele fur die stereoselektive Synthese von Allylalkoholen 10, a,P-ungesattigten Carbonylverbindungen 11 und Olefinen 12 durch Carbonyladdition und Acylierung (Tab. 2) bzw. Alkylierung von 2 werden angegeben. Bei der Methylierung der Cycloalkenyllithiumverbindungen 2j -n mit Methyliodid ist es wichtig, dal3 man T H F als Losungsmittel verwendet und uberschussiges Alkylierungsmittel vermeidet, da sonst neben oder statt der gewunschten C -C-Verknupfungsprodukte 13 Vinyliodide 4 entstehen (Tabellen 3 und 4). Br/Li-Exchange in Vinyl Bromides with 2 Molequivalents of tert-Butyllithium. Reactions of Vinyllithium Compounds with Hetero and Carbon Electrophiles'.2)Haloalkane-free solutions of vinyllithium compounds 2 -terminal ones at temperatures below -110°C -in T H F or ether are generated from vinyl bromides 1 with two motequivalents of tert-butyllithium [eq. (l)]. The scope and limitations of the method are discussed. Iodinations, silylations, sulfenylations, and oxygenations leading to 4, 5, 6, and 8, respectively, are described (table 1). The usefulness of these reactions in the synthesis of carbonyl compounds is compared with that of alternative recent methods. Examples of the stereoselective preparation of allylic alcohols 10, a,P-unsaturated carbonyl compounds 11 and olefins 12 by addition of 2 to aldehydes and ketones and acylation (table 2) or alkylation are given. In the alkylations ofcyclic representatives 2j-n with iodomethane, it was noticed that it is important to work in T H F solvent and to avoid excess halide. Otherwise (table 3 and 4) vinyl iodides 4 can be the main products instead of the desired methylated compounds 13.

Synthesis and Reactivity Toward Nucleophilic Amino Acids of 2,5-[13C]-Dimethyl-p-benzoquinonediimine

“…To avoid the deprotonation of the tert-butoxy carbamate protected amino groups by the resulting ortho-lithiate intermediate, compound 4 was previously treated with 2 equiv of methyllithium (23). The the bis-ortho-lithiate intermediate was obtained quickly, probably favored by the reaction of the excess tert-butyllithium with the tert-butylbromide byproduct, forming inert lithium bromide and shifting, in this manner, the equilibrium to the product side (24). The bis-ortho-lithiate intermediate was in the end quenched by 13 C-methyl iodide to give 5 with a yield of 73%.…”

Synthesis of Functionalized Indole- and Benzo-Fused Heterocyclic Derivatives through Anionic Benzyne Cyclization

“…For the formation of indoles 2 and 3 we assumed that amines 1 first reacted with tBuLi at À 110 8C to give N-(2-lithioallyl)amines 4, through halogen ± metal exchange; [23] this was confirmed by deuteration and isolation of the deuteriated amine 5 a (Scheme 2). Intermediate 4, which is stable for several hours at À 110 8C, probably undergoes proton-abstraction ortho to the fluorine atom by the additional equivalents of tBuLi when the temperature is raised to À 40 8C giving the intermediate 6.…”

Modular Asymmetric Synthesis of Functionalized Azaspirocycles Based on the Sulfoximine Auxiliary

“…At first the bromide has to be treated with 2 equivalents of t-butyllithium to furnish via lithium-bromine exchange the corresponding organolithium compound, which can then be transformed into the GILLMAN cuprate using 0.5 equivalent of copper(I). 45,60,61,62 Iodides are even better substrates for the conversion to the corresponding cuprate because of their better capacity to undergo lithium-halogen exchange.…”