An unexpected influence of the nature of stabilizing additives to alkyllithium compounds on an aggregate's reactivity was examined experimentally and theoretically.
Alkyllithium compounds are not generally stable at room temperature, therefore strategies were established to overcome this limitation. We present a systematic approach to obtain a stereochemically enriched benzyllithium compound, starting with the simple addition of a chiral auxiliary and ending by incorporation of the auxiliary in the substrate. Thereby, a very unusual dimer of a lithiated benzylsilane was obtained, which could be split into stereochemically enriched monomers by the addition of Lewis bases. Furthermore, we were able to understand the factors responsible for this stereochemical enrichment by using quantum chemical calculations and clarify the configuration of the lithiated compound and the corresponding trapping product by crystallisation. This enabled us to determine the stereochemical course of the deprotonation and the subsequent metathesis reaction.
Described herein is a selective way to control the reaction of allylic amines with metalorganic bases depending on the amine handle as well as the metalorganic base is used. Depending on the number of coordinating groups within the amine handle either a selective carbometalation or deprotonation reaction can be performed. By changing the alkali metal within the base from lithium to either sodium or potassium, a change of chemoselectivity takes place and the reaction of piperidinoallylamine can be controlled.
The reaction of benzyl lithiums is an important aspect in organic and organometallic synthesis. Reported herein are detailed insights into the reactivity of benzyl lithiums as regulated by intermediate structures. By discussing the carbometalation of allylamines and the reaction of the formed benzyl-lithium compounds with electrophiles, the influence of the metal as well as the solvent on the electronic structure of the intermediate is described. This molecular structure strongly influences the reactivity of these intermediates. By choosing the appropriate reaction conditions, the regioselectivity of reactions with electrophiles can be regulated. With trimethylchlorosilane in n-pentane a selective reaction at the para-position takes place. In contrast, selective reaction at the benzylic position, with trimethylchlorostannane in tetrahydrofuran (THF) as a solvent, is accomplished.
The reaction of benzyl lithiums is an important aspect in organic and organometallic synthesis.R eported herein are detailed insights into the reactivity of benzyl lithiums as regulated by intermediate structures.B yd iscussing the carbometalation of allylamines and the reaction of the formed benzyl-lithium compounds with electrophiles,t he influence of the metal as well as the solvent on the electronic structure of the intermediate is described. This molecular structure strongly influences the reactivity of these intermediates.Bychoosing the appropriate reaction conditions,t he regioselectivity of reactions with electrophiles can be regulated. With trimethylchlorosilane in n-pentane as elective reaction at the para-position takes place.I nc ontrast, selective reaction at the benzylic position, with trimethylchlorostannane in tetrahydrofuran (THF) as asolvent, is accomplished.
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