We report ar ange of highly regioselective openings of [1.1.1]propellane with various allylic zinc halides,aswell as zinc enolates of ketones,e sters and nitriles.T he resulting zincated bicyclopentanes (BCPs) were trapped with arange of electrophiles including acyl chlorides,sulfonothioates,hydroxylamino benzoates,t osyl cyanide as well as aryl and allyl halides,generating highly functionalized BCP-derivatives.The unusually high regioselectivity of these reactions has been rationalized using DFT calculations.Abioisostere of the synthetic opioid pethidine was prepared in 95 %y ield in one step using this method.
We report the metalation of the 1,3,4-oxadiazole
and 1,2,4-triazole scaffolds via regioselective zincation or magnesiation
using the TMP bases (TMP = 2,2,6,6-tetramethylpiperidyl) TMP2Zn·2LiCl, TMP2Zn·2MgCl2·2LiCl,
TMPMgCl·LiCl, and TMPZnCl·LiCl under mild conditions in
THF. Subsequent trapping with various electrophiles including hydroxylamino
benzoates gives access to functionalized heterocycles while tolerating
many functional groups.
The selectivea ddition of organomagnesium reagents to 2,4,6-trichlorophenyl isocyanide leading to magnesiated aldimines is reported. These aldimines reactw ith Weinreb amides, ketones, or carbonates to provide the corresponding carbonyl derivativesa fter acidic cleavage. This allows for an efficient synthesis of 1,2-dicarbonyl compoundsa nd a-hydroxy ketones.
Secondary alkyllithium reagents were prepared stereoselectively via an iodo–lithium exchange by using tert-butyllithium. The resulting secondary alkyllithiums were converted directly into the corresponding alkylcopper reagents by transmetalation with copper(I) bromide–triethyl phosphite [CuBr·P(OEt)3] with retention of configuration and without significant loss of stereoselectivity. The resulting alkylcopper reagents were used for carbocupration or acylation reactions. In addition, a new intramolecular carbolithiation of secondary alkyllithium reagents possessing a remote alkyne moiety was also investigated, allowing the stereoselective production of alkylidenecylobutane derivatives with very high stereocontrol.
Polyfunctional organometallics of magnesium and zinc are readily prepared from organic halides via a direct metal insertion in the presence of LiCl or a Br/Mg-exchange using iPrMgCl·LiCl (turbo-Grignard) or related...
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