A new synthetic route leading to 2-methyleneaziridines has been developed by base-induced 1,2-dehydrobromination of 2-(bromomethyl)aziridines. Several base-solvent pairs did not lead to 2-methyleneaziridines. Only potassium tert-butoxide in tetrahydrofuran afforded 2-methyleneaziridines in competition with the substitution products, i.e. 2-(tert-butoxymethyl)aziridines. Various attempted functionalizations of 1-(arylmethyl)-2-methyleneaziridines failed, but they proved to be excellent substrates for the synthesis of beta-lactam derivatives, i.e. 1-(arylmethyl)-2-iminoazetidines, through ring expansion with azides carrying electron-withdrawing substituents.
Selective substitution of secondary amines in the presence of primary amines is performed by using the reaction solvent, methyl isobutylketone (MIBK), as a temporary protecting group for the primary amine. After acylation or alkylation of the secondary amine, the resulting imine intermediate is smoothly hydrolysed, leading to the free primary amine in high yield and purity. This procedure represents a cheap and scalable alternative to multistep methods requiring several protections and deprotections.
N-(Alkylidene or 1-arylmethylidene)-2-propenylamines were regiospecifically functionalized to novel N-(alkylidene or 1-arylmethylidene)-3-bromo-2-fluoropropylamines, which were proven to be excellent precursors for 3-fluoroazetidines.
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