Solvent Free N-Heterocyclization of Primary Amines to N-Substituted Azacyclopentanes Using Hydrotalcite as Solid Base Catalyst

An ecofriendly catalytic route for selective synthesis of N-substituted azacyclopentanes, nitrogen-containing heterocyclic intermediates for many bioactive compounds, was established by carrying out N-heterocyclization (di N-alkylation) of primary amines with 1,4-dichloro butane (as dialkylating agent) using catalytic amount of hydrotalcite as solid base catalyst. The hydrotalcite was found to be efficient solid base catalyst for di N-alkylation of different primary amines (aniline, benzyl amine, cyclohexyl amine and n-butyl amine) giving 82 to 96% conversion (at optimized reaction condition) of 1,4-dichloro butane and >99% selectivity of respective N-substituted azacyclopentanes within 30 min. under solvent free condition. The reaction parameters significantly influence the conversion of 1,4-dichloro butane to N-substituted azacyclopentanes. The nature of substituent present on amino group affects the reactivity of amine substrates for di N-alkylation reaction with 1,4-dichloro butane. The 1,4-dichloro butane was found to be highly reactive alkylating agent for di N-alkylation of amines as compared to 1,4-dihydroxy butane. The reusability of the catalyst and its chemical stability in the reaction was demonstrated.