Nitrogen‐containing molecules are the key structural constituent of many pharmaceutical compounds that play a pivotal role in drug development. Owing to their multifaceted medicinal importance, several synthetic approaches have been delineated in the recent past for their construction. Over the past few decades the augmented use of donor–acceptor cyclopropanes (DACs) as three‐carbon synthetic equivalents, despite their ring strain, for the construction of innumerable hetero‐ and carbocycles of pharmaceutical importance has raised the interest of synthetic chemists to this topic. Owing to their zwitterionic nature due to the vicinal disposition of donor and acceptor groups, they have been frequently used in ring‐opening reactions, cycloadditions, and rearrangements. This review is mainly focused on assorted reactions of DACs with various nitrogen‐containing dipolarophiles like imines, azides, cyanates, isothiocyanates, nitrosocarbonyls, hydrazines, diaziridines, triazinanes, diazenes, etc. towards the synthesis of nitrogen‐containing molecules of pharmaceutical and industrial importance. This review is in continuation of our review published in the Israel Journal of Chemistry in April 2016, and includes the literature from April 2016 to May 2019.
A highly
efficient protocol to access carbazole from donor–acceptor
cyclopropane and indonyl alcohol via [3+3] annulation in the presence
of a Lewis acid has been demonstrated. This method facilitates the
post functionalization of the substituted carbazole into a fully conjugated
π-system exhibiting intense emission bands in the visible range
of the spectrum and also offers a convenient route toward the synthesis
of pityriazole derivatives.
Substituent and Lewis acid promoted generation of functionalized enolates from epoxides is developed. Divergent attack of the enolate on donor‐acceptor cyclopropanes, i.e. C‐attack or O‐attack depending upon substituents present in both reacting partners, produced different products. C‐attack gave functionalized cyclopentane derivatives, whereas O‐attack furnished tetrahydrofuran derivatives through [3+2]‐annulation reactions. Moreover, to increase the utility of our method, synthesized diastereomeric cyclopentane derivatives were converted into synthetically useful cyclopentene and cyclopentanone analogs.
Copper-catalyzed
[5+3] cycloaddition of N-aromatic zwitterions
and enol diazoacetates produced enantio-enriched diazocine derivatives.
A sterically encumbered BOX ligand and NaBArF additive played significant
roles in driving the overall catalytic process via the unfavorable
dearomatization to construct the desired eight-membered heterocyclic
compounds. The induced stereoselectivity was preserved after further
modifications of the skeleton, which demonstrates the potential applications
of the developed asymmetric catalysis.
Lewis acid catalyzed [3 + 3] annulation of N-tosylaziridinedicarboxylates and oxiranes with in situ generated mercaptoaldehyde for the synthesis of functionalized thiazine and oxathiane derivatives has been developed. Additionally, this method facilitates the derivatization of thiazines by detosylation and Krapcho monodecarboxylation.
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