A Catalyst and Base Free Approach to Polycyclic Aromatic Compounds via Intramolecular [2+2] and retro‐[2+2] Cycloadditions

Abstract

An efficient one-pot strategy for the preparation of polycyclic aromatic compounds (PACs) has been developed. The catalyst and base free conditions, short reaction time under microwave irradiation, as well as the moderate to high yields of products, make the methodology more convenient and feasible. The mechanism study reveals that a novel cascade of thermal induced intramolecular [2 + 2] cycloaddition of bis-N-tosylhydrazones and retro-[2 + 2] cycloaddition of 1,2-diazetidines was involved in the reaction between biaryl dicarbonyl compounds and p-tolylsulfonylhydrazine.

Emerging Trends in N‐Tosylhydrazone Mediated Transition‐Metal‐Free Reactions

“…Lu et al [96] . describe the one‐pot synthesis of polycyclic aromatic compounds 88 via microwave‐induced [2+2] intramolecular cycloaddition of bis‐ N ‐tosylhydrazone 86 and retro‐[2+2]‐cycloaddition of diazetidine 87 without using base and catalyst conditions.…”

“…Lu et al [96] describe the one-pot synthesis of polycyclic aromatic compounds 88 via microwave-induced [2 + 2] intramolecular cycloaddition of bis-N-tosylhydrazone 86 and retro-[2 + 2]-cycloaddition of diazetidine 87 without using base and catalyst conditions. The reaction proceeded in an oil bath using various solvents like dimethylacetamide (DMA) and dimethylformamide (DMF) to increase the yield however 1,4-dioxane Li et al [97] introduced a carbene transfer metal-free reaction of N -tosylhydrazones 3 using water with alkynes followed by the formation of diazo intermediate 89 and promoted by the low energy blue light to permit systematic XÀ H insertion reactions, cyclopropenizations, and cyclopropanation 91.…”

Synthesis of a novel tetra-phenol π-extended phenazine and its application as an organo-photocatalyst

“…In detail, the synthesis started with a Pd catalysed cross coupling between 2 and 3 resulting in dialdehyde derivative 4 in almost quantitative yield (Scheme 1). Treatment of the latter with p -toluensulfonic hydrazide in n BuOH under microwave (MW) irradiation 25 afforded phenanthrene 5 in a 53% yield. Subsequent treatment of 5 with N -bromosuccinimide (NBS) in CHCl 3 afforded 6 which could be used in the synthesis of phenazine 7 .…”