Tandem aldol condensation-Diels–Alder-aromatization sequence of reactions: a new pathway for the synthesis of 2-tetralone derivatives

Abstract

A series of new polysubstituted derivatives of 2-tetralones possessing two ester 1 groups were synthesized via a tandem aldol condensation-Diels-Alder-aromatization 2 sequence of reactions. All the three steps took place in one pot and in the presence of 3 aminofunctionalized silica coated Fe 3 O 4 nanoparticles as the catalyst. In situ formed dienes 4 reacted with diethyl acetylenedicarboxylate at room temperature and the process was followed 5 by spontaneous aromatization of the cycloadducts to produce high yields of the final tetralone 6products. Further studies suggest that the process goes through an initial aldol condensation-7 cycloaddition sequence followed by oxidation and rearrangement steps. After completion of 8 the reactions, the catalyst could be recycled and reused efficiently in next reactions. 910

A Tandem Aldol Condensation/Diels‐Alder Sequence of Reactions for One‐Pot Synthesis of a New Series of Polysubstituted‐Decalines

“…The endo configuration of the products was concluded from the coupling constants of the CH−Ar and CH−CN single protons with their adjacent CH 2 groups. Such assignment for the cycloaddition reactions of styrylcyclohexyl dienes with other dienophiles is reported before in the literature [25–28] . To further support the assignment, we performed molecular mechanics calculations to verify the endo configuration.…”

“…The new products ( 4 a – j ) were identified based on their full spectroscopic analyses. Other products were known and their identities were verified by comparing with those of authentic samples [25,28] …”

“…, [13] leading to efficient synthesis of pharmaceuticals, [14] natural products, [15] and other molecules of choice. [16] Illustrative multicomponent syntheses involving a DA reaction as the key step include a tandem sequential double DA/ Nazarov reaction in an unsymmetrically substituted diynone to yield a tricyclic scaffolds (such as taiwaniaquinol D), [17] the synthesis of chromenoquinolones via an imine formation/aza-DA/aromatization tandem process, [18] a sequence of DA and intramolecular [3 + 2] cycloadditions of dienylcyclopropane 1,1diesters for rapid construction of fused carbocyclic structures (such as brussonol), [19] a domino Knoevenagel-hetero-DA reaction to access various chromenones, [20] a twelve-step synthetic rout, having the DA reaction as the key step, to the structural core of aflavinines, [21] synthesis of ring-fused 2-cyclopentenone moieties, found in the skeleton of many natural and bioactive compounds like helenalin, via a gold-catalyzed cycloisomerization/hetero-DA/ring-opening sequence of tandem reactions of enynyl acetates, [22] an organocatalyzed sequence of oxa-Michael/Michael/Michael/aldol condensation reactions followed by an intramolecular DA cycloaddition leading to asymmetric synthesis of functionalized tricycles, [23] asymmetric multicomponent synthesis of bioactive alkaloid-type polycycles through catalytic aza-DA reaction of indoles having oxetane as the directing group, [24] and a tandem aldol condensation-DAaromatization sequence of reactions to access 2-tetralones (like serteraline) [25] [Figure 1].…”

Intramolecular O‐arylation using nano‐magnetite supportedN‐heterocyclic carbene‐copper complex with wingtip ferrocene

“…Out of various MNPs, nano‐magnetite finds a myriad of applications in the diverse areas including catalysis, bioengineering,[9a–d] drug delivery,[9e] sensing,[9f] environmental treatment, bioseparation, biomaterials and food analysis . The ease of surface functionalization of nano‐magnetite with desired precursors have provided significant versatility to design task specific catalytic systems [14a]. Amongst various precursors, organosiloxane precursors have been extensively employed for coating of silica on nano‐magnetite which serves as a shell and hydroxyl‐rich surface for high degree of organofunctionalization [8p].…”

“…Amongst various precursors, organosiloxane precursors have been extensively employed for coating of silica on nano‐magnetite which serves as a shell and hydroxyl‐rich surface for high degree of organofunctionalization [8p]. Owing to unique physicochemical properties such as good dispersivity, high surface area, low toxicity, superparamagnetic behavior and biocompatibility, nano‐magnetite has emerged as promising support material [14b, c]. Consequently, nano‐magnetite supported catalytic systems have received significant attention in synthetic chemistry .…”