Synthesis and Photophysical Properties of C₃‐Symmetric Star‐Shaped Molecules Containing Heterocycles: A New Tactics for Multiple Fischer Indolization

Abstract

We report synthesis of several C3‐symmetric molecules containing three indole units with benzene ring as a central core. Triple Fischer indolization has been accomplished under green conditions using low melting mixture of L‐(+)‐tartaric acid (TA) and N,N′‐dimethyl urea (DMU). In addition to Fischer indolization, another three popular reactions such as Friedel–Crafts acylation, Grignard reaction, and Suzuki–Miyaura cross‐coupling have been used as key steps to build C3‐symmetric star‐shaped molecules containing indole, furan, and thiophene moieties. Readily available inexpensive chemicals such as acetone, acetophenone, 4‐bromo acetophenone have been used as starting materials.

Low Melting Mixture of L-(+)-Tartaric Acid and N,N′-Dimethyl Urea: A New Arrival in the Green Organic Synthesis

“…Inspiring form this simple yet powerful procedure and also from the applications of the indole moiety containing molecules, two years later to this report, in 2014, Kotha and his teammates have successfully employed this strategy for the synthesis of C 2 -and C s -symmetric bis-indole Low Melting Mixture of L-(+)-Tartaric Acid and N,N′-Dimethyl Urea: A New Arrival... DOI: http://dx.doi.org/10.5772/intechopen.97392 systems (52, 53, 58, 60-62) from bicyclo-3,7-diones and 1-methyl-1-phenylhydrazine under DMU/TA (7:3) reaction conditions (Figure 5) [29]. Later on, Kotha's team nicely expanded this delightful method for the generation of a variety of carbazole derivatives (32)(33)(34)(35) including pyrano-carbazole (36) and aza-cyclophane based carbazoles (37 and 38) as depicted Figure 4 [30][31][32] in Figure 4. Interestingly, utilizing this tactic, they have also prepared carbazole-based natural products such as tijapinazole D (32) and tijapinazole I (33) in addition to the crown-based indolocarbazole (47).…”

“…Moreover, in the laboratory of Kotha's group, diverse heteropolycyclic compounds (39)(40)(41)(42)(43) in addition to the propellane derivatives (44) have been assembled by using ring-closing metathesis (RCM) and Fischer indolization in a low melting mixture of DMU/TA as crucial steps, (Figure 4) [33][34][35]. Keeping the importance of C 3 -symmetric molecules in medicinal and bioorganic chemistry besides their vital role in material science and technology, the same group has also prepared star-shaped C 3 -symmetric compounds 45 and 46 involving cyclotrimerization and DMU/TA mediated indolization approach (Figure 4) [36]. Furthermore, as can be inspected from the Figure 5, they design and constructed varied cyclophane derivatives (48, 49, 54, 55 and 59) through the involvement of the Grignard reaction, RCM and a low melting mixture mediated indolization sequences in respectable yields because of their applicability in supramolecular chemistry [37][38][39][40][41].…”

Synthetic Approaches to Star‐Shaped Molecules with 1,3,5‐Trisubstituted Aromatic Cores

“…In view of our interest in indole chemistry,w ed eveloped a simple route to indole-based star-shaped molecules by employing Fischer indolization (FI), startingfrom the readily accessible 1,3,5-triacetylbenzene (316;S cheme 103). [74] Thus, the reaction of 1,3,5-triacetylbenzene (316)w ith 1-methyl-1-phenylhydrazine (317)i nt he presence of l-(+ +)-tartaric acid/dimethyl urea (TA/DMU) gave tris-hydrazone derivative 318 (84 %y ield). Compound 318 was heated with ZnCl 2 at reflux in toluene to provide the desired star-shaped molecule (319;7 5% yield).…”

C3-Symmetric Indole-Based Truxenes: Design, Synthesis, and Photophysical Studies

“…On the other hand, indole has been unearthed as a vital heterocyclic scaffold because of its existence in numerous natural products and also the promising applications of indole-based compounds in pharmaceuticals. − Moreover, indole-3-carbinol and 3,3′-diindolylmethanes have been noticed to induce apoptosis in “ cancerous cells ,” whereas a plethora of bis-(indolyl) alkanes have been found in numerous bioactive metabolites of terrestrial/marine origin . Remarkably, to date, several indole-based drugs are present in the world market, and many hundreds are under clinical trials, creating curiosity among the scientific community worldwide to synthesize a diversified indole derivatives.…”