Metal-Catalyzed Domino Synthesis of Benzophenanthridines and 6H-Naphtho[2,3-c]-chromenes

Abstract

A new and efficient synthesis of tetracyclic phenanthridines and benzo[ c]chromenes has been described involving a metal-mediated two-step domino strategy. The first step involved efficient palladium-catalyzed domino carbopalladation/cross coupling, and the second step involved iron-catalyzed domino isomerization/cyclodehydration. The important features of this strategy include high yields, generality, wide substrate scope, and broad functional group tolerance. A plausible mechanism has been proposed to explain the formation of the product.

Transition-Metal-Catalyzed Functionalization of Alkynes with Organoboron Reagents: New Trends, Mechanistic Insights, and Applications

“…The first step consists of a Heck–Suzuki coupling reaction between alkynes containing an aryl halide moiety with o -formylboronic acids, followed by an Fe-catalyzed isomerization/cyclodehydration. This strategy was applied to the synthesis of benzo­[ b ]­carbazole derivatives, dibenzofurans, 3-(inden-1-yl)­indoles, benzo-phenanthridines, and benzo­[ c ]­chromenes (Scheme ).…”

Recent Advances in Transition Metal‐Catalyzed Domino‐Cyclization Strategies for Functionalized Heterocyclic/Carbocyclic Compounds

“…In 2018, Chakraborty [83] et al have described the Pdcatalyzed domino carbopalladation/cross-coupling reaction followed by an iron-catalyzed domino isomerization/cyclodehydration strategy for the synthesis of tetracyclic phenanthridines 216, benzo[j] chromenes and 6H-Naphtho[2,3-c]chromene derivatives (Scheme 44). In this reaction initially dihydroquinoline derivatives 216 have been constructed via domino carbopalladation/Suzuki coupling of 2-formylphenylboronic acid 213 and ortho halo aryloxy derivatives 212 in the presence of 10 mol % of Pd(PPh 3 ) 4 (10 mol %), K 2 CO 3 in toluene and ethanol solvent at 65-80 °C.…”

“…In 2018, Chakraborty [83] et al. have described the Pd‐catalyzed domino carbopalladation/cross‐coupling reaction followed by an iron‐catalyzed domino isomerization/cyclodehydration strategy for the synthesis of tetracyclic phenanthridines 216 , benzo[j] chromenes and 6H‐Naphtho[2,3‐c]chromene derivatives (Scheme 44).…”

Chemoselective and diastereoselective construction of 4-alkylidene-tetrahydroquinoline via a redox-neutral vinylogous cascade [1,7]-hydride transfer/6-endo-trig cyclization strategy

“…1). 2,6 Owing to the enormous benefits of these compounds, not surprisingly, great efforts have been devoted to the development of synthetic methodologies for accessing 4-alkylidene-THQs, for instance, the Heck reaction, 7 relay photocatalytic intramolecular radical cyclization, 3 Pd(0)-catalyzed carbocyclization of 1,7-enynes, 8 Zn-mediated aza-Barbier/C–N coupling, 9 Rh( i )-catalyzed Alder–ene-type cyclo-isomerization of 1,7-enynes, 10 Brønsted acid-catalyzed sequential electrophilic addition/Friedel–Crafts annulation, 11 etc . Despite the above-mentioned elegant progress, most of these classical synthetic methods can only furnish products with a narrow scope of structural diversity, and also suffer from certain limitations such as harsh conditions, employment of transition metal catalysts, tedious preparation of complex starting materials, etc .…”