Palladium‐Catalyzed Synthesis of 6 H ‐Dibenzo[ c,h ]chromenes and 5,6‐Dihydrobenzo[ c ]phenanthridines: Application to the Synthesis of Dibenzo[ c,h ]chromene‐6‐ones, Benzo[ c ]phenanthridines, and Arnottin I

A solvent controlled regioselective synthesis of 2- and 4-substituted α-carbolines under palladium catalysis

A facile method for the chemodivergent synthesis of α-carbolines 1via palladium catalyzed [3+3] annulations of tosyliminoindolines 6 with α, β-unsaturated aldehydes 7 is described. Mechanistically, this cascade reaction proceeds through either a carba-Michael (in DMF) or aza-Michael (in NMA) pathway followed by intramolecular cyclization of the intermediate. A preliminary photo-physical study on selected products is also reported.

Ligand-controlled regiodivergent Ni-catalyzed trans-hydroboration/carboboration of internal alkynes with B2pin2

Unprecedented regioselective trans-hydroboration and carboboration of unbiased electronically internal alkynes were realized via a nickel catalysis system with the aid of the directing group strategy. Furthermore, the excellent α- and β-regioselectivity could be accurately switched by the nitrogen ligand (terpy) and phosphine ligand (Xantphos). Mechanistic studies provided an insight into the rational reaction process, that underwent the cis-to-trans isomerization of alkenyl nickel species. This transformation not only expands the scope of transition-metal-catalyzed boration of internal alkynes but also, more particularly, portrays the vast prospects of the directing group strategy in the selective functionalization of unactivated alkynes.

Enaminone-directed ruthenium(II)-catalyzed C-H activation and annulation of arenes with diazonaphthoquinones for polycyclic benzocoumarins

The weakly coordinating enaminone functionality has been leveraged for a C-H bond activation strategy under ruthenium catalysis and employed in the regioselective annulative coupling of arenes with diazonaphthoquinones, offering polycyclic benzocoumarins in very high yields. The enaminone motif plays a dual role and the protocol operates through a Ru(II)/Ru(IV) catalytic pathway which is amenable to the diversification of various pharmacophore-coupled substrates.

One-Pot Synthesis of Benzo[c]phenanthridine Alkaloids from 7-Azabenzonorbornadienes and Aryl Nitrones

An efficient synthesis of benzo[c]phenanthridine alkaloids via a synergistic combination of C-C bond formation and a cycloaromatization reaction is described. Aryl nitrones react with 7-azabenzonorbornadienes in the presence of a Rh(III) catalyst, providing pharmaceutically useful benzo[c]phenanthridine derivatives in good to moderate yields. Using this methodology, highly useful alkaloids such as norfagaronine, norchelerythrine, decarine, norsanguinarine, and nornitidine were prepared in a single step.

A Review on Synthetic Approaches of Phenanthridine

Abstract:

The phenanthridine family is widely found in medicinal chemistry and material science because of the biological activity and its presence in a variety of significant natural products and synthetic dye stuffs. The phenanthridine has many clinical applications, for e.g., being used as an anticancer agent, possessing antibacterial, antiprotozoal, pharmaceutical, and optoelectronic properties. Many methods have been reported for the synthesis of phenanthridine and phenanthridine alkaloids, such as Pd catalyzed C-C bond formation, a reaction involving C-H activation, radical, microwave-assisted, transition metal-catalyzed, one-pot cascade, benzyne mediated, photochemical, hypervalent iodine promoted methods, etc. Here, we have summarized the literature data from 2014 to the present concerning novel or improved synthetic approaches.

"Golden" Cascade Cyclization to Benzo[c]-Phenanthridines

Herein, we describe a gold-catalyzed cascade cyclization of Boc-protected benzylamines bearing two tethered alkyne moieties in a domino reaction initiated by a 6-endo-dig cyclization. The reaction was screened intensively, and the scope was explored, resulting in nine new Boc-protected dihydrobenzo[c]phenanthridines with yields of up to 98 %; even a π-extension and two bidirectional approaches were successful. Furthermore, thermal cleavage of the Boc group and subsequent oxidation gave substituted benzo[c]phenanthridines in up to quantitative yields. Two bidirectional approaches under the optimized conditions were successful, and the resulting π-extended molecules were tested as organic semiconductors in organic thin-film transistors.

Iodo- and Chalcogenoannulation of Morita-Baylis-Hillman Alcohols of Propiolaldehydes: Entry to Functionalized 2-Pyrones

An efficient intramolecular annulation of Morita-Baylis-Hillman (MBH) alcohols of propiolaldehydes is developed in the presence of ICl or PhSeSePh/PhSSPh-CuCl₂. This cyclization offers access to a wide variety of iodinated or chalcogenated 3-(chloromethyl)-2-pyrones in good yields. The chloromethyl group of the obtained 2-pyrones has been easily converted to introduce other handy functionalities, which allowed for further transformations to synthesize diverse 2-pyrone containing molecules.

Palladium-Catalyzed Synthesis of 1-Vinyltetrahydro-β-carbolines and Aza-spiroindolenines: Access to the Syntheses of 1-Vinyl-β-carbolines and Eudistomins Y1 and Y2

A general synthesis of 1-vinyltetrahydro-β-carbolines (THBCs) has been achieved via palladium(0)-catalyzed cyclocondensation between allenyltryptamines and aryl iodides. Aza-spiroindolenines could also be accessed from the N-unsubstituted indole substrates by simply tweaking the reaction conditions. DDQ-mediated oxidation of THBCs easily afforded β-carbolines, which could be synthetically transformed into 1-aroyl-β-carbolines of pharmacological interest. Formal total syntheses of eudistomins Y1 and Y2 have also been achieved.