Rh(III)-Catalyzed Chemodivergent Annulations between Indoles and Iodonium Carbenes: A Rapid Access to Tricyclic and Tetracyclic N-Heterocylces

Abstract

Herein, we report an acid-controlled highly tunable selectivity of Rh(III)-catalyzed [4 + 2] and [3 + 3] annulations of N-carboxamide indoles with iodonium ylides lead to form synthetically important tricyclic and tetracyclic N-heterocycles. Here, iodonium ylide serves as a carbene precursor. The protocol proceeds under operationally simple conditions and provides novel tricyclic and tetracyclic scaffolds such as 3,4-dihydroindolo[1,2-c]quinazoline-1,6(2H,5H)-dione and 1H-[1,3]oxazino [3,4-a]indol-1one derivatives with a broad range of functional group tolerance and moderate to excellent yields. Furthermore, the protocol synthetic utility was extended for various chemical transformations and was easily scaled up to a large-scale level.

Synthesis of dihydroindazolo[2,3-f]phenanthridin-5(6H)-onesviaRh(iii)-catalyzed C–H activation of 2-aryl indazoles and annulation with iodonium ylides

“…Based on the above experimental results and literature reports, [12][13][14] a plausible reaction mechanism was proposed and is shown in Scheme 5. First, an active catalyst [RhCp*(SbF 6 ) 2 ] is generated from ligand exchange, and then undergoes direct C-H activation to afford a five-membered intermediate A.…”

“…12,13 The Kanchupalli group achieved selective access to tricyclic or tetracyclic N-heterocycles by changing the solvent of a [Cp*RhCl 2 ] 2 -AgOAc catalyzed reaction of N -carboxamide indoles and iodonium ylides (Scheme 1e). 14 Ji presented the synthesis of indoloquinazolinone derivatives via a [Cp*RhCl 2 ] 2 -AgOAc catalyzed reaction of N -carboxamide indole and iodonium reagents (Scheme 1f). 15 The above reactions provide attractive routes to heterocyclic derivatives using iodonium ylides, however, the synthetic potential of iodonium ylides is far from being fully exploited.…”

Recent advances in transition-metal-catalyzed carbene insertion to C–H bonds

“…333 (76) An acid-controlled carbene insertion to the (C(2)-H) bond of indoles of type 308/annulation sequence was investigated to access indolones of type 311 as well as those of type 311 0 from the [3+3] annulation under Rh(III) catalysis by means of iodonium ylides 312 as the carbene source (Scheme 96). 334 In the presence of 3 mol% [Cp*RhCl 2 ] 2 /AgOAc (1 equiv.) in CH 2 Cl 2 at room temperature, the reaction of N-carboxamide indoles 308 gave the target products 311 in up to 92% yields, while addition of acetic acid (1 equiv.)…”

Lewis Acid-Catalyzed [3 + 2]-Cyclization of Iodonium Ylides with Azadienes: Access to Spiro[benzofuran-2,2′-furan]-3-ones

“…These results indicated the practicability of this approach in organic synthesis. However, acyclic iodonium ylides did not work well under the standard reaction conditions, perhaps due to the transformation might be sensitive to the steric hindrance of iodonium ylides …”