Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review

Abstract

Phenanthrenes and their aza-analogues have important applications in materials science and in medicine. Aim of this review is to collect recent reports describing their synthesis, which make use of radical cyclizations promoted by a visible light-triggered photocatalytic process.

Keywords: phenanthrenes; phenanthridines; photocatalysis; radicals; visible light.

Figure 1

Bioactive phenanthridine and phenanthridinium derivatives.

Scheme 1

Synthesis of phenanthrenes by a photo-Pschorr reaction.

Scheme 2

Synthesis of phenanthrenes by a benzannulation reaction.

Scheme 3

Photocatalytic cyclization of α-bromochalcones for the synthesis of phenanthrenes.

Figure 2

Carbon-centered and nitrogen-centered radicals used for the synthesis of phenanthridines.

Scheme 4

General scheme describing the synthesis of phenanthridines from isocyanides via imidoyl radicals.

Scheme 5

Synthesis of substituted phenanthridines involving the intermediacy of electrophilic radicals.

Scheme 6

Photocatalyzed synthesis of 6-β-ketoalkyl phenanthridines.

Scheme 7

Synthesis of 6-substituted phenanthridines through the addition of trifluoromethyl (path a), phenyl (path b), and phosphonyl (path c) radicals to isonitriles.

Scheme 8

Synthesis of 6-(trifluoromethyl)-7,8-dihydrobenzo[k]phenanthridine.

Scheme 9

Phenanthridine syntheses by using photogenerated radicals formed through a C–H bond homolytic cleavage in THF (path a) and N,N-dimethylacetamide (path b).

Scheme 10

Trifluoroacetimidoyl chlorides as starting substrates for the synthesis of 6-(trifluoromethyl)phenanthridines 10.3a–e.

Scheme 11

Synthesis of phenanthridines via aryl–aryl-bond formation.

Scheme 12

Oxidative conversion of N-biarylglycine esters to phenanthridine-6-carboxylates.

Scheme 13

Photocatalytic synthesis of benzo[f]quinolines from 2-heteroaryl-substituted anilines and heteroarylalkynes.

Scheme 14

Synthesis of noravicine (14.2a) and nornitidine (14.2b) alkaloids.

Scheme 15

Gram-scale synthesis of the alkaloid trisphaeridine (15.3).

Scheme 16

Synthesis of phenanthridines starting from vinyl azides.

Scheme 17

Synthesis of pyrido[4,3,2-gh]phenanthridines 17.5a–d through the radical trifluoromethylthiolation of N-(o-cyanobiaryl)acrylamides 17.1a–d.

Scheme 18

The direct oxidative C–H amidation involving amidyl radicals for the synthesis of phenanthridones.