Photocatalyzed Csp3-Csp3 cross-dehydrogenative coupling of N-Boc-tetrahydroisoquinolines with α,β-unsaturated ketones

Photomediated One-Pot Three-Component Approach Enables the Formal Direct N-Acylation/Sulfonylation and α-C-H Functionalization of 1,2,3,4-Tetrahydroisoquinoline

N-Acyl/sulfonyl-α-functionalized 1,2,3,4-tetrahydroisoquinolines (THIQs) are significant structural motifs in organic synthesis and drug discovery. However, the one-pot approach enabling direct difunctionalization of THIQs remains challenging. Herein we report a photomediated one-pot three-component strategy to access N-acyl/sulfonyl-α-functionalized THIQs. This method features the use of oxygen (from air) as the green oxidant, high atom and step economy, and decent structural diversity. The synthetic applicability of the method was further demonstrated via the facile construction of valuable bioactive molecules. Mechanistic studies indicated that oxidation with singlet oxygen and the acceptor-less dehydrogenation were involved in the photoredox process.

Visible light-promoted photocatalyst-free activation of persulfates: a promising strategy for C-H functionalization reactions

The employment of renewable energy resources is highly desirable according to the twelve principles of green chemistry. In this context, visible light promoted organic transformations have gained much attention from synthetic chemists due to the employment of renewable energy. However, the inability of the majority of organic molecules to absorb visible light encouraged the use of photocatalysts in visible light-mediated organic transformations. As a result, different types of photocatalysts like transition-metal containing photoredox catalysts, organophotoredox catalysts, heterogeneous photocatalysts, etc. have emerged over the years. On the other hand, persulphates (K₂S₂O₈, Na₂S₂O₈, and (NH₄)₂S₂O₈) have been widely used as oxidants in various oxidative organic transformations under thermal and photochemical conditions. The initial formation of an active persulfate radical anion from a persulfate anion is the crucial step for these oxidative transformations and the conversions under visible light are generally carried out employing different photocatalysts. Although numerous methodologies have been successfully developed employing these photocatalysts, the development of new processes under photocatalyst-free conditions are more preferable from the viewpoint of sustainable development. Persulphates could be very useful for various organic transformations through C-H functionalizations under photocatalyst-free visible light irradiation. In this review, we will exemplify the efficiency of persulphates in various oxidative organic transformations under visible light irradiation without the employment of any photocatalysts. The utilities and mechanistic pathways of the methodologies will also be highlighted.

The Photocatalyst-Free Cross-Dehydrogenative Coupling Reaction Enabled by Visible-Light Direct Excitation of Substrate

A new photocatalyst-free strategy for the cross-dehydrogenative C-C and C-P coupling reaction has been described. This protocol provides a concise method to synthesize various 1-substituted tetrahydroisoquinoline (THIQ) derivatives enabled by visible-light direct excitation of substrates without using any photocatalyst. Moreover, a wide substrate scope demonstrated good synthetic versatility and practicality.