ipso-Annulation represents an attractive approach to synthesize a variety of spirocyclic compounds having a quaternary carbon center. Furthermore, these compounds also serve as a handy synthon for the construction of various complex molecules. This review presents various useful approaches for the intramolecular ipso-cyclization to afford a wide range of spirocyclohexadienones. In addition, the utility of spirocyclic compounds towards the synthesis of complex molecules is also included.

A novel methodology for the synthesis of 5-selenyl/sulfenyl nicotinates involving copper-catalyzed organochalcogenyl aza-annulation of enynyl azide with diorganyl-dichalcogenides has been described. This method offers difunctionalization of alkynes via regioselective intramolecular chalcogenoamination in one pot to provide substituted 5-chalcogenyl nicotinates in good to excellent yields. The resulting nicotinates provide access to their oxides, sulfones, and acid derivatives.

An unprecedented copper-catalyzed aminative aza-annulation of enynyl azide using commercially available N-fluorobenzenesulfonimide (NFSI) as an amination reagent is described. The reaction proceeds via regioselective inter-/intramolecular diamination, incorporating one nitrogen from the NFSI and the other from the azide, to provide amino-substituted nicotinate derivatives in a single step with moderate to high yield. This method represents an efficient way to access diverse aminonicotinates through direct C-N bond-coupling processes.

Pt is the best cocatalyst for hydrogen production. It is also well-known that the surface atomic layer is critical for catalysis. To minimize the Pt content as cocatalyst, herein we report on half-a-monolayer of Pt (0.5θ Pt ) decorated on earthabundant Ni−Cu cocatalyst, which is integrated with a quasiartificial leaf (QuAL) device (TiO 2 /ZnS/CdS) and demonstrated for efficient solar hydrogen production. For the QuAL, TiO 2 is sensitized with ZnS and CdS quantum dots by the SILAR method. The 0.5θ Pt -decorated Ni−Cu shows an onset potential of 0.05 V vs reversible hydrogen electrode for the hydrogen evolution reaction, which is almost similar to that of commercial Pt/C. Photoactivity of the present QuAL device with either bulk Pt or 0.5θ Pt -coated Ni−Cu cocatalyst is, surprisingly, equal. Our findings underscore that a fraction of a monolayer of Pt can enhance the activity of the cocatalyst, and it is worth exploring further for the high activity associated with atomic Pt and other noble metals.

The emerging metal-free carbon nitride (C3N4) offers prominent possibilities for realizing the highly effective hydrogen evolution reaction (HER). However, its poor surface conductivity and insufficient catalytic sites hinder the HER performance. Herein, a one-dimensional vermicular rope-like graphitic carbon nitride nanostructure is demonstrated that consists of multichannel tubular pores and high nitrogen content, which is fabricated through a cost-effective approach having the final stoichiometry g-C3N4.7 for HER application. The present g-C3N4.7 is unique owing to the presence of abundant channels for the diffusion process, modulated surface chemistry with rich-electroactive sites from N-electron lone pairs, greatly reduced recombination rate of photoexcited exciton pairs, and a high donor concentration (4.26 × 1017 cm3). The catalyst offers a visible-light-driven photocatalytic H2 evolution rate as high as 4910 μ mol h–1 g–1 with an apparent quantum yield of 14.07% at band gap absorption (2.59 eV, 479 nm) under 7.68 mW cm–2 illumination. The number of hydrogen gas molecules produced is 1.307 × 1015 s–1 cm–2, which remained constant for a minimum of 18 h of repeated cycling in the HER without any degradation of the catalyst. In density functional theory calculations, a significant change in the band offset is observed due to N doping into the system in favor of electron catalysis. The theoretical band gap of a monolayer of g-C3N4.7 was enormously reduced because of the presence of additional densities of states from the doped N atom inside the band gap. These impurity or donor bands are formed inside the band gap region, which ultimately enhance the hydrogen ion reduction reaction enormously.

Ordered honeycomb-like mesoporous carbon nitride nanosheets with excess nitrogen (g-C₃N_4.5) were developed, which afford exclusive photocatalytic H₂ evolution from water.

Work function alteration due to any chemical/electronic changes can be measured precisely by NAPUPS and correlated to the activity changes.

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