Transition metal-catalyzed substitution of alcohols by N-nucleophiles (or N-alkylation of amines and related compounds with alcohols) avoids the use of alkylating agents by means of borrowing hydrogen (BH) activation of the alcohol substrates. Water is produced as the only by-product, which makes the "BH" processes atom-economic and environmentally benign. Diverse types of homogeneous organometallic and heterogeneous transition metal catalysts, and substrates such as N-nucleophiles including amines, amides, sulfonamides and ammonia, and various alcohols, can be used for this purpose, demonstrating the promising potential of "BH" processes to replace the procedures using traditional alkylating agents in pharmaceutical and chemical industries. Borrowing hydrogen activation of alcohols for C-N bond formation has recently been paid more and more attention, and a lot of new and novel procedures and examples have been documented. This critical review summarizes the recent advances in "BH" substitution of alcohols by N-nucleophiles since 2009. "Semi-BH" N-alkylation processes with or without an external hydrogen acceptor are also briefly presented. Suitable discussion of the "BH" strategy provides new principles for establishing green processes to replace the relevant traditional synthetic methods for C-N bond formation.

Five new compounds, pinazaphilones A and B (1, 2), two phenolic compounds (4, 5), and penicidone D (6), together with the known Sch 1385568 (3), (±)-penifupyrone (7), 3-O-methylfunicone (8), 5-methylbenzene-1,3-diol (9), and 2,4-dihydroxy-6-methylbenzoic acid (10) were obtained from the culture of the endophytic fungus Penicillium sp. HN29-3B1, which was isolated from a fresh branch of the mangrove plant Cerbera manghas collected from the South China Sea. Their structures were determined by analysis of 1D and 2D NMR and mass spectroscopic data. Structures of compounds 4 and 7 were further confirmed by a single-crystal X-ray diffraction experiment using Cu Kα radiation. The absolute configurations of compounds 1-3 were assigned by quantum chemical calculations of the electronic circular dichroic spectra. Compounds 2, 3, 5, and 7 inhibited α-glucosidase with IC50 values of 28.0, 16.6, 2.2, and 14.4 μM, respectively, and are thus more potent than the positive control, acarbose.

Vibrational spectroscopy represents an active frontier for the identification and characterization of molecular species in the context of astrochemistry and astrobiology. As new missions will provide more data over broader ranges and at higher resolution, especially in the infrared region, which could be complemented with new spectrometers in the future, support from laboratory experiments and theory is crucial. In particular, computational spectroscopy is playing an increasing role in deepening our understanding of the origin and nature of the observed bands in extreme conditions characterizing the interstellar medium or some planetary atmospheres, not easily reproducible on Earth. In this connection, the best compromise between reliability, feasibility and ease of interpretation is still a matter of concern due to the interplay of several factors in determining the final spectral outcome, with larger molecular systems and non-covalent complexes further exacerbating the dichotomy between accuracy and computational cost. In this context, second-order vibrational perturbation theory (VPT2) together with density functional theory (DFT) has become particularly appealing. The well-known problem of the reliability of exchange-correlation functionals, coupled with the treatment of resonances in VPT2, represents a challenge for the determination of standardized or “black-box” protocols, despite successful examples in the literature. With the aim of getting a clear picture of the achievable accuracy and reliability of DFT-based VPT2 calculations, a multi-step study will be carried out here. Beyond the definition of the functional, the impact of the basis set and the influence of the resonance treatment in VPT2 will be analyzed. For a better understanding of the computational aspects and the results, a short summary of vibrational perturbation theory and the overall treatment of resonances for both energies and intensities will be given. The first part of the benchmark will focus on small molecules, for which very accurate experimental and theoretical data are available, to investigate electronic structure calculation methods. Beyond the reliability of energies, widely used for such systems, the issue of intensities will also be investigated in detail. The best performing electronic structure methods will then be used to treat larger molecular systems, with more complex topologies and resonance patterns.

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