Piancatelli–Margarita oxidation is a reaction where primary and secondary alcohols are converted to aldehydes and ketones, respectively. It utilizes TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl), a stable aminoxy radical, as the catalyst and BAIB (bis(acetoxy)iodobenzene), a hypervalent iodine compound, as the stoichiometric oxidant. The reaction proceeds at room temperature, without the need for strong acids, bases, or anhydrous conditions. Mild reaction conditions allow for the chemoselective oxidation of complex and sensitive substrates and the selective oxidation of primary alcohols in the presence of secondary alcohols. The reaction conditions can be controlled to favor the oxidation of primary alcohols to aldehydes or promote the overoxidation of aldehydes to carboxylic acids. This review highlights some recent applications (2020–2025), especially in total synthesis, with special emphasis on large-scale reactions. This review aims to honor the memory of Prof. Piancatelli (1936–2025) and Dr. Roberto Margarita (1970–2016), who developed this reaction.

Solketal, the chiral acetonide of glycerol, has been employed as the starting material in the design of a novel punctually chiral phosphate sodium salt for catalytic applications in organic and asymmetric synthesis. The racemate and the two enantiomers of the substrate are economic and commercially available, straightforwardly prepared in high yields from naturally occurring feedstocks. Therefore, remarkably, both enantiomers of the final catalyst can be synthesized by simple procedures in high yield and in compliance with several principles of green chemistry. To further demonstrate the usefulness of the novel catalyst, its application in a solventless protocol for cyanohydrin synthesis from a series of aldehydes has been presented.

Benzazetidines are a class of N-heterocycles potentially very interesting for a variety of purposes, including biological applications and drug design. In the past, their high ring strain has hampered the development of trustable, general, and efficient synthetic methodologies for their preparation. In this review article, the aim is to disclose all the literature contributions about the synthesis of these compounds and the study of their reactivity, from the early examples to the most recent synthetic approaches. Recently, there has been a growth of interest for this heterocycle, driven by the publication of novel synthetic methodologies based on palladium-catalyzed intramolecular C-H amination and organocatalyzed ring-closure of 2-(N-Boc-anilino)-alpha-ketoesters/amides.

Benzazetidines are highly strained and inherently unstable heterocycles. There are only few methodologies for assembling these compounds. Here, a protocol is presented to trap an elusive cyclic, four-membered hemiaminal structure. This method affords several benzazetidines in moderate to good yields (up to 81%), and it uses inexpensive materials and does not require catalysts based on transition metals. The high ring strain energy of these benzazetidine systems was estimated by density functional theory calculations to be about 32 kcal mol-1. This synthesis can be applied also on gram scale with reaction yield essentially unchanged.

A common problem encountered in enantioselective organocatalysis is the aggregation of the catalyst, which can result in a relevant decrease of the efficiency and selectivity of the process. In the asymmetric synthesis of chiral benzofuranones, recently reported by us, we noted a remarkable increase of the reaction yield upon the addition of one of the reagents in a portionwise manner rather than in a single addition. We investigated this phenomenon by several experimental techniques such as 1D and 2D NMR experiments, UV-Vis spectroscopy, circular dichroism and dynamic light scattering. In addition, we studied the kinetic profile of this reaction using a simple numerical model and carried out in silico investigations. All these different approaches point to the conclusion that in the reaction medium a supramolecular polymerization/aggregation phenomenon, based on weak interactions, occurs and such a process is promoted by a quinone, which is one of the reagents of the benzofuranone synthesis. The portionwise mode of addition is a known strategy which can improve the performance of many synthetic procedures and this strategy is commonly adopted on account of empirical experience. However, our results provide an explanation, based on a chemical kinetic model, of the reason why the portionwise addition affects in such a dramatic way the yield of the benzofuranone synthesis catalyzed by Cinchona alkaloids.

The organocatalyzed addition of several malonates to 1,4-benzoquinones affords benzofuranones bearing a quaternary stereocenter with good enantioselectivity. This reaction is an intramolecular desymmetrization since it proceeds through the formation of an arylated achiral malonate that cyclizes to give the reaction product. The addition rate of the quinone dramatically affects the reaction yield which was originally low. The yield was considerably increased, in some cases, from less than 20 % to over 95 %, by adding the quinone in portions rather than at once, keeping similar enantioselectivity. A possible rationalization for the preferential formation of the indicated enantiomer has been investigated by DFT calculations.

A rapid synthesis of enantioenriched 2,3,4-trisubstituted tetrahydropyrans in good yields and stereoselectivities is reported. The first step is a domino organocatalytic reaction between ambident electrophilic and 1,4-bis-nucleophilic 1,2-ketoamides and 1,3-bis-electrophilic enals, leading to aza-oxa-bicyclo[3.2.1]octane. Then, the TiCl4/Et3SiH system ensures a chemoselective cleavage of the C−N bond and affords the desired trisubstituted tetrahydropyran in good yield and with conservation of the precursors optical purity. This final synthetic operation includes two consecutive oxocarbenium ion formation and reductions.

Simple quinine as an organocatalyst mediates the addition of various naphthols to halogenated quinones to afford non-C2 -symmetrical, axially chiral biaryl products, which are promising compounds as chiral ligands and organocatalysts. The rotational barrier required to have two distinct atropisomers has been evaluated in the products generated from the addition of naphthols to various quinones by means of DFT calculations and HPLC. The use of halogenated quinones as reagents was necessary to have configurationally stable enantiomeric products which can be obtained in good yield and stereoselectivity. These compounds have also been prepared in gram quantities and recrystallized to near enantiopurity.

Cinchona alkaloid derivatives featuring a guanidinium group in diverse positions efficiently catalyze the cleavage of the RNA model compound 2-hydroxypropyl p-nitrophenyl phosphate (HPNP).

The presence of a "invisible mending" has been proposed as an explanation for medieval radiocarbon dating measurements made on the Shroud of Turin. Here we show that the chemical analysis which was to support this theory is not consistent, and no scientific data confirm these speculations. Specifically, the samples of the Shroud image fibers underwent a different cleaning procedure with regards to those allegedly belonging to the medieval mending. There is no reliable indication of the supposedly diagnostic compounds (e.g. gum Arabic, pentoses). The only detectable difference between the samples is the presence of a compound with an aliphatic chain which cannot be identified more in detail, e.g. as sebum. (C) 2016 Elsevier B.V. All rights reserved.

This is an editorial regarding a paper published on Thermochimica Acta (R.N. Rogers, Thermochimca Acta, 425 (2005) 189-194). A close-up analysis of the pyrolysis-mass spectra reported in the original paper reveals that the differences found between the samples coming from different parts of the Shroud are just due to the presence of a contaminant with a long aliphatic chain. Except for the presence of the contaminant, the two pyrolysis-mass spectra look alike rather than different. Therefore, the pseudoscientific theory stating that the C14 sample might come from a "medieval invisible mending" remains unsupported by evidences. (C) 2015 Elsevier B.V. All rights reserved.

A catalyst's catalyst Investigation of the leucinol-catalyzed aldol reaction of isatin with acetone revealed an intriguing and unusual mechanistic concept: apart from being a substrate, isatin also acts as a dichotomous co-catalyst that accelerates the turnover-limiting step: the formation of the reactive syn-enamine. This concept resembles that of a wind turbine: only when the wind is blowing, that is, when the starting material is present, rotation commences and gives rise to the desired product. For more details, see the Full Paper by M. A. Kabeshov, A. V. Malkov, P. Kočovský, and co-workers on page 12026 ff.

The aldol addition of hydroxy esters to propargyl aldehydes provides 1,2‐diols with moderate to high yields and low to moderate diastereoselectivities.

Comprehensive mechanistic studies on the enantioselective aldol reaction between isatin (1 a) and acetone, catalyzed by L-leucinol (3 a), unraveled that isatin, apart from being a substrate, also plays an active catalytic role. Conversion of the intermediate oxazolidine 4 into the reactive syn-enamine 6, catalyzed by isatin, was identified as the rate-determining step by both the calculations (ΔG(≠) =26.1 kcal mol(-1) for the analogous L-alaninol, 3 b) and the kinetic isotope effect (kH /kD =2.7 observed for the reaction using [D6 ]acetone). The subsequent reaction of the syn-enamine 6 with isatin produces (S)-2 a (calculated ΔG(≠) =11.6 kcal mol(-1) ). The calculations suggest that the overall stereochemistry is controlled by two key events: 1) the isatin-catalyzed formation of the syn-enamine 6, which is thermodynamically favored over its anti-rotamer 7 by 2.3 kcal mol(-1) ; and 2) the high preference of the syn-enamine 6 to produce (S)-2 a on reaction with isatin (1 a) rather than its enantiomer (ΔΔG(≠) =2.6 kcal mol(-1) ).

In this Focus Review, a selection of organocatalyzed reactions in which alkynes have been used are presented. Catalysis by tertiary and secondary amines, by phase-transfer catalysis, by phosphines and carbenes, as well as bifunctional and multiple catalysis are discussed. Alkynes are versatile intermediates which can open novel synthetic opportunities as their reactivity is enhanced with respect to the corresponding alkenes and further elaboration to develop domino processes is possible.

1,2-Diols 3 have been synthesized by the aldol addition of hydroxy esters 1 to propargyl aldehydes 2 in dichloromethane. These 1,2-diols undergo a base-initiated rearrangement under mild conditions in methanol with an unusual 1,2-alkyl shift to afford interesting alpha,beta-unsaturated gamma-butyrolactones 4. A possible mechanism is postulated on the basis of experimental evidence and the results of DFT calculations.

The organocatalytic kinetic resolution of 4-substituted oxazinones has been optimised (selectivity factor S up to 98, chiral oxazinone ee values up to 99.6 % (1 a-g) and product ee values up to 90 % (3 a-g)) in a rational way by applying the Design of Experiments (DoE) approach.