Diarylethenes provide light-controllable generation of reactive species (such as Brønsted and Lewis acids) to trigger various processes with high spatial and temporal resolution. At the same time, the opposite light-induced deactivation has not been developed yet. A promising way to achieve such controllable "removal" of acidity is the introduction of a carboxyl group at one of the reactive carbons. To address this issue, we studied the irreversible photoreactions of the corresponding substrates in the diphenylethene and phenyloxazolylethene series. Indeed, exposure to UV light led to the irreversible elimination of the carboxyl group during transformation to phenanthrene or naphthalene products. The efficiency of this reaction, competing processes, and the reactivity of the related esters and salts are discussed. Our results show that the carboxyl group (or its derivatives) can serve as the leaving group in the photochemical reactions of diarylethenes, thus providing "photoswitching-off" of acidity.

We have developed a multicomponent synthesis of a new family of stable selones, 3-acylarylethenyl-1-alkylimidazole-2-selones, in 28-86% yields by intercepting (MeCN, 70 °C) N-alkyl-N-alkenylimidazolium carbenes, generated in situ from substituted imidazoles and acylarylacetylenes, with elemental selenium. The basic reactivity (E/Z-photoisomerization, reduction, hydrolysis/oxidation, and oximation) of the synthesized imidazole-2-selones has been evaluated.

The chemodivergent base-mediated (KOH, 90 degrees C, 10 min) reaction of aromatic (heteroaromatic) nitriles with acetylene gas to yield 2,4-di(het)aryl pyrimidines (self-organization of two molecules of nitrile and one molecule of acetylene) and 2-(het)aryl pyridines (self-organization of one molecule of nitrile and two molecules of acetylene) has been developed. The chemoselectivity of these cascade processes was found to be unusually strongly controlled by the composition of the solvent. The effect of sulfolane was especially pronounced: When added to DMSO, it enabled the synthesis of pyrimidines exclusively in yields of up to 71%, whereas in DMSO with a small amount of MeOH, only pyridines were formed in yields of up to 36%. Given the fact that acetylene gas is an industrially available feedstock, the synthesis of 2,4-di(het)aryl pyrimidines developed here is becoming technologically feasible.

The oxidative photocyclization of 1,2-diarylethenes to phenanthrenes or their isoelectronic analogues (Mallory reaction) has been tested on a wide range of substrates; however, 1,4-naphthoquinone derivatives have not previously been involved in this reaction. In this work, the photoactivity of various symmetric 2,3-di(het)aryl-substituted naphthoquinones was probed for the first time. It was found that thiophene derivatives are photoactive and demonstrate the formation of Mallory products upon irradiation in an oxygen environment. Photolysis of these naphthoquinones in an inert atmosphere revealed the occurrence of a redox process leading to the formation of naphthalene-1,4-diol paired with the Mallory product.

A convenient synthesis of spiro-fused cyclohexadienones/pyrrolizines from pyrrolyl ynones and p-quinone methides through a base-catalyzed 1,6-conjugate addition/ipso-cyclization tandem reaction is described. The protocols feature good substrate tolerance, mild reaction conditions, and high yields of target products. The problem of reaction stereoselectivity raised during the scope study is easily solved by employing a one-pot, two-step approach that allows directing the reaction sequence to obtain the desired products exclusively with the (Z)-configuration of the enone moiety. A tentative reaction mechanism is proposed with the support of experimental studies.

Semistabilized azaallyl anions, generated from N-benzyl ketimines in the NaOtBu/DMSO superbase medium, undergo conditions-controlled formal [3 + 2] or [4 + 3] cyclization with diaryldiynes. Consequently, selective switchable syntheses of triarylsubstituted α-arylated N-vinyl pyrroles (in up to 64% yield) and tetraarylated 2H-azepines (in up to 75% yield) have been developed. The synthetic value of this strategy has been validated by successful gram-scale syntheses of both products.

A one-pot approach was proposed for the synthesis of functionalized 1-alkenyl-3-methylimidazole-2-thiones (yields up to 30

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) cyclizes with a,b-ynones under catalyst-free conditions (MeCN, 3 h) to give a mixture of isolable diverse fused heterocycles including [3 + 3]- and [4 + 2]-cycloadducts as well as DBU ring expansion products, 14-and 15-membered heterocyclic systems incorporating the pyridinone moiety, in 48-58% total yield. Some of the synthesized cycloadducts exhibit blue-green fluorescence with large Stokes shift.

Light offers a unique means of controlling matter with high precision, yet the development of robust photoresponsive transition-metal complexes remains a challenge. Here we report a self-tuning photochromic system based on a diarylethene-derived bis-NHC-palladium complex. The trans-anti complex (1oo) undergoes efficient stepwise photocyclization as well as unprecedented light-induced trans/cis isomerization at the metal center. Isolation and crystallographic characterization of the cis-anti isomer (2oo) reveal a thermodynamically more stable structure with enhanced photochromic performance and reversible multistate switching. Thermal studies uncover interconversion with additional rotamer, establishing a dynamic equilibrium among several photoactive palladium species. Spectroscopic and computational investigations elucidate the electronic transitions that drive both diarylethene cyclization and Pd─NHC geometric rearrangements. We demonstrate that the catalytic activity in the Suzuki-Miyaura coupling reaction can be reversibly switched by light, with the photocyclized catalyst forms showing negligible catalytic activity, while the open forms achieve high efficiency. This establishes a direct link between photoisomerization and predicted catalytic performance. Pre-catalyst evolution demonstrates that the geometry of the complex controls the balance between nanoparticle-mediated and homogeneous reactivity, delineating a novel strategy for adaptive catalysis.

A stereoselective, base-catalyzed [3 + 2]-cyclization of 2-acylethynylpyrroles with diacetyl (DBU/benzene, room temperature) afforded bipyrrolo[1,2-c]oxazoles or 3-acetylpyrrolo[1,2-c]oxazoles, both integrated with alpha,beta-ethylenic ketones, in 51-76% and 23-74% yields, respectively. Switching between these products was controlled by the concentration of diacetyl. Replacing the catalyst with NaOH triggered an unexpected Patern & ograve;-B & uuml;chi dimerization of diacetyl, followed by a [3 + 2]-cyclization to yield pyrrolo[1,2-c]oxazole-oxetane ensembles (21-29%) alongside the aforementioned pyrrolo- and bipyrrolo[1,2-c]oxazoles.

A transition metal- and catalyst-free cascade assembly of pyrrolyl-pyrrolo[1,2-c]thiazoles from 2-acylethynylpyrroles and sodium sulfide has been developed. The assembly rapidly proceeds under mild conditions (dioxane/H2O, room temperature, 1 h) to furnish target products in up to 88% yield and strictly Z-configuration of alkenone moiety. Regio- and stereoselectivity of the reaction, availability and structural diversity of the substrates, air tolerance, and chromatography free purification are advantages of the synthesis. The synthesized pyrrolyl-pyrrolo[1,2-c]thiazoles contain multiple reactive sites available for further modifications, and, therefore, represent interest for medicinal chemistry and materials science.

An efficient approach to access diversely substituted pyridines via a three-component reaction of industrially available acetylene gas, nitriles, and ketones under basic conditions has been developed. This multimolecular self-organization is triggered by the addition of acetylenic carbanions to the C≡N bond of nitrile followed by the involvement of the ketone molecule to build up the pyridine ring. The broad range of simple substrates, one-pot operation, transition-metal-free conditions, and wide variety of synthesized pyridine-tailored heterocyclic systems make the approach of high practical value alone theoretically significant.

A convenient, catalyst-free protocol for the synthesis of hitherto unknown alkyne-tethered N-acyl pyrazolines from readily available hydrazides and skipped diynones has been developed. The subsequent acid-catalyzed dehydration of the synthesized hydroxy derivatives opened a shortcut toward a representative set of 5-alkynyl-1-acylpyrazoles. The elaborated approaches possess competitive advantages such as complete chemo- and regioselectivity, availability of starting materials and excellent yields (up to quantitative) of target products having rich functionality patterns for further derivatization.

A one-pot highly selective approach to the synthesis of hitherto unknown tetrahydropyrrolo[2',1':3,4]pyrazino[1,2-b]pyrrolo[2',1':3,4]pyrazino[1,2-e][1,2,4,5]tetrazine ensembles from simple and available N-allenylpyrrole-2-carbaldehydes and hydrazines has been developed. The reaction proceeds in a very facile manner and tolerates different substituents in both pyrroles and hydrazines. The novel class of organic compounds, tetrahydrodipyrrolodipyrazinotetrazines, proves to be promising pH-sensitive switchers to deliver N-aminopyrrolopyrazinium salts in acidic media and then again tetrahydrodipyrrolodipyrazinotetrazines in basic media. Both transformations give the products in quantitative yields.

Non-cyclic diarylethenes are a very accessible but underappreciated class of photoswitches in terms of their functional applications. The main reason for this is the preconception that successful performance of these molecules as 6π-photoswitches would be hampered by the side Z/E-isomerization. In our work, on a series of novel 2,3-dioxazolylbut-2-enes, we demonstrate that E-isomers of non-cyclic diarylethenes are rapidly eliminated from the system by a “self-tuning” process and do not interfere with efficient two-state photoswitching. In particular, irradiation of E/Z-isomeric mixtures by UV light with subsequent exposure to visible light provides pure Z-isomers of 2,3-dioxazolylbut-2-enes, which further undergo thermally irreversible switching to the closed-ring isomers. This observation perfectly corroborates with some underestimated results from the literature and should bring non-cyclic diarylethenes back into focus as accessible and efficient photoswitches for functional applications in materials chemistry, catalysis and photopharmacology.

New cationic palladium(II) complexes of the type [Pd(O,O '-hfac)(L)n]BF4 (hfac = hexafluoroacetylacetonate; n = 2: L = MeCN (1), PPh3 (2), PCyPh2 (3), PCy2Ph (4), PCy3 (5), P(i-Pr)3 (6), tris(2-methoxyphenyl)phosphine (7); n = 1: L = dppf (8), dppp (9), dppb (10), 1,5-bis(diphenylphosphino)pentane (11)) have been prepared and fully characterized. For the ligand 1,6-bis(diphenylphosphino)hexane (dpph), a mixture of the mononuclear complex [Pd(O,O '-hfac)(dpph)]BF4 (12a) and the dinuclear species [Pd(O,O '-hfac)(mu-dpph)]2(BF4)2 (12b) was obtained. The structures of 2, 3, and 6 were confirmed by single-crystal X-ray diffraction. Catalytic activity of the complexes was tested in two model reactions: norbornene polymerization and Tsuji-Trost N-allylation of morpholine with allyl alcohol.

A convenient synthesis of spiro-fused cyclohexadienones/pyrrolizines from pyrrolyl ynones and p-quinone methides through a base-catalyzed 1,6-conjugate addition/ipso-cyclization tandem reaction is described. The protocols feature good substrate tolerance, mild reaction conditions, and high yields of target products. The problem of reaction stereoselectivity raised during the scope study is easily solved by employing a one-pot, two-step approach that allows directing the reaction sequence to obtain the desired products exclusively with the (Z)-configuration of the enone moiety. A tentative reaction mechanism is proposed with the support of experimental studies.

Terminal (het)arylacetylenes react (KOBut/DMSO, 60 °C, 1 h) with N-allyl ketimines to afford 2-(het)aryl-4-(het)arylmetyl-5-ethylpyrroles in up to 71% yield as a result of the interaction of acetylenic and azadienic carbanions with C=N and C≡C bonds. This new reaction opens a one-pot access to synthetically and pharmaceutically prospective compounds.

Herein, we disclose that two molecules of (het)arylacetylenes and two molecules of aliphatic nitriles readily undergo organization in the KOBut/DMSO system at 40 °C, forming dihydropyridines bearing imine, acetylenic, (het)aromatic and aliphatic substituents in up to 77% yield. This unprecedented reaction highlights the generality of the recently discovered self-organization of complex molecules where several acetylene units combine with simple nucleophiles, a phenomenon steered by acetylenic carbanions.

Base-catalyzed cycloaddition of 2-acylethynylpyrroles with carbon disulfide (NaOH, DMSO, room temperature) proceeds stereoselectively to provide spirobi[pyrrolo[1,2-c]thiazoles] and pyrrolo[1,2-c]thiazole-3-thiones, both integrated with Z-α,β-ethylenic ketones in 40-81 and 35-86% yields, respectively. The switching between spirobi[pyrrolo[1,2-c]thiazoles] and pyrrolo[1,2-c]thiazole-3-thiones is controlled by the reactant ratio or the substituents in the pyrrole ring. Thus, unique pyrrolothiazole/Z-α,β-ethylenic ketone hybrids as prospective for medicinal chemistry, materials science, and organic synthesis are becoming readily accessible.