Katarzyna Urbaniak

1,3-Thiazolidine-dicarboxylates from Thioketones and Thermally Generated Azomethine Ylides

The reaction of 9H-fluorene-9-thione (1) with the cis- and trans-isomers of dimethyl 1-(4-methoxyphenyl)-aziridine-2,3-dicarboxylate (cis- and trans-2, resp.) in xylene at 110° yielded exclusively the spirocyclic cycloadduct with trans- and cis-configurations, respectively (trans- and cis-3, resp.; Scheme 1). Analogously, less- reactive thioketones, e.g., thiobenzophenone (5), and cis-2 reacted stereoselectively to give the corresponding trans-1,3-thiazolidine-2,4-dicarboxylate (e.g., trans-8; Scheme 2). On the other hand, the reaction of 5 and trans-2 proceeded in a nonstereoselective course to provide a mixture of trans- and cis-substituted cycloadducts. This result can be explained by an isomerization of the intermediate azomethine ylide. Dimethyl 1,3-thiazolidine-2,2-dicarboxylates 14 and 15 were formed in the thermal reaction of dimethyl aziridine-2,2-dicarboxylate 11 with aromatic thioketones (Scheme3). On treatment of 14 and 15 with Raney-Ni in refluxing EtOH, a desulfurization and ring-contraction led to the formation of azetidine-2,2-dicarboxylates 17 and 18, respectively (Scheme 4).

Unexpected formation of dimethylthioketene cycloadducts in the reaction of 1,3-diphenylaziridine-2,2-dicarboxylate with cyclobutanethione derivatives

The reaction of 2,2,4,4-tetramethyl-3-thioxocyclobutanone (1) with cis-1-alkyl-2,3-diphenylaziridines 5 in boiling toluene yielded the expected trans-configured spirocyclic 1,3-thiazolidines 6 (Scheme 1). Analogously, dimethyl trans-1-(4-methoxyphenyl)aziridine-2,3-dicarboxylate (trans-7) reacted with 1 and the corresponding dithione 2, respectively, to give spirocyclic 1,3-thiazolidine-2,4-dicarboxylates 8 (Scheme 2). However, mixtures of cis- and trans-derivatives were obtained in these cases. Unexpectedly, the reaction of 1 with dimethyl 1,3- diphenylaziridine-2,2-dicarboxylate (11) led to a mixture of the cycloadduct 13 and 5-(isopropylidene)-4-phenyl-1,3-thiazolidine-2,2-dicarboxylate (14), a formal cycloadduct of azomethine ylide 12 with dimethylthioketene (Scheme 3). The regioisomeric adduct 16 was obtained from the reaction between 2 and 11. The structures of 6b, cis-8a, cis-8b, 10, and 16 have been established by X-ray crystallography.

Aryl, hetaryl, and ferrocenyl thioketones as versatile building blocks for exploration in the organic chemistry of sulfur

GRAPHICAL ABSTRACT ABSTRACT Methods for the synthesis of hetaryl and ferrocenyl thioketones as well as applications of this class of organic sulfur compounds in the synthesis of both sulfur-containing and sulfur-free organic products are summarized. The most important applications relate to [2+2]-, [3+2]-, and [4+2]-cycloadditions. Aromatic thioketones react with diazomethane at −70°C, and the formed 1,3,4-thiadiazolines can be used as convenient precursors of reactive thiocarbonyl S-methanides. In contrast, the hetaryl thioketones do not form this type of cycloadducts. Reactions of hetaryl thioketones with thiocarbonyl S-methanides are proposed to occur via a stepwise diradical mechanism. Aryl and hetaryl thioketones react as prone heterodienophiles with cyclic and acyclic dienes. The first asymmetric synthesis of dihydrothiopyranes from aryl and hetaryl thioketones was performed using a l-proline-derived organocatalyst. Hetaryl thiochalcones are useful heterodienes for the preparation of hetaryl-substituted dihydrothiopyrans.

Exploration of Fluoral Hydrazones Derived from Carbohydrazides for the Synthesis of Trifluoromethylated Heterocycles

The reaction of fluoral hydrate with carbohydrazides in methanol in the presence of molecular sieves (4 Å) gave the desired N-acylated fluoral hydrazones (3a–f) in fair yields. Treatment of the latter with mercaptoacetic acid in benzene led to the corresponding 2-trifluoromethyl-1,3-thiazolidinone derivatives (4a–f), whereas the reaction with acetic anhydride gave 3-acetyl-2,3-dihydro-2-trifluoromethyl-1,3,4-oxadiazoles (5a–f). The structures of each type of product have been established by X-ray crystallography. INTRODUCTION In the synthesis of fluorine-containing organic compounds, fluoral hydrate and fluoral ethyl hemiacetal play an important role. Of special importance are the imines of fluoral, which are available via reactions of fluoral hemiacetals with primary amines. The initially formed fluoral aminals are relatively stable compounds, and the elimination of water is performed by adding molecular sieves or by azeotropic removal of water. Carbohydrazides and their hydrazones are widely applied in the synthesis of diverse heterocycles. Recently, we published a series of papers in which heterocyclizations of some hydrazones derived from imidazole carboxylic acid and proline, respectively, were used as starting materials. To the best of our knowledge, there are only a few publications dealing with preparations of carbohydrazide hydrazones HETEROCYCLES, Vol. 88, No. 1, 2014 387

Dimerization reactions of aryl selenophen-2-yl-substituted thiocarbonyl S-methanides as diradical processes: a computational study

An intriguing stepwise diradical mechanism of the dimerization of the reactive intermediate (thiocarbonyl S-methanide) appearing in the reaction of phenyl selenophen-2-yl thioketone with diazomethane was studied by means of computational methods. The preferred formation of the unusual macroheterocycle, competitive with the 1,3-ring closure leading to a thiirane and the head-to-head dimerization yielding a 1,4-dithiane derivative, respectively, was explained based on the analysis of the structure of the favored conformer of the intermediate, delocalized diradical species. The influence of selenium as a ‘heavy atom’ for stabilization of this intermediate has been emphasized.

Nitro-Grela-type complexes containing iodides - robust and selective catalysts for olefin metathesis under challenging conditions

Summary Iodide-containing nitro-Grela-type catalysts have been synthesized and applied to ring closing metathesis (RCM) and cross metathesis (CM) reactions. These new catalysts have exhibited improved efficiency in the transformation of sterically, non-demanding alkenes. Additional steric hindrance in the vicinity of ruthenium related to the presence of iodides ensures enhanced catalyst stability. The benefits are most apparent under challenging conditions, such as very low reaction concentrations, protic solvents or with the occurrence of impurities.

Formation of phosphonylated thiiranes in the reaction of a diazomethanephosphonate and cycloaliphatic thioketones

The reaction of diethyl diazomethanephosphonate (1) with cycloaliphatic thioketones (6) in THF at room temperature leads to the corresponding thiirane-2-phosphonates (7) in good yield. A reaction mechanism via 1,3-dipolar cycloaddition of the diazo compound with the C=S group to give the 2,5-dihydro-l,3,4-thiadiazole-2-phosphonate as an intermediate, which spontaneously eliminates nitrogen is most likely. The resulting thiocarbonyl ylide undergoes a 1,3-dipolar electrocyclization to yield a thiirane. These products can be desulfurized smoothly by treatment with tris(diethylamino)phosphine to give α,β-unsaturated phosphonates.

Microwave-assisted reactions of α-diazoketones with hetaryl and ferrocenyl thioketones*

ABSTRACT Differently substituted hetaryl thioketones react with less reactive diazoketones under microwave (MW) irradiation in toluene solution. After only 2 min, the reactions were complete and, depending on the type of the used diazoketone, α,β-unsaturated ketones, acyl substituted thiiranes or 1,3-oxathioles were obtained as final products. In the case of azibenzil and di(thiophen-2-yl) thioketone, a new type of 1,5-dipolar electrocyclization of the intermediate thiocarbonyl ylide involving a thiophene ring led to a fused sulfur heterocycle. In contrast to hetaryl thioketones, the ferrocenyl analogues decompose under MW irradiation. Alternatively, they react with diazopropanone and 2-diazo-1-phenylethanone in boiling THF in the presence of LiClO4 to give α,β-unsaturated ketones as sole products. In these cases, the reactions require long reaction times. GRAPHICAL ABSTRACT

Hockey-stick liquid crystalline 6-oxoverdazyl§

ABSTRACT A series of hockey-stick shaped 6-oxoverdazyl radicals 1[n]–3[n], containing CH3 (a), CF3 (b) and CN (c) groups in the short ‘arm’, were prepared and their physical properties were investigated. Mesogenic behaviour was found only in the CN derivatives with the COO (1[n]c) and N=N (2[12]c) linking groups, which exhibited a nematic phase. Analysis of binary mixtures of selected compounds with bent-core nematic host 4[12] gave virtual nematic-isotropic transition temperatures, [TNI], which follow the order 1[12]b < 1[12]c < 1[12]a in one series and 1[12]c < 2[12]c < (3[12]c) in another. The observed effectiveness of the short-arm substituent, CF3 < CN < CH3, was related to the magnitude and orientation of the molecular dipole moment calculated with density functional theory methods. Graphical Abstract

A convenient access to 1,2-diferrocenyl-substituted ethylenes via [3 + 2]-cycloelimination of 2-silylated 4,4,5,5-tetrasubstituted 1,3-dithiolanes

ABSTRACT Ferrocenyl thioketones bearing a hetaryl, phenyl or alkyl group as the second substituent react with (trimethylsilyl)diazomethane at ca. −30°C in THF solution without formation of a stable [3 + 2]-cycloadduct. After the spontaneous evolution of N2, the corresponding sterically crowded 4,4,5,5-tetrasubstituted 2-silylated 1,3-dithiolanes are formed as products of the second [3 + 2]-cycloaddition of the intermediate thiocarbonyl S-methanide with the starting thioketone. After desilylation by treatment with TBAF, they are converted into the corresponding carbanions, which display different stability depending on the type of substituent. The presence of hetaryl and phenyl groups results in the exclusive formation of 1,2-diferrocenyl ethylenes. In contrast, the presence of methyl groups significantly enhances the stability of the carbanion, which by protonation yields trans-4,5-diferrocenyl-4,5-dimethyl-1,3-dithiolane. GRAPHICAL ABSTRACT