An improved synthesis of cyclohexenothioxanthenones

Abstract

An improved synthesis of cyclohexanothioxanthenones in high yield (70‐90%) by treatment of thiosalicylic acid (4) or 2,2′‐dithiosalicylic acid with 1,2,3,4‐tetrahydronaphthalene (5) in the presence of concentrated sulfuric acid or a mixture of 95% sulfuric acid with 27‐30% fuming sulfuric acid (in 5:1 to 2:1 v/v ratio) was described. The crude product consisted of three isomers which were isolated and identified. These isomers are 1,2‐, 2,3‐ and 3,4‐cyclohexanothioxantenone (1, 2, and 3).

A Novel and Efficient Method for the Synthesis of New Hydroxythioxanthone Derivatives

“…The results also show the importance of using both Al 2 O 3 and CH 3 SO 3 H (compare entries 9 and 10 with 11). The use of two equivalents of phenol 1 15 and one equivalent of TSA (2) for 1-hydroxythioxanthone (3) does not improve the yield of thioxanthone in comparison with the case where one equivalent of phenol 1 and one equivalent of TSA (2) were used. Because of this initial observation, it seemed advantageous to investigate this method as a new and more suitable way to hydroxythioxanthones synthesis.…”

“…6 The syntheses of thioxanthone and substituted thioxanthones have been carried out by different methods. [4][5][6][7][8][9][10]15 These compounds are generally synthesized by condensation of appropriately substituted potassium 2-chlorobenzoates with thiophenoles, or condensation of substituted thiosalicylic acids with benzene derivatives followed by cyclization of the intermediate 2-phenylmercaptobenzoic acids in sulfuric acid, 10,16,17 AlCl 3 , 3,6 or PPA. 5 However, these methods have some disadvantages such as low yields, long reaction times, the use of large amount of concentrated sulfuric acid, and lack of regiochemical control in the ring closure step.…”

Electrochemical reduction of 2,4‐dimethyl(diethyl)‐9‐oxo‐10‐(4‐heptoxyphenyl)‐9H‐thioxanthenium hexafluorophosphates and 2,4‐dimethyl(diethyl)‐9H‐thioxanthene‐9‐ones

“…The first peak potentials of the electrochemical reduction of 9H ‐thioxanthene‐9‐one and related compounds in MeCN and other solvents have been described . Good correspondence between experimental potentials and LUMO energies of thioxanthones calculated by semiempirical, ab initio Hartree‐Fock and density functional theory (DFT) methods, was demonstrated. On the other hand, the cations 1 , 2 contain a heptoxyphenyl substituent, which can potentially be used as a linker for modification of electrode surface to obtain modified electrodes with electrochemically active thioxanthenium group for practical applications, for example, in electrochemical biosensor technologies …”

Intramolecular Friedel–Crafts Reaction with Trifluoroacetic Acid: Synthesizing Some New Functionalized 9-Aryl/Alkyl Thioxanthenes

“…44 The most common method involves the reduction of thioxanthone derivatives. 45,46 Thioxanthones are traditionally made by condensing thiosalicylic acids with benzene derivatives, then cycling the resulting thioether in the presence of sulfuric acid, phosphoric acid, or Lewis acids like AlCl 3 . 47 However, these conventional techniques have not been favored in recent years due to the low yields obtained with the use of sulfuric acid, the absence of regioselectivity, and the lengthy reaction durations.…”