Microwave‐Assisted Synthesis of Sulfurated Heterocycles with Herbicidal Activity: Reaction of 2‐Alkynylbenzoic Acids with Lawesson's Reagent

Abstract

The reactivity of 2‐alkynylbenzoic acids toward Lawesson's reagent (LR) under microwave irradiation (300 W, 100 °C, CH2Cl2) was assessed. It was found that, depending on reaction conditions, either a dithionation‐ or a monothionation‐cycloisomerization process takes place with formation of important sulfurated heterocycles. In particular, using 1 equivalent of LR for 1 h, dithionation occurred, with formation of benzo[c]thiophene‐1(3H)‐thiones or 1H‐isothiochromene‐1‐thiones, while with 0.5 equiv. of LR for 10–30 min, monothionated products were selectively obtained (benzo[c]thiophen‐1(3H)‐ones or 1H‐isothiochromen‐1‐ones). The regiochemical output of the process strongly depended on the substitution pattern of the starting 2‐alkynylbenzoic acid derivatives. These compounds were also assayed as potential herbicides by assessing their phytotoxic activity on seedling growth and development of the model species Arabidopsis thaliana. All compounds, to different extents, influenced the morpho‐physiological parameters that were monitored; in particular, the fresh weight (FW) was significantly affected, with ED50 values ranging from 4.81–63.7 μM.

Iodolactonization of 3‐Alkynylthiophene‐2‐Carboxylic and 3‐Alkynylpicolinic Acids for the Synthesis of Fused Heterocycles

“…1 H NMR (CDCl 3 , 300 MHz): δ = 7.63–7.54 (m, 2 H), 7.48–7.43 (m, 1 H), 7.39–7.31 (m, 3 H), 7.22–7.17 (m, 1 H), 3.93 (s, 3 H); 13 CNMR (CDCl 3 , 75 MHz): δ = 161.8, 133.4, 132.1, 131.8, 130.5, 128.8, 128.4, 127.4, 122.9, 95.3, 84.0, 52.2; IR (KBr): ν̃ = 2210 (w), 1717 (s), 1697 (s), 1439 (m), 1238 (s), 1099 (m), 1076 (m), 772 (m), 756 (m), 691 (w) cm –1 ; GC–MS (EI, 70 eV): m/z = 242 (M + , 100), 227 (73), 211 (35), 199 (27), 171 (18), 139 (99); HRMS‐ESI ( m/z ): [[M + H] + ] cald for C 14 H 11 O 2 S + : 243.0463, found 243.0467. The spectroscopic data agreed with those reported …”

“…1 H NMR ([D 6 ]DMSO, 300 MHz): δ = 7.92 (d, J = 5.1, 1 H), 7.61–7.51 (m, 2 H), 7.51–7.41 (m, 3 H), 7.36 (d, J = 5.1, 1 H); 13 CNMR ([D 6 ]DMSO, 75 MHz): δ = 161.8, 135.0, 132.0, 131.9, 131.3, 129.0, 128.7, 125.7, 122.3, 94.1, 84.4; IR (KBr): ν̃ = 2210 (vw), 1744 (s), 1678 (m), 1423 (m), 1258 (w), 918 (m), 775 (m), 752 (s), 691 (m) cm –1 ; HRMS‐ESI ( m/z ): [[M – H] – ] cald for C 13 H 7 O 2 S – : 227.0172, found 227.0172. The spectroscopic data agreed with those reported …”

A Focused Review of Synthetic Applications of Lawesson’s Reagent in Organic Synthesis

“…The biological significance of sulfurated heterocyclic derivatives with promising herbicidal properties was further researched by Salvatore et al [52].…”

“…The hetaryl and ferrocenylsubstituted ketones were converted into secondary alcohols via reduction with NaBH 4 in THF solution and lithium aluminum hydride, in the case of phenyl/ferrocenyl ketones. Scheme 19 exemplifies the synthesis of thiols using secondary alcohols (52,55). The ketones ketones.…”

Diversity of Lawesson's Reagent: Advances and Scope

“…monothionated products were obtained where there were carbonyl groups instead of thiocarbonyls ( 95 and 96) . All the mono and di‐thionated compounds were found to posses as potential herbicides having phytotoxic activity on seedling growth …”