Replacing DMF by Cyrene™ drives the syntheses of pentathiepines towards sustainability, conveniency, and/or higher yields

Building on previous efforts in optimizing the synthesis of 1,2,3,4,5-pentathiepino[6,7-a]indolizines mediated by the molybdenum oxo bistetrasulfido complex, this study advances the respective preparation procedures by introducing an environmentally friendly approach with a concomitant focus on increasing yields and efficiency, and generally improved reaction conditions. Incorporating the sustainable solvent Cyrene™ into the established protocol enables the synthesis of various substituted 1,2,3,4,5-pentathiepino[6,7-a]indolizines in a more environmentally friendly manner, complemented by a new purification approach. Derivatives studied include substituents CF 3 , CN, CHO, COOMe, and a urea group at C-9. Realized modifications with a COOMe group at positions C-8, C-10, and C-11 are reported for the first time. Testing three different sets of conditions confirmed that the green Cyrene™ is a valid practical alternative to dimethylformamide (DMF). Although yields and reaction times did not improve in each and every case, the research demonstrates a method utilizing a non-toxic, biodegradable solvent to comprise a significant advancement over traditional, more toxic, and harsh methods for this compound class. Sublimation as a new purification technique was also explored in order to minimize the generation of organic solvent waste. Notably, the CN-substituted compound showed unusual behaviour during synthesis, with no product formation under N 2 conditions, and unexpected tetrasulfide side products could be identified for two COOMe derivatives. To understand the observed differences in reactivity and the chemical/molecular and electronic structures of these compounds, comprehensive analytical characterization was performed on all derivatives supported by computational analysis.