Phosphorous Heteroatom Bond Formation Strategies and the Development of Green Synthetic Methods

Strategies to forge phosphorous heteroatom bonds are in high demand as organophosphorus compounds have seen a variety of uses in medicinal chemistry, materials chemistry, and agricultural chemistry. Phosphorous monoacids are a challenging functional group to synthesize and current methods suffer from harsh conditions and limited substrate scope. Furthermore, fluorophosphine oxides have not yet been made in a sustainable way. An electrochemical synthetic is an attractive strategy as it would remove the need for conventional metal catalysts. However, a potential challenge to overcome is the low reactivity of fluoride. Synthetic methods to synthesize phosphorous monoacids and the electrochemical synthesis of fluorophosphine oxide are presented. Thiophosphates are another functional group that interests organic chemists as they display important biological activity. The use and study of P(O)OEt2SH as a synthon for this functional group allow for unprecedented access to new synthetic methods to forge thiophosphates. The dual role of P(O)OEt2SH behaving as a Brønsted acid and thiolate nucleophile can be harnessed to synthesize thiophosphates under highly atom-economic, energy-neutral, catalyst-free, and additive-free conditions. This strategy has been used to develop green synthetic methodologies to access diaryl thiophosphate and phosphorous disulfides.Another organosulfur functional group that has not been well studied is the hydrogen persulfide. Only three examples of hydrogen persulfides have been synthesized in the literature. Access to hydrogen persulfides is hampered by a difficult synthetic preparation method and their inherent instability. New hydrogen persulfides have been synthesized and applied in the hydrothiolation of alkenes. Mechanism studies such as control experiments and isotope labeling experiments have been performed to elucidate the mechanism of this new transformation. The hydrothiolation of alkenes using hydrogen persulfides is a green strategy to access thioethers. This transformation is solvent-free, atom-economical, and an energy-neutral method. Lastly, a Friedel-Crafts type reaction of beta naphthol has been explored to access allylation and benzylation products. The beta naphthol motif is important and has been used in medicinal chemistry and as an imaging reagent. The challenge of regioselectivity and allylic alcohol activation has been studied. Different reactions, such as phosphorylation and intramolecular annulation, also demonstrated the synthetic utility. This strategy is a catalytic, regioselective, and atom economical method, which can serve as a general strategy to functionalize arenols.