Reaction of Acyl Chlorides withIn SituFormed Zinc Selenolates: Synthesis of SelenoestersversusRing-Opening Reaction of Tetrahydrofuran

Abstract

Attempting to apply thein situproduction of PhSeZnSePh to the synthesis of selenoesters, an unexpected reaction involving the solvent (tetrahydrofuran) was observed and studied. We reported here some evidences about the mechanism and the possibility to control the chemoselectivity of this new reaction that afforded the formation of interesting selenoderivatives in which the selenium moiety and the carboxylic one are spaced by four carbon units.

Atom Efficient Preparation of Zinc Selenates for the Synthesis of Selenol Esters under “On Water” Conditions

“…To better understand and prevent the side reaction observed in the presence of THF [56], DFT calculations were performed comparing [(PhCh) 2 Zn] (Ch=S, Se) with the previously reported PhChZnX (Ch=S, Se; X=Cl, Br) [57]. …”

“…This orbital contributes to the LUMO+14 and LUMO+15 of (PhS) 2 Zn·2THF and (PhSe) 2 Zn·2THF, respectively, which are stabilized in energy by 0.887 eV (ε = +0.1063 Hartree for both virtual MOs). The strength of the interaction between THF and (PhCh) 2 Zn accompanied by a low-lying MO with remarkable C–O antibonding character partly localized on the coordinated THF units may account for the ring opening reactions of coordinated solvents observed experimentally [56]. …”

“…Considering that [(PhSe) 2 Zn] is characterized by a higher atom economy respect to the PhSeZn-halides in the insertion of PhSe groups, the possibility to obtain it in a bench stable form is desirable. It could improve the versatility of its synthetic application (avoiding the strong acidic conditions of the biphasic system), controlling or preventing undesired side reactions like those observed when it was prepared and used in situ in the presence of THF [56]. …”

Water and Aqueous Mixtures as Convenient Alternative Media for Organoselenium Chemistry

“…The acyl substitution, probably due to the presence of a zinc atom that coordinates the carboxylic moiety, brings the selenium atom nearer to the electrophilic carbon, facilitating the competition of acyl substitution with respect to the most predictable hydrolysis [28]. Is worth mentioning that the use of the biphasic water/diethyl ether system prevents a side reaction that was recently observed when the oxidative zinc insertion and the subsequent reaction with benzoyl chloride were performed in refluxing THF (using trifluoroacetic acid or triflic An interesting application of this procedure was reported by Braga and coworkers, who described the synthesis of a series of chiral β-seleno amines by the ring-opening reaction of unprotected aziridines.…”

“…Is worth mentioning that the use of the biphasic water/diethyl ether system prevents a side reaction that was recently observed when the oxidative zinc insertion and the subsequent reaction with benzoyl chloride were performed in refluxing THF (using trifluoroacetic acid or triflic acid as catalyst). In these circumstances the ring-opening reaction of the solvent competes with the acyl substitution, producing selenoderivatives in which the selenium moiety and the carboxylic one are spaced by four carbon units [28] (Figure 5). Flemer recently reported the synthesis of cysteine (Cys) and selenocysteine (Sec) derivatives as building blocks in the preparation of chalcogen-containing peptides [29].…”