Breaking bonds with electrons: stepwise and concerted reductive cleavage of C-S, C-Se and Se-CN bonds in phenacyl thiocyanates and phenacyl selenocyanates

BOUCHET, LYDIA M.; ALICIA B. PEÑÉÑORY; MARC ROBERT; ARGÜELLO, JUAN E.

RSC Advances

Royal Society of Chemistry

Año: 2015 vol. 5 p. 11753 - 11760

2046-2069

The mechanistic aspects of the electrochemical reduction of phenacylthio- and selenocyanates have beenstudied. With phenacylthiocyanates (1), a change in the reductive cleavage mechanism is observed as afunction of the substituent on the phenyl ring. While a stepwise mechanism involving the intermediacyof a radical anion is followed for substrates bearing a strong electron withdrawing group, such as cyanoand nitro substituent (1d, 1e), and a concerted mechanism is favoured for compounds bearing anelectron-donating or no substituent on the phenyl ring (1a?c). A regioselective bond cleavage leads tothe fragmentation of the CH2?S bond with all compounds1a?e, further yielding the corresponding 1,4-diketone (3) as products. Contrastingly, with phenacylselenocyanates (2), two different reductivecleavages occur involving the breaking of both the CH2?Se and Se?CN bonds. Several products areobtained, all coming from nucleophilic attack at thea(phenacyl) carbon or the selenium atom.