2,3-Diaryl-5-oxocyclopentane-l-carboxylates (4) were synthesized in yields of 7-60% by electrolytic hydrodimerization of trans cinnamate esters in anhydrous acetonitrile-tetraethylammonium bromide at constant, controlled cathode potential. For ethyl cinnamate as substrate the hydrodimer was found to have the froras-diphenyl geometry. A mechanism for the formation of 4, involving steps of (a) ß,ß coupling of oriented anion radicals at the electrode surface, (b) protonation of the dinegative anion by an available proton source, and (c) Dieckmann-type cyclization, is suggested. When ethyl 3',4'-dimethoxycinnamate was hydrodimerized in the presence of ethyl crotonate (nonreducible at the cathode potential used), the latter underwent concurrent catalyzed dimerization, presumably by means of acid-base interaction.
A one-step synthesis of dihydrocyclolignan lactones (including r-apopicropodophyllin, 2c) from ¿rans-oinnamyl chlorides and sodium phenylpropiolates is described. Studies on polarographic and macroscale electroreductions of model a,¿3-unsaturated esters in the solvent-electrolyte acetonitrile-tetraethyl ammonium bromide are presented. In particular, electroreduction of 2c at controlled cathode potential gives rac-deoxypicropodophyllin (3) by trans addition of hydrogen to the conjugated carbon-carbon double bond.In previous papers2-4 we reported syntheses of cyclolignan lactones 2 by means of the intramolecular Diels-Alder reaction of irons-cinnamyl phenylpropiolates (1) in refluxing acetic anhydride. Formation of 1 from the corresponding phenylpropiolyl chloride and transcinnamyl alcohol, however, proved to be difficult or capricious in many cases.6 We now report an alternative synthetic procedure for 2 wherein the ester 1 is formed (from the corresponding (rans-cinnamyl chloride and sodium phenylpropiolate) in refluxing anhydrous dimethylformamide (DMF) and is cyclized in situ.6 Thus, cyclolignans 2a-c were obtained by this a
Treatment of phenanthrene with hydrogen sulfide and an alumina catalyst at 630° gives phenthro[4,5‐bcd]thiophene (XVII). Spectral properties of XVII, its sulfoxide, and its sulfone are presented. Other examples of the direct insertion of a sulfur bridging atom into an aromatic molecule are reviewed.
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