Carbon-oxygen bond-cleavage reactions by electron transfer. 4. Electrochemical and alkali-metal reductions of phenoxynaphthalenes

• Published in: Journal of the American Chemical Society Vol. 111; no. 7; pp. 2434 - 2440
• Main Authors: Thornton, Todd A, Ross, Gerald A, Patil, Dilip, Mukaida, Kenichi, Warwick, Jeffrey O, Woolsey, Neil F, Bartak, Duane E
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.03.1989
• Subjects: 400400 - Electrochemistry; ANIONS; AROMATICS; ARYL RADICALS; CARBON; CHARGED PARTICLES; CHEMICAL BONDS; CHEMICAL REACTION YIELD; CHEMICAL REACTIONS; CHEMISTRY; CONDENSED AROMATICS; DATA; ELECTROCHEMISTRY; ELECTRON TRANSFER; ELEMENTS; EXPERIMENTAL DATA; INFORMATION; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; IONS; NAPHTHYL RADICALS; NONMETALS; NUMERICAL DATA; ORGANIC COMPOUNDS; OXYGEN; RADICALS; REACTION INTERMEDIATES; REDUCTION; VOLTAMETRY; YIELDS
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja00189a010

The reductions of 1- (1) and 2-phenoxynaphthalene (2) to their respective radical anions were observed at {minus}2.42 and {minus}2.48 V vs SCE. Cyclic voltammetric and chronoamperometric studies indicate that both radical anions have half-lives that are greater than 100 s in dry N,N-dimethylformamide. Controlled-potential electrolysis of the ethers resulted in relatively slow, regioselective carbon-oxygen bond cleavage to produce phenol and naphthalene. The intermediacy of the naphthyl radical or the naphthyl anion in the reductive pathway was tested by the use of an intramolecular radical trap in the form of a 2-(3'-butenyl) substituent, i.e., 2-(3'-butenyl)-1-phenoxynaphthalene (3). Formation of 1-methylbenz(e)indan (4) upon the electrochemical reduction of 3 in the absence and presence of D{sub 2}O confirmed the presence of the 2-(3'-butenyl)naphthyl radical in the radical-anion cleavage mechanism. Reduction of the phenoxynaphthalenes with Na/HMPA in tetrahydrofuran resulted in slow regioselective cleavage while reduction with Na-K alloy/tetraglyme quantitatively cleaved the ether bond more rapidly. The intermediacy of the naphthyl anion, which is produced via the ether dianion in the Na-K alloy reduction, was demonstrated by the reduction of 3 at {minus}78 and 0{degree}C. Reduction of 3 at {minus}78{degree}C produced only 2-(3'-butenyl)naphthalene (5) whereas reduction at 0{degree}C produced both 5 and 4, the latter by anionic cyclization.