Electrooxidative Coupling of Furans and Silyl Enol Ethers: Application to the Synthesis of Annulated Furans.

Abstract

Synthesis of Annulated Furans. -A general and effective method to prepare benzofuran derivatives is developed. The key step is electrochemical cyclization of silyl enol ethers of type (IV). It proceeds with high cis selectivity and tolerates a range of functional groups. -(SPERRY, J. B.; WHITEHEAD, C. R.; GHIVIRIGA, I.; WALCZAK, R. M.; WRIGHT*, D. L.; J. Org. Chem. 69 (2004) 11, 3726-3734; Dep. Chem., Dartmouth Coll., Hanover, NH 03755, USA; Eng.) -Jannicke 39-099

Convergent Strategies in Total Syntheses of Complex Terpenoids

“…The authors achieved this challenging transformation by application of an anodic oxidation, resulting in formation of tetracycle 57 as a single isomer. The mechanism of the intriguing cyclization was proposed as follows . Oxidation of the silyl enol ether 53 to the corresponding radical cation 54 and the following intramolecular Friedel–Crafts cyclization provide intermediate 55 .…”

Electrochemically Driven Desaturation of Carbonyl Compounds

“…trace amounts of enone were isolated as a by-product (<5% yield). [23][24][25] Building on these encouraging studies, we report herein an electrochemically driven approach to elicit desaturation that requires no metals or chemical oxidants and features a broad substrate scope with inherent scalability. The utility of this method is placed in the context of the most popular and recently disclosed methods, and a simple method for predicting reactivity is also described.…”

“…A twostep in situ EDD protocol was also developed to afford enones 6, 12 and 17 in decent yields directly from the respective ketone starting material. Esters and lactones, substrate classes that have only recently succumbed to direct dehydrogenation, 14,17,18 can also be subjected to EDD using the corresponding diphenylphosphate ester derivatives (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31). Such enol derivatives are easily prepared and hydrolytically stable unlike the corresponding silyl ketene acetals.…”

“…The electrochemical oxidation of silyl enol ethers has been previously disclosed by Moeller and studied mechanistically by Wright. 25 These studies demonstrated that initial anodic oxidation leads to the formation of an enol ether radical cation intermediate by using a cyclopropyl ring-opening clock. A similar conclusion was made by Moeller and co-workers when they oxidized various alkylenol ethers and thio-enol ethers.…”

Electrochemically Driven Desaturation of Carbonyl Compounds

“…21,22 Similar reactivity was also observed by Moeller and co-workers in their studies of silyl enol ether alkylation where trace amounts of enone were isolated as a by-product (<5% yield). [23][24][25] Building on these encouraging studies, we report herein an electrochemically driven approach to elicit desaturation that requires no metals or chemical oxidants and features a broad substrate scope with inherent scalability. The utility of this method is placed in the context of the most popular and recently disclosed methods, and a simple method for predicting reactivity is also described.…”