Electrooxidative Inter- and Intramolecular Carbon−Carbon Bond Formation Using Organothio Groups as Electroauxiliaries

Abstract

The introduction of an organothio group to an alpha-carbon of ethers results in significant decrease of the oxidation potentials. Anodic oxidation of alpha-organothioethers gives rise to facile cleavage of the C-S bond and the introduction of carbon nucleophiles on the carbon. Allylsilanes, silyl enol ethers, and trimethylsilyl cyanide serve as effective carbon nucleophiles. The anodic oxidation of the alpha-organothioethers having a carbon-carbon double bond in an appropriate position using Bu(4)NBF(4) as the supporting electrolyte leads to the effective cyclization and the introduction of the fluoride to one of the formal olefinic carbon. The present study demonstrates the effectiveness of organothio groups as electroauxiliaries in electrooxidative inter- and intramolecular carbon-carbon bond formation.

Stereoselective Synthesis of <i>cis</i>-Substituted-3’-anilino-2’, 3’-dihydro-4-2’-benzo[<i>b</i>]furanylcoumarins via Intramolecular Aldol Reactions

“…Hence carbon nucleophiles are generally unstable under electro-oxidative conditions because most of the nucleophiles possess electron-rich heteroatoms or aromatic rings. Therefore the electrolytic potential is limited to the lower of those of the co-existing nucleophiles and those of the products [25]. On the other hand, it is difficult to construct the corresponding dihydrobenzofuranols directly by the [3 + 2] cycloaddition of unactivated alkenes with hydroxy aldehydes.…”

“…The intramolecular reaction of carbon nucleophiles with an electrochemically generated intermediate can provide a unique means for generating new carbon-carbon bonds, and this may also be used to generate a reactive intermediate to construct the dihydrobenzofuran skeletons under mild conditions [19]. Similarly proline catalyzed aldol reaction plays an important role as carbon-carbon bond formation 2 [20][21][22][23] Further mechanistic studies, that is Nitrones undergo deoxygenative reductive coupling and subsequent cyclisation to 3 [24]. Hence carbon nucleophiles are generally unstable under electro-oxidative conditions because most of the nucleophiles possess electron-rich heteroatoms or aromatic rings.…”

An Electroinitiated Cation Chain Reaction: Intramolecular Carbon–Carbon Bond Formation between Thioacetal and Olefin Groups

“…This work stems from our earlier observation [5] that the low-temperature electrochemical oxidation of ArSSAr [6] leads to the formation of ArS(ArSSAr) + , [7] an equivalent of ArS + [8] that reacts with thioacetal 1 [9] to give the corresponding alkoxycarbenium ion 2 [10] and ArSSAr (Scheme 1). We envisaged that the reaction of the thus-obtained alkoxycarbenium ion with an olefin 3 leads to the formation of a second cation 4, [11] which might react with ArSSAr to give a sulfenylated product 5 to regenerate "ArS + ".…”

“…Thus, thioacetal 6 a (Scheme 2, R = C 7 H 15 , Ar= p-FC 6 H 4 ) bearing a carboncarbon double bond was allowed to react with ArS-(ArSSAr) + BF 4 À (1 equiv), which was prepared by anodic oxidation of ArSSAr using Bu 4 NBF 4 as a supporting electrolyte in CH 2 Cl 2 at À78 8C (0.67 F mol À1 based on ArSSAr). [14] As shown in Scheme 2, the reaction at À78 8C led to the formation of cyclized compound 7 a [15] (81 % yield) as a mixture of two diastereomers (cis/trans 6.8:1). Fluoride, instead of ArS, is introduced onto the olefinic carbon atom, indicating that BF 4 À or a fluoride ion derived from BF 4 À serves as a nucleophile.…”

An Electroinitiated Cation Chain Reaction: Intramolecular Carbon–Carbon Bond Formation between Thioacetal and Olefin Groups

“…[14] As shown in Scheme 2, the reaction at À78 8C led to the formation of cyclized compound 7 a [15] (81 % yield) as a mixture of two diastereomers (cis/trans 6.8:1). Fluoride, instead of ArS, is introduced onto the olefinic carbon atom, indicating that BF 4 À or a fluoride ion derived from BF 4 À serves as a nucleophile.…”