Radical Addition to Isonitriles:  A Route to Polyfunctionalized Alkenes through a Novel Three-Component Radical Cascade Reaction

Abstract

The reaction of aromatic disulfides, alkynes, and isonitriles under photolytic conditions affords polyfunctionalized alkenes--beta-arylthio-substituted acrylamides or acrylonitriles--in fair yields through a novel three-component radical cascade reaction. The procedure entails addition of a sulfanyl radical to the alkyne followed by attack of the resulting vinyl radical to the isonitrile. A fast reaction, e.g., scavenging by a nitro derivative or beta-fragmentation, is necessary in order to trap the final imidoyl radical, since addition of vinyl radicals to isonitriles seems to be a reversible process. The stereochemistry of the reaction is discussed, particularly with respect to the stereochemical outcome of related hydrogen abstraction reactions by the same vinyl radicals. The lower or even inverted preference for either geometrical isomer observed in our cases with respect to that encountered in hydrogen abstraction reactions is explained in terms of transition-state interactions and/or isomerization of the final imidoyl radical. The latter possibility is supported by semiempirical calculations, which show that the spin distribution in the imidoyl radical can allow rotation of the adjacent carbon-carbon double bond prior to beta-fragmentation.

Free‐Radical‐Mediated Multicomponent Coupling Reactions

“…The intermolecular CaC bond-forming processes (arrow 2 and 3) are sequenced by 5-exo cyclization (arrow 4) onto the newly formed CaC double bond [11]. Scheme 6.6 illustrates a coupling reaction related to the third example of Scheme 6.4, but with diphenyl disulfide and m-dinitrobenzene [12]. The resulting imidoyl radical is trapped by m-dinitrobenzene to give the corresponding amide, such as A, via elimination of nitroxide and subsequent H-abstraction.…”

Recent advances in sulfur- and phosphorous-centered radical reactions for the formation of S–C and P–C bonds

“…Nanni group reported the synthesis of benzothiophene-containing heterocyclic compounds 165 and 166 by the reaction of an aryl isocyanide with phenyl sulfenyl radical generated from a disulfide (Scheme 73) 131. The same group also introduced a sulfenyl radical-initiated three-component reactions of aromatic disulfides, alkynes, and isonitriles for the synthesis of polyfunctionalized alkenes 167 and 168 132. This complicated reaction system could give many possible products.…”

Selenium‐Containing Heterocycles from Isoselenocyanates: Synthesis of 1H‐5‐Selena‐1,3,6‐triazaaceanthrylene Derivatives

“…and N-(4-bromophenyl)formamide were prepared according to [23] by heating the corresponding aniline (20 mmol) in 95% formic acid under reflux for 30 min. After workup, the products were recrystallized from H 2 O. N-(4-Methoxyphenyl)formamide was prepared according to [24]. After evaporation of the solvent, the residue was dissolved in AcOEt and the soln.…”