Free‐Radical Carbocyanation of Olefins

Abstract

The free-radical three-component carbocyanation of electron-rich olefins was investigated with p-tosyl cyanide as cyanide source. The scope and limitations of the process were established by varying the nature of the alkene and radical precursor. Carbocyanation of chiral allylsilanes was shown to occur with high diastereocontrol, leading to syn β-silyl nitriles. The origin of the stereocontrol was rationalized by a Felkin-Anh-type transition-state model. Finally, a tin-free carbocyanation process was also devised, based on the use of a new alkylsulfonyl cyanide incorporating both carbon fragments to be added across the olefinic π system.

Eosin-Mediated Alkylsulfonyl Cyanation of Olefins

“…23 Therefore, we expect that 3 EY* undergoes oxidative PET with the EY-CN adduct, and that the ensuing EY •+ then oxidizes sulfinate into the sulfonyl radical II. Reversible addition of the latter onto the olefin affords a nucleophilic C-centered radical III, which may evolve through two different pathways: (1) a cyano group radical transfer to afford product V, 14 or (2) the oxidation of III into a carbocation IV, eventually trapped by a cyanide anion. In the latter case, EY •+ is reduced back to EY.…”

“…α-Pinene led to nitrile 3f in excellent yield, in agreement with a radical-based reaction mechanism. 14 Lower yields were, however, obtained from 1,1-disubstituted olefins (i.e. 3i-j-3p), but this could be circumvented using a larger amount of sulfonyl cyanide (e.g.…”

“…The reaction of vinyl pivalate with sulfonyl cyanide 1e led to the carbocyanation product 4l in good yield. 14 Here, loss of SO2 is fast as a result of the formation of a stabilized C-centered radical resulting from the α-scission.…”

“…α-Pinene led to nitrile 3f in excellent yield, in agreement with a radical-based reaction mechanism. 14 Lower yields were, however, obtained from 1,1-disubstituted olefins (i.e., 3i−j, 3p), but this could be circumvented using a larger amount of sulfonyl cyanide (e.g., 3i). The reaction was also found to be compatible with various functional groups including ketones (3b), bromides (3c), ester (3e), carbamate (3g), and silyl protecting groups (3l).…”

Iron‐Catalyzed Three‐Component Cyanoalkylsulfonylation of 2,3‐Allenoic Acids, Sulfur Dioxide, and Cycloketone Oxime Esters: Access to Cyanoalkylsulfonylated Butenolides

“…In 2008, Felton [12] reported the electrochemical reduction of alkyl vinyl sulfones with acetonitrile to obtain cyanoalkylsulfonyl groups. Later, Landais and coworkers [13] demonstrated the three‐component cyanoalkylsulfonylation of α‐bromosulfone, olefin, and p ‐tosyl cyanide. Moreover, Chen [14] reported the copper‐catalyzed cross‐coupling of oxime esters and sulfinates for the synthesis of cyanoalkylsulfonyl groups.…”