Catalytic Functionalization of Styrenyl Epoxides via 2‐Nickela(II)oxetanes

Low‐valent nickel is shown to preferentially isomerize mono‐ or disubstituted epoxides into their corresponding aldehydes. Experiments with tetrasubstituted epoxides demonstrate that these reactions proceed via reactive 2‐nickelaoxetane intermediates, and that the oxidative addition step likely occurs with retention of configuration. The monosubstituted aldehyde isomerization products were found to rapidly react with HBpin to form boronate esters. These hydroboration reactions could be performed catalytically. Nickel squares up: Low‐valent nickel(0) is shown to isomerize styrenyl epoxides to aldehydes in high yields. Mechanistic studies indicate that these isomerizations occur via 2‐nickelaoxetane intermediates. Catalytic hydroboration of styrene oxide with HBpin was also demonstrated to be facile.