LAUSR

Carbenes are highly enabling reactive intermediates that facilitate a diverse range of otherwise inaccessible chemistry, including small-ring formation and insertion into strong σ bonds. To access such valuable reactivity, reagents with high entropic or enthalpic driving forces are often used, including explosive (diazo) or unstable (gem-dihalo) compounds. Here, we report that common aldehydes are readily converted (via stable α-acyloxy halide intermediates) to electronically diverse (donor or neutral) carbenes to facilitate >10 reaction classes. This strategy enables safe reactivity of nonstabilized carbenes from alkyl, aryl, and formyl aldehydes via zinc carbenoids. Earth-abundant metal salts [iron(II) chloride (FeCl2), cobalt(II) chloride (CoCl2), copper(I) chloride (CuCl)] are effective catalysts for these chemoselective carbene additions to σ and π bonds. Description Carbonyls to carbenes Carbenes are versatile chemical intermediates because of their highly reactive divalent carbon centers. Unfortunately, typical carbene precursors such as diazo compounds are often sensitive and decompose explosively. Zhang et al. now report a comparatively safe protocol to generate carbenes from aldehydes, a plentiful and easily diversified substrate class (see the Perspective by West and Rousseaux). The sequence entails successive reactions of the aldehyde with pivaloyl chloride and zinc, followed by catalytic activation using iron, cobalt, or copper. Demonstrated applications included wide-ranging examples of three-membered ring formation and sigma-bond insertion. —JSY Reaction of aldehydes with pivaloyl chloride and then zinc offers versatile and comparatively safe access to carbenes.