Halogen-Atom Transfer Enabled Z-Selective Styrene Synthesis via Dual Cobalt and Photocatalysis Through Coupling of Unactivated Alkyl Iodides With Terminal Arylalkynes

Abstract

An efficient Z-selective cobalt-catalyzed reductive hydroalkylation of terminal aryl alkynes with unactivated alkyl iodides has been achieved, providing a straightforward and modular route to access 1,2-disubstituted Z-styrenes. This reaction operates under mild conditions without requiring over-stoichiometric amounts of metal terminal reductants. Excellent Z/E ratios and good to excellent yields can be achieved for diverse and complex scaffolds with remarkable functional-group compatibility. One potential utility of this reaction is demonstrated by the efficient synthesis of several syn homoallylic alcohols in a one-pot two-step sequence. Control experiments strongly support that the halogen-atom transfer (XAT) process is the key to generating carbon radicals. DFT studies suggest that the catalytic system involves the Co(II)/Co(III) cycle and the steric repulsion between the Co(II) catalyst, and the alkenyl radical in radical capture by Co(II) is the dominant factor controlling the Z/E selectivity. This approach represents the first example of merging photo-XAT with cobalt-catalyzed reductive coupling of terminal aryl alkynes with unactivated alkyl iodides.