Z-Selective Synthesis of Vinyl Boronates through Fe-Catalyzed Alkyl Radical Addition

Z-Selective synthesis of vinyl boronates is challenging. This work describes Fe-catalyzed addition of alkyl radicals, formed by the corresponding alkyl halides, to ethynyl ethynylboronic acid pinacol ester that gives rise to Z-vinyl boronates in high stereoselectivity. The method works best for tertiary and secondary alkyl iodides. The Z-vinyl boronate products are easily converted to other Z-alkenes by transformation of the boronate group. The method is applied for the formal total synthesis of a 5-HT2c receptor agonist.