Photoredox/Nickel-Catalyzed Diastereoselective Allylation of Aldehydes with Morita–Baylis–Hillman Adducts

A practical diastereoselective photoredox nickel-mediated allylation of aliphatic and aromatic aldehydes with Morita-Baylis-Hillman (MBH) acetates is reported here. The reaction proceeds under visible-light irradiation using MBH derivatives, which are easily prepared from inexpensive and available starting materials, affording functionalized alcohols as a single diastereoisomer (>20:1 for the <i>syn</i> diastereoisomer). The popular organic dye 3DPAFIPN is used as a photocatalyst in combination with Hantzsch ester in the presence of a catalytic amount of stable nickel complexes and <i>o</i>-phenanthroline as a ligand. The reaction shows a broad scope, avoiding the use of Ni(0), as well as the stoichiometric metal reductants such as Zn and Mn. The relevance of the reaction was confirmed by using the prepared products for rapid access to α-methylene-β-lactones, which are useful intermediates for the synthesis of natural or biologically active relevant products. DFT calculations suggest that the allyl acetate-coordinated Ni(0) species plays the role of active catalyst and the nickel catalytic cycle operates through the Ni(0)-Ni(II)-Ni(I)-Ni(0) pathway.