Anti-Selective Michael Addition of Thiols and Their Analogues to Nitro Olefins

Article abstract of DOI:10.1021/jo00295a036

The reaction of nitro olefins with thiolate anions followed by protonation at -78 deg C gives anti-β-nitro sulfides.This procedure can be applied to the anti-selective preparation of β-nitro ethers and β-nitro selenides.The reaction of cyclic nitro olefins with aryl thiol gives cis-β-nitro sulfide in excellent selectivity.The conjugate addition of alkylaluminum reagents to phenylthio β-nitro olefins followed by protonation at -78 deg C also results in selective formation of anti-β-nitro sulfides.The anti isomers are also prepared through the deprotonation-protonation procedure at - 78 deg C from a mixture of syn- and anti-β-nitro-sulfides.The protonation process of the nitronate anion intermediates at -78 deg C is important for the occurence of high anti selectivity.However, the selectivity is not observed in the conjugate addition of an alkyl group to a simple nitro olefin.This difference in stereoselectivity can be explained on the basis of the differences of the preferable conformations of the nitronate anion intermediates.Theoretical calculations show that the methylthio group on β-position covers one side of the nitronate plane effectively to give the anti isomer in a stereoseletive way.