Abstrakt
Two different enantioselective organocatalytic cascade reactions to form new sulfur-containing spirocyclic scaffolds are described. In the first approach, benzothiophen-2-one and enals react in the presence of a secondary amine catalyst through a Michael/Michael/Aldol sequence to afford the final spiro-cyclohexene carbaldehydes in good yields (up to 68%) and with excellent selectivities [20:1 diastereomeric ratio (dr), up to 99%ee].
In the second approach, the double Michael addition of benzothiophen-2-one to aromatic dienones with primary amine catalysis produces the corresponding spiro-cyclohexanones in good yields (up to 76%) and with moderate-to-high selectivities (up to 12:1 dr, up to 90%ee). Moreover, the use of N-phenylrhodanine as the bis-nucleophile for these reactions also allowed the formation of the corresponding spirocyclic adducts.