The title compounds, namely dimethyl (2RS)-2,3-diphenyl-1,3-thiazolidine-5-spiro-2'-adamantane-4,4-dicarboxylate methanol solvate, C(28)H(31)NO(4)S.0.275CH(4)O, and dimethyl (4RS)-3,4-diphenyl-1,3-thiazolidine-5-spiro-9'-(9'H-fluorene)-2,2-dicarboxylate, C(31)H(25)NO(4)S, were obtained from dipolar [2+3]-cycloadditions of an azomethine ylide with adamantanethione and thiofluorenone, respectively. The structures show that the choice of thioketone affects the regioselectivity of the cycloaddition. The asymmetric unit of the former structure contains two molecules of the thiazolidine derivative plus a site for a partial occupancy (55%) methanol molecule. O-H...O and C-H...O interactions link two of each of these entities into closed centrosymmetric hexamers. The five-membered ring in each structure has an envelope conformation.