1. 5: Glutaraldehyde [1] (Aldrich, 2.5 M aqueous solution, 29.2 mL, 72.9 mmol), Meldrum's acid [2] (10.0 g, 69.4 mmol), thiophenol [3] (7.3 mL, 71.1 mmol), and piperidinium acetate are stirred in 100 mL acetonitrile. The product began spontaneously to crystallize after about 3 h. After 6 h, aqueous 5% citric acid (100 mL) was added and the solution was cooled to 5°. The product was filtered, washed with water and dried to yield 16.4 g (70%) of 5. Crystallization from CH2Cl2/hexane. M.p. 151–153° dec. IR: 3441s, 2938w, 1765m, 1717s, 1445m, 1406m, 1395s, 1380s, 1299s, 1239m, 1231m, 1206m, 1080s, 1055s, 1043m, 1025m, 929m, 749m, 692m. 1H-NMR (CDCl3): 7.45–7.26 (m, 5H); 4.18 (dd, J = 4.8, 11.8, 1H, H-C(2)); 3.51 (dd, J = 4.5, 12.9, 1H, H-C(6)); 2.43 (br.s, 1H); 2.28–2.02 (m, 2H); 1.95–1.80 (m, 3H); 1.85 (s, 3H); 1.81 (s, 3H); 1.42–1.29 (m, 1H). NOE: between H-C(2) (5.5%) and H-C(6) (5%). 13C-NMR (CDCl3): 170.2; 164.4; 133.3; 133.0; 129.1; 128.2; 107.1; 60.5; 76.2; 53.0; 29.7; 29.5; 29.0; 28.9; 22.9. MS: 336 (M+, 76), 279 (34), 261 (27), 169 (47), 151 (29), 150 (23), 110(88), 84 (27), 68 (35), 66 (37), 53 (26), 43 (100). Anal. calc. for C17H20O5S : C 60.70, H 5.99, S 9.53, found C 60.79, H 6.04, S 9.48
2. Using the above procedure: 6-p-tolythio derivative, mp 148–149°C; 6-acetylthio derivative, mp 122–124°C; 6-o-carboxyphenylthio derivative, mp 153°C; 6-2-hydroxyethylthio derivative, mp 130–131°C.
3. a) Baer, H.H. Adv. Carbohydr. Chem. Biochem. 1969, 24, 67; b) Lichtenthaler, F.W. Angew. Chemie 1964, 76, 84. c) Padeken, H.G.; von Schickh, O.; Segnitz, A. Houben-Weyl, Bd. X/1 1971, 259, 262. d) Angyal, S.J.; Gero, S.D. Austr. J. Chem. 1965, 18, 1973.
4. a) Lopez Aparicio, F.J.; Espinosa Ubeda, A.; Gallo Mezo, M.A. An. Quim. Ser. C 1976, 72, 981. b) Lopez Aparicio, F.J.; Espinosa Ubeda, A.; Gallo Mezo, M.A. An. Quim. Ser. C 1979, 75, 916.
5. For a review of Meldrum's acid chemistry see McNab, H. Chem. Soc. Reviews 1978, 7, 345.