Synthesis of polysubstituted 3-thiofurans by regiospecific mono-ipso-substitution and ortho-metallation from 3,4-dibromofuran
✍ Scribed by Carlos Alvarez-Ibarra; Maria L. Quiroga; Emilio Toledano
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- French
- Weight
- 691 KB
- Volume
- 52
- Category
- Article
- ISSN
- 0040-4020
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✦ Synopsis
The synthetic potential of 3,4-dibromofuran has been assessed by its conversion into 3,4-disubstituted furans via mono-S-ipso-substitution. The ability of 3-methylthio and 3-phanylthio substituents for directing the metallation at position ct-rclative to the substitucnt has allowed the regiospccific alkylation. It provides a straightforward approach to several 3-monothiosubstituted furans which are receiving increasing interest as odour and flavour chemicals. C. ALVAREZ-IBARRA et al. RESULTS AND DISCUSSION Br Br 1 (30%t0 H2SO4 (7.5%)/140*C ii) K2Cr207/H2SO4 cone. Br~ Br L~Bu/Et20 2 l i) LDA/THF (80%)~ ii) Me2SO 4 7 ..... l i) LDNTNF oo-,' 0j~ ii) Me2SO 4 8 MeSSMe (89%) 3 H20 (71%) PhSSPh (58%) 10 ~ i) H2SO 4 (7.5%)/85"(3 ii) K2Cr2OT/H2SO4 conc. HO OH = Br 9 > Br,~SMe 4 Me2SO4( 76%) > Br,~ § Br 6 11 Scheme 1 ar Me2SO4 > (80%) 12
The synthesis of 3,4-dibromofuran 2 was achieved from 2,3-dibromo-2-buten-l,4-diol 1 by the one-pot method previously described by Riwicki et al. z° However, this method was unsuccessful for obtaining 3,4-dibromo-2,5-dimethyifuran 8 from 3,4-dibromo-3-hexcn-2,5-diol 9. The synthesis of 8 was achieved by mono-ortho-metallation of compound 2 and subsequent methylatiort, yielding 3,4-dibromo-2-methylfuran 7,