Premium
Temperature Dependence of the Reduction of Phthalic Thioanhydrides by NaBH 4 : Competition between 3‐Hydroxythiolactone and Phthalide Formation
Author(s) -
Polec Iwona,
Lutsen Laurence,
Vanderzande Dirk,
Gelan Jan
Publication year - 2002
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200203)2002:6<1033::aid-ejoc1033>3.0.co;2-s
Subject(s) - phthalide , chemistry , phthalic anhydride , phthalic acid , kinetic control , derivative (finance) , aqueous solution , organic chemistry , medicinal chemistry , catalysis , financial economics , economics
The reduction of phthalic thioanhydrides with NaBH 4 at between 0 and −20 °C leads to the selective formation of 3‐hydroxy‐2‐thiophthalides, whereas higher temperatures favour the formation of the corresponding phthalide derivatives. A mechanism is proposed that can explain these observations. Kinetic control at low temperatures leads to an improved stability of the intermediate alkoxide, thus allowing isolation of the γ‐hydroxythiolactone after subsequent acidification of the reaction mixture. In this way the formation of the thermodynamically favoured phthalide derivative is avoided. Further reduction of the γ‐hydroxythiolactone with AcOH/57% aqueous HI yields 2‐thiophthalides, useful precursors for conducting polymers. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)