Temperature Dependence of the Reduction of Phthalic Thioanhydrides by NaBH4: Competition between 3-Hydroxythiolactone and Phthalide Formation
2002; Wiley; Volume: 2002; Issue: 6 Linguagem: Inglês
10.1002/1099-0690(200203)2002
ISSN1434-193X
AutoresI. Połeć, Laurence Lutsen, Dirk Vanderzande, J. Gelan,
Tópico(s)Coordination Chemistry and Organometallics
ResumoThe reduction of phthalic thioanhydrides with NaBH4 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)
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