Preparation of (+)- and (−)- β-phenyl- and β-(4-chlorophenyl)-γ- butyrolactones: Key Intermediates in the Synthesis of β-phenyl-GABA and Baclofen
The preparation of b-phenyl- and b-(4-chlorophenyl)-g-butyrolactones (<strong>±</strong>)<strong>-3</strong> and (<strong>±</strong>)<strong>-4</strong> and their resolution to the corresponding (+)-(<em>S</em>)-<strong>3</strong>, (-)-(<em>R</em>)-<strong>3</strong> and (+)-(<em>S</em>)-<strong>4, </strong>(<strong>-</strong>)-(<em>R</em>)-<strong>4</strong> through formation, flash column chromatography separation and subsequent hydrolysis of diastereoisomeric 4-hydroxybutyramides (2’<em>R</em>,3<em>S</em>)-<strong>5</strong>, (2’<em>R</em>,3<em>R</em>)-<strong>5</strong>, (2’<em>R</em>,3<em>S</em>)-<strong>6</strong> and (2’<em>R</em>,3<em>R</em>)-<strong>6</strong> is described. The absolute configuration assignment of enantiopure <strong>3</strong> and <strong>4</strong> was supported by X-ray crystallographic structures of (2’<em>R</em>,3<em>R</em>)-<strong>5</strong>,<strong> </strong>(2’<em>R</em>,3<em>S</em>)-<strong>6</strong> and (2’<em>R</em>,3<em>R</em>)-<strong>6</strong>.