Efficient Enantioselective Syntheses of Sertraline, 2‐Epicatalponol and Catalponol from Tetralin‐1,4‐dione

Tetralin‐1,4‐dione, the stable tautomer of dihydroxynaphthalene, was reduced with catecholborane in the presence of 3,3‐diphenyl‐1‐butyltetrahydro‐3H‐pyrrolo[1,2‐c][1,3,2]oxazaborole as catalyst to give enantiomerically highly enriched 4‐hydroxy‐1‐tetralone (99% ee) in an efficient one‐pot procedure. The R‐enantiomer provided a rapid access to sertraline while the S‐enantiomer was converted into 2‐epicatalponol and catalponol. A more selective enantioselective route to the antithermitic catalponol made use of the planar chiral tricarbonylchromium complex of hydroxytetralone. Its precursor chromium(tricarbonyl)[η⁶‐(1‐4,4a,8a)‐tetralin‐5,8‐dione] was obtained via direct complexation of 1,4‐dihydroxynaphthalene using chromium(tricarbonyl)‐ tris(ammonia) and boron trifluoride etherate as source of the chromium(tricarbonyl) fragment. Enolate prenylation was best carried out in the presence of a tetraamine ligand. Complete inversion of the stereogenic center bearing the prenyl group of the initially obtained tetralone complex was achieved via enolate formation followed by protonation.