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Scheme 5 | Chemistry Central Journal

Scheme 5

From: New phosphine-diamine and phosphine-amino-alcohol tridentate ligands for ruthenium catalysed enantioselective hydrogenation of ketones and a concise lactone synthesis enabled by asymmetric reduction of cyano-ketones

Scheme 5

A retrosynthesis of δ-lactones from commodity/bulk chemicals in 3 steps, and the reactions used to generate compound 15 and 18. (i) 20 mol% cyclohexylamine, 7 mol% acetic acid, 0.2 mol% hydroquinone, 180°C, dropwise addition of acrylonitrile over 4 hours, heat for further 12 h (30% yield). (ii) Enantioselective hydrogenation according to Table 3. (iii) KOH (5 eq.), ethylene glycol, reflux, 3 days, then 10% HCl (62% yield). (iv) 0.5% catalyst 3, 1% KOBut. 50°C, 50 bar H2, IPA, 16 h, (>99% yield, 74% e.e.). (v) KOH (5 eq.), ethylene glycol, reflux, 24 h, then 10% HCl (76% yield, 74% e.e).

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