α‐Amino ketones derived from L‐proline, as precursors for isomitosanes and mitosenes

2‐Benzoyl‐ and 2‐(2‐naphthoyl)pyrrolidines which can be viewed as aryl α‐amino ketones, have been prepared from L‐proline via Grignard reactions, bromo‐to‐lithium exchange, or by Friedel‐Crafts acylations. It was impossible to convert the ketone function of these aryl α‐amino ketones into a tert‐alcohol group. The BOC‐protected (S)‐2‐acetyl‐l‐pyrrolidine (15), obtained by reaction of BOC‐proline 2‐pyridinethiol ester (2) with LiMe₂Cu, could be converted in two steps into the amino alcohol 17, which contains a tert‐alcohol function. Upon treatment of 17 with BBr₃, followed by air oxidation, mitosene 20 was obtained in a low yield. The Friedel‐Crafts reaction products 23 of 1,4‐dimethoxynaphthalene, or 2,5‐dimethoxytoluene and (S)‐l‐(trifluoroacetyl)–2‐pyrrolidinecarbonyl chloride, could be converted in two steps into the isomitosanes 25. The isomitosanes 25 could easily be dehydrated, using acid, to the corresponding mitosenes 26. Upon reduction of the isomitosanes 25 with Na₂S,₂O₄ to the corresponding hydroquinones 28, spontaneous dehydration occurred.