The alkylation of phenacetin (1) with dimethyl sulfate gives N-methylphenetidine (2). Treatment with 2-bromopropanoyl bromide gives 2-bromo-N-(4-ethoxyphenyl)-N-methylpropanamide (3). Treatment with aluminium trichloride results in 1,3-dimethyl-5-hydroxyoxindole (4). Alkylation with diethyl sulfate gives 5-ethoxy-1,3-dimethylindolin-2-one (5). Base-catalyzed treatment with chloroacetonitrile gives 2-(5-ethoxy-1,3-dimethyl-2-oxoindol-3-yl)acetonitrile (6). Catalytic hydrogenation of the nitrile group gives (7). Mono-methylation of the primary amine gives (8). Intramolecular reductive amination gives eserethole (9). Cleavage of the ethyl ether protecting group gave (-)-eseroline (10). Optional treatment with methyl isocyanide (MIC) leads to physostigmine.
References
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^Kulkarni MG, Dhondge AP, Borhade AS, Gaikwad DD, Chavhan SW, Shaikh YB, et al. (2009). "A novel and efficient total synthesis of (±)-physostigmine". Tetrahedron Letters. 50 (20): 2411–2413. doi:10.1016/j.tetlet.2009.03.012.
^Harley-Mason J, Jackson AH (1954). "Hydroxytryptamines. Part II. A new synthesis of physostigmine". Journal of the Chemical Society (Resumed): 3651–3654. doi:10.1039/JR9540003651.
^Wijberg JB, Speckamp WN (January 1978). "New total synthesis of dl-physostigmine (dl-eserine) via regioselective NaBH4-reduction of imides". Tetrahedron. 34 (15): 2399–2404. doi:10.1016/0040-4020(78)89058-9.