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The N-protected cis-4-aminocyclohexanol derivatives have proven to be valuable intermediates in the syntheses of active pharmaceutical ingredients (APIs). A novel continuous flow process for hydrogenation of N-protected 2-oxa-3-azabicyclo[2.2.2]oct-5-ene cycloadducts to the corresponding cis-4-aminocyclohexanols has been reported using H-Cube Pro. A > 99% selectivity towards the desired product was obtained using Raney nickel catalyst cartridge. Under carefully selected hydrogenation parameters the reduction could stop at the also valuable 2-oxa-3-azabicyclo[2.2.2] octane intermediate, with a selectivity of >99%. The N-protected 2-oxa-3-azabicyclo[2.2.2]oct-5-ene producing nitroso hetero-Diels-Alder cycloaddition was also accomplished in a flow system using an Omnifit column packed with MnO2. The two flow reactions were successfully merged in a system, thus the product was obtained in a multistep flow synthesis without any isolation or purification steps. Compared with the previously reported batch processes, the present multistep procedure facilitates an efficient cis selective preparation of numerous synthetically valuable 4-aminocyclohexanol derivatives. [ABSTRACT FROM AUTHOR]

Flow chemistry proved to be a valuable technique to improve the synthesis route to melanin-concentrating hormone receptor 1 (MCHr1) antagonists with the 1 H,2 H,3 H,4 H,5 H-[1,4]diazepino[1,7- a]indole scaffold. A one-step route for the heterogeneous catalytic hydrogenation of ethyl 4-(2-nitrophenyl)-3-oxobutanoate for the synthesis of ethyl 2-(2,3-dihydro-1 H-indol-2-yl)acetate was developed, and the use of common reducing chemicals was avoided. N-Alkylation of the indoline nitrogen atom was also optimized by using a purpose-built flow reactor and by design of experiment (DoE). Applying an optimal set of parameters allowed us to decrease the amount of carcinogenic 1,2-dibromoethane used by a factor of 10. Additionally, nearly complete conversion was achieved in a fraction of the original reaction time (30 min vs. 4 d); therefore, the productivity (space-time yield) of the flow-reactor system was proven to be ca. 200 times higher than that of the batch process. [ABSTRACT FROM AUTHOR]