The Stereoselective Nitro-Mannich Reaction in the Synthesis of Active Pharmaceutical Ingredients and Other Biologically Active Compounds

The nitro-Mannich (aza-Henry) reaction, in which a nitroalkane and an imine react to form a β-nitroamine, is a versatile tool for target-oriented synthesis. Although the first stereoselective reaction was developed only 20 years ago, and enantioselective and diastereoselective versions for the synthesis of non-racemic compounds soon after, there are nowadays a variety of reliable methods which can be used for the synthesis of APIs and other biologically active substances. Hence many anticancer drugs, antivirals, antimicrobials, enzyme inhibitors and many more substances, containing C-N bonds, have been synthesized using this reaction. Several transition metal complexes and organocatalysts were shown to be compatible with the presence of a wide range of functional groups in these molecules, and very high levels of asymmetric induction have been achieved in some cases. The reaction has also been applied in cascade processes. The structural diversity of the products, ranging from simple heterocycles or azabicycles to complex alkaloids, iminosugars, amino acids or diamino acids and phosphonates, shows the versatility of the nitro-Mannich reaction and its potential for future developments.

Concise, stereodivergent and highly stereoselective synthesis of cis- and trans-2-substituted 3-hydroxypiperidines - development of a phosphite-driven cyclodehydration

A concise (5 to 6 steps), stereodivergent, highly diastereoselective (dr up to >19:1 for both stereoisomers) and scalable synthesis (up to 14 g) of cis- and trans-2-substituted 3-piperidinols, a core motif in numerous bioactive compounds, is presented. This sequence allowed an efficient synthesis of the NK-1 inhibitor L-733,060 in 8 steps. Additionally, a cyclodehydration-realizing simple triethylphosphite as a substitute for triphenylphosphine is developed. Here the stoichiometric oxidized P(V)-byproduct (triethylphosphate) is easily removed during the work up through saponification overcoming separation difficulties usually associated to triphenylphosphine oxide.

Efficient, stereodivergent access to 3-piperidinols by traceless P(OEt)3 cyclodehydration

A stereodivergent and highly diastereoselective (dr up to >19:1 for both isomers), step economic (5-6 steps), and scalable synthesis (up to 14 g) of cis- and trans-2-substituted 3-piperidinols, the core motif of numerous bioactive compounds, providing efficient access to the NK-1 inhibitor L-733,060 is presented. Additionally, a "traceless" (referring to the simplified byproduct separation) cyclodehydration realizing simple P(OEt)3 as a substitute for PPh3 is developed.