1‐Oxa‐2,6‐Diazaspiro[3.3]heptane as a New Potential Piperazine Bioisostere – Flow‐Assisted Preparation and Derivatisation by Strain‐Release of Azabicyclo[1.1.0]butanes.

The development of novel strained spiro heterocycles (SSHs) as bioisosteres for aromatic or non‐strained aliphatic rings is highly sought after for improving drug design. Their high molecular rigidity and predictable vectorization can enhance drug‐likeness, target selectivity and clinical success. Towards this goal, 1‐oxa‐2,6‐diazaspiro[3.3]heptane (ODASE) is reported as a novel potential SSH‐bioisostere. We demonstrate through theoretical studies the potential of this strained spiro heterocycle to act as a bioisostere for piperazine. We have developed its synthesis from the highly strained azabicyclo[1.1.0]butyl intermediate through a robust and mild flow technology‐assisted two‐step protocol. Its tolerance and stability towards medicinally relevant N‐functionalisation protocols are studied, as well as its mild reduction to the C3‐aminoalkylazetidinol motif found in the anti‐cancer drug cobimetinib. [ABSTRACT FROM AUTHOR]