Tert-Butyl 1-oxa-4,9-diazaspiro[5.5]undecane-9-carboxylate

This compound is typically isolated as a white to off-white crystalline powder. Its molecular formula is C13H24N2O3, corresponding to a molecular weight of 256.34. The melting point generally falls within the range of 82–86 °C, reflecting a well-defined crystal lattice. The calculated density is approximately 1.14 g/cm³ under ambient conditions. It exhibits good solubility in common organic solvents including dichloromethane, tetrahydrofuran, ethyl acetate, and methanol, while showing limited solubility in water and negligible affinity for aliphatic hydrocarbons such as hexane. The molecule contains a spirocyclic framework with both oxygen and nitrogen atoms incorporated into the ring system, and a tert-butoxycarbonyl (Boc) protecting group on one of the nitrogen atoms. The Boc group is stable under basic conditions but readily cleaved under acidic conditions to reveal the free amine. Storage in a tightly sealed container under inert atmosphere at reduced temperature (2–8 °C) is recommended to prevent hydrolysis and decomposition. Contact with strong acids, strong bases, and strong oxidizing agents should be avoided.

Tert-Butyl 1-oxa-4,9-diazaspiro[5.5]undecane-9-carboxylate features a spirocyclic architecture where a piperidine ring and a morpholine-like ring share a common quaternary carbon center. The 1-oxa-4,9-diazaspiro[5.5]undecane core incorporates both oxygen and nitrogen heteroatoms within a rigid, three-dimensional framework. This spirocyclic arrangement imposes conformational constraints that can be exploited to orient substituents in specific spatial arrangements for optimal interaction with biological targets. The Boc group on the piperidine nitrogen serves as a protecting group, masking the basic amine during synthetic manipulations while remaining removable under mild acidic conditions when the free amine is required. The combination of a rigid spirocyclic scaffold with orthogonal protecting group strategy makes this compound a valuable building block for constructing complex molecules in medicinal chemistry, where three-dimensionality and controlled stereochemistry are increasingly prized for modulating pharmacokinetic properties and target selectivity.

Pharmaceutical Intermediate
In drug discovery, this spirocyclic building block is employed to introduce conformational rigidity into drug candidates targeting Gprotein coupled receptors and enzymes. The spiro framework can improve metabolic stability by restricting flexibility and reducing susceptibility to oxidative metabolism. The Boc-protected amine enables late-stage diversification through deprotection followed by acylation, alkylation, or reductive amination to optimize pharmacological properties.

Scaffold for Kinase Inhibitors
Spirocyclic amines are increasingly utilized in the design of kinase inhibitors where rigid frameworks can achieve selectivity by accessing unique binding conformations. This compound serves as a starting point for constructing molecules that probe ATP-binding pockets with enhanced three-dimensional complementarity, potentially overcoming resistance mutations in oncology targets.

Building Block for PROTACs
The orthogonal functionality of this spirocyclic amine makes it suitable as a linker component in proteolysis targeting chimeras. After deprotection, the exposed amine can be conjugated to E3 ligase ligands or target warheads, while the rigid spiro core provides defined spatial separation between the two binding elements, potentially improving degradation efficiency and ternary complex formation.

Ligand Design for Metal Complexes
The nitrogen and oxygen atoms within the spirocyclic framework can serve as coordination sites for transition metals, enabling the construction of chiral metal complexes for asymmetric catalysis. The rigid architecture imparts well-defined geometries to the resulting complexes, which can influence enantioselectivity in transformations such as hydrogenation, epoxidation, and cross-coupling reactions.