Strain‐Release Driven Spirocyclization of Azabicyclo[1.1.0]butyl Ketones

Abstract

Due to their intrinsic rigidity, three‐dimensionality and structural novelty, spirocyclic molecules have become increasingly sought‐after moieties in drug discovery. Herein, we report a strain‐release driven synthesis of azetidine‐containing spirocycles by harnessing the inherent ring strain of the azabicyclo[1.1.0]butane (ABB) fragment. Novel ABB‐ketone precursors bearing silyl‐protected alcohols were synthesized in a single step and shown to engage in electrophile‐induced spirocyclization‐desilylation reactions. Primary, secondary and tertiary silyl ethers were effectively transformed into a library of new spiro‐azetidines, with a range of substituents and ring sizes. In addition, the products are generated with synthetically useful ketone and protected‐amine functional groups, which provides the potential for further elaboration and for this chemistry to be utilized in the rapid assembly of medicinally relevant compounds.

Constructing All-Carbon Quaternary Centers from Ketones via Titanacyclobutanes: Rapid Access to Azaspiro[3.n]alkanes

“…12 While unassuming at first glance, azaspirocycles are intricate structures that continue to inspire new advances in heterocyclic chemistry. 13,14 Nevertheless, as a consequence of the quaternary center embedded within azaspiro [3.n]alkanes, this substructure remains laborious to prepare. For example, monoprotected 2,6diazaspiro [3.3]heptanes require an 8-step synthesis that begins from a quaternary carbon fragment.…”