Reaction of 1,3‐Disubstituted Acetone Derivatives with Pseudohalides: A Simple Approach to Spiro[4.4]nonane‐Type Bis‐Oxazolidines and ‐Imidazolidines (Bicyclic Carbamates, Thiocarbamates, Ureas, and Thioureas)
Prochiral 1,3-dihydroxyacetone forms racemic oxazolidine- and oxazoline-type spiro[4.4]nonanes upon reactions with potassium (thio)cyanate and cyanamide. In contrast, 1,3-diaminoacetone yields only the corresponding spiro-bisimidazolidinethione under similar conditions together with monocyclic by-products, but the spiro-bisimidazolidinone is accessible by reaction of 1,3-dichloroacetone with urea. The resolution of the racemic spiro-bisoxazolidinethione 2a was achieved by using brucine as the resolving agent.