A four-step approach to the “hydrated imidazoline ring expansion” (HIRE) is presented. In most cases, the ring expansion was the sole process. However, for the first time, an alternative course of the hydrated imidazoline evolution was discovered which gave N-aminoethyl derivatives. These can, in principle, be converted into the target HIRE products under sufficiently forcing conditions. The approach offers improved flexibility with respect to the peripheral substituents and is also applicable to the synthesis of eleven-membered lactams. We observed that the latter can exist in two stable isomeric forms due to lactam–amide bond isomerization. The latter finding further demonstrates the value of medium-sized rings as multiple-conformer probes for biological target interrogation.
Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry