AbstractSubstrates that are insufficiently activated towards the hydrated imidazoline ring expansion (HIRE) process have been previously found to deliver exclusively the products of aminoalkyl side-chain ring expansion. Attempted reversal of the process by thermal activation towards HIRE failed. We have found that for such problematic substrates the HIRE-type ring expansion can be effectively achieved by applying lithium hexamethyldisilazide (LHMDS) in toluene. LHMDS is thought to promote intramolecular transamidation, which leads to ring-expanded 10- and 11-membered heterocyclic products in modest to good yields. The process significantly broadens the substrate scope amenable to the HIRE strategy.
摘要:以前发现,对水合咪唑啉环扩展(HIRE)过程不足激活的底物仅产生氨基烷基侧链环扩展产物。尝试通过热激活向HIRE反转该过程失败。我们发现,对于这类问题底物,可以通过在甲苯中应用六甲基二硅氮化锂(LHMDS)有效实现HIRE型环扩展。认为LHMDS促进分子内转酰胺化,导致产率适中至良好的环扩展的10和11元杂环产物。该过程显著扩大了适用于HIRE策略的底物范围。