Nitrogen substituted cyclic enediynes: synthesis, thermal reactivity and complexation with metal ions

Abstract

A number of N-substituted cyclic enediynes (azaenediynes) have been synthesized via Pd(0)-catalysed ene-yne coupling followed by N-alkylation. The simplest of them, a 10-membered monocyclic enediyne 1, underwent Bergman cyclization (BC) at 23 ЊC with a half-life of 72 h. The kinetics of BC slowed down considerably by fusing a benzene ring onto the enediyne. Several novel bis(azaenediyne)s and bis(diazaenediyne)s 3-6 have been synthesized. Their onset temperatures for BC were lowered under metal ion complexation conditions.

10.1007/s11176-008-2012-z

“…Syntheses of diindenofused 4H-cyclopenta[def]fenanthren-4-ones and related compounds by Claisen rearrangement of benzo-fused acetylenic alcohols were also reported [85]. [92]. Unlike analogs 146 (t 1/2 = 36 h at 30oC), benzo-fused enediynes like 147 are stable at room temperature [93].…”

Geometric and Electronic Control of Thermal Bergman Cyclization

“…111,112,114 A representative comparison of metalloenediyne structures with corresponding thermal reactivities ( Table 1) empirically suggests that the more rigid the enediyne ligand and the smaller the chelate size, the greater the response of the ligand to metal complexation, whereas the flexibility afforded by the additional aliphatic atoms in the chelate can dramatically reduce the thermal cyclization temperature. Increased flexibility and lower base ligand cyclization temperatures, do however, come at the expense of ligand response to chelation and changes in metal geometry.…”

Recent Developments in Enediyne Chemistry

“…Basak et al [125] synthesized the macrocyclic aza-enediynes 265 and 266 by multiple-step syntheses. These aza-enediynes were used for the preparation of welldefined complexes.…”