Base-Mediated Synthesis of Imidazole-Fused 1,4-Benzoxazepines via 7-exo-dig Cyclizations: Propargyl Group Transformation
Nalan Korkmaz Cokol, Fevzi Can Inyurt, İpek Öktem, Ertan Sahin, Ozlem Sari, Cagatay Dengiz, Metin Balci
TL;DR
This paper presents a new method for synthesizing imidazole-fused 1,4-benzoxazepines using base-mediated cyclization and propargyl group transformations.
Contribution
The study introduces a novel base-mediated 1,3-H shift to convert exocyclic to endocyclic products and explains unexpected isomer formation via DFT calculations.
Findings
Disubstituted alkyne substrates smoothly produce exocyclic E/Z configured products.
Terminal alkynes lead to isomeric products with altered structures due to O-to-N-propargyl transfer reactions.
Base-mediated 1,3-H shift effectively converts exocyclic to endocyclic products.
Abstract
Herein, we describe the synthesis of a series of imidazole-fused 1,4-benzoxazepines using 7-exo-dig cyclizations. Two sets of substrates, one containing disubstituted alkyne functional groups and the other featuring terminal alkynes, were synthesized by using O-propargylation, Sonogashira cross-coupling, and condensation reactions between aldehydes and o-diaminobenzene. While the disubstituted substrates yielded exocyclic E/Z configured cyclization products smoothly, the reactions involving terminal alkynes resulted in the formation of isomeric products with altered skeletal structures, in addition to the expected 7-exo-dig cyclization products. Density functional theory (DFT) calculations were used to clarify the mechanisms underlying the formation of these products. It is suggested that these unexpected products are formed through a series of intermolecular O-to-N-propargyl transfer…
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Taxonomy
TopicsSynthesis and Biological Evaluation · Phenothiazines and Benzothiazines Synthesis and Activities · Synthesis and Catalytic Reactions