Contrasting Reactivity of 2‐chloro‐1‐formyl‐3‐hydroxymethylenecyclohexene and its Schiff Bases towards Disodium Diselenide: Isolation of Selenospirocycles versus Azapentalenes

Abstract

AbstractA convenient approach for the synthesis of alicyclic selenospirocycles, 24 and 25, stabilized by intramolecular chalcogen bonding (IChB) is reported by the reaction of 5‐alkyl‐2‐chloro‐1‐formyl‐3‐hydroxymethylenecyclohexene derivatives {alkyl=H (22), Me (23)} with in situ generated disodium diselenide (Na2Se2). However, when 2‐chloro‐1‐formyl‐3‐hydroxymethylenecyclohexene, 22 is condensed with aniline or 4‐methoxyaniline and the resulting Schiff bases 26 and 27 are subjected to identical reactions, the Schiff bases undergo cyclisation to afford brightly colored, fused 1,6‐diaza‐6a‐selenapentalene derivatives 28–29, instead of the expected selenospirocycles. The aromatic nucleophilic substitution (SNAr) reaction of N‐(2‐bromo‐3‐nitrobenzyl)naphthylamine, 33 with nBuSeLi affords N‐[2‐(butylselanyl)‐3‐nitrobenzyl]naphthylamine, 34. The bromination of 34 results in the formation of cyclic isoselenazolines, 35. Selenospirocycles 24 and 25, 1,6‐diaza‐6a‐selenapentalenes 28 and 29 and isoselenazoline 35 are authenticated by single‐crystal X‐ray diffraction studies. Compounds 24, 25 and 35 are stabilized by intramolecular secondary interactions.