Synthesis of novel heterocycles containing Se-O/Se-N linkages: role of intramolecular coordination

The contrasting structure and reactivity of the mono ortho-coordinated aryl-and alkyl-selenium derivatives and 2,6-dibsubstituted aryl- and alkyl-selenium derivatives are described. The 2,6-disubstituted diaryl diselenides with Se···O intramolecular coordination and steric congestion around selenium undergo intramolecular cyclization to give the corresponding Se-O/Se-N heterocycles. The aliphatic analogue, 2-chlorocyclohex-1-ene-1,3-dicarbaldehyde (13), undergoes intramolecular cyclization upon reaction with disodium diselenide to form a resonance stabilized cyclic diselenide (15). However, 2-chlorocyclohex-1-enecarbaldehyde (16), with one coordinating formyl group, does not undergo an intramolecular cyclization under similar reaction conditions. Diselenides, 2,2'-bis(5-tert-butyl-benzene-1,3-dimethanol)diselenide (22) and bis(5-tertbutyl- isophthaladehyde) diselenide (23), with cissoid conformations are orange in color and show absorbances at longer wavelengths (368 and 380 nm respectively, n→σ<SUP>∗</SUP>). The diselenides, bis(5-tert-butyl-isophthalic acid dimethyl ester)diselenide (24) and bis(5-tert-butyl-isophthalic acid diisopropyl ester)diselenide (25), with transoid conformations, are pale yellow in color with absorbances at shorter wavelengths (324 and 323 nm respectively, n→σ<SUP>∗</SUP>). The intramolecularly stabilized arylselenenyl bromides with 2,6-disubstitution underwent interesting cyclization reactions to afford novel cyclic selenenate esters (with Se-O bond) and selenenamides and benzisoselenazoline (with Se-N bond) derivatives depending upon the ortho functions