Azo Bridges from Azines, XXII. [2 + 2] Photocycloaddition and 1,5-Laticyclic Conjugation Between Parallel Azo Groups and π-Systems The Symmetry Criterion in Azo-Carbonyl Interactions

✍ Scribed by Brand, Uwe ;Hünig, Siegfried ;Martin, Hans-Dieter ;Mayer, Bernhard

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 626 KB
• Volume: 1996
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.199619960910

✦ Synopsis

Abstract

The known 1,5‐lacticyclic interaction between parallel CC/ NN bridges in 1 in expressed by a bathochromic shift of the azo n‐π^*^ transition of +7–10 nm. A CCCN bridge (2, 6) increases the bathochromic shift slightly, whereas a CC–OSiR~3~ bridge (3) cases a hypsochromic shift of −6 nm. In a R~3~SiO–C = C–CN bridge (4) the effect of the two substituents cancel each other. All these compounds (1–6, 13) undergo quantitative [2 + 2] photocycloaddition by n‐π^*^ excitation. A novel transannular interaction between azo and carbonyl (20, 21: +8 nm) and 1,2‐dicarbonyl groups (24: ca. +20 nm) is observed. From photoelectron spectra and MO calculations neighboring group effects on the orbital energies in 20, 21, and 24 are assessed and discussed.